Monster C4 Thread Text - Edited (Way Long)
Author: R Code (RC)
From: Fresno CA
Posted: 1/7/03 4:12am
--------------------------------------------------------------------------------
I made the mistake of volunteering to do some editing on the content of the monster thread.
Youch. Many, many hours of work later and the thing is still not done. Have a look at the
current state and e-mail me with feedback, or I guess you could just post.
C4 MONSTER THREAD
This is a compilation of a monstrous thread from FordMuscle.com's tech board on the subject of
C4 modifications. Over 100 individual posts were made on the thread and thousands of views have
been registered. Unfortunately, the thread wandered all over the subject matter making reading
the thread a bit of a challenge. To facilitate better use of the captured information, and to
more easily respond to quite a few requests, we are rearranging the info to create summaries
and brief discussions organized by sub-topic. You will find that the posters are quite experienced
builders who have learned their C4 tricks the hard way: they have tried them out. This is an
international group with Greg Aust (GA) from Australia, Mario Van Wiechen (MVW) from
Canada, and 89Coupe (89C), Winsoreight (W8) and TimR (TR) all from the US. One
of the posters pulled apart a Performance Automatics Super Stock C4 and reverse engineered it.
Clearly the C4 is a very stout unit that our panel has made live over hundreds of passes, behind
ultra-high power BBFs and deep into the 8 second ET range. The information is more topline in most
of the sections with some really in depth discussions farther down in the piece. So whether you
want to skim or go deep, here is a mountain of info on the C4.
Introduction
Most of the builders describe their trannys as nothing too tricky. Several use stock H or R servos,
many do no welding on the forward drum, some even use run of the mill clutches. Most seem to agree
though that starting with the later, 26 spline factory unit, a good hard shift engagement, an extra
clutch in each pack, careful attention to clutch pack clearances and use of the best parts available
will result in a VERY stout little tranny. Many more details and opinions to come, but first, what
have you got?
Identifying the tranny
Lots of confusion exists here, and the thread didn't do a wonderful job of clearing things up. There
is the early C4, with its 24 spline input shaft, which is inappropriate for all but the mild small
block. The pan fill case, introduced in 1965 is considered a stronger unit. The later C4 introduced
in 1970 with its 26 spline input shaft is considered the heavy duty unit and is the choice of the
builders on this site. This basic HD C4 was again redesigned in 1982 with a convertor clutch and a
number of other different internals and named the C5. All three versions can be either case-fill or
pan fill.Of course there are a couple bastard versions you may run across. The 1965-1966 "green dot"
shift pattern versions are in a ton of Mustangs. A good upgrade is to retrofit a 1967-1969 valve body
to those units. A rarer one is the 1970 26 spline version which was a one-year deal. Both ends of the
input shaft have 26 splines which was changed to 26 on the converter end and 24 on the forward clutch
housing end for all subsequent years.
So the various versions-
- C4 - 64-83
- Case fill 24x24 spline {C4 to C9}
- Case fill 26x26 spline {D0}
- Case fill 26x24 spline {D1 to D9, & E1SP)
- Pan fill 24x24 spline {C5 to C9}
- Pan fill 26x26 spline {D0}
- Pan fill 26x24 spline {D1 to D9}
- C5 - 82-86
- Case fill {E2AP only)
- Pan fill {E2TP only}
Build level suggestions
- RC - I have a 2500 lb car with a 250 HP carbureted motor. What would I want to do to a C4 to
get it to propel my dedicated bracket car to the lowest E.T.s?
- 89C - 250HP in 2500# car only requires a good working V-8 C-4 which would work great stock or with
a shift kit. No other mods needed.
- RC - If he is looking to squeeze some ET by modding his C4?
- 89C - A full manual valve body is going to bump up the line pressure considerably, which takes power
from the engine to do. No need to spend a lot of money on a trans that will already hold up to 250HP.
The governor assembly doesn't add significant weight to the reciprocating assembly and doesn't use any
power. About the only way you will reduce parasitic drag in the C-4 is to completely convert it to a full
roller, which is expensive for the small ET gain and not needed unless you plan on having 600+HP.
- JJ - I'm wondering if all this stuff about adding clutches and roller bearings is really needed on a
mild, say 350HP, or under application. Wouldn't a good rebuild using 5 Red Eagle or similar clutches
in the forward pack and 4 in the high/reverse pack be OK? Nothing wrong with buiding up a C4 to stand
up to high HP but is it really necessary in a mild application?
- W8 - Yes. For a mild motor that would hold up fine.
- 89C - I called PA and said I have a little over 1200HP on the dyno, may add a shot of nitrous and
need to know what I should upgrade while I was in my PA S/C C-4. He said, "it can handle that power".
Input shafts
- RC - Early transmissions used a 24-spline input shaft that is smaller and weaker than the 26.
The early 24 spline input shafts have a diameter of .788" and the 26 spline shafts are .839". The shafts
can't be interchanged without swapping the stator support and the hi/reverse and the forward drum.
- GA - It is said that the 26 spline input shaft will take up to 600 hp.
- TR - Use of an after market hardened input shaft is only needed for the very high powered cars and
heavy trucks. Up to 450 HP is fine for the stock one, above that it would be good insurance.
- 89C - Very few factory C-4 input shafts are hardened and seems that only the original C-4s that had
the "R" servos had them (all mine came from trucks with yoke that bolts on tail shaft and 4WD C-4s
with transfer cases bolted on where tail shaft goes.) If you can scratch the input shaft, then it
isn't hardened. I have 3 that you can take a razor blade to and try to dig in and sratch and they
will not scratch. I have tweaked the splines and shafts of the non hardend inputs but not the
hardened ones. (Once I found out they do exist from the factory.)
Case differences
- GH - I run the C5 case. C5s are easy to identify because of the 1/4" NPT fittings for lines instead
of the 1/8NPT fittings. Those cases have larger circuits through them and hence more volume.
- GA - There is no real problem with the early cases, it all depends on the final use. The early case
has the bell housing retained by the same bolts that hold the front pump in where the later ones have
a larger flange on the case to allow the bell housing to be fitted separately and this is considered
to be stronger.
- JS - The bells that bolt to the case were a heavy duty version.
- W8 - The C5 case is better because of its improvements but is as strong as the older cases, but I have
never heard of any problems with the strength of the main case.
Valve bodies
- GA - A good valve body helps the trans live. I have used the transgo stage 2 kits. There are some mods
in the article posted that also work well. I use those mods.
- TR - I only use good manual valve bodies and transbrakes for my modified trans builds so there is no
comparison of the shift quality of them and shift kit or stock builds etc. mine all shift hard and
firm and no slip.
- MVW - Use valve body gaskets for better sealing, has helped several different trannies seal better.
Use them even with full manual valve bodies.
- 89C - PA said they use gaskets in the valve body separator plate too for the full manual reverse
pattern bodies but not in the trans brake valve bodies with billet transfer plate. (Deeper discussion
on this subject below.)
Servo choices
- RC - There are a few different opinions on the subject, although there is a bit of convergence
on the issue around stock R and H servos.
- GA - I like the R servos.
- MVW - I like the R servos but have used H's with good success. I spoke to Epping and they use stock
servos with the letter machined off. They said the servo makes no difference in their trannies.
- GH - I use the H model servo because it gives very solid shifts. It is the largest factory unit,
highly desirable and plentiful. Make sure you use a stout spring inside the servo (I use a std 351
cleveland valve spring).
- W8 - I use an H servo with the outer seal removed and 3 flats ground on the surface and I plug the
hole in the case.
- 89C - I never modified any servos, never needed to. An "H" or "R" servo with a
Kevlar rigid or flex band has always been more than enough for the 9 second big blocks and small
blocks my trannies have been behind. The weakness isn't in the apply area. It's in the release area
and until very recently where somebody here posted the apply and release areas of different letter
servos, I saw why the "H" allowed a small flareup from 2-3 shift and the "R" didn't. The "R" has a
smaller release area that fills quicker thus allowing fluid to pass to the direct clutches quicker to
prevent the flareup. "R" servo has a smaller apply area but that is insignificant seeing that properly
setup the 1-2 shift and 1st/2nd gears don't have problems. It's the 3rd gear shift that causes the wear
on the direct clutches and making 3rd shift harder and quicker is what makes the C-4 live.
Planetaries
- MV - I use the stock planetaries and they seem to hold up fine.
- GA - I rebuild the front planetaries using parts from the rear planets as per the article in
the archives.
- 89C - My PS Super Comp has the 6 gear planetary set.
Teflon vs. cast sealing rings
- RC - One of the builders likes the teflon sealing rings, but that doesn't seem too universal.
- GA - I personally use the steel sealing rings but some guys do prefer the teflon.
- TR - I have used only cast seal rings like stock with very good luck, but feel that there is some
merit to the Teflon ones and some day will try them myself.
- GH - I get the Teflon seals for forward and direct from H&R Transmissions in Indy.
Clutch manufacturers
- 89C - I like Kolene steels and Blue clutches for the harder shifts and less slippage.
- GH - I run Alto race clutches and Kolene steels.
- TR - There is some debate as to need for high dollar clutches and bands I have used new rebuilder
kits for most of my builds with no problems mostly Raybestos, Borg-Warner and others.
- 89C - PA said the red Alto and Blue Raybestos clutches are just personal preferences and that's
why they offer both but they both work as good as the other so you can pay more for the blue clutches or
less for the red clutches and have the same performance either way.
Adding clutches
- GA - I use 5 forward + 5 hi/rev clutches.
- W8 - I am now using 5 clutches in the hi/rev drum using the
lower plate from a forward drum and the smooth red clutches. I use 6 clutches in the forward drum by
having the snap ring groove widened higher. Performance also has a kit to do something similar.
- TR - I use as many as 11 clutches in my C4 transmissions and I do this by using thinned stock steels.
I take large batches of them to a machine shop that can surface grind them with a magnetic chuck surface
grinder and have them take them down to .061-.065 and then use smooth surface forward clutches that are
.061 thick in both clutch packs, final clearance is set at .020-.025 in both packs and this is done by
machining the stock pressure plate down to a thickness that gives this much clearance and don't worry
about it being too thin as there are stock ones that are listed at only .141 thick. You can make them
pretty thin without trouble. I usually don't need to take them down that far, usually about .160 or so,
but be sure to check yours before you machine it unless you have lots of spares. Gregaust and others here
have suggested that you can also machine just the edge of the pressure plate to create a lip for the snap
ring to set in and I think this would work well. Just watch out for clearances of the assemblies when this
is done. And a word of caution I do not believe it is a good idea to machine the snap ring land higher in
the drum because you may raise the pressure plate out of the locate lands in the outer perimeter of the
drum and this will allow it to turn in the drum and not drive the drum as it is supposed to along with the
steels in the pack.
- GA - On the subject of the 6 clutch fwd hub you need to be careful with the inner hub
length for the clutches to engage. I haven't actually measured but more than 5 plates with stock thickness
steels would go close to running off the edge of the inner teeth for the clutches.
Here is a link to a place here in Australia that
has a long skirt hub to overcome this prob.
- 89C - I used to machine down some high/direct pistons (exactly the thickness of 1 friction and one steel
removed from piston) to fit 1 extra clutch. I then used the curved pressure plate from forward clutch
turned upside down (has thin outer edge which a snap ring barely fits into when used as top pressure plate)
and used as a pressure plate to add 1 more clutch for 6 total with ease. I didn't use the deeper C-5 clutch
drum for that would have let me fit 7 with no problem but 6 is enough using the regular waffle clutches
and standard thickness steels. I also used that curved plate on the forward clutch pack as a pressure plate
for 6 clutches there too. It all worked out very well with hard shifts but the #8 thrust washer would sheer
the tangs off and spin. That was my problem.
- 89C - PA says if you use the thinner forward smooth clutches in high drum, it will slip more before lockup
and will not shift as hard or quick. The grooves in the direct clutches are like tire tread and give the
fluid a place to go when the clutches are applied. The smooth clutches work good in forward drum because
they are applied from the start and thus don't need the quick fluid evacuating grooves. However, when 3rd
is engaged, the clutches need to get rid of the fluid between the clutches as quick as possible and the
grooved clutches are there for that reason. I have never used forward clutches in high drum for the same
belief and now I'm glad I was right about that for the right reasons.
- RC - Maybe, maybe not. TR has done this successfully and the Alto power pack uses 6 smooth Red
Eagles. Additionally, all the Red Eagles are smooth irrespective of which drum they are for.
- MVW - I never really thought about it, I just have some 5 clutch drums and I use them. I have one
I bought from PA, I needed a drum and clutches so I bought a direct drum kit from them. Came with 5 blue clutches
in it. When I rebuilt it I grabbed a stack of 5 Alto Red Eagle smooth clutches from a kit I had. I also
grabbed 5 kolene steels and my pressure plate which is a thinner one than one I had in my spare parts box.
(Possibly a .140" C5 pressure plate.) I put it together using the snap ring that had come out. Clearance
was .05 with a .065 ring so I put an .080 ring in and I was done. I may have to do some measuring and get
back to you with the thicknesses of everything.
- Ford Papa - If you have an extra 4 clutch drum take the stepped pressure plate from the bottom of the
forward clutch hub and use it as the top pressure plate in the direct clutch like Windsor Eight does
since the step is only approx .125". It's thinner so you can get 5 clutches in the standard 4 clutch
drum. Other times I have used two steels together as a pressure plate to get clearance. It just depends
on the frictions, steels and snap rings you have. It works and is easy. The five clutch drums are hard
to find, but I do have one that came out of a c-4 with a yoke on the tranny, likely a truck application.
- GA - I hadn't heard of a 5 clutch direct as original, just the c5 drum which has the snap ring groove
slightly higher.
- MVW - I always looked harder for panfill cores which tend to be out of heavier vehicles so maybe I take
5 clutch directs a bit for granted.
- GA - We have lots of pan fill c4's here but they still only come with 4 direct clutches...Very
interesting..You learn something new every day.
Bands
- GA - I use Kevlar bands.
- W8 - I use Kevlar bands.
- GH - Use Kevlar bands.
- JS - My thoughts on killing bands is the use of the "Flex-Band" not the servos or the servo mods
mentioned above. I have never killed a band when using or re-using the rigid front bands.
- 89C - I have never had or seen a flex band break but I went with the rigid band for peace of mind.
PA said they prefer the intermediate Kevlar lined flex band instead of the "rigid" intermediate
Kevlar lined band because it can wrap around the drum easier therefore having better and more surface
contact with drum. The rigid band needs time to seat in and wear to the contours of the drum before
they become better than the flex band but most racers don't have extra time to wear the rigid bands
in before the race so they aren't used. In a street car, they become better as they get more wear
for increased contact surface.
Oiling mods
- GA - Remove the check ball from the stator support for increased cooler flow.
- MVW - More oil volume is good, deeper pan with filter extension of some kind.
- 89C - How are you modifying the C-4 cases? I haven't modified a C-4 case and haven't had any problems
other than spinning the #8 thrust washer.
- GH - My transmission runs about 215-217 psi line pressure. (MVW's C4 runs 200) I go in and put a small
radius around the openings for feed from the oil pump as they are razor sharp from machining and this
seems to help.
- DR - I have had several C4s that have spun the tangs off of the #9 thrust washer (the one behind the
one way clutch that seats to the case) I noticed the C5 case has an extra lube hole in the thrust
washer and of course a matching hole in the case. The return lube circuit from the cooler is the feed
hole for this circuit and is larger. I have added this circuit to the C4 cases and have eliminated
problems with knocking the tangs off the thrust washer.
- GA - To improve oiling to the #9 thrust washer, drill through the back of the case into the rear
oil cooler return line passage to pick up direct lubrication for that thrust washer and drill the
washer to match. Drill this passage to 3/16" to open it up slightly from 5/32". The hole in the
case for the cooler fitting is quite a restriction so opening it up should improve flow slightly.
- GA - One of the C4's I rebuilt had this mod done already. I didn't realize that was the same as a c5.
- W8 - I prefer the heavy duty C4 case (bell to case-dipstick in pan). I believe that they are stronger
overall. I have just been modifying my C4 cases for better flow.
- GA - I have noticed that some of the earlier 26 spline type front planetaries don't have a lube hole
in the planetary case that the later ones have. This is in the area of the front thrust washer drilled
through to the center of the case. It would be easy to drill and may be worth drilling if it's not
there already.
Drilling the drums
- W8 - I drill holes in the outside of the hi/rev drum to stop too much fluid from building up.
- GA - I drill both the hi/rev and low drum. The holes in the direct drum are evenly spaced,
4 holes at 5/16" in the outside circumfrence to help evacuate the fluid. Those holes are in the center of
where the clutches ride. Measure down the inside of the drum to the approximate center of where the clutches
run, then mark the outside. It works out pretty much the center.
Stator support bushing
- JS - Since the early 80's, I have always used the C6 pump bushing in the C4/C5 pumps with no
problems.
- 89C - I compared the C-6 pump to converter bearing to the C-4 bearing and the C-6 is nearly
twice as wide and I guess I will use them from now on instead of the C-4 bushings. Better wear and stability.
Endplay
- GH - Make sure you set the clutch clearances to factory clearances.
- MVW - Keep tranny endplay to a minimum, especially with iron sealing rings but helps all around.
- JS - I think a killer of the C4 and other transmissions is not paying attention to the clutch pack and
endplay clearances. Most home builders don't take time to acquire a selection of selective snap rings
and selective thrust washer combos since they might build one or two C4's before getting frustrated
and buying one from a company. Get the selective thrust washers and snap rings at any transmission
parts house. I use Recon or Transtar. I still have my old Peterson Publishing Auto Repair book that
was released back in the 70's and reference it quite often for specs on endplay and clutch packs.
- W8 - Clearances are very important and that is where most people fail. I also found an H gauge to be a
very handy tool for checking the end clearances. It will help keep you out of trouble. I build
transmissions everyday but just for everyday vehicles.
- 89C - One of the most important things is to allow .005" clearance for each friction clutch for minimum
piston movement and quicker engagement. 5 frictions should have .025" and 7 should have .035" like in my
reverse/high packs which I have been calling "direct clutches" for obvious reasons. However PA told me
.010" clearance per clutch in the drums will causes the least "drag" and will ET better but wear quicker
and require more regular freshening. Said if running .005" clearance per clutch, you will lose a tenth or
two depending on how many clutches are being used.
- MVW - The tight clearance on the direct clutch causes drag in first gear in particular. Remember that
in first gear the clutches in the direct drum are spinning the opposite way that the steels are. Tighter
clearances mean more friction and drag. Clearances become a guessing game between ET and clutch life.
Roller thrust bearing conversion
- RC - TR has detail on the roller conversion eliminating the thrust washers.
- GA - The roller bearings will obviously free up a bit of power but a bigger advantage is there will
be less contamination of the oil from the wearing of the stock thrusts. I build mine with roller thrusts as
per TR's info. The roller bearing mod also solves the problem that 89C mentioned a while ago. He
was shearing the tangs from the stock thrust washers when on the gas.
- TR - Interesting note in the current issue of Muscle Mustang and Fast Fords April 2002. There is an
article about PA C4 build up and in it they show at least 2 more places to put bearings in the trans
other than the places that I already do. I have seen bearings used in these places before in other
companies transmission builds, but never had the sizes of the bearings so I had never put them there,
but now I may try these places as well. They use the same Turbo 350 pump bearings there too, at least
it looks to be the same ones in the pictures.
- 89C - The PA Super Comp has roller thrust bearings all over. Hell, even the front pump has a roller
needle bearing set behind the front pump instead of a selective plastic thrust washer. My front pump
has the roller thrust on #1 and therfore I have no way to control the endplay. I guess you're supposed
to know exactly what the #1 thrust washer thickness is for optimum endplay before you have the front
pump machined for the roller. That way you can get it dead on by just measuring #1 roller thrust
thickness and cutting the receiver groove for the roller accordingly. Then endplay will not change
and will always be right as long as the other regular thrust washers are not excessively wearing.
- W8 - Hey, 89C you can shim the Torrington bearings. They make different thickness flat
steel shims.
- 89C - But what holds the shim in place and keeps it from sneaking out? I have never seen a #1
plastic thrust washer worn or even slightly worn in any way. #1 isn't under stress and just takes up clearance
for proper endplay and to keep the assembly from walking too much but under power everything is thrust
rearward. I wonder why PA chose to use a roller there. I bought 2 TH350 front pump thrust roller bearings
locally for $12.45 each and I think that is a bit high. I really would like to find those TH350 roller
bearings cheaper.
- TR - I am sure BulkParts has them (now they are also on the web site.) And if you need
someone to machine your parts let me know I have done several sets for myself and had very good luck,
I'd be willing to do some for folks who are interested for a modest fee. I may set up an exchange
system - send me good cores and I'll send you back machined parts ready to install. If there is interest
I could even get the bearings and sell roller setups complete.
- 89C - Thanks guys. $5 each is a whole bunch cheaper than $12.45 each. I'll order 20 so I can totally
make my other 2 race C-4s (already built and ready to race) fully rollerized in every position except
for 2. I'll also make the rear planetary in my PA C-4 rollerized too while I'm at it since they have
started doing that. By the way, I checked a place here in town and they didn't find any roller thrust
bearing selective shims in their listings. I did ask so i could set the end play with the roller on
#1 position.
- GA - You could try a bearing place for a shim for #1 if you need it. Try Torrington, part# TRA-3446.
This is a .030 steel shim that is the same diameters as the T350 bearing. I am able to buy here .020"
+ .030" shims to go behind the #1 plastic thrust to get correct clearances. You could use them if needed
to. With careful machining hopefully you'd get by without any shims. Did you check out the link one of
the guys posted above for the JPT C4? Noticed that they machine the back of the rear planet for the
bearing instead of the ring gear.
- 89C - I checked my PA C4 and the ring gear is machined for the roller bearing instead of the backside
of the rear planetary. It also has a roller bearing behind the ring gear against the reverse band drum.
It's just missing the roller in front of the rear planetary but not for long. I am going have a machine
shop machine the back of the case on the inside for a roller bearing but it will be a challenge because
of how far back the machining will take place inside. Eliminating ALL thrust bearings with rollers is
my goal now.
- GA - Check out the mighty mouse article and the light-o-matic article above for the rear #9 roller.
It looks like the roller is machined into the inner race for the roller clutch. Machining the trans
case may not be necessary. There's also the roller for behind the park gear. The bearing from a c6
fwd hub is the correct size for that one.
- 89C - I just checked out the possibility of machining the inner sprag race and it looks like it will
not work. The little sheet metal cage that keeps the rollers and springs intact will be in the way.
Without machining, the roller thrust does clear everything but having to machine .080" off the race
for proper clearance will put the roller thrust into the metal cage and possibly even the rollers.
There are tiny "nipples" that stick out along the cage and even with those sanded down there isn't
enough clearance. Looks like machining the inside of the case is the only possible way to convert
#9 to roller. What roller from the C-6 are you talking about? When did they start using rollers in
C-6s forward hub? How much are those rollers or have you checked yet? It would be nice to find a
roller that can be put in place of the smaller #3 forward clutch thrust bearing where the kidney
holes are. A small roller for #2 reverse clutch thrust bearing at end of pump. Then a completely
and totally rollerized C-4 can be built and should free up power a bit more(how much I don't know)
but should definitely be better anyway. Any ideas?
- GA - The roller bearing from a C6 is in the #3 position and sits in the backside of the fwd hub and
the front planetaries run against. All c6's have them. It looks like it would fit the park gear to
case and i just checked and it would be pretty close to the #3 spot over the jelly bean holes too.
The bearing measures 2.105" x 1.365" x.140".
- 89C - I'll check into the C-6 roller for price and availability. I sure hope it fits #3 position too.
That would be great. I found a machine shop here that will machine everything for the roller thrusts
but they are checking into doing the inside rear of the case. They may not be able to machine that.
Thanks for the info. This is really starting to look easy and affordable to do in all positions except
#2 unless there is a small roller thrust that will fit there too. Maybe somebody already knows of a
small bearing for the #2 at the end of the pump. I just got word from the machine shop that they can
machine the back roller bearing register on inside of case for $70-$75 with CNC but if I bring them
my 5 cases at once (3 will have to be disassembled) they said then can probably do them for around $35
each so I will do that. All other machining they can do too so now I will tear my other 2 race C-4s
apart and 2 stock C-4s and have ALL machine work done at one time for rollers in every position. I have
buckets of extra C-4 parts from years of accumulating which I will have machine also for spares. Damn,
maybe i can sell some FULL roller C-4s around here and make some money. That would be nice but I won't
count on it till it happens. I have yet to get that #3 C-6 roller thrust to see if it will work on #3
position over the jelly bean holes and between the park gear and the case.
Do you need to weld the forward drum jellybean holes?
- RC - Some do weld them up while others don't. Clearly there is disagreement over whether this
is necessary.
- W8 - I weld up the 3 peanut holes in the forward drum.
- GA - The weak link, as mentioned in another post here, is the fwd drum jelly bean holes.
I weld them.
- TR - I think it is a good idea to weld or braze the kidney shaped holes in the forward clutch
hub to prevent them from breaking out as this is a known weak spot.
- MVW - I've never welded my forward drums. I have never broken one but having said that it will let go
on the first pass of the year. ( Note: the drum lasted fine after 140 passes.)
- 89C - I just disassembled my Performance Automatics (PA) Super Comp C-4 and the kidney holes in the
forward drum are still there: no welding of any kind on the forward drum. PA says welding or brazing
in the kidney shaped holes on the forward drum is only necessary if planning on making over 1000HP
and I myself have never stripped out the splines or broken a forward drum even with 1.32 60ft times
and I wasn't even close to making 1000HP.
- TR - I am surprised at the info you shared about PA saying that the kidney holes don't need to be
welded I always thought that was a weak point.
- 89C - There are too many people running 8s with unwelded drums to think the drums are a weak link.
A high mileage drum with a lot of wear in the spline area would cause a problem but not a closely
inspected drum with nice tight fitting input shaft. I have seen worn out forward drums that I
wouldn't use and I carefully inspect the ones I do use along with "feeling" the spline clearance
using the input shaft.
- MVW - The last parts tranny I pulled apart had the drum broken though along with being the most
burnt up C-4 I had ever seen. I wonder what kind of abuse it takes to so severely ruin a tranny.
Lots of pedal to the metal in reverse then drop to 1st gear maybe.
Forward drum welding how-to
- RC - Some weld, while some of the builders braze the holes shut. Each seems to have advantages.
The "King of the Cs" article in the Sept 88 Hot Rod says, "the C4 clutch drums tend to crack through
their center jelly-bean holes, so they should be MIG welded shut. Welding heat also tends to reduce
the i.d. of the center hole in the drum, yielding the added benefit of a tighter fitting and more
positively retained input shaft." At least one of the builders, maybe Dynamic brazes theirs.
- W8 - I mig weld them slowly, a little at a time cooling the drum down after every little
bit so it doesn't get overheated. Just make sure you drill the lube hole through It is the hole in
one of the peanut holes and you will cover it when you weld it up. Just drill it through the same
size as the original hole or slightly larger. I also drill a corresponding hole in the thrust washer
and chamfer it with a large drill bit. Alternatively, you can make a groove under the thrust washer
to one of the holes already in the thrust washer.
- GA - I mig weld the jelly bean holes in the forward hub. Here's a little
tip to help. Make sure to soak the hub in some solvent and get it nice and clean before welding.
Soaking in a solvent removes all traces of oil, which is required for a good weld. On the oil hole,
I like to redrill the hole then die grind a small groove under the thrust washer to link up with the
original hole in the thrust washer.
Servo modification discussion
- MVW - I do not like the servo mod where the small sealing ring is taken out. The only C-4's I
see that take 2nd gear band out have this mod and I believe it is hard on high gear also. My thought is if
the small sealing ring is removed on the servo piston and some oil transfer slots cut the pressures on both
sides of the piston will be the same. The problem with that is if the valvebody does the same thing as
a stock one when the tranny goes to high gear the apply pressure on the servo piston is not released.
This means the only thing moving the piston up and disengaging the band is the spring. I have never seen
this tech tip come with the advice to use a heavier spring. Using an H servo for an example there is a
4.4 square inch area difference between the two seal areas. If line pressure was 150 PSI, with both seals
in use there is 660 lbs of force pushing the piston up the bore. The band disengages quickly and the
pressure gets to the direct clutch quicker and with less lag. There is an 8 sec Fairmont running here
that has the servo mod done and the band lasts about 10 runs. While I only run high 10's I have never
killed a band. I believe Dynamic has a valve body that releases the 2nd gear pressure when high gear
comes on. I spoke to them at Epping and they use stock servos with the letter machined off and he said
the servo makes no difference in their trannies. This is my theory and I am sticking to it. Poke enough
holes in it and I will try the mod late in the year just to prove my point only with an A servo so I do
not waste my good servos.
- W8 - I think it depends on the valve body too. I do the mod only on the C4's I build with manual valve
bodies. I have been using TCI or ATI valve bodies and all of them want you to do this mod. I have not
had a broken band yet. I Have a C4 in a friends 67 mustang with a 429 running 10's and in 4 seasons he
has not broken a band. Same with the others I have done. I have seen some of the stock bands come apart
though, with runaway line pressure. I am using Kevlar bands and they seem to hold up well.
- TR - I have used the servo mod on many of my builds with only one that ever gave me any trouble and I
think that the cover is flexing on that one so I plan to build a girdle for it and see if that will help.
C4 websites
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