After 35+years you get to know a transmission pretty well. Thanks for the comments and I hope it helps.
Hoping you can add to this. My C4 behind a 302 sat for about 12 years before I resurected the car. I drained all the fluid including the torque converter and changed the filter etc. transmission actually shifts really good through all gears under slow to medium aceleration. but on harder acceleration 2 things happen. 1 it shifts from 1st to second way to early about 3000rpm like 30 mi / hr and it will stay in 2nd nicely until 5000 + but slips badly into 3rd like if I don't let off it would likely burn up. I rebuilt the motor and used comp XE 262 cam (not big enough to cause vacuum issues I thought) anywy just looking for the best sequence of test / repairs to do. in the best order.
It sounds to me like the frictions have glazed. When a transmission sits for a time the frictions dry out. When you put fluid in the transmission and take it for a spin the friction material is still not soaked with oil and the material glazes over and becomes very smooth and hard. Then they slip - and it gets worse. Once the frictions become glazed the only fix is to replace them. The way to prevent it is to fill the transmission with as close to four quarts as the C4 will hold without starting the engine. Let it soak for at least 20 minutes before you start it. Then start the engine with the transmission in Park and fill the transmission to 1/2 way between the FULL and ADD mark. With the wheels off the ground run it through all the gears several times and then top the fluid off to 1/2 way between the FULL and ADD marks. Shut the engine off, lower the car, and take it for a short drive at low speeds monitoring the shifts and feel. Check the Fluid level with the engine idling in Park. Just keep it 1/2 way Between FULL and ADD on the dipstick. Let the engine sit overnight and then drive it normally. This process can prevent glazing of the friction materials but the only cure after it hapens is a complete overhaul. Sorry for the bad news.
I was thinking i can live with the sloppy shift from 2nd to 3rd....as it is only when I am hard on the gas... the problem I have more so is the horiible early shift from 1st to 2nd at like 3000 or so. I can do it manually but would like it to shift between 4500 and 5000 on its own if that is possible. if not I can live with it until I drum up the cash for a TCI unit or something. don't need radical but nice firm shifts in the 5000 range would be cool.I had a c6 kitted years ago tied to a 390 and it would shift religiously at 4800RPM and the tires would chirp every time. If I can do this by changing the mod valve and adjusting the band (until I get a new transmission) this would be cool. any thoughts?
By early shift at 3000 I will assume that you are talking about a wide open throttle shift and not normal street driving. Try disconnecting the modulator hose and plugging it - If it then shifts at around 45-4800 rpm then reconnect it and make sure the throttle is fully opening with the gas pedal and that the kick down linkage is travelling completely to the stop (less than .060" play at Wide Open Throttle (WOT). If those items are properly adjusted then you might check your manifold vacuum at the time it shifts. If you have manifold vacuum above 10" Hg then your carb is too small. Manifold vacuum over-rides the governor. You should be using a "Green stripe" modulator with a modulator pin that is 1.625" (1 5/8") long. You might have a stuck governor - you can get at it by removing the tail housing and pulling the four small bolts that hold it on. Disassemble (keep track of how the valves, springs and shim come out of it) polish each valve with 600 grit emery paper and lube with some Vaseline before installation. They should move freely in their bores. Clean the small thimble filter and reinstall it in the governor mounting block before remounting the governor on the tail shaft. Use a new gasket on the tail housing and put a thin film of loctite or permatex 518 on both sides. If none of that fixes it then you will have to remove the transmission to go further. I would recommend a Broader Performance C4 over any other builder. You get a much more reliable transmission for less money.
Sick C4 with no reverse or 1st gear I rebuilt my c4 last year and have about 300 miles on it now. It wasn't a stock rebuild but it was my first auto trans rebuild. A circlip had come off inside the tailshaft and the guts of the trans had started moving backwards adn started wearing on the housing causing me to lose 1st gear. I rebuilt it and everything was great. I do not use the van modulator or kickdown as of yet, I was still breaking in the new motor also. Yesterday I went to back up and there was no reverse, and selecting 1st manually also didn't work. I finally got reverse after about 2 mintues and the car went into 1st while in D but not if manaully selecting, it would go in second then. (I have a rachet shifter in the car) The fluid is full and clean, The linkage is adjusted properly but I redid it to be sure. I tried to readjust the Reverse band but my torque wrench would not fit in the tunnel.... I did take the adjuster and turned it in an extra 1/2 turn. I refired the motor and it still has no reverse or 1st. I also hooked up the vac mod, which was new with the trans rebuild kit, but it immediatly starting leaking when the car fired up and sucked trans fluid up into the carb/started smoking in the exhuast, I unhooked it again. I am out of ideas. HELP????? Could the Circlip have come off again??? The trans ran fine home shifting by itself in D......... Jarrad jarrads@me.com
Paul, I've been reading your posts around the web for a while now, and I am thoroughly impressed with your amazing knowledge of the C4...that's why I came straight here when I had a problem with my new rebuild! I'm a motorhead (like most guys here), but the auto trans has always been a mystery to me; I decided to try to rebuild my own, and with the help from the Hayne's C4 Tech manual, it turned out to be a breeze, EXCEPT for one thing, and that's why I'm here.... After getting it reinstalled in the car, I fired it up (with the appropriate amounts of fluid, of course), and found that it wants to move FORWARD in all gearshift detents....reverse, neutral, etc, etc....boy, was I ever disappointed! I was told by some that either the big attaching nut for the inner lever was loose (green arrow in pic), or the kick down lever is not engaging the kick down valve on the valve body (and I missed the alignment putting the vb back in--red arrow in pic)(this is not my trans--I snagged this pic off the web).... I was careful to replace the 3 check balls in the valve body rebuild (I used Vaseline), the shifter linkage hook-up is correct, and there were no leftover parts after the rebuild....and that's why I'm stumped! Being the c4 guru that you are, I've come here to ask you what YOU think the problem is; any help you can give will be deeply appreciated, and plus, will save my 46-year old pride---I've got 5 bucks riding on a bet with my smart-arsed 18 year old son, because he said I couldn't rebuild it and make it work! Thanks, Rob
You didn't have the manual valve lined up with the pin on the "rooster comb". That pin has to go in the first groove in the manual valve spool. The down shift lever has to tuck into the space behind the kick-down valve. To make it easier on yourself when you install the valve body use a couple pieces of threaded rod (1/4" NC x 4" long and a couple of nuts to hold the valve body in place while you line up the two levers. Check them often as you start to install the bolts. It can be a real pain to get everything lined up when you are under the transmission and oil is dripping down your arms but it can be done.
Thanks for the reply, Paul...I'm going to put her back up on the jack stands this afternoon, drop the pan, and get back into her guts....I'll let you know how it works out! You're the best, man! Rob
starting to get a little "morning sickness" and i want to put off rebuilding the c4 until i swap the engine. this is at least about a year away from happening. and im considering going to a manual 5 speed when i do swap the engine so im looking for some tips on prolonging the transmission. im very familiar with driving soft until it warms up and i check the fluid levels weekly just to make sure its not losing too much fluid (it had a serious fluid problem when i bought it that i fixed.) the engine is an I6 200. There are a couple of other minor issues besides the "morning sickness". the shift into second at mid to wide open throttle is pretty hard. sometimes it feels like a little flare is happening. tends to smooth out once its well warmed up though. no issues shifting into high. i have driven mostly automatics and have been used to dealing with "morning sickness" once it sets in but i would really like to get on top of this before it gets bad without having to rebuild.
SUCCESS!! Paul....I did just what you told me, and now that baby shifts like a scalded dog! I went out and dropped the pan, and lo, the lever was just like you said....the stud on the rooster comb was behind the end of the manual shift valve....I used three 1/4"x 4" x 20 studs and nuts as guides, and floated the valve body up into place, while aligning the rooster comb stud into the last groove of the manual valve...I felt it 'click' into place, and when I moved the shift lever, I could hear the kick-down valve "popping" as the lever released it and the manual valve slid out smoothly...I bolted that sucker up, replaced the pan, and refilled it; I started her up, and moved the shifter thru the motions, and had ALL the of the forward gears, reverse and neutral! Although I have to take it on a longer test run tomorrow, I'm just stoked to know that the darn thing works, and that I rebuilt it correctly...and on top of that, I won my boy's 5 dollars! Thanks again, Paul, for your help and information...you are a life-saver! Rob
MSSmith, Make sure your bands are adjusted. Keep the oil level between the ADD and FULL marks with the engine idling in Park. When you shift into gear first thing in the morning don't rev the engine to get it to go into gear - just waiy for it. That way you don't burn or glaze the clutches. Putting the transmission into manual low will increase the pressure so that may help. I nursed mine for three years before getting time to build a good transmission for myself. when I tore the C4 down I found the forward clutch apply pison seal broken in two places and it was as hard as a carbon seal - and just as brittle. If you give it time and let it warm a little before driving you can make it for a year.
