C4 won't shift into 3rd gear when cold

The c4 in my 79 Pace Car recently started acting up, when the trans is cold it won't shift into 3rd gear. If the shifter is in Drive it will just hang in second gear (to redline) and never shift into 3rd, if I stop and manually shift from 1-2 it shifts fine, then when I go for 3rd (D) it acts like I shifted into neutral (free revs with no slipping or partial engagement), if I pull it back into 2nd it drops into 2nd right away, if I drive a mile or so in 2nd gear and come to a stop, put it into drive (or manually shift it up through the gears) it will drop right into 3rd gear nice and crisp and pulls good with no problems for the rest of the time it's driven. If I stop for gas or whatever it's fine when I start up and leave. So it only acts up when it's cold. The motor is a carb'd 306 roller with about 320 hp. The trans has a B&M converter and a transpak set to stage 2 hi performance and shifts hard and pulls well in all gears including 3rd (after it is warmed up for about a mile). It also drops into reverse nice and hard all the time. The fluid is fresh and does not smell burnt. The trans worked fine until about a week ago, now it goes through this ritual every time it is cold. I checked the vacuum line to the modulator, no leaks there.

Any suggestions?

Thanks

The modulator is not part of the problem. I would suspect the B&M shift kit. They are problematic at best.
If I did not know it had that shift kit in it I would say that the seals in the direct drum are hard or worn and they soften and swell with the heat. A rebuild is indicated when that happens.
With a B&M kit in there I would recommend pulling the valve body and checking the valves for free movement. Check the gaskets for tears, and then using the minimum torque spec tighten the valve body up from the center out in three steps. Don't install the filter until the final step but use the bolts without the filter as you torque it down. Then remove them and make the final torque.
Give that a try and see how it works.

Originally Posted by PaulS1950

The modulator is not part of the problem. I would suspect the B&M shift kit. They are problematic at best.
If I did not know it had that shift kit in it I would say that the seals in the direct drum are hard or worn and they soften and swell with the heat. A rebuild is indicated when that happens.
With a B&M kit in there I would recommend pulling the valve body and checking the valves for free movement. Check the gaskets for tears, and then using the minimum torque spec tighten the valve body up from the center out in three steps. Don't install the filter until the final step but use the bolts without the filter as you torque it down. Then remove them and make the final torque.
Give that a try and see how it works.

Hi Paul,

I'm new to the boards, after doing some reading I saw that you reply to a lot of the trouble shooting questions, thanks for responding to mine. I've spent most of my life with engines and manual transmissions (T10 and T5), so this C4 is my first go around with a performance automatic. I have two follow up questions. First question, I was checking the fluid level last night and the top of the dip stick is loose where the cap attaches to the stick, after I replace the stick the trans now shows about 3/4" over full on the new stick, would that cause the problems that have mysteriously started? Second, I prefer not to do repairs 2 or 3 times, and I was not aware the BM transpak kits were problematic, should I just scrap the valve body and buy a hi performance valve body from another trans builder? If so, who would you recommend?

Thanks again!

I think, if the trans is original, that you just have a hard seal problem. 2-3 shift is the releasing of the intermediate band (front band) and the application of the rev/high clutch (in the drum that the intermediate band runs on). If anything gets in the way of that clutch, then you get no third. Sticking piston, messed up VB, etc.

I'd not a "chemical fix" kind of guy, but you can try a can of Trans-X or Seafoam in the trans with fresh fluid and see if there is a change. Surprisingly, that stuff can free up stuck seals for a bit. If a change is noted, then internal trans work is indicated. If no change is noted, then possibly you have a VB issue. You can also pull the VB and do a air pressure test to see how the front clutch responds when cold.

Broader is a good source of C4 performance items and experience.

Ps - I've had decent luck with the B&M kits, less so with the Trans Go stuff. So go figure. After years of screwing with C4s, I've come to the conclusion that VB are like carbs - you get a good one, keep it. And if one gets to not working right it can give you a real rash.

Originally Posted by ckelly

I think, if the trans is original, that you just have a hard seal problem. 2-3 shift is the releasing of the intermediate band (front band) and the application of the rev/high clutch (in the drum that the intermediate band runs on). If anything gets in the way of that clutch, then you get no third. Sticking piston, messed up VB, etc.
I'd not a "chemical fix" kind of guy, but you can try a can of Trans-X or Seafoam in the trans with fresh fluid and see if there is a change. Surprisingly, that stuff can free up stuck seals for a bit. If a change is noted, then internal trans work is indicated. If no change is noted, then possibly you have a VB issue. You can also pull the VB and do a air pressure test to see how the front clutch responds when cold.
Broader is a good source of C4 performance items and experience.
Ps - I've had decent luck with the B&M kits, less so with the Trans Go stuff. So go figure. After years of screwing with C4s, I've come to the conclusion that VB are like carbs - you get a good one, keep it. And if one gets to not working right it can give you a real rash.

The trans is not original, it was rebuilt and the Transpak added before I purchased the car by the previous owner, that said, I don't know how old the rebuild is, and the car has seen some bracket racing plus some performance street play behind a mild 320hp 306. So it's not original, but it's also not fresh, is what I'm trying to say. If I can get away with a simple fix for a while that would be great as I wasn't planning on doing a trans rebuild at this time. I wanted to wait when I install a 347 motor later this summer. I suppose nobody plans for a trans failure (lol) so if that is the only way to go after I try cleaning the VB and adding some Trans-X then I will cross that bridge at that time.

Thanks for the tips.

Hmm - has it worked right previously? If not, then I'm leaning toward the VB or a seal install problem. The high/rev clutch piston seal is a bugger to get in correctly. It's a simple install, but a tight fit and the seal can get damaged with a heavy handed installation.

Originally Posted by PaceFever79

The trans is not original, it was rebuilt and the Transpak added before I purchased the car by the previous owner, that said, I don't know how old the rebuild is, and the car has seen some bracket racing plus some performance street play behind a mild 320hp 306. So it's not original, but it's also not fresh, is what I'm trying to say. If I can get away with a simple fix for a while that would be great as I wasn't planning on doing a trans rebuild at this time. I wanted to wait when I install a 347 motor later this summer. I suppose nobody plans for a trans failure (lol) so if that is the only way to go after I try cleaning the VB and adding some Trans-X then I will cross that bridge at that time.

Thanks for the tips.

PaceFever,
I plan for failures. I built my wife's tranny when I saw that the adjustment was about gone on the front band. It had't given any signs of failing yet. I am building a tranny for one of my Mavericks right now because it has developed "morning sickness" (slow to engage in forward when cold). I will have it ready to install whenthe local community college is doing transmissions next fall. Having said all that and hearing you say that you are not a guy that likes to do a job two or three times I will try to make my answers fit.
The higher than normal oil level wouldn't cause the problem.
If you have reverse when the transmission is cold but no high gear (they use the same clutch) and all the other forward gears work properly when cold (they use the other clutch that high gear does) then I would say it must be the valve body. I would like you to check whether or not the vacuum hose on the modulator (just behind and slightly above the pan) has any oil in it. If there is oil there then you should replace the modulator first. Use a green stripe modulator and don't lose the pin that is between the modulator and the valve. If that doesn't fix the problem then you have replaced a part that was going to give trouble in the future and have not wasted time or money. If that does fix it then I have prevented wasting your money on a valve body that you don't need. If it does nothing then by all indications your valve body needs to be replaced and I would recommend the valve body of your choice from Broader Performance. Get it with the idea of what you will want when you install your new engine. Broader is the best place to go for performance C4s and their parts. I build excellent C4s but I believe that Broader's C4s are at least as good as my own. I would not have a problem buying one for my own use. They are the only rebuilder that I would buy from for my own use.

Hey Paul,

I tried the Seafoam additive just for the heck of it, drove it around for 10 miles, let it sit over night, and still no sign of third gear for the first mile when cold. No big surprise, but I thought I'd try it anyway. I did however notice this time that when it is cold and hanging in 2nd gear while in the drive position, when it shifts to "neutral" instead of 3rd gear, if I mash down on the throttle to about 4,000 RPM it will suddenly drop into 3rd gear and chirp the tires with a good firm shift. There is a bit more intel for you to consider; it will shift into 3rd when cold, I just have to get the pressure high enough by revving the motor real high. When it does shift into 3rd gear it is super crisp, no slipping at all. And when it warms up after a few miles it shifts through all the gears normally in drive.

On a side note, I think my MSD6AL ignition box crapped out on my last transmission test drive -- the car was running great, I hopped on it at a light and shifted hard to 70. Came to the next light and suddenly it just died, started right up, then died three times while I was driving it home, then the 4th time, it starting missing and losing power, I barely got it back to the garage and opened the hood before it died again and now it won't start. It has spark, but it is weak at the plugs, it will try to start but it won't actually start. I'm pretty sure it's the MSD6AL.

LOL

So much for cruising this weekend :-(

Originally Posted by ckelly

Hmm - has it worked right previously? If not, then I'm leaning toward the VB or a seal install problem. The high/rev clutch piston seal is a bugger to get in correctly. It's a simple install, but a tight fit and the seal can get damaged with a heavy handed installation.

Yes, it worked fine before. Shifted fine when cold. And very crisp under power. The only thing that changed is no cold shift into 3rd. It still shifts firmly into 2 and 3 after it is warmed up.

If it goes into third under very hard throttle it might be the pressure or it might be the shear volume of oil going to the clutch. You might look at the 2-3 shift valve and related spring. You might have a sticky valve that has just enough more clearance once the aluminum valve body warms up and expands. If you remove it and polish it in a drill press or lather using ATF and 600 grit emery paper it may free it up and work right.
You will have to pull the Valve body out of the C4 to do this.