C4 - Rebuilt No Low Gear

[jeffncs]

Over the past couple weeks I rebuilt my c4 following the Bad Show videos (awesome BTW!!). Found damaged parts, had to wait on some other parts and life got in the way.

It’s now 12:45am after 8 hrs of final trans assembly and install. No leaks, all good. Test drive… seems to be starting in 2nd. Reverse is fine. 2-3 shift is fine. Just no first. Shifter has to be pulled down below where standard D would be so that tells me I’m probably not getting 1st engagement.

Readjusted the pass side low-reverse. A stall and dead battery killed my test drive but seemed to still be in 2nd and the shift lever had to be pulled down below standard D again.

Before pulling the pan and valve body… anything else to check or do?

All air tests passed with activation of the pistons and clutch packs during final assembly.

Hoping valve body at worst to avoid pulling it apart again…. But willing to do what it takes to get it right.

Thanks in advance.

 

[Yeller]

If it will shift to first when pulled there manually the governor is stuck. Common after a rebuild. Any microscopic piece of dirt you missed always seems to find it and cause it to stick. Unfortunately in a c4 that’s a transfer case removal, but better than a valve body and less fluid loss than pulling the pan.

 

[jeffncs]

Thanks @Yeller it doesn’t go into first at all. Does that point to the valve body?

Adding - when I built the valve body, the springs got jumbled. I think I got them right…. Would that creat a problem if wrong?

 

[Yeller]

Valve body or the drum is leaking, drum leaking is my guess. That can be air tested with the valve body off, I would have to research to which port, been nearly 30 years since I’ve done that.

 

[Broncobowsher]

Back when I took my automatic transmission class, 30 years ago, our training transmissions were C4s. The stuck governor fix without getting into it. Sounds crazy. Car on a hoist, get up to about 30 MPH, hold that throttle and shift into reverse. That often saved having to pull it apart and clean the governor. Good news with a Bronco, just put the transfer case in neutral. Select drive, come up to about 2000 RPM, shift into reverse. Next step is turn off the engine, you don't want to shift to park with the transfer case in neutral, the parking pawl will hate you for it. Once the engine is off, put the transfer case in gear and shift to park. Go test drive.

 

[jeffncs]

Thanks guys.

Couple more details…

When I did the air check on the bench, one of the clutch packs was slow (rearmost which should be low-reverse).

Also - I reused the low-reverse piston because the integrated rubber was still soft. That servo seems to work fine though - will do that check too.

I’m going tackle this logically and least labor intense to most.

Sanity check the linkage. Highly unlikely the issue but it’s a few mins and free.

Pull the valve body and redo air checks. I’ll take video - if anyone willing to help please text me a cell # and I’ll send the videos to you.

If air tests fail, I’ll pull it apart again.

If they pass and while the valve body is out - check each valve assembly against a fresh, never touched assembly for correct springs and valve orientation.

If nothing found, I’ll pull t-case to check modulator (guessing unlikely since I can’t get it to go into first at all).

 

[jeffncs]

Here’s video for the air tests. Any thoughts? I’m going to look at the valve body until I hear from you guys.

 

[jeffncs]

 

[jeffncs]

 

[jeffncs]

Valve body checked out clean…. I’m wondering about the direct clutch pack as it sounds different.

 

[Broncobowsher]

I think you missed a couple of us telling you that it is probably in the governor.

 

[jeffncs]

I think you missed a couple of us telling you that it is probably in the governor.

Sorry. Maybe I misunderstood but I thought the governor was ruled out when it won’t go into first ant all. Should I check that more closely? StrictlymR, 2 and 3. No first manually or in auto mode.

I have to reseal the intermediate housing anyway.

 

[Yeller]

With no first gear at all the forward clutch is t working. Unless…… you forgot to install the sprag, aka 1 way clutch. But it wouldn’t have reverse either if that was the case. You’re on the right track.

 

[jeffncs]

Out comes the trans tomorrow! Oldest going to “help”. Rebuilding the C4 is a first for me but I’ve pulled and installed more trans and engines than I care to remember! It may take longer with his help but it’ll be good for him to learn as he drives a 33yo mustang and it’s inevitable that we’ll be pulling that driveline at some point too.

Thanks much @Yeller and @Broncobowsher !!

 

[Broncobowsher]

The governor being stuck at too high of an output pressure, the transmission thinks it is moving at speed. The higher the speed, the higher the pressure.
Thus the valve body is seeing a speed too high for 1st gear, thus it won't shift.
The drive to reverse while on a hoist (or transfer case in neutral) was taught be my instructor who was an old Ford field service guy from the 70s/80s. A couple seconds could save you from pulling the transmission.

 

[Yeller]

The governor being stuck at too high of an output pressure, the transmission thinks it is moving at speed. The higher the speed, the higher the pressure.
Thus the valve body is seeing a speed too high for 1st gear, thus it won't shift.
The drive to reverse while on a hoist (or transfer case in neutral) was taught be my instructor who was an old Ford field service guy from the 70s/80s. A couple seconds could save you from pulling the transmission.

It has no 1st gear even pulled into manual low. This would over ride that. Listen to the video, air festering the forward clutch you can hear it leaking and not applying. Hope I’m wrong but either a shaft seal got cut or a lip seal in the drum is cut.

 

[jeffncs]

Here’s my plan on the day. I have to reseal the intermediate housing anyway (leaking trans fluid). Before pulling the trans, I’ll remove the governor to check for a stuck valve. I’d expect it to be a quick, obvious find and easy to do before yanking the trans out.

That air test with the bubbling fluid sounds different from the direct clutch though. I’m prepared to go into the trans today as I may have boogered up a, o-ring or seal when installing.

Being a first time auto trans builder, I’m not sure which is right and the labor / time under the truck is killing my body. .

 

[Broncobowsher]

It has no 1st gear even pulled into manual low. This would over ride that. Listen to the video, air festering the forward clutch you can hear it leaking and not applying. Hope I’m wrong but either a shaft seal got cut or a lip seal in the drum is cut.

It has been many orbits around the sun since I last drove a C4. But I was pretty sure that manual 1 had a max speed engagment with it. That is if you were at highway speeds and yanked it into 1st, it won't go until you were slow enough. Once there it held as long as you wanted, feel free to float the valves all you want.
As for how that would apply to this, if the governor pressure is high enough that the valve body sees it as too high of a speed, this you don't get 1st.

There were a few vintage automatics that would go into 1st at any speed. The GM one (I think from a Vega) that was used un the Grumman LLV postal vehicles, they will go into 1st at any speed.

IF you go to the clutch apply charts for a C4, the forward clutch is applied in all forward gears. The fact you have 2nd and 3rd shows it is applying. At least to a degree good enough to get those gears. That will also be enough to get 1st gear.
Next is the 2nd gear band is applying. Without it you will not have second gear. And it is releasing because you have 3rd gear. So the 2nd gear circuit is working correctly.
The normal 1-2 shift is just the 2nd gear band being applied. The sprag for 1st releases. So far we can't test that sprag as we can't get first gear. If it were completely bad and that was the only problem, 1st gear would be a neutral. If the sprag were locked, the transmission would gear lock in any gear besides 1st.

Going through the clutch charts, The only options are bad governor with too much pressure while stopped or a valve body issue. The normal 2-3 shift and the valve body was re-gone through without fixing makes me think it isn't the issue. I was looking for a pressure curve chart for the governor, can't find one. But there are 2 valves in the governor. Due to the exponential curves due to speed, the 2 valves work in tandem. One is the low speed and it maxes out quickly, the other is the high speed that doesn't have the resolution at low speeds. If you can find the governor pressure curve chart, there is a curve, a kink to the line and the curve flattens out. It is what they had to do to make a governor work in this application.

 

[jeffncs]

T-case is out. Checked governor - no issues valves move freely. Recleaned and torqued back into place. Trans coming out now.

 

[jeffncs]

FaceTime with @Yeller and I think the pistons sound a lot better after his diagnostic ear!

Huge thank you to Yeller!!!!!