Hey everyone. I'm back for some more help and I've got some strange tranny problems.

Background: New Rebuilt 302 Engine in a 74 F100.
New TCI C4 Street Fighter Transmission and Torque Converter
Stock rearend.

Issue: When the truck gets warm about 20 mins after starting out, the transmission will stop downshifting to first gear at redlights. I also notice that the 1-2 shift is somewhat rough and "unsure". When the tranny is cold I do not experience this. There also may be a slight hum coming from the tranny once things warm up. I can't tell exactly what the source of the hum is but its a low droning that I don't think is normal.

What I've Checked: Fluid level is good, I am running Napa Brand Type FA fluid, it's also new fluid within the last 2 months and I've not driven the truck much. Steady vacuum reading from the engine at 22 in.

I have ordered an infrared temp gun to check and see if the fluid is overheating but after my troubleshooting tonight, I don't think that's the issue. I'm worried it could be torque converter issues. Is it possible to have the torque converter installed wrong but the truck still operates? Back in my younger days, I installed a C4 and had the torque converter in a bind, but you realize that pretty quickly when the engine won't turn over...

Anyway, you folks have any thoughts? Otherwise, I may end up at the transmission shop...

Thanks in advance

 

A little more info... I just got off the phone with a TCI tech rep. He seemed quite knowledgeable on the subject.

Here were his thoughts:
Potentially the piston that actuates with the vacuum modulator is hanging up. When the tranny is cold the viscosity and operating pressure are a bit higher and can overcome the hangup. Once it warms up and the operating pressure drops some, the piston begins hanging up. He said the same thought could be applied to the governor as well. I've had the governor apart a little while back and it was clean and moved freely... so I'm not saying that's not it, but most likely that's not it.

Furthermore, he said if I was overheating, the first thing I'd see was the transmission spitting fluid out on the ground from the vent on top of the tranny. Also didn't think it was torque converter related. He didn't think fluid temp could play any role in torque converter function.

Anyone agree/disagree with this assessment?

 

Well I am still messing with the transmission... I purchased the Haynes Techbook and a pressure gauge and ran some tests on the truck (I also installed a cooler).

I have learned that the pressure in my drive range (D) is below the spec that the Haynes manual calls: Haynes says 60-90 psi at idle with the brake applied. When cool I'm at about 62 psi, but once the transmission warmed up (trans temp ~180F) it dropped to about 55 psi. All other ranges are toward the low end of the spec, but still within the Haynes requirements.

I'm not sure where to go from here though. They manual mentions checking for leaks in the servo's and practically all of the clutches, but it doesn't explain how to do that and I'm sure the transmission has to be completely taken apart to inspect all of these items... I'm thinking it may be time to let an expert take a look at it.

If anyone has any last minute advice or can help out I would appreciate it. Otherwise I will let you know what the shop says...

If anyone has a recommendation for a shop around Raleigh NC let me know! C4 experts aren't that easy to come by these days.

 

Closing the loop on this thread...

I ended up sending the tranny back to TCI and although they never found any issues during the teardown, I told them to go ahead and replace clutches and seals. Seems to have solved the issue. Drove the truck a few days and shifting seems to be on par.

I will note, I am running ~22 in vacuum at the modulator valve on the transmission and it took a good bit of adjustment to get the shifts to spread out. I've heard the rules about not tightening too many turns and whatnot, but I probably had to go 7 turns in before the shifting was in the right spot. TCI tech actually advised me to do it... I was afraid to go more than 3 turns. It is a TCI modulator so maybe they have more room for adjustment.