Need help with a TH350 problem

[JunkCollector]

I have a '78 C10, 350/TH350, first turbo 350 I've ever had "major" problems with and I can't seem to find any posts with the exact same symptoms I have.

Reverse works fine. Put it into Drive and it does nothing at all, acts like neutral. Put it into 2nd and it still does nothing. Put it into first and it goes into first gear fine. Get it rolling a few miles an hour and put it back in D and it shifts normally through all 3 gears, nice firm shifts, no slipping, kicks down like its supposed to. I can leave it in D if I come to a rolling "stop" and take off again, if I come to a dead stop it neutrals out and I have to put it back into first again to take off. It acts the same cold or hot.

The fluid is clean and full. The shift lever is adjusted properly. Good vacuum to the modulator and the modulator holds vacuum. I pulled the governor out and checked it out, gear is perfect and the weights & valve move free. Everything beyond this is over my head. I am an experienced mechanic, I can build an engine or a standard trans but my SOP on slush boxes has always been pull it and send it to the tranny shop if its more than a fluid/filter change or seals. I've been wanting to learn more about repairing autos and I figure my own personal Th350 is the best place to start. TIA for any suggestions/help

 

[C10MixMaster]

I have a '78 C10, 350/TH350, first turbo 350 I've ever had "major" problems with and I can't seem to find any posts with the exact same symptoms I have.

Reverse works fine. Put it into Drive and it does nothing at all, acts like neutral. Put it into 2nd and it still does nothing. Put it into first and it goes into first gear fine. Get it rolling a few miles an hour and put it back in D and it shifts normally through all 3 gears, nice firm shifts, no slipping, kicks down like its supposed to. I can leave it in D if I come to a rolling "stop" and take off again, if I come to a dead stop it neutrals out and I have to put it back into first again to take off. It acts the same cold or hot.

The fluid is clean and full. The shift lever is adjusted properly. Good vacuum to the modulator and the modulator holds vacuum. I pulled the governor out and checked it out, gear is perfect and the weights & valve move free. Everything beyond this is over my head. I am an experienced mechanic, I can build an engine or a standard trans but my SOP on slush boxes has always been pull it and send it to the tranny shop if its more than a fluid/filter change or seals. I've been wanting to learn more about repairing autos and I figure my own personal Th350 is the best place to start. TIA for any suggestions/help

my best guess is low reverse roller clutch has failed. that will require a rebuild.

in low and reverse the low reverse clutch engages. in drive it uses the roller clutch to engage.

 

[Matt69olds]

I’d lean towards a roller clutch issue as well. TH350 aren’t hard to rebuild if you take your time. The tools needed are easily fabricated.

 

[HotRodPC]

I'm going to go with the direct clutch pack is wore out time for rebuild. Or am I backwards and it's the forward clutch pack.

So 1st gear is made differently in both D and Manual 1st. The fact you can only get 1st gear manually and R works good tells us the Low/Reverse Clutch pack is good since it's needed to make both of those gears. In D, I thnk the common denominator is the Direct clutch pack for all forward gears as if Forward clutch pack. So the direct clutch pack is worn to the point it won't hold good enough to get you rolling and going. Using manual 1st with the Low Reverse and Forward clutch packs to get you going, then you shift to D the strain to get rolling is now worked around.

So without looking at the flow chart diagram to verify what clutch packs, band and roller clutches are active and not active in any given gear, I'm tossing up a guess as to what EXACTLY is wore, but nonetheless, regardless of which pack it is worn, there is a clutch pack worn and it needs to be rebuilt.

 

[HotRodPC]

BTW, I know it's not the intermediate roller clutch or intermediate clutches. If that was the case, even in D, you'd have 1st, then wind it up real good and it would go to 3rd skipping 2nd, but you say no 1st in D either, so that's NOT the problem. My guess is, no broken hard parts, but there is a wore out clutch pack.

 

[JunkCollector]

Thanks everybody! I was hoping it would be something simple but looks like I'll be attempting my first auto rebuild soon. I'm going to dig a core trans out of my spare parts pile to rebuild so I can continue to drive it for the time being, pretty sure I have an identical trans from a '77. Any recommended overhaul kits before I go buy a Pioneer 753026?

 

[71RAT]

X'3 for low roller. Direct clutch failure, would result in no 3rd or reverse. You can up date to a th700/4L60E support, uses a wider/taller roler clutch.

 

[Matt69olds]

Th350 drive range, it’s gear needs the forward clutch to apply, the low roller clutch is locked and holding. 2nd gear brings the intermediate clutch on, 3rd gear adds the direct clutch. The forward clutch is applied in every forward gear. The intermediate band is used to keep the direct drum from overrunning in manual second, providing engine braking. The low clutches provide engine braking in manual first gear. The get reverse, the direct clutch becomes the driving clutch, the low clutches hold, and the low roller clutch free wheels, or overruns. Usually, lack of drive, or “chattering” is caused by weak springs or damaged rollers. Sometimes, the outer race of the roller clutch will be shattered, usually from rocking a car/truck stuck in snow or ice. Spinning the tires in reverse has the roller clutch overrunning, putting it in drive makes the roller clutch lock, the strain of locking the sprag with the tires spinning causes a huge shock to the sprag. The same kind of damage is common in trucks with snow plows. The 700 roller clutch had larger rollers, with a wider inner race. It’s a easy swap.