Hey guy, hopefully someone can point me in the right direction here. Been a mechanic my whole life, been a HD diesel mechanic the last 10 years, have worked on a few transmission before but at this point it was many many moons ago.
rebuilt a th350 for my buddy’s 1966 Pontiac, he just picked it up used so I have no idea how she drove before hand. Put new clutches, seals, bushings in it, the kit he got came with a shift kit in it also. Swapped it out with the th350 that was in his car. Has forward and reverse but seems to only have second gear. Pulling it down into manual low feels like it is applying two gears at once, car will not move, if slightly rolling it will drag car to a stop. Called the shift kit hotline, he said direct clutch must have rolled seal, bleeding off pressure.
take two. Removed trans and tore down again, direct clutch seals all look great, figured while in there a second time had piston turned down and installed 5th friction disk, clutch clearance ended up at .038”
also found 2-4 shift valve in valve body was Very sticky, installed the one from the original working transmission. Put all back together, and tried again.....
same thing. The car is running like a bag of **** for some reason which makes trying to diagnose the trans a pain in the ***, it did shift one time, I believe from second to third, but still no first and if you pull it down into manual low it locks up. What did I do wrong? Part of me wants to install the valve body from the old trans to eliminate that. Another part of me wants to remove the shift kit parts all together?
Any ideas???
thanks for your time

 

Put in old VB
check shift linkage too. Make sure ML isnt actually park

 

When the transmission is in Manual 1st:
-The Forward clutch is applied.
-The Low-Reverse clutch is applied.

When the transmission is in Reverse:
-The Low-Reverse clutch is applied.
-The Direct clutch is applied.

If the transmission seems to lock and not move, when in Manual 1st...
Most likely there is an internal leak that is applying the Direct clutch when it should not be applied.

The combination of the Forward, Low-Reverse, and Direct clutches... are what is used for a Trans-Brake to hold the car in place.
This sounds like what is occurring with your THM350.

What is this "Shift-Kit" that you used?
I would be baffled if they did not give you the same information that I just typed.

Did the shift-kit include "Dual-Feeding" the direct clutch?
Making a mistake with this modification can cause what you are describing.

 

The kit that came with it is a TCI 350000 trans-scat
. Basically was a new separator plate, an additional oil transfer plate and 3 new springs. One for pressure reg, one for man low and one for 2-3 shift.
monounsaturated installed 2 of the check ***** as per instructions. The second time I had it apart air checking direct clutch on the pump was good, checked again once pump was in, didn’t hear any leaks but hard to say. accumulator spring was broken in this trans but I installed a new one.

 

What they told me over the phone was direct clutch was bleeding down, I don’t seem to find anything wrong with it though

 

Nothing mentioned about dual feeding, and I didn’t do anything to accomplish this.

thanks again for your help

 

You mentioned an "additional oil transfer plate"...?

As in a separator plate for the valve-body?
If so... some of these do "dual-feed" the direct clutch.

 

I just looked up that shift kit.

I do not like it at all... far from ideal in terms of transmission life expectancy.
Sorry... I would consider the TransGo THM350 "shift-kit" instead.

Yes, the separator plate included "created a new oil circuit"... this is a "dual-feed" modification.

You definitely have an internal circuit leak that is applying the direct clutch, when it should not be applied.

 

I thought that extra transfer plate was hokey, it says it doesn’t use gaskets( which I think is wrong) even over the phone I asked the guy and he said it doesn’t need gaskets.
I think I’ll pull the valve body out and get rid of the shift kit
thanks

 

Aluminum separator-plates often will not use paper gaskets on PowerGlides, THM350s, and THM400s.

Is the plate that you have aluminum?

 

If you do remove that shift-kit...
I would recommend the "TransGo 350-1&2" model shift-kit instead.

Good luck!

 

How many intermediate clutches did you install (2 or 3)and what size intermediate apply piston did you use. Remove your pump and if the piston is taller than the spring cage you have a two clutch piston. When this clutch pack is stacked it causes a manual low bind you described. The shift kit you have will work fine no need to get another.

 

Other possible causes would be a cross-leak at the Low-Reverse piston, a cross-leak at the Direct piston, 1-2 valve-train issue, 2-3 valve-train issue, or separator plate/ gaskets cross-leaking.

 

Have the trans back out and completely torn down to the bare case, all piston seals look perfect. Separator plate gaskets look good, can’t see anywhere where fluid has been crossing anywhere. Intermediate has 3 friction disks, intermediate piston is below spring cage( and when I calliper pump/ case to wavy steel I have clearance)
no idea, I think it’s going back together with the known working valve body out of the old trans.

 

 

only thing I don’t like is this area in the direct clutch passage that looks like it’s been hogged out... unless this is normal. Makes the sealing ledge look thin, but again gasket in that area looked good

 

Just looked on the old trans and it doesn’t look like this

 

Did you assemble the Forward-Drum and the Direct-Drum into the Pump-Assembly (Outside of the transmission Case), and Air Test the circuits?

 

Has the case passage in the pump-flange (that is shown in the image below) ever been plugged/ blocked-off?

 

Yes I did, seems good to me