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Discussion Starter · #1 ·
I am working in a group for a school project where we are building a small pulling tractor. We have decided to convert a TH-350 tranny from an Oldmobile into a manual shifting tranny. We have rebuilt the trans ourselves and installed a TCI reverse shift pattern manual valve body in the trans. We removed the torque converter and replaced it with a TCI front pump drive. We have been trying to test the setup on our test stand but we are unable to start out in first gear, it starts in second. Actually, the driveshaft RPM drops slightly when we shift from 1 to 2, but 3 seems fine, but reverse is sluggish to engage. The trans seems to heat up quickly and we are reluctant to run it very long so we do not burn it up. I have talked with TCI already and they say that we have setup and installed the valve body correctly, so we are thinking that the problem must be internal. We did not rebuild the clutch pistons, but before we dig into it again, I was hoping someone would have some ideas about what might be wrong with the trans. Please let me know.

Thanks, Jackson
 

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jackson.king said:
I am working in a group for a school project where we are building a small pulling tractor. We have decided to convert a TH-350 tranny from an Oldmobile into a manual shifting tranny. We have rebuilt the trans ourselves and installed a TCI reverse shift pattern manual valve body in the trans. We removed the torque converter and replaced it with a TCI front pump drive. We have been trying to test the setup on our test stand but we are unable to start out in first gear, it starts in second. Actually, the driveshaft RPM drops slightly when we shift from 1 to 2, but 3 seems fine, but reverse is sluggish to engage. The trans seems to heat up quickly and we are reluctant to run it very long so we do not burn it up. I have talked with TCI already and they say that we have setup and installed the valve body correctly, so we are thinking that the problem must be internal. We did not rebuild the clutch pistons, but before we dig into it again, I was hoping someone would have some ideas about what might be wrong with the trans. Please let me know.

Thanks, Jackson
DID you rebuild the trans at all? Or simply look inside at the parts?

Its possible you cut/broke some sealing rings if you had the pump assembly out.

:cool:
 

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Discussion Starter · #3 ·
We replaced the friction disks and steels plates and thrust washers. Also replaced the seals on the piston attached to the front pump. We purchased an overhaul kit that has everything short of the planetaries.

The other mods we have made to this trans are: removing the "non-removeable" bell housing, tapping into the pressure side of the pump and installing a hydraulic ball valve that we can open and close to control pressure to the clutch packs, when we first installed the front pump coupler drive (replaces the torque converter) and tested the trans, we found that the pressure supplied to the pump drive want to push the drive out of the trans, so we tapped into the front pump again in the converter feed port and installed a bypass line and pressure guage, with line installed, the pressure in the converter feed is around 30psi (GM recall notice we found states that 30 psi will provide proper lubrication for the trans, but will also stop the thrust load on the pump drive/converter), both lines we have installed return the fluid to the pan to be reused.

When we were done with the mods to the trans, we cleaned the trans housing the best we could, flushing out every port and gallery we could find. Unfortunately, when we removed the the pan to trouble shoot after our first test runs, we found a lot of aluminum filings in the pan that we must not have been able to remove (the filter had a good layer on it too). Would those filings shred the seals in the pistons? Also, this tranny was removed from a junked '81 Chev 1/2 ton 2wd truck, it had the imfamous 5.7 liter diesel, when we tore into the tranny, we found that someone along the way had installed an Olds tranny in it, the truck had about 30-40000 on the rebuilt trans (my family owned it since '85), and when my dad parked it, he said the trans was feeling soft. Could it be nothing more than the piston seals are old and worn out and need to be replaced, is there a good way to test the seals without removing them from the trans and physically looking at them?
 

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OK.... from what I gather here you did not perform a full proper rebuild on the trans..... and now the pan was full of metal.

I can safely say that now the trans needs a full rebuild IMHO.

I am curious what type of test stand you are using to test the trans if you have cut the bell housing off.

next question is ; if this trans came out of a 1981 vehicle... is it a t-350C lock up trans?

the 5.7 diesel engine was a BOP bell housing design as I recall... :confused:
 
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