TH350 Rebuild Questions

[Matt69olds]

https://www.chevydiy.com/gm-th350-transmission-assembly-guide/

pretty good info

 

[scenic760]

https://www.chevydiy.com/gm-th350-transmission-assembly-guide/

pretty good info

Thanks Matt.. I have been switching back and forth between that link, a you tube video and this forum, haha...

I think I got it right and hopefully will see sooner rather than later! Now I'm on to the transfer case and driveshafts but from what I remember that was pretty straight forward.

When I go to put it back in, I'm planning on installing the transfer case in the truck and putting the trans on the engine and picking the whole assembly back in. Does that sounds like the preferred method?

 

[scenic760]

Ok... I'm getting ready to put everything together and I did something I'm not so sure I should have done now...

When I was torquing up the pump bolts, sure as heck the last one (I think right at 6 o'clock), started to feel soft so I backed out the bolt and looked down the hole.. didn't see any shredded aluminum but thought it best (at the time anyways) to take precautions to not completely strip the hole. I did the old copper strands in the hole and it worked well and I was able to torque the bolt down to 21 ft lbs... Now I read a little further, does ATF flow through the bolt holes?

 

[Matt69olds]

I don’t think any of the holes go all the way thru to the inside of the case. You shouldn’t have any problems with oil leaking around the bolt.

If you have any doubt about the bolt torque, pull the pump and helicoil the threads. The 2nd gear piston puts a bunch of force on the pump bolts. If you think about it, the piston basically tries to push the pump out of the case in 2nd gear. The only thing stopping it is those bolts.

 

[scenic760]

I don’t think any of the holes go all the way thru to the inside of the case. You shouldn’t have any problems with oil leaking around the bolt.

If you have any doubt about the bolt torque, pull the pump and helicoil the threads. The 2nd gear piston puts a bunch of force on the pump bolts. If you think about it, the piston basically tries to push the pump out of the case in 2nd gear. The only thing stopping it is those bolts.

Thanks Matt!

I needed to hear that from someone with more experience than I! I'm relatively confident in the holding power of that bolt as it didn't "technically" strip but I could feel it wasn't going to finish torquing up. I've done the copper strand trick a few time with excellent results.

Only one way to find out right?!

 

[scenic760]

Well...reporting back after I took her on the maiden voyage to fill up the gas tank and hopes for a smog check...

Seemed to reverse out of the driveway fine and headed on down the road. I went about 2 miles to hopefully fill up at a Costco and saw the line and said I'll pay the extra twenty cents per gallon at the Mobil...I needed to make a u-turn at a light and I noticed transmission was slipping.. jumped on the freeway and headed home. After the 2 miles home I stopped and got gas, and was able to drive away but seemed to be slipping worse. I live on a slight incline and had some trouble making it up the hill, slipping all the way.

I tried manually shifting it just in case and it seemed that if I went down to 1st, it slipped worse and then if I shifted to 2nd it caught for a second and then started slipping again. It seemed only the shift to 2nd (from either 1st or 3rd) would produce any sort of grab.

First thing I did was check the fluid which seemed a little low so I added some fluid and tried again, same results. It's a 350c so the next thing I did was disconnect the vacuum to the lockup switch and nothing changed. I read a round a little bit and I checked the vacuum to the modulator which seemed fine. When I crawled under to look at the modulator it looked like fluid was coming out of the bellhousing...does this mean I have a pump problem?!

Thanks again all!

 

[Bextreme04]

Well...reporting back after I took her on the maiden voyage to fill up the gas tank and hopes for a smog check...

Seemed to reverse out of the driveway fine and headed on down the road. I went about 2 miles to hopefully fill up at a Costco and saw the line and said I'll pay the extra twenty cents per gallon at the Mobil...I needed to make a u-turn at a light and I noticed transmission was slipping.. jumped on the freeway and headed home. After the 2 miles home I stopped and got gas, and was able to drive away but seemed to be slipping worse. I live on a slight incline and had some trouble making it up the hill, slipping all the way.

I tried manually shifting it just in case and it seemed that if I went down to 1st, it slipped worse and then if I shifted to 2nd it caught for a second and then started slipping again. It seemed only the shift to 2nd (from either 1st or 3rd) would produce any sort of grab.

First thing I did was check the fluid which seemed a little low so I added some fluid and tried again, same results. It's a 350c so the next thing I did was disconnect the vacuum to the lockup switch and nothing changed. I read a round a little bit and I checked the vacuum to the modulator which seemed fine. When I crawled under to look at the modulator it looked like fluid was coming out of the bellhousing...does this mean I have a pump problem?!

Thanks again all!

Has it not been driven since last June?!?! For it to be slipping right after a rebuild, you either messed something up in the pump, valve body, or maybe a piston problem? I have no real experience rebuilding a TH350 TBH. My first thought would be to check line pressure in every gear. I wouldn't drive it much if at all in that condition though, unless it was to take it to a transmission shop for troubleshooting.

 

[scenic760]

Has it not been driven since last June?!?! For it to be slipping right after a rebuild, you either messed something up in the pump, valve body, or maybe a piston problem? I have no real experience rebuilding a TH350 TBH. My first thought would be to check line pressure in every gear. I wouldn't drive it much if at all in that condition though, unless it was to take it to a transmission shop for troubleshooting.

It has not...long story short is I had all of the components rebuilt and sitting in the garage to go back in and then I ended up buying a house that needed a lot of work... priorities changed...

I agree with the fact I shouldn't be driving it all that much...it would be cheaper for me to swap it out with a rebuilt unit than even pulling into any shop bay around these parts...

Feeling a bit defeated at this point but like Vince Lombardi said, we all get knocked down- what matters is who gets back up!

 

[scenic760]

After racking my brain and going through the links and notes I have, I did do the dual feed mod as recommend but I really don't remember tapping and plugging the reverse feed hole... Would that give me the behavior I'm experiencing?

 

[scenic760]

So after doing some more reading, it seems if the vacuum modulator diaphram is bad it will suck tranny fluid and you will get smelly white exhaust.

That is actually something I have happening as well which I thought was odd with a rebuilt engine but given the truck sat for 5 years I thought is may have been bad stuff from before just being blown out the exhaust. I pulled the modulator and used a vacuum pump on it and I'm not really sure how these things work but there didn't seem to be ANY air getting through at max vacuum?

 

[scenic760]

So I looked at the modulator, vacuum line and everything in between it and all good. Hooked it back up and tried it out...seemed to do fine up and down the driveway and street so I'm thinking it only happens when the tranny gets warm...if the cooler lines are backwards would that have anything to do with it?

 

[scenic760]

Ok...yet another twist... I went to stomp down on the ebrake and it doesn't even get to the first click...

I rebuilt the brakes/master cylinder while it was in the driveway and adjusted the drums to what I thought was good...I have to say I was impressed at how well it stopped! However, is it possible the brakes were dragging on my maiden voyage and heating up the tranny to the point of slipping?

I will jack up the back wheels tomorrow and see if there is an issue