TH350 Rebuild Questions

[scenic760]

There is a lot of metallurgy in those sprags. It’s not just the heat treat, it’s the case hardening and the metal they are made from that’s the biggest concern. You can have a sprag with the right heat treat, but if it’s not case hardened and “tempered” correctly it will be to brittle. It needs to be hard where the rollers ride, but soft enough in the center to allow the part to flex instead of cracking. I hesitate to even suggest aftermarket replacements because there is some really poor quality parts being made.

I built a 350 for a friend, the trans went into a mild small block Camaro. The bought the sprag and overhaul kit from eBay, it didn’t last 3 weeks before it exploded. Tore up the pump, obviously the direct drum, and lots of shrapnel. The stock drum a and stock sprag race I reinstalled are still going last I heard.

Same thing with the 4L60/4L60E aftermarket 5 pinion carriers. You need to buy that kind of stuff from a reputable place. The money saved buying junk won’t go far having to fix the damage.

Agreed!

I tried to order the Hughes sprag race from a few different places but they were out of stock...the place I ordered from seemed reputable but I have tried emailing them 3 times now to verify they indeed sent out a hardened sprag race with no reply...not really wanting to take a chance...I think I'm going to send it back and order the Sonnax item from Summit.. interesting video they posted on their website re: how they redesigned the whole thing

I was looking into the torrington bearing vs thrust washer and was thinking there isn't much benefit to switching those out as the entire assembly is floating in trans fluid? Almost the opposite as the bearing could explode?!

 

[Raider L]

@Matt69olds,

Coming from a position of almost total ignorance about transmissions, almost. As in going from a cast iron crank shaft to a 4140 steel crank, why don't people go to a 4140 sprag instead of a iron one heat treated? Like you just said, where the unit is weak and upgrade to a stronger part, etc., just make one out of a stronger material to start with and step over the meticulous process of heat treating. Then you would know the part was strong. I am taking into consideration what you said about , Where it needs to be hard and where it needs to be soft, etc... still why not make the sprag out of Chromemoly and other parts as well?

 

[Matt69olds]

I know next to nothing about metallurgy. I know a LITTLE about heat treat, only because I use to load/unload heat treat furnaces at the factory I worked in. The furnaces were HUGE. Good Lord, that was hot hard work, I lost 25 pounds the 2 years I worked in that Dept.

The gears that I loaded were in the furnaces for about 18 hours. There were people who were in charge of the internal environment (atmosphere inside the furnace, temperature, things like that) of the furnace, and the time the parts were inside was carefully controlled. If the environment is correct, and the time spent in the furnace is correct, then you should get a part with the correct heat treat and case hardness. Every 20 cycles someone from the metallurgy lab would take a part, check the Rockwell, and then cut it in half to verify the case hardening was correct. I don’t understand all of it, way beyond my pay grade. It was a interesting job though.

Im sure the kind of steel used has a big influence on the “recipe” used to heat treat. Once again, well beyond my pay scale! It takes someone with far more knowledge and training to figure all that stuff out.

I would think any company making parts like that would have to go thru a similar process. It would be pretty expensive and take a lot of trial and error to get it right.

 

[Vbb199]

I know next to nothing about metallurgy. I know a LITTLE about heat treat, only because I use to load/unload heat treat furnaces at the factory I worked in. The furnaces were HUGE. Good Lord, that was hot hard work, I lost 25 pounds the 2 years I worked in that Dept.

The gears that I loaded were in the furnaces for about 18 hours. There were people who were in charge of the internal environment (atmosphere inside the furnace, temperature, things like that) of the furnace, and the time the parts were inside was carefully controlled. If the environment is correct, and the time spent in the furnace is correct, then you should get a part with the correct heat treat and case hardness. Every 20 cycles someone from the metallurgy lab would take a part, check the Rockwell, and then cut it in half to verify the case hardening was correct. I don’t understand all of it, way beyond my pay grade. It was a interesting job though.

Im sure the kind of steel used has a big influence on the “recipe” used to heat treat. Once again, well beyond my pay scale! It takes someone with far more knowledge and training to figure all that stuff out.

I would think any company making parts like that would have to go thru a similar process. It would be pretty expensive and take a lot of trial and error to get it right.

Ahhh man, another dead end!
No problem tho matt! Once day i'll find someone who can give me answers regarding the steels in drivetrains

 

[scenic760]

Ok...so I went to replace the output shaft bushing and nothing there....there is a plastic bushing that looks like it fits right in there?

The shaft assembly has some "slop" to it, is it supposed to or is it supposed to be solid?

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[Matt69olds]

Originally they had a bushing. Later in the production run they went to plastic as a cost savings. Technically, it’s not a bushing, it’s a seal to keep lube oil from leaking between the forward clutch housing and output shaft.

Personally, I’d want the metal bushing. As far as GM is concerned it’s not a bushing. While that may be the case, I’d think a bushing would help keep things running on center much better than a plastic sleeve.

 

[scenic760]

Originally they had a bushing. Later in the production run they went to plastic as a cost savings. Technically, it’s not a bushing, it’s a seal to keep lube oil from leaking between the forward clutch housing and output shaft.

Personally, I’d want the metal bushing. As far as GM is concerned it’s not a bushing. While that may be the case, I’d think a bushing would help keep things running on center much better than a plastic sleeve.

That's why accountants shouldn't design cars! I like the idea of a metal bushing too... I will order one

I order an additional 2 sun bushings a couple days back too..someone should make a legit bushing pack instead of just throwing the stock ones out there!

 

[Matt69olds]

If the bean counters would stay away from engineering, then the chevy Vega, Olds Diesel engine, Cadillac 4100, and countless other screwups wouldn’t have happen. Seems like most of the new design problems eventually get figure out and go on to be pretty successful. Unfortunately, by the time things get figured out and become pretty reliable, the bad reputation is well known.

 

[scenic760]

Ok...it's coming along...I think....

I have the bushings back in the stator and tested it on the shaft and it turns but not very freely...is there any level of tolerance to it or do I need to pull it off and adjust the drive on the bushings?

 

[Matt69olds]

You may need to polish the bushings to get a good fit. Sometimes the bushing driver roughs up the bushing driving them in place. I have a wheel cylinder hone that I use to polish the bushings. A few passes with some sandpaper might be all it takes.

 

[scenic760]

Is there any kind of cutaway diagram of the lip seals? I've seen a lot of videos, and read a lot, but I think this is a case where a picture would be worth a thousand words in where/how they are supposed to seal.

Hang on...I think I got it....your basically making sure the outer seal doesn't bind up and flip the other way? I was practicing with old seals and the direct piston..

 

[Matt69olds]

The pistons are machines so the seals only fit one way. The bottom of the piston is narrower so the seal lip kinda hangs over the edge. Same thing with the center seal in the drum.

The service manual has a diagram.

 

[scenic760]

The pistons are machines so the seals only fit one way. The bottom of the piston is narrower so the seal lip kinda hangs over the edge. Same thing with the center seal in the drum.

The service manual has a diagram.

Thanks Matt! Yeah.... I thought about it conceptually for a minute and realized exactly what they were they to do and it all made sense...

 

[scenic760]

Ok...so I got everything put back together and when i test fitted everything for endplay all went well...everything moved freely and all was good..

When I put all the clutches, pump rings and oring in the pump doesn't seem to fully seat- but will bolt down and everything is extremely tight and won't move by hand and BARELY with a pair of vice grips..is this normal with the clutches in or is something binding up?

 

[Bextreme04]

Ok...so I got everything put back together and when i test fitted everything for endplay all went well...everything moved freely and all was good..

When I put all the clutches, pump rings and oring in the pump doesn't seem to fully seat- but will bolt down and everything is extremely tight and won't move by hand and BARELY with a pair of vice grips..is this normal with the clutches in or is something binding up?

No, not normal. You probably have a clutch not set all the way in and that makes it bind up when you put the pump on. It should turn freely when all bolted together or you are going to burn it up.