A few TH350 questions

[frankenstien]

Ok, back story... so as you can see from the pictures, i decided to relocate my intermediate roller clutch/sprag into the pan, and that race wasnt happy being 1 piece. that was a TCI hardened race. the 1-2 accumulator spring broke and hammered the piss out of the accumulator piston, as well as the bore.

trans was a 76 case out of a 2wd something, i built it myself about 8 years ago(my first trans ever) i used a full tci rebuild kit, with trans scat shift kit, hardened outer race, trans worked fine until it didnt. it also had the direct clutch piston machined down to fit more frictions/steels

it has been driven hard along the way, twisted off the imput shaft, ripped the bolts out of the b&m converter and broke flexplate, destroyed another b&m converter. fixed witha hughes 2500 stall converter to match new cam that was swapped in, ATI input shaft and scat SFI flexplate, ran for about 5 years like that before the sprag let go. it sits behind a dart headed 10.5:1 383 with a full roller valvetrain with an erson 284/296(IIRC) cam with .548 lift, and a quick fuel tech. 750 double pumper.

ok, now for the problem at hand

the 1-2 accumulator bore is not looking so hot, i know there are sleeve kits available, but would like to avoid that. i kept the original th350 out of the truck from 1974, 29k miles on it, can still read borg warner on the frictions, case looks immaculate.

i would like to use this case. everything looks the same, except this ones front pump only has 5 stator rings, the pump in my current unit has 6. i already went and bought a replacement pump as the old one was damaged from the sprag failure. it is a 6 stator with teflon rings. can i use the case with all my hard parts and 6 stator pump? i was thinking so, but couldnt find any solid info.

next thing is, my valve body i had in my failed trans has a different number stamped on it vs the one i got out of my core trans, the core one is out of a 1/2 ton and failed trans is a 3/4 ton

also i have been reading about people double bushing' the sunshell(dont know the name of it) part with the gear on top and bottom, then drilling out the hole in new bushing, is this common practice?

sorry for the long post, thanks for any and all info

 

[frankenstien]

heres pictures of the 2 valve bodies in question, gm28 came out of the 73 3/4(failed unit) and the 30 out of the 74 1/2(core)

 

[crazy4offroad]

Honestly it sounds like it's time for a TH400. You could do the 32 element roller clutch and see if that holds better, the thought being the pressure is spread out across more rollers and should help the hardened race at the same time. I've done the double bushing on the sun shell, not a hard mod to do, just be sure to double them on both ends not just one, and DEFINITELY remember to re-drill the lube holes lol. I also made mine internal dual-feed on the direct piston, supposed to double the clamping force of the directs. Re-drilling the separator plate's 2nd and 3rd gear feed ports to 1/8" will increase line pressure just enough, not too much. Allegedly these mods along with hardened shafts will be good to 600 hp but I have my doubts, more like 450. As for your other questions, the difference in the pump, not sure what difference that would make. I would check the case ports at the pump and make sure they match since that's how the pump feeds the trans. And the difference in the valve body, again, it would just come down to checking everything and making sure they are the same. Here are a couple links I used in my rebuild, might have some helpful info...

http://www.hotrodders.com/forum/t-350-rebuild-tech-145361.html
http://www.crankshaftcoalition.com/wiki/T-350_rebuild_tech

 

[frankenstien]

Honestly it sounds like it's time for a TH400. You could do the 32 element roller clutch and see if that holds better, the thought being the pressure is spread out across more rollers and should help the hardened race at the same time. I've done the double bushing on the sun shell, not a hard mod to do, just be sure to double them on both ends not just one, and DEFINITELY remember to re-drill the lube holes lol. I also made mine internal dual-feed on the direct piston, supposed to double the clamping force of the directs. Re-drilling the separator plate's 2nd and 3rd gear feed ports to 1/8" will increase line pressure just enough, not too much. Allegedly these mods along with hardened shafts will be good to 600 hp but I have my doubts, more like 450. As for your other questions, the difference in the pump, not sure what difference that would make. I would check the case ports at the pump and make sure they match since that's how the pump feeds the trans. And the difference in the valve body, again, it would just come down to checking everything and making sure they are the same. Here are a couple links I used in my rebuild, might have some helpful info...

http://www.hotrodders.com/forum/t-350-rebuild-tech-145361.html
http://www.crankshaftcoalition.com/wiki/T-350_rebuild_tech

yeah, i know its time for a th400, if i break this set up, ill probably nut up, but people want a retarded amount of money for a th400/205 set up anywhere from 500-1000$ which seems a little outrageous to me.

as for the dual feed, i have been reading a bit about that, but in my case i dont know that its needed, the trans has been beat on for 8 years and never slipped. also the kit i have may do that already, theres a 2nd spacer plate that goes between the upper smaller plate on the VB that has a fluid path in it.

the motor is maybe 500hp? and the truck is 6200lbs. i will check the 2nd/3rd gear holes in the spacer plate and drill them out if not already.

thanks for the links, ill take a look and check some more on what i exactly have

 

[crazy4offroad]

Yeah shift kits usually set up dual feed by the separator plate. Gotta think outside the box when searching craigslist. I can do a search for "th400" and turn up little but do a search for "chevy 400" looking for a 400 smallblock and came across a TH400 for $100 "needs rebuilt" and matching NP205 $250, all because someone don't know how to put tags on their post.

 

[frankenstien]

Talked to a local trans shop today, having him hot tank the cases, as well as look over some of the parts and replace some bushings as needed, also talked about double bushing the sun gear.

He also showed me a larger version of the low/reverse support? The one witb the rollers in it, the one he had was approx 1/3 wider than mine, said it would help out alot with strength.

 

[SkinnyG]

I would dual-feed the direct clutch. That's what all the shift kits do, and can be done during the rebuild for the cost of a 3/8" set screw. It will more than double the holding power of 3rd gear.

I also machined the direct piston down and added another clutch and steel.

Also highly recommend the heavy duty sprag race, if anything. Yours broke.

I keep all the check balls, and keep the 1-2 accumulator, but I lock out the 2-3 accumulator so that it doesn't operate. With the separator plate drilled 1/8", it shifts firm, but not brutal.

 

[frankenstien]

I would dual-feed the direct clutch. That's what all the shift kits do, and can be done during the rebuild for the cost of a 3/8" set screw. It will more than double the holding power of 3rd gear.

I also machined the direct piston down and added another clutch and steel.

Also highly recommend the heavy duty sprag race, if anything. Yours broke.

I keep all the check balls, and keep the 1-2 accumulator, but I lock out the 2-3 accumulator so that it doesn't operate. With the separator plate drilled 1/8", it shifts firm, but not brutal.

i have the direct piston already turned down for the extra plate.

that was a heavy duty sprag race. i upgraded to the TCI 36 element sprag with hardened race, came as a kit with drum and all

it already had a trasn scat shift kit in it with 2 balls only.

what does locking out the 2-3 accumulator do?

 

[SkinnyG]

I didn't notice your transmission already had a kit in it. My bad.

If you installed a shift kit that came with its own large valve body separator plate, it probably blocks out the 2-3 accumulator feed. The B&M kit does this. Blocking out the accumulator firms up the shifts, whether it's by a blocked hole in the plate or "fixing" the accumulator so it doesn't move.

If your shift kit came with the extra wee gold separator plate (small, funny-shaped), it dual-feeds the direct clutch for you, and you don't need to make the changes internally. Pretty much all shift kits have this extra plate to dual-feed the direct clutch.

Removing the check balls (typical of B&M shift kit), and removing the 1-2 accumulator spring (typical of most shift kits) makes the transmission shift VERY hard, especially hard on the weak intermediate sprag (which you broke). Do consider putting all the check balls back in. The less violent shifts will make this transmission last longer.

 

[frankenstien]

I didn't notice your transmission already had a kit in it. My bad.

If you installed a shift kit that came with its own large valve body separator plate, it probably blocks out the 2-3 accumulator feed. The B&M kit does this. Blocking out the accumulator firms up the shifts, whether it's by a blocked hole in the plate or "fixing" the accumulator so it doesn't move.

If your shift kit came with the extra wee gold separator plate (small, funny-shaped), it dual-feeds the direct clutch for you, and you don't need to make the changes internally. Pretty much all shift kits have this extra plate to dual-feed the direct clutch.

Removing the check balls (typical of B&M shift kit), and removing the 1-2 accumulator spring (typical of most shift kits) makes the transmission shift VERY hard, especially hard on the weak intermediate sprag (which you broke). Do consider putting all the check balls back in. The less violent shifts will make this transmission last longer.

ok, gotcha, yes mine does have the smaller seperator plate, i did not removed the 1-2 accumulator spring when built, but the spring did break, which im guessing cause my very hard 1-2 resulting in sprag failure.

will do on the balls, the new rebuild kit i got came with a new set of 4 balls

 

[SkinnyG]

I forgot to mention, if the original main valve body separator plate has had the 2nd and 3rd feed holes drilled to 3/16" (0.1875), that is too big, and puts too much strain on the guts. I recommend 0.125" for 2nd, and 0.140 for 3rd.

But if it's already back together, run with it - let me know how it shifts.

 

[frankenstien]

alright, so putting this thing back together, had some issues, pump slipped from my hand, and broke the end of the stator, only fell about 3 inches.

putting it back together, i measured the 1-2 accumulator spring, it measured 3.112, book says it should be 3 3/16, i know people cay you can run with out them but risk damaging the intermediate roller clutch. i have a TCI 36 element intermediate drum with a hardened outer race, i am a little gun shy with this spring, as it broke into pieces on my last one, and ruined the case,i looked into sleeving it, but it didnt look like it was worth the time.

so what say you guys, spring out or replace with a new one?

 

[crazy4offroad]

When in doubt always go with new parts. If it fails later with the old one you'll be kicking yourself.

 

[frankenstien]

Yeah, makes sense. Local drivetrain dodnt have the 1-2 accumulator spring. Looks like ill have to order one, so i will probably run with out the spring until i get a new one, its winter, so i wont be too hard on the 1-2 shift, and ill only be driving it until my duramax is back on the road. The 74 usually just sits in the winter

 

[frankenstien]

Quck question, can an overfilled th350 cause 3rd to feel like its slipping? Not bad, just 300 rpms higher than normal at 55.