TH350C rebuild

[Caddis]

Hey guys, I thought I would let you know I just finnished my first tranny rebuild with great success.
It was a '86 350C from a Chevy Van.
I did have a couple surprises but nothing serious.
It took me about 4 days, but a lot was spent on just cleaning the case and parts. Oven cleaner worked the best.
As far as the rebuild went I was quite surprised at GM's decision to use that dumb little snap-ring on the top of the output shaft. I've seen proper cir-clips on my 74 Honda 125 transmission.
But everything went pretty good and I'd like to thank HotRod for his th350 thread.

 

[Irishman999]

Hey guys, I thought I would let you know I just finnished my first tranny rebuild with great success.
It was a '86 350C from a Chevy Van.
I did have a couple surprises but nothing serious.
It took me about 4 days, but a lot was spent on just cleaning the case and parts. Oven cleaner worked the best.
As far as the rebuild went I was quite surprised at GM's decision to use that dumb little snap-ring on the top of the output shaft. I've seen proper cir-clips on my 74 Honda 125 transmission.
But everything went pretty good and I'd like to thank HotRod for his th350 thread.

Kick ass dude! way to go

 

[HotRodPC]

Welcome Aboard Caddis. Glad to hear of the success. That snap ring you speak of is a bitch. It's not only small, is tucked away back in that recess from the planetary not giving much room.

 

[89Suburban]

Good job.

 

[Caddis]

Hi HotRodPC
Is there a way to tighten up the shifts just from the V plate on my 350C.?
Cuz after the build ,I wish I could of done something cheap in there while I had it apart. I realize the Vb is different from the 350 and I just left it alone, ...playing it safe.

 

[Caddis]

Welcome Aboard Caddis. Glad to hear of the success. That snap ring you speak of is a bitch. It's not only small, is tucked away back in that recess from the planetary not giving much room.

Hi HotRodPC
Is there a way to tighten up the shifts just from the V plate on my 350C.?
Cuz after the build ,I wish I could of done something cheap in there while I had it apart. I realize the Vb is different from the 350 and I just left it alone, ...playing it safe.

 

[HotRodPC]

What do you mean tighten up the shift? Make if firmer, or stretch out the shift points? or make the shift points closer?

You can change the shift points with detent cable (aka kickdown) adjustment, or vac modulator adjustment.

Now the 350C is a bit more trickier to firm up the shift than the Th350. Reason being the seperator plate (I assume what you mean by V plate) are different. On the standard Th350 you can use a transfer plate that allows dual feeding. The Th350 uses that portion though for the Lock Up feature. There are other ways to get dual feeding. Like leaving a seal out of the I believe intermediate drum. The drum that used 3 seals, you leave the seal off the drum and that allows dual feeding and firms up the shift too. Otherwise, Transgo does make a shift kit that requires removal of the valve body, work over some springs and that will firm up the shift with Transgo technology.

 

[Caddis]

What do you mean tighten up the shift? Make if firmer, or stretch out the shift points? or make the shift points closer?

You can change the shift points with detent cable (aka kickdown) adjustment, or vac modulator adjustment.

Now the 350C is a bit more trickier to firm up the shift than the Th350. Reason being the seperator plate (I assume what you mean by V plate) are different. On the standard Th350 you can use a transfer plate that allows dual feeding. The Th350 uses that portion though for the Lock Up feature. There are other ways to get dual feeding. Like leaving a seal out of the I believe intermediate drum. The drum that used 3 seals, you leave the seal off the drum and that allows dual feeding and firms up the shift too. Otherwise, Transgo does make a shift kit that requires removal of the valve body, work over some springs and that will firm up the shift with Transgo technology.

Yes, firm up the shifts, as in they are too soft.
Shift kits are about $150 up here. I rebuilt the whole tranny for that. So I'm not going to bother. But thanks anyway.
It also seems to shift early too, especially the 2-3 shift.
I turned in the vac mod 1.5 turns, its a little better but may need more I guess.

 

[HotRodPC]

To hell with $150. I'd never pay near that for a shift kit. Maybe for a full manual valve body kit, but not for an improver kit.
$39.95
http://www.ebay.com/itm/THM350-350-...Parts_Accessories&vxp=mtr&hash=item2eaa23441a

$27.50
http://www.ebay.com/itm/GM-TH350-35...Parts_Accessories&vxp=mtr&hash=item27b27366ee

 

[HotRodPC]

How about your detent cable? Is it hooked up? Is it hooked up right? Adjust it a bit to make the shifts a tad later. That will also allow fluid pressure to build a little higher at point of shift and firm up the shift. I usually had mine adjusted to where I was getting a full pull on the detent valve at about 3/4 throttle instead of full throttle.
Another question, did you re install your accumulator spring in the side of the case? It should have been a big heavy orange or purple spring. You don't need it. If you did use it, take it out. Leave the piston in though. Just take out the spring and reinstall the cover. The accumulator just works as a cushion for the 1-2 shift. Take the spring out, no more cushion and it'll hit a little harder.

 

[Caddis]

How about your detent cable? Is it hooked up? Is it hooked up right? Adjust it a bit to make the shifts a tad later. That will also allow fluid pressure to build a little higher at point of shift and firm up the shift. I usually had mine adjusted to where I was getting a full pull on the detent valve at about 3/4 throttle instead of full throttle.
Another question, did you re install your accumulator spring in the side of the case? It should have been a big heavy orange or purple spring. You don't need it. If you did use it, take it out. Leave the piston in though. Just take out the spring and reinstall the cover. The accumulator just works as a cushion for the 1-2 shift. Take the spring out, no more cushion and it'll hit a little harder.

I did put that monster spring back, but I can pull it easily.
But the detent, I was thinking about . That was my next idea, thanx for the heads up on that. It kicks down fine on the gas, but if Im just driving normally it seems to upshift so soon.
On first test the 2-3 shift happened almost imediate.
Like I said I screwed in the Vac Acum 1.5 turns and it got better, but under light throttle it seems like it wants to be in 3rd as soon a can.
How much CAN you adjust the vacum mod.?

Thanks bud..

 

[HotRodPC]

Yeah, you can take that spring out, no problem. I've ran a vac mod screw in as many as 4 full turns if I recall. I'd say you're on the right track. Vac mod and detent cable adjustments will do the trick, and the spring coming out will firm up the 1-2 shift.

 

[Caddis]

Another thing I thought about.
the tranny used viton checkballs, and I replaced them with steel check from the kit. These heavier checkballs could make a diference right. They are 5 times slower to block the passage. GM would have made somekind of adjustments when they switched over to these checkballs. Maybe different spring tensions in the VB to comensate.
Maybe Im being an idiot , Just guessin.

 

[HotRodPC]

ACtually slower might be better. I nornally only run 2 check balls in the Th350. I run #1 and #2, lose #3 and #4. It's actually part of the instructions in the shift improver kits to discard 2 check balls. If not mistaken, the 350C uses 5 check balls IIRC??? No lock up used 4, but I only use 2.

 

[Caddis]

Thanks bud, Ill try that, but the 2-3 shift is the real dog.