jthomas

Backstory: 100k miles on a bone stock trailblazer SS. Started slipping in 3-4 and 4-3 downshift. I attempted to overhaul the trans, install shift kit, and new 3k stall converter. Truck drove fine afterwards. I then cracked the Tcase adapter while launching the truck. i drove it about 5 miles home in hopes it would be okay. i drained the fluid to see how much was left, and i received about 2-3 quarts back, and it was totally black. (there was approx 100 miles on trans at this time). I replaced fluid and filter in hopes everything would be okay (after replacing Tcase adapter). The truck was actually running and driving "okay" except after a couple trips to work, it started slamming really hard during the 1-2 shift. So hard, that i kept trying to reduce the shift pressure in the tune. The trans felt "soft" to me while driving on the freeway, but i wasn't sure if maybe its the new feel of the converter, since i had never driven a vehicle with a higher than factory stall. I put a pressure gauge on it, and in every gear @ idle i had 200psi.

I stopped driving the truck after about 300 or so miles on it. Checked the pan again, alotttt of clutch and bushing in the pan. I parked the truck and tore the trans down.

Here are the results...

So my main question is, assuming that the loss of trans fluid was the ultimate cause of the clutch failure. Why would that be the only clutch pack with damage. All other clutch packs looked brand new. What else could cause that damage besides low fluid?

jthomas

front pump bushing is trashed

tailshaft bushing is also heavily worn. Both into the babbit

During the rebuild, i replaced both of these. I remember when installing the torque converter, it felt really tight... but i assumed thats just because its a brand new converter and brand new bushing. Whats the clearance spec on that?
i feel like maybe the bushing and or converter hub were not correctly sized???
I installed the bushings with a driver, so id assume they were installed straight.

jthomas

This damage in the drum was not there during first rebuild. Would this be from that banging 1-2 shift? The lugs in the case look fine.

jthomas

Is this failure actually from fluid loss???

bbond105

Could be or a leak in the 3-4 clutch circuit. Check for fluid leaks where the input shaft is pressed into the drum.

01ssreda4

iTrader: (96)

I hate to be captain obvious, but why in the hell were you launching a freshly rebuilt transmission!!!!

clinebarger

Fluid loss/Low fluid level can smoke the 3-4's really quick...... The Forwards & Band can show distress but it's not a given if you were just limping it back to the house.

I would replace that Input Drum as cheap as they are from GM. ($125)

The case bushing wear could be from the T-Case adapter cracking & causing the output shaft to run off center.

The pump bushing should be removed & reinstalled from the PUMP POCKET as there is a small lip to prevent bushing walk-out. If you beat it in from the SEAL SIDE.....The converter hub will be tight on the bushing, There will be aluminum debris under the bushing, The bushing will be distorted.
100% check the bushing on the converter hub before assembling the pump.
Beating bushing in with a hammer is a poor practice in my opinion.....Use a Arbor Press!

At idle with no load.....You should have around 75-80 psi (Depending on the PR Spring) & 230-240 psi at full EPC/Torque signal boost (Depending on Boost Valve)

mOtOrHeAd MiKe

iTrader: (8)

I know this feeling all too well.

AnotherWs6

iTrader: (17)

Cuz it's new, good for another 100K!

jthomas

during more investigation i found the overrun piston would fall out of the forward piston when tipped upside down (probable leak)

ive been told by multiple people that there isn't a break-in period.

i installed the bushing with a driver, so i assumed they would be straight enough. maybe i did install them from the wrong side??

Is a new drum really necessary? Its a DD, not a racer.



why would i only totally destroy one friction?


I had a sonnax boost valve and whatever shift kit that came in my rebuild kit.

TCI kit that contains Raybestos BPZs
I dont remember the clutch clearance, but i did set it to the spec they recommended (i think it was something like .008" per disk???)

what causes the drum to get beat up like that?


the reason i ask all these questions is to simply better my education on automatics

jthomas

how do i go about doing this?

bbond105

Read the wet air test instructions on the last page of the attachment.

jthomas

Thanks!

01ssreda4

iTrader: (96)

My trans builder would strongly disagree. I will give you his advice as he gave me. 250-500 miles of light throttle WITH stop and go driving. Good luck, trans issues can be frustrating.

jthomas

Do i really need a new drum?

In my 400s ive completely removed lugs from the case after seasons of abuse...

bbond105

If the surface is flat then no. Put a strait edge across the drum and check.

clinebarger

I believe he is talking about the input drum.....It looks like a lot of wear in the picture from the 3-4 steels rattling against the drum from the TCC locking up to early & possibly the absents of damper springs in the TCC piston.
If you can feel ANY harmonics in the truck with the TCC engaged.....It's real bad in the trans!

You can try to smooth the lugs out a little with some emroy cloth, But I would replace it, Make sure the 3-4 steels are indexed correctly also.

bbond105

My bad, I think you're right.

jthomas

I believe my shift kit instructions had me remove the dampening springs (ill double check)

Also, i had a random missfire from a bad o2, and you could feel it BAD when the converter was locked up.


So would the banging 1-2 shift have nothing to do with the drum damage?

Game ova

Why the hell not? After a few miles of easy driving/running through the gears.....its playtime. Not sure what caused his failure....but I've got money on it NOT being because he was at the track with a new transmission.