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Discussion Starter · #1 ·
My truck is shuddering in overdrive when driven at constant speeds and constant loads. Pressing the gas to take it out of lockup results in a harsh release of the clutch. No codes found. I have a scanner that reads transmission, abs, airbag, etc.

At 55mph, constant load, level ground (for example) the rpm gauge will oscillate between 1400 and 1600 rpms. It will do this indefinitely until I put the hammer down enough to unlock but not go into 3rd gear (it releases very harshly). It feels like the clutch is locking and unlocking constantly. Fluid is full and clean.
I had transmission rebuilt at 165k in 2019. Now at 221k today.

Side notes:
Transmission previously failed due to rusted lines. Replaced them.

I drive very hard. Lead foot is an understatement.

Auxiliary cooler installed.

I had to change a coolant hose on the passenger side of the car a few days ago and spilled coolant all over the frame of the car. Possible electrical damage?

Recently I've driven on some extremely bumpy dirt roads, and on my way to work I drove through a giant puddle of water that I didn't see. Once again possibly an electrical issue?

I don't know where to start. I've heard it could be the tcc itself. I want some help before I take it back to the shop. Any help is appreciated.
 

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Discussion Starter · #2 ·
Sorry for making the post so long. I like to give as much information as possible.
 

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2004 chevy trailblazer_ls
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The bore in the valve body for the TCC is worn. There's a kit to repair it that invoves a sleeve. I've never done one so have no idea of the difficulty.
 

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Discussion Starter · #4 ·
Ok. I'm also noticing a hard 1-2 shift. I'm going to attach a video of the symptoms. I highly doubt it's a misfire like I've read on other forums. I haven't done a fluid change yet so should I try that? The transmission has 61k miles on it.
 

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Discussion Starter · #6 ·
I'm looking into part # a74741cb by fitzall. They say it doesn't require any boring and can be installed without pan removal. There's limited info on it though. I'm probably going to order this along with a new pan and some fluid. Wish me luck.
 

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I think thats the kit for 2nd gear harsh shifts, basically a Corvette servo. The TC shudder is the valve/bore in the throttle body.
 

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Discussion Starter · #8 ·
The part came in. Looks like a tcc valve. I'll update when I install it.
56887
 

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Discussion Starter · #9 ·
Update: Problem Solved
1: I removed the pan (what a pita)
2: I removed the filter
3: I spent about 1 hour removing a clip from the valve body that is installed upside down (from your point of view) so I could avoid removing the valve body. This was by far the hardest part and it's near impossible to be honest. (Here's a video explaining it: Teckpak / Fitzall transmission parts and tools)
4: I installed the valve. It was a very tight fit. I reinstalled the clip the opposite of the way I took it off, it'll work fine.
5: I installed a new deep pan filter, (I didn't change the seal since I'm lazy. Definitely change it if you do this or any filter service)
6: new gasket and a pan with a drain plug. Tourqe it down to 8 lb ft and add 4-6 quarts of fluid if you didn't do any flushes etc and only lost fluid from pan pull.

Everything works great again, I'm surprised something so simple could cause such a confusing issue. I'll be sure to change my fluid every 50k or so. But my truck will probably die before than.

Total costs:
ATF: $40
New Valve: $28
AcDelco Filter and gasket combo: $36
Pan with plug (optional): $40
4 Hours of time: free for me
This beats going to the shop any day. Thanks for pointing me in the right direction NJT
 

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Hmmmmmmm .... I wonder if this TCC update is a DELETE for the PWM way it worked before..... I don't like the PWM way of partially applying the TCC and never quite getting it into full lock up.

The RPM will roll a little up 'n down at cruise when the PWM version is active - I've never had it just click in.

So-o-oooo --- my thoughts are if this turns the TCC into a YES/NO application - then I'm all for it.
 

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The bad 1-2 shift might be a collapsed accumulator spring (usually this happens) and possibly a scored and now useless 2-4 servo bore.
 

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Discussion Starter · #13 ·
I can take a video of the rpm gauge. I can't really tell if it's pwm or not. All I know is it fixed the problem without needing to pull the valve body.
 

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Here's a thought ----> IF you gently ride on the brake pedal - just enough to turn the brake lights ON but not enough to actually apply the brakes ---- and the trouble goes away - then YES --- it is your PWM or TCC.
 
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