NEED HELP Transmission problems (tcc, shifting)

Leukay

Original poster
Member
Jul 17, 2017
6
Columbus, OH
Hi All,

Warning: Long read below. For summary, jump to bottom of post!

For my first post here, I'd like to get some input on what I might be dealing with. I got my 08 Trailblazer LT (4.2) about a year ago, and ever since I've been dealing with the TCC intermittently locking/unlocking over and over, along with some other shifting issues. The TCC locking/unlocking happens at cruising speed and it is very intermittent. It may go days without happening but when it does it locks/unlocks over and over for no apparent reason. It also seems to occasionally try to lock up while I am still accelerating, much sooner than anticipated, and this often triggers the lock/unlock condition, but that is also very intermittent.

After reading about this TCC issue in numerous threads, I ordered the transgo shiftkit and went to install it, only to find that the previous owner had already done so. While inside the transmission, we noticed that the PO also had the 1-2 accumulator piston replaced/modified, and there was still debris inside the bore and that accumulator was stuck
eek.gif
We also looked at the separator plate and everything looked fine with no noticeably worn holes. Nevertheless, we installed the new stuff from the shift kit and got the accumulator freed up and got it back together. The 1-2 shift was much better (go figure), but the TCC issue was still occurring.

Since we saw that the transmission had been modified, the trailblazer has over 130k on the odo and I plan on keeping the vehicle for a while, we decided to buy a remanufactured transmission directly from GM thinking this would solve all of the transmission problems, which it unfortunately did not... Most of the shifts feel much better, but there is still a bad hitch between shifts, usually accompanied by a clunk sound/feeling which I believed the famed "torque management" system, but it sure send clunky and not enjoyable to drive. The big problem is that the TCC is still unlocking/locking at cruising speeds, and I've just started getting (4-5 times in the past couple weeks) a real hard 1-2 shift, which almost feels like I'm being rear-ended.

We've since installed a new brake switch and a new accelerator pedal both directly from GM, along with new spark plugs just in case. There are NO codes being set, and I'm totally at a loss for where to start with this thing... I'm hoping someone might have some input of things I can check before I keep throwing money at this problem. I appreciate any input in advance!

Summary of above:

Main issues:
1. TCC sporadic locking/unlocking at constant speed
2. Sometimes tries to shift into 3rd way too early
3. Overall clunky/slow shifting
3. No codes to indicate any problem

Attempted fixes:
1. Remanufactured transmission direct from GM
2. New accelerator pedal from GM
3. New spark plugs

[Mod edit: Please do not post successively. Posts merged and edited.]
 
Last edited by a moderator:

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
With the new tranny, it could be that you need to reset the PCM back to "new" transmission pressures. You would need someone or a dealer with a Tech 2 to reset that. Only reason I know about it is because I saw it while playing around with my Tech 2.

I think the way it works is that as the tranny ages, it will increase the shift pressures to keep the shifts from getting too soft. With a fresh tranny, the pressures may be too high for it.
 

Sparky

Member
Dec 4, 2011
12,927
Reset the PCM - maybe even just pulling the battery for 30 min may help that (clean the throttle body while you're waiting, why not).
Grease the slip yoke - common source for the "rear-ended" complaint.
Inspect U joints - worn joints can lead to a clunky, nasty experience.

Did you install the kit into the new trans? Possible that the rebuilt trans still has a non-rebuilt (and worn) TCC valve bore. And the kit is a worthwhile install anyway. But check the others first.
 

Leukay

Original poster
Member
Jul 17, 2017
6
Columbus, OH
Thanks for the feedback! I have disconnected the battery for at least 30 minutes a few times since the transmission was replaced. Would that reset the PCM to a new trans or is a tech 2 or similar scan tool required for this?

I was considering purchasing and installing another transgo kit, but I wanted to limit the variables while I am diagnosing the problem. My dad works at the transmission plant in Toledo and I believe the reman transmissions get new valve bodies.

I was also considering getting the PCM tuned in order to shorten up the shifts, but again, I wanted to avoid adding variables to the equation while trying to solve the root problem.

I have been suspecting a sensor, at mid throttle it shifts as if it would at lower speeds, causing a clunky slow shift. But I can't imagine a sensor that would cause this without setting a code..
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Would that reset the PCM to a new trans or is a tech 2 or similar scan tool required for this?

For this particular parameter, I believe so, contrary to the reset when you clean the throttle body. The transmission reset specifically is in the Tech 2 as opposed to the throttle body one, which is not.

Good plan on doing just one change at a time.
 

Leukay

Original poster
Member
Jul 17, 2017
6
Columbus, OH
Ok, I'll have to find someone with a tech 2 or go to a dealer to try that first. Anything else I can look at in the mean time? The big symptom to me is when it tries to lock up way too early while I'm still accelerating at a moderate pace, which then kicks off the lock/unlock fits. The fits also happen without this condition as I just get up to speed, but it really seems like the PCM is getting a faulty input from something. But again, with no codes it's hard to know where to start..

On another note, in my frustration I went and test drove a trailblazer SS yesterday, and I couldn't believe how clean and crisp the shifts were. If I could get mine feeling like that I'd be ecstatic! Let alone the sound of the LS2 and the power, my trailblazer is a year newer and cleaner than that SS, and I can't financially justify the upgrade since I have 3 other "fun" cars in addition to the TB.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
In reality, the tranny shop should have known about this and had it done since it would affect shift quality. It's possible the effect of this minimal and could be why they don't bother with it.
 

Leukay

Original poster
Member
Jul 17, 2017
6
Columbus, OH
My dad and I swapped the transmission ourselves, so I know there was nothing done to reset the transmission as new in the PCM. The transmission was purchased directly from a GM dealership. I wouldn't expect that to make a huge difference but it should still be done I suppose.

I have an appointment with the dealership on Monday to try to diagnose the problem. The last time around a different dealership concluded it was the brake switch, and it that didn't fix it it was the throttle pedal. Now that both are replaced and the problem is still there, we'll see what they come up with. I'm still looking forward to all of your replies so I have some things to check if they can't figure it out!

Thanks,
Lucas
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
They should also look for possible updates for the PCM and TCM as well as resetting it. Might as well while you're there. I hate sending people to the dealer. Most are morons.
 

Leukay

Original poster
Member
Jul 17, 2017
6
Columbus, OH
Well, after days of the dealer having the car and collecting a cool $1000 I'm still in the same spot.

Story:
After a couple days, I had authorized $330 in diagnostics. The following day I got a call saying they figured it out and it's 100% fixed. They concluded that the Transfer Case Control Module was sending a false 4 Low signal to the PCM which was unlocking the converter. They replaced the TCCM and cleaned the connections to try to be 100% sure that was the issue. The problem is, that put me in an awkward position, because I didn't authorize $1000 worth of work, just the $330, and I couldn't feel right about telling them to reverse the work and I would just pay the $330 I agreed to. So I had to swallow it, pay the bill and take the car home.

Now the real problem is it is behaving exactly as it was before. I've spent about $4000 (directly to GM dealerships) trying to fix this problem after buying the thing for $8000 because it was super clean. Really getting fed up with sinking money into this. I left a message last night for the technician that was working on the car, so we'll see what he says hopefully today.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Hence my comment about dealers :frown:
 
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Reprise

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Well, after days of the dealer having the car and collecting a cool $1000 I'm still in the same spot.

Story:
After a couple days, I had authorized $330 in diagnostics. The following day I got a call saying they figured it out and it's 100% fixed. They concluded that the Transfer Case Control Module was sending a false 4 Low signal to the PCM which was unlocking the converter. They replaced the TCCM and cleaned the connections to try to be 100% sure that was the issue. The problem is, that put me in an awkward position, because I didn't authorize $1000 worth of work, just the $330, and I couldn't feel right about telling them to reverse the work and I would just pay the $330 I agreed to. So I had to swallow it, pay the bill and take the car home.

Now the real problem is it is behaving exactly as it was before. I've spent about $4000 (directly to GM dealerships) trying to fix this problem after buying the thing for $8000 because it was super clean. Really getting fed up with sinking money into this. I left a message last night for the technician that was working on the car, so we'll see what he says hopefully today.

It's a bit late now, as you've already paid the bill - but if you ever go to the dealer again, there should be a spot on the work order notating if you want to be contacted before going over $x , or if you pre-authorize them to put in 'whatever it takes' to fix the issue (there's also a 3rd condition, where they're supposed to contact you for authorization for anything). Whatever you do, don't pre-auth them for all work & parts.

Since the vehicle is doing the same thing, they should be willing to make it right. Unfortunately, that means they get to charge for the *new* parts / labor of whatever they do - unless you select that "contact me first" option, as I mention above. That way, if it's a simple part replacement (as the TCCM was, I'm afraid to say) - you can choose whether to do it yourself vs. having them perform the work.

Finally - if that new transmission is indeed a reman (and from GM to boot) - you should not need the Transgo kit for many, many miles - at least to 'fix a problem' - because there shouldn't *be* a problem. Whether the VB is 'new' or 'reman' - the TCC valve / bore should be at 'new' OEM spec (e.g.; if you were to remove it and check the TCC valve, you should see it has the OEM parts, and no wear / excessive clearance between the valve / bore - and, also - no Sonnax oversized valve / reamed bore, which would be the other way to fix that issue vs. the Transgo solution (Transgo's is more of a 'cover up', but it does work)

I'd hold off on that Transgo kit for awhile; there's a good chance that if you modify that trans in any way right now, you'll void whatever warranty GM issued on it.
Am I saying "keep taking it in to them" ? Not if they're going to charge you every time the wheels roll into their service bay.

Since their last 'fix' didn't seem to eliminate or reduce the problem at all, they should make an effort to work with you a bit. But you'll probably have to fight them to some extent. If they get really nasty about it, a follow-up with the Service Mgr (if you haven't spoken to him already), and then to GM would be in order, and preserves your rights. Unfortunately, if the you and the dealership can't come to agreement, the dealer will likely call for an arbitrator, which in theory is supposed to be 'neutral' to both parties - but in reality, there's a good chance they'll rule for the dealer, if the dealer claims that the trans is working 'within specs' and can 'back it up' (correctly or otherwise). Hopefully, things don't go that far, and the dealer's service dept / mgr helps make it right for you. A new (reman) transmission should not exhibit the same issue that the old one did - the fact that it does suggests (to me, anyway), that there was a good chance you didn't need a new one.

I read through your first post again, where you mention several hard 1-2 shifts - was the vehicle 'cold' each time (like overnight or at least 5-6 hours since starting?) And / or - how hot has it been in the Columbus / mid-OH area the last couple of weeks? The trans shifts harder during the first couple of 1-2 shifts when cold, and also when the trans fluid is hotter than it should be (like a high ambient temp along with extended stop/go traffic).

Remember that 1st gear in the 4L60 has a fairly tall 3.06 first gear, relative to the others, and you're going to feel that shift the most, compared to the others (2nd is 1.62 - so that ratio between the two is 'roughly' 50% reduction).

(on edit: removed references to incorrect transmission model used in the TBSS - it uses a 4L70e (see Sparky's correction below).
 
Last edited:

Sparky

Member
Dec 4, 2011
12,927
Actually the TBSS does not have a 4L80E. It has the 4L70E which is just a somewhat factory beefed up 4L60E.

If the TBSS had a 4L80E it wouldn't get blown up so easily :wink:
 

Reprise

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Jul 22, 2015
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I give up... Mooseman corrected me a couple of days ago, and I *still* got it wrong. :Banghead::Banghead::Banghead: :dunce: :dunce: :dunce:

Apologies, folks...I will edit the inaccuracies out of my post. For the OP - the main difference between the 4L60 and the 4L70 is what's called a 'five pin planetary gear' - other than that, they're basically the same transmission, with the exact same gear ratios - so ignore what I said about that.
 

Leukay

Original poster
Member
Jul 17, 2017
6
Columbus, OH
Well I guess for $1000 I at least got a clue to a possible false 4 low signal from the tccm to the PCM. I've found that specific wire in the wiring diagrams last night, and I will look for it in the car tonight to remove it from the PCM connector and drive it for a while to see if the problem is isolated to that circuit. That would be nice to narrow down, but my condition really doesn't seem to fit that diagnosis... There really seems to be more going on but we'll see after a week or two of driving with that pin removed from the PCM connector.

I will also try greasing the slip yoke to see if that takes care of my occasional, but very jarring "rear ended" feeling while accelerating in 1st gear.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
You could just disconnect the TCCM however you will get a service 4x4 light.
 

seanpooh

Member
Jan 24, 2012
461
When my TCC was locking and unlocking, I modified the PMW solenoid. http://www.s10forum.com/forum/f13/e...m-function-with-solenoid-modification-552450/

The pictures aren't there anymore unfortunately... Pretty much, you do what he explains. Remove the rubber O-ring at the tip of the solenoid and cut a notch. Now when my torque converter locks up, it doesn't slip in or out of it. It just "shifts" into it. There's a youtube video of what it looks like on the 4l60e and where it is. Also there a tutorial of the mod.

Maybe it will help you, maybe not. It did help me though. Maybe I was crazy to try it, but again, got rid of that stupid slipping.

Surprisingly you have the same issue with a new trans. Everything was included with the trans, even the torque converter?
 

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