Aaron Ryan

I have a 2007 Trailblazer SS with 103,000 miles on it. My 4L70E transmission went out at 98,000 miles (planetary gear cracked).


I had it rebuilt for $2200 at my local transmission shop in Brea, CA in August 2013. They have a 1 year warranty on the transmission.
Here is a Box of all the parts they replaced in the rebuild.


After the rebuild, there was no issue, but now that 5,000 miles and 7 months have passed, I now have this clunk sound when shifting from Drive to Reverse and back. I also hear the sound sometimes when it downshifts from 2nd to 1st gear when stopping at a stop light.

I have brought the truck in twice to the transmission shop, and they have worked on it, but the issue is still there.

The first time in, I had only noticed the downshifting clunk sounds, so they thought it was the bands in the transmission, so they removed the transmission and adjusted the bands and replaced the oil at no charge to me. However the downshifting clunk still existed, but happened less frequently.

The second time in (this week, March 20th 2014), they thought it was the drive shaft, so they removed the drive shaft and had it rebuilt and replaced the U-Joints (costing me $207). However, that made no difference either.

So I made a video of the issue with my iPhone when shifting from Drive to Reverse, and you can hear the clunk which sounds like it's from inside the transmission.


Anyone have any idea what this could be, and what the expected life left on the transmission. I'm scared that on day 1 of the warranty being over it will fail. :bonk:

I drove my truck really hard today to see if any other sounds come up, but there is nothing, just the clunking when shifting from D to R, and the occasional 2nd to 1st downshift clunk.

I'm hoping I can find a way to fix this issue before it gets worse, but if not,
I'm considering getting a Level 1 Performabuilt 2 yr warranty transmission.

redtan

iTrader: (5)

I have the same issue with mine and this was the builders response:

"This happens because we do not use the stock anti clunk spring but rather a piece called a case saver that prevents the center support from digging into the aluminum case during hard launchs. The down side is you do indeed he a clack / clunk sound during the mode you described."

I read around a little bit about case savers and found that those are usually used as a bandaid for a worn transmission case.

So far a year later and some 7,000 miles and no issues with the unit.

mrvedit

It looked to me like the transmission case moved more than it should - was the rear trans mount replaced?

Only the builder would know, but I doubt a case saver was used in a 2007 trans; they are more often used in ancient 700R4. I don't have any experience with how much clunk a missing anti-cluck spring would cause, but think it would be minor and sound "internal". This clunk sounds "external". But, I would expect the trans shop to immediately suspect the trans mount.
IIRC, we had a recent thread (or maybe on another forum) where a trans mount was manufactured wrong and had metal-to-metal contact after only a little bit of wear and appeared perfect.

Aaron Ryan

I found this youtube teardown of the 4L60E which supports the "Anti clunk spring" theory that you suggest. The link fast-forwards to the point where he talks about it (at 26:40 minutes)


Here is the re-assembly version - with the anti-clunk ring (at 48:49 min.)

The question is, will the absence or incorrectly installed anti clunk spring going to damage anything?

performabuilt

iTrader: (25)

If the spring is missing and no case saver is installed it will hasten the low roller support diggng into the case. However if a case saver has been use no this will cause no damage and will in fact prevent damage to the case in hard launches. But it does indeed have the characteristic clunk aluminum clack sound on downshifts and reverse drive engagements.
It is also possible the spring was installed and is weak or broken.

Aaron Ryan

I assume there is no easy way to access the Anti Clunk Spring, or confirm the existence of this spring, without a full tear down, correct?

mrvedit

That is correct.

Aaron Ryan

I went back to the transmission place, and they pulled out the transmission again and took it apart and replaced the front planetary, but the issue still exists.

They then referred me to this technical bulletin from GM, pretty much saying it ok to have the "lash" clunk sound. I took a picture so I could share the info:

tango68ss

EXCELLENT POST! I too have this issue on my freshly rebuilt 4L70E out of a TBSS... I took it back to the tranny guy once already and he could not see anything wrong with it (quick drive, no issues...figures)... I went down the TCM programming route, to no avail!!

Now that I am "armed" with this info, maybe this is the problem... It's under warrantee and hopefully fix-able!! I will let you guys know if in fact it is the anti-clunk spring!

BTW, this tranny is in my resto-modded '68 'vert.

TC

69CamaroLS3

Hey guys,

I have a 69 Camaro with an LS3 480 4l70e connect and cruise kit. I to have the same clunky noise only from 2-3 gear otherwise it is fine at all other shiftpoints. I went in today to the driveline shop got new U-joints and re-balance the drive shaft but nothing worked. Any help here would be appreciated. I barely have 3k miles on the engine and trans.

tayto

you should really start your own thread vs reviving multiple 7+ year old threads. there's no mention of a 2-3 clunk here BTW... while at the driveline place did they check the lash on the rear end? what mounts are you using? rubber, urethane? Is your transmission built? if so do you have any details on what was done to it, shift kit, etc?