1ksprint

I have a 2008 HHRSS 136,000 miles with auto trans that just started a clunk when shifting between first and second and second to third with remaining gears shifting smooth. No check engine light any no codes with code reader. Don't drive hard so I have not serviced transmission yet. Thought I wouldget that done first. Any other suggestions.

843de

A couple of things to check, engine mounts and the inner CV/Tripod joints on the halfshafts, they can clunk during shifts.

136k is way overdue for a transmission service.

But be forewarned, a transmission that has an issue before a service which is overdue, may fail entirely after being serviced.

The old fluid is full of friction material worn from the clutch packs, replacing it with clean fluid can remove the only thing still allowing the transmission to function.

87ninefiveone

I'll second the staying away from servicing a failing transmission. I had a 95 cutlass with a 4t60e that was completely fine after 95k miles or so. I decided to do a trans flush since the service records from the previous owner indicated it hadn't been done before. I drained it, cleaned out the pan, replaced the trans filter and then flushed the system. Two days later I put it in reverse to back out of the garage and it literally blew up the reverse reaction drum. $3500 to fix because I decided to be proactive. Same sort of thing happened with a 944 Turbo that I had. Had some minor synchro grinding in 2nd and third, changed the transmission fluid in the hope of helping it out a bit and bam grinding was 100x worse. Moral of the story to me is that trans fluid shouldn't be serviced.

whopper

You might want to try a different code reader as basic ones will not show all codes - or a GM scanner which will do a more comprehensive scan/read. As you probably know, hard shifting is often generated by a code being thrown.

I'd be leery of doing a transmission service as well, unless a full scan is done.

donbrew

Coolant temp? Does 2008 SS have VVT? Motor/trans mounts?

1ksprint

Went out next morning and added some coolant which was a little low and took it for a test drive and all's well. What would coolant have to do with a shifting issue?

donbrew

Because the engine temp was not "right" for the computer.

Next step: Where did the coolant go? Ever check it before? No Check Engine Light?

1ksprint

Checked coolant earlier in the year when I was running hotter than usual when it was 110 degrees outside and running the A/C in traffic. There were no codes today when I had a shop plug in their smog scanner here in CA. Temp on the car hangs between 199 and 203 during normal use. Finally getting cold here and I will be flushing the coolant system and changing the thermostat this weekend. Thanks for the assistance.

truvoice1

I have had a similar problem with my 08 SS with now 109k on it. At around somewhere around 95k, the transmission would 'clunk' when shifting from 1st to 2nd and to a lesser extent, from 2nd to 3rd. Since I bought the car as a Certified Pre Owned (CPO) from a Chevy dealer, I also bought the extended warranty.

The dealer could not replicate the problem. Then, as time went on I was able to isolate it. It only happens if once underway, the car is put into 'Park' and NOT turned off. As an example, when I got to the drive thru window at Sonic and put it into 'Park' to get my wallet out of my rear pocket. A few months later, I then figured out that if I pull over to the side of the road and turn off the car, wait 30 seconds or so, and then restart, the clunk goes away! Kind of like a reboot of a computer. LOL!

By the time I had documented all of this and brought it back to the dealer, I only had about 300 miles left on my extended warranty. Even though the dealer was able to replicate the problem, the GM warranty people refused to authorize the claim, saying it was 'normal' wear and tear. What a bunch of B.S.!! More than likely it was because of the fact that I used the extended warranty to fix several problems (sunroof, powertrain control module, front suspension issues, etc.) that added up to more than double the $2000 I paid for the warranty!

I am planning on doing the motor mount upgrade as soon as I can afford it and maybe that will help. I was also considering doing a trans fluid change and upgrading the fluid to Red Line fluid. Has anybody out there tried the Red Line fluid in their HHR or SS? However, I am wary of trying that now that I have read of the horror stories after changing the trans fluid.

Thanks in advance for any ideas you may have!