I have a 2008 RWD Trailblazer with the 4.2L straight-6, When it's been cold in the morning and I start my car and drive through the first couple of stop signs there's a vibration coming from the drive train but it's not present when the car is in reverse, it doesn't behave abnormally driving, it just vibrates when the brake is applied in drive, but once the car warms up some it doesn't do it. Any ideas what might be causing this? It doesn't sound like a misfire it's more of a grinding/vibration from the engine/transmission.
2008 4.2L Trailblazer vibration when brake applied in drive when cold
- Thread starter blufeb95
- Start date
AutoMechanic
Site Donor 2024
Did you ever figure it out?
one of the hydraulic engine mounts has failed most likely
Check your motor mounts.
I read around and determined it's probably the motor mounts, I might take a stab at replacing them when it warms up in the spring but it's too cold and you can't really jack up an engine when there's snow and ice.
When you do replace them, only use OEM motor mounts. Rock Auto carries the actual OE motor mounts 
I've read plenty about that when you consider the effort involved or the cost of labor paying someone else to do it, you save nothing by buying no name engine mounts that'll just break in 6 months or never work right in the first place.When you do replace them, only use OEM motor mounts. Rock Auto carries the actual OE motor mounts
Also clean your throttle body. Disconnect the battery and pull the tb. Give it a good wash and reinstall. This cleaned up engine vibrations on mine.
Nick1994
$100 site donor 2024
Yes, bite the bullet and only buy OEM. My grandparents had an 02’ Trailblazer and we had the motor mounts replaced with aftermarket. Was nice and smooth for a few months, then the vibrations were back.
The rubber becomes malleable as it warms up and the vibration goes away.
Only been happening when it's been below freezing
I'm a bit wary about disconnecting the battery on these trucks. When the HVAC does a full sweep to recalibrate actuators, aged plastic components can cause all sorts of problems and require removing the dashboard. Even when replacing the battery, I use a memory saver.
I usually pull fuses 10 and 28 for a good half hour, and that does the trick.
It's been even colder lately, I've noticed it really doesn't do it in reverse only forward drive, had a mechanic looking at it after it had already warmed up, he said the mounts seemed fine, it had cooled off a little when I went to pick it up after he replaced a bad tie rod end, when he looked at it again he seemed to suggest it may be the torque converter, the pump has been kind of loud, I had a friend swap out the filter and put in a new pan with a drain bolt to see if the filter was plugged, but it's still doing it, and it seems to be getting worse since it's been even colder out.
The fluid was dark reddish to maroon, didn't smell burnt just like Dexron. I had exchanged a few quarts of fluid and put some lubegard red in about 6 months ago the fluid at that time may have been a little lighter red but it just smelled like Dexron nothing burnt not a whole lot of black crap in the fluid, the magnet and it's surround was pretty dirty and loaded but it wasn't a glitter fest, I assumed that the amount of crap around the magnet was probably pretty normal for a tranny with 175k on it that's probably never been serviced.
The common failure point on these mounts is up top, where the stud mounts to the engine bracket; more so on the driver's side than passenger side for whatever reason. You'd have to pull the bracket off to see if the rubber separating from the stud. With that being said, these are not regular rubber mounts and are fluid filled.
As for the torque converter, what sort of rpms are you seeing at highway speeds? Any slipping or shuddering? What sort of noise is coming from it?
I haven't really noticed any shuddering, the torque converter comments wasn't from deep diagnostics either, but I'm wondering if the tranny pump may be worn, I have noticed some whining, and I can hear the pressure build in the accumulator for the 1-2 upshift, and I've noticed when it's really cold out the 1-2 upshift seems to be taking longer like I'll be going closer to 20mph at near 2000rpm when it up shifts when I'm crawling down the neighborhood streets to the stop signs, normally I can hold around 1500rpm and it upshifts around 15mph. Once the car is warm I don't really notice anything unusual.
Taking longer to shift could very well be because the transmission is cold. Maybe Clinebarger will chime in. Did you happen to tear open the old filter to see if there was anything unusual?
Could be worth doing another pan drop at this point, and inspecting what's in the current filter. As for fluid, I'd suggest using something that is TES-295 approved instead of Dexron VI this time.
Could be worth doing another pan drop at this point, and inspecting what's in the current filter. As for fluid, I'd suggest using something that is TES-295 approved instead of Dexron VI this time.
I didn't open the filter, what I could see of the media looked like it was a little dark but there weren't any solids coming out, I noticed in the pan that was plastic, I don't know where it came from, it was cold out and my driveway is covered over in ice, and it's asphalt and uneven and I can't really jack the car up right now, so I paid a someone I went to school with who is a mechanic a few bucks to drop the pan and put in the new pan and filter I brought him so I didn't get under the vehicle and it was cold out so it was a quick in and out job, I used a transfer pump to remove about 2.5qts out the dipstick hole so it'd make less mess dropping the pan, and then he unfastened the pan, took the old filter off, put the new filter in cleaned the magnet and put it in the new pan and put the pan up. I noticed when I was dumping the fluid out into a bottle that there was that plastic piece in the pan. he was already putting the pan up so I didn't look any further, and I've tried to not drive it much since then
