Front Differential...Motor Mounts...

Evan

Original poster
Member
Mar 19, 2013
3
Hi everyone. My first post here, but dont take me as a newbie, I use to be on the Trailvoy forums and was a active member. Its been a few years since I was last there (the trailblazer has been mostly problem free) and I see there was a mass exodus to GMTnation.

So here is my issue.

In the beginning of February, I was struck in the passenger side by a car in the passenger side front wheel/fender area. It caused the Control arms to bend forward into the wheel well.
The controls arms both failed at there outer joints and sparred the TB from any structrul damage. The driver did not have insurance and I no longer carried collision on the TB anymore (190k miles). So I went about repairing the damage myself.

In the course of of this project I decided to rebuild both the driver and passenger side suspension.

Here is what was replaced.
-Upper and Lower Control arms, Drivers and Passengers
-Upper and Lower Ball Joints, Drivers and Passengers
-Tie Rods, Inner and Outer, Both sides
-Passenger side CV Axle
-4WD Disconnect and Actuator

Now obviously the Car is out of alignment, I did my best eye balling it to get it back alignment myself so I Can get it to a shop down the road for a real alignment. In the course of pulling it out of the Garage and testing the different functions in the drive way I noticed a problem.

There is a bad vibration coming from the front end. At first I noticed in 4wd (I wanted to test the disconnect and actuator, so I drove it in my yard). its a rough vibration when the engine/drivetrain is under load and stopped while still in gear. Goes (mostly) away when put in neutral. Later I did this test on my road in 2WD and again once the engine is loaded the vibration returns. Seems like a engine mount problem?

But Im not sure, So I did alot more testing. I jacked up all four wheels (with the front two being jacked under the control arms). What I noticed was that when 4WD is engaged and then put in gear, that under the truck you could see the whole engine and tranny rocking back and forth side to side. So I stopped. Now I was concerned I have a front differential problem.

I then tested some other things. In 2WD, If I rotate the drivers side tire, the engine rocks back and forth, about an inch or so side to side. When I rotate the passenger side, there is no rocking.

To my best understanding there are no noises coming from the front end when I rotate the tire, Just the rocking.

So my questions are, or if any one is willing to try it out for me themselves and report back.
-Should the engine rock side to side when rotating the front drivers side tire?
-Is this a sign of a bad motor mount
-Or is it a drivetrain issue?

Up until the accident, the 4WD worked perfectly. Fluids in the TC and both diffs were replaced frequently
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Evan said:
Seems like a engine mount problem?
Welcome! Yes. How did you find we'd moved, by the way?
-Should the engine rock side to side when rotating the front drivers side tire?
Not at all. That's usually due to a bad CV joint. In your case, it may be a bent intermediate shaft - that goes through the oil pan to the passenger side splined disconnect. Or damage internal to the front diff from the side impact load.

Even though the other driver didn't have insurance, are they judgement-proof? Trying to not pay ANYTHING? No assets at all?
 

Evan

Original poster
Member
Mar 19, 2013
3
I drifted in from time to time and once saw mention of "the roadie is gone". Alittle google work and passing mentions on OffRoadTB, I found out what happened.


By the looks of the person I decided in my head that it wouldnt be worth my time, Also it seemed at the time the damage wasnt to terrible. But who knows now.

Ill try to post of a video of what Im seeing. Again there is no audible noise when rotating the tire just the rocking motion, Also the vibration and noise I hear while driving, does not noticeably occur while driving in 2wd, or coasting.

Im just not sure what play would occur do to a bad motor mount. That the torquing of the front Drive shaft while in 4wd and its U Joint would be causing the differential (and by design the whole engine) to wobble as it does and make the motor mount issue even more noticeable.
 

tblazerdude

Member
Dec 4, 2011
321
just a few questions to help me understand...

Did you replace the hub bearing assemblies? there is a good chance they were damaged, depending on impact location. They also contain the wheel studs, which if bent could give you a wobble like feel in motion.

Did you get any new rims or tires? was there any impact in those areas? Could a tire have a broken belt or bubble? Rim slightly bent?
 

Sparky

Member
Dec 4, 2011
12,927
When you took apart the driver side suspension to replace the ball joints, did you flex the CV axle around? Notice anything odd or rough about its movement perhaps? How old is that axle, original?

Maybe try yanking the CV axle, checking its range of motion with it disconnected from the truck, then stick a gatorade cap in the seal (the roadie trick :biggrin:), engage 4x4, and see if the rocking still occurs or not. If it does, it rules out the CV axle. If it doesn't, it might be that CV axle that is the problem. If the axle is old it might be worth it at that point to go ahead and pop a new one in there as they are only 50-60 bucks.

Just thinking of ways to narrow down the issue.
 

Evan

Original poster
Member
Mar 19, 2013
3
Sparky said:
When you took apart the driver side suspension to replace the ball joints, did you flex the CV axle around? Notice anything odd or rough about its movement perhaps? How old is that axle, original?

Maybe try yanking the CV axle, checking its range of motion with it disconnected from the truck, then stick a gatorade cap in the seal (the roadie trick :biggrin:), engage 4x4, and see if the rocking still occurs or not. If it does, it rules out the CV axle. If it doesn't, it might be that CV axle that is the problem. If the axle is old it might be worth it at that point to go ahead and pop a new one in there as they are only 50-60 bucks.

Just thinking of ways to narrow down the issue.



Well it ended up being the drivers side CV axle. All the other problems have cleared up. Off to get it aligned and back on the road.....

Thanks everyone, good to be back:thumbsup:
 

Sparky

Member
Dec 4, 2011
12,927
Awesome, glad it was the CV and not something in the front diff. That would have been a pain and expensive!
 

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