What did you do to your GMT today?

[maricard]

Today I changed for a second time a motor support. This time it was the driver side. It was very painful to replace it. Passenger side was easier two months ago. Anyway less motor vibrations but still have something wrong under the hood.

[mason10198]

added a Real tree windshield decal for personalization. petty, I know, but I love making my TB "my TB".

~Sent from Tapatalk for Android~

[Trail X]

Today I changed for a second time a motor support. This time it was the driver side. It was very painful to replace it. Passenger side was easier two months ago. Anyway less motor vibrations but still have something wrong under the hood.

I chased a motor vibration for years and could never locate it. Replaced everything I could top-side.

It ended up being that my exhaust manifold had a crack in it. It wasn't enough of a crack to hear much noise, but it was enough for the ECU to attempt to compensate for what it thought was a lack of exhaust gasses on a few cylinders. The crack finally got bad enough that I noticed it, and with changing the O2 and the manifold, the vibrations faded away.

[tarsh]

I've got a bad vibration myself right now. Adv i just put new motor mounts on. Mashed me angry. I have another set showing up today I'll swap out

[DirtyBacon04]

I enjoy my massaging steering wheel and pedals. dont know what y'all are talking about!

[TBYODA]

I enjoy my massaging steering wheel and pedals. dont know what y'all are talking about!

BWHAHAHAHAHAHAHAHA!

[v7guy]

Supposedly only the GM mounts have the right goop in em to quell the vibrations. Just a heads up.

The envoy needs em replaced... I ought to take the new ones outta the trailblazer and put em in the envoy where they'll actually do some good LOL

[moose1]

joined the crowd and removed the damn squeek maker out back.

working on parts list to chase the vib up front.

[maricard]

Today I changed for a second time a motor support. This time it was the driver side. It was very painful to replace it. Passenger side was easier two months ago. Anyway less motor vibrations but still have something wrong under the hood.

I chased a motor vibration for years and could never locate it. Replaced everything I could top-side.

It ended up being that my exhaust manifold had a crack in it. It wasn't enough of a crack to hear much noise, but it was enough for the ECU to attempt to compensate for what it thought was a lack of exhaust gasses on a few cylinders. The crack finally got bad enough that I noticed it, and with changing the O2 and the manifold, the vibrations faded away.

I know that I have a crack on my manifold. But I didn't think that could be connected. Did you have a lot of difficulties to remove it? Did you remove it from the top or bottom? Did you break any bolt when you tried to remove them. It's not really expensive part specially on Ebay but look like hard to do.
I don't have any check engine light on, so is it possible that my vibration come from of my manifold crack?

[TBYODA]

joined the crowd and removed the damn squeak maker out back.

rear sway bar.jpg

At least you removed it completely before you hit the trails unlike me and got it hung up on some rocks that popped the curved part over the rear diff with mounts hanging down. http://forums.offroadtb.com/viewtopic.php?f=57&t=5264#p104247

[moose1]

I wanted it to stay in good shape so i can re-install it at a later date. I think eventually i am going to lower it a bit and throw on some Z71 springs before i pass it on to my teenager.that is unless i trash it too bad.

[Trail X]

Today I changed for a second time a motor support. This time it was the driver side. It was very painful to replace it. Passenger side was easier two months ago. Anyway less motor vibrations but still have something wrong under the hood.

I chased a motor vibration for years and could never locate it. Replaced everything I could top-side.

It ended up being that my exhaust manifold had a crack in it. It wasn't enough of a crack to hear much noise, but it was enough for the ECU to attempt to compensate for what it thought was a lack of exhaust gasses on a few cylinders. The crack finally got bad enough that I noticed it, and with changing the O2 and the manifold, the vibrations faded away.

I know that I have a crack on my manifold. But I didn't think that could be connected. Did you have a lot of difficulties to remove it? Did you remove it from the top or bottom? Did you break any bolt when you tried to remove them. It's not really expensive part specially on Ebay but look like hard to do.
I don't have any check engine light on, so is it possible that my vibration come from of my manifold crack?

I didn't have a check engine light either. There's no sensor in the engine that checks for exhaust gasses escaping from the manifold. The engine does however see that the O2 sensor sees less exhaust gasses when the cylinders near the crack expel their gasses. The O2 sensor reports this to the PCM as lean or rich burn in those cylinders (I'm not sure which). The PCM then attempts to compensate by adding more or less fuel to those cylinders. Those cylinders then get a non optimal combustion, which vibrates the engine. Sometimes you'll get a misfire code on that cylinder, but often you have to let the engine idle for a while to let the PCM attempt to tune out the vibration.

The manifold is a bitch to get out. I had two broken bolts before I started removing bolts. The remaining bolts all came out without issue. The manifold barely fits out of the bay, and the bolt access to some of the bolts sucks. The broken bolts were removed by welding a nut to the exposed stud. Also - if you get replacement bolts, be sure to get GM bolts that have the high temp locktite applied.

[KingBird]

This makes me glad that I have a spare manifold from the engine swap. I didn't have any stuck bolts but I had the luxury of soaking them all in PB Blast with the engine out. I'm not looking forward to ever having to pull the exhaust manifold with the engine in the vehicle.

Trail X, did you re-install the heat shield or go without?

[Trail X]

I reinstalled it, but I think I only have one bolt holding it on right now. I think its a good idea to keep water off of it as much as possible.

[KingBird]

I think I'll do the same, I didn't want a bunch of gunk gathering under it promoting corrosion but I definitely don't want it cracking either!

[moose1]

Just an FYI on the manifolds. mine cracked at around 115k and while looking for parts and info I found out that GM extended the warranty period on these manifolds to 120k. I had the dealer replace it at 119.5k.

[TBYODA]

Just an FYI on the manifolds. mine cracked at around 115k and while looking for parts and info I found out that GM extended the warranty period on these manifolds to 120k. I had the dealer replace it at 119.5k.

Kevin I am pretty sure that is only on 08+ models.

[moose1]

Ok, my bad I thought it was 05 on, but either way I think if I had one cracked and I was under 120k I would still call up GM and try. It looked like a PITA repair.

[maricard]

I know that I have a crack on my manifold. But I didn't think that could be connected. Did you have a lot of difficulties to remove it? Did you remove it from the top or bottom? Did you break any bolt when you tried to remove them. It's not really expensive part specially on Ebay but look like hard to do.
I don't have any check engine light on, so is it possible that my vibration come from of my manifold crack?

I didn't have a check engine light either. There's no sensor in the engine that checks for exhaust gasses escaping from the manifold. The engine does however see that the O2 sensor sees less exhaust gasses when the cylinders near the crack expel their gasses. The O2 sensor reports this to the PCM as lean or rich burn in those cylinders (I'm not sure which). The PCM then attempts to compensate by adding more or less fuel to those cylinders. Those cylinders then get a non optimal combustion, which vibrates the engine. Sometimes you'll get a misfire code on that cylinder, but often you have to let the engine idle for a while to let the PCM attempt to tune out the vibration.

The manifold is a bitch to get out. I had two broken bolts before I started removing bolts. The remaining bolts all came out without issue. The manifold barely fits out of the bay, and the bolt access to some of the bolts sucks. The broken bolts were removed by welding a nut to the exposed stud. Also - if you get replacement bolts, be sure to get GM bolts that have the high temp locktite applied.

Thank for the advices. I think I'll have to do the job because those vibrations are really unpleasant and I tried a lot of things to fix it without any result.
It it a good idea to heat each bolt before started removing bolts?
Did you lub (WD40) it before to start the job?
How much time did you spend to finish the job?
I'm a bit nervous begin this job I use my truck for my daily drive and I want advice as much as possible.

[navigator]

There are better penetrating oils than WD-40. Below is something I copy/pasted from another board

"Machinist Workshop magazine studied the most popular penetrating oils to see
what did the best job of removing rusted bolts by measuring the pounds of torque
required to loosen the bolt. I'm not sure just what flavor bolt they were using
that would take 516 pounds of torque but it must have been a monster.
These were the results they published:
Penetrating oil: Average load:
None...................................516 lbs.
WD-40.................................238 lbs.
PB Blaster.............................214 lbs.
Liquid Wrench........................127 lbs.
Kano Kroil..............................106 lbs.
ATF-Acetone mix......................53 lbs.
“The Auto Trans fluid- acetone mix was a "home-brew" mix of 50-50 ATF-acetone.
The home brew tested better than the commercial products in this test. Note that
Liquid Wrench is about as good as "Kroil" for about 20% of the price.”