'88 GL 4wd -- rear differential attachment at U-joint -- explained! Thank you.

[Hank Roberts]

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Question answered in the first few replies, thank you all

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Ok, I was tracking this question in the "vibration" thread I started earlier.

*And I've done an hour of web searching and not come up with a description or picture of what I'm asking about, so ... help?

 

Give me a sanity check, someone who knows parts?

 

--the mount for the rear differential, at its front end, where the U-joint connects -- does it have some openings all the way through it so the rubber can flex and the bolt move a bit? So a flashlight can shine right through the big ring mounted on the body of the car, from which the differential is hanging, past the bolt and washers on either side of that ring? The thing shouldn't be solid rubber at all?

--I'll go apologize to the mechanic if so.

 

Meanwhile--

 

The clunking that developed getting home turns out NOT to be any of the above:

 

Mechanic called. Part of the left rear brake had broken off and was causing the clanking that I drove it in with. (It didn't pull at all when braking, though I noticed a bit more whooshing than usual with brakes applied -- go figure).

 

He says he's looked at the area I suspected -- where the front of the rear differential hangs from the body -- and he says it's normal to be able to shine a flashlight through that opening alongside the bolt, that the rubber piece there is not solid, it has gaps in it to let that connection move around.

 

Ok, I can believe it. But the car did have the mysterious shaking when going uphill in first gear 2wd all along. I assume it still will when the brake is repaired. I asked him to go drive it up the steepest road in town [straight up Marin from the "Bears" fountain circle for those who know Berkeley] once he gets the brakes fixed.

 

The 'vibration when going up hill in first gear' was variously thought to be U-joints, engine/transmission/differential mounts, struts -- is still is an open question. To be addressed after the brakes are repaired.

 

And should I still ask him, if the vibration is still there, to drop the driveshaft and check the U-joints and that mount?

[Will Smith]

 

--the mount for the rear differential, at its front end, where the U-joint connects -- does it have some openings all the way through it so the rubber can flex and the bolt move a bit? So a flashlight can shine right through the big ring mounted on the body of the car, from which the differential is hanging, past the bolt and washers on either side of that ring? The thing shouldn't be solid rubber at all?

--I'll go apologize to the mechanic if so.

 

need to take your mechanic a beer. there is lots of room for "play" on that bushing.

 

Meanwhile--

 

The clunking that developed getting home turns out NOT to be any of the above:

 

Mechanic called. Part of the left rear brake had broken off and was causing the clanking that I drove it in with. (It didn't pull at all when braking, though I noticed a bit more whooshing than usual with brakes applied -- go figure).

 

He says he's looked at the area I suspected -- where the front of the rear differential hangs from the body -- and he says it's normal to be able to shine a flashlight through that opening alongside the bolt, that the rubber piece there is not solid, it has gaps in it to let that connection move around.

 

Ok, I can believe it. But the car did have the mysterious shaking when going uphill in first gear 2wd all along. I assume it still will when the brake is repaired. I asked him to go drive it up the steepest road in town [straight up Marin from the "Bears" fountain circle for those who know Berkeley] once he gets the brakes fixed.

 

The 'vibration when going up hill in first gear' was variously thought to be U-joints, engine/transmission/differential mounts, struts -- is still is an open question. To be addressed after the brakes are repaired.

 

And should I still ask him, if the vibration is still there, to drop the driveshaft and check the U-joints and that mount?

 

unlikely the rear dif and related parts are causing the problems unless you are in 4 wheel drive, my guess is the problem is in the front end. just my 2 cents.

[GeneralDisorder]

Yes - the mount you speak of for the diff should not be solid rubber - think of it as a "wheel" of rubber with spokes of rubber connecting the outer large ring with the inner bolt hole. Between the spokes the rubber is left out to make that bushing "softer" to dampen vibration better.

 

Glad they located the really horrible noise. Good luck with the vibration.

 

GD

[DaveT]

I have had a couple of u joints go bad. Symptoms were humming vibration at highway speeds. 4WD on/off changed the tone / sound of the hum. Low speeds made little to no noise. Sometimes, when parking (tight corners, etc.) 4WD would cause creaking / weird metalic noises.

[Hank Roberts]

Yes - the mount you speak of for the diff should not be solid rubber - think of it as a "wheel" of rubber with spokes of rubber connecting the outer large ring with the inner bolt hole. Between the spokes the rubber is left out to make that bushing "softer" to dampen vibration better.

 

GD

 

OK -- I'll find something the mechanic can put on display, like a "thank you, I'm an idiot" card (wry grin). He deserves it.