90 740GL w/aw70L and Regina

Had some noise from the driveshaft support bearing at first. Did front brakes, engine and trans mounts, and rear shocks. Driveline noise went from an occasional "buh duh duh" rattle on the highway to an un-ignorable EEEEEEEEE in about 10 miles.

So I pulled the driveshaft apart and did the support bearing and all 3 u-joints. Still have the same exact noise.

I checked the front brake rotor splash shields and the noise does not stop when brakes are applied, including the e-brake.
Rear shocks were original at 240k, engine mounts not terrible, trans mount was terrible. I do plan to do the front struts soon.


My plan now is to shim the carrier bearing, since the whole car was quite soggy before. Buuut do I put it up or down? I can go out and give it a shot, but I'm not sure which way would be better. The rear axle is a little bit lower now than it was with the soggy shocks, so this makes sense to me. I'll put washers between the mounting plate and the center frame rail, not between the bolt heads and the plate.

The last time I saw a link to the procedure, it was no more than 1/2" up or down.

Will update with results. Hm. Maybe there is a rock in the rear brake splash shields...

For clarity, the final problem/fix for this was replacing the rear axle. Replacement rear axle solved the issue and the drain plugs were seized on both. I removed the old differential's speed sensor and found metal shavings on the magnet and wear marks on the big ring gear. I also added more 75w-90 gear oil to the rear end.

Make sure the driveshaft universal yoke joints are inline with each other and your two piece shaft lines up all the yokes and your rubber center bearing support is new. Check you driveshaft bolts

Do you have the self adjusting shocks (sorry, can't think of the name at the moment)-- Volvos I've had that had those shocks needed to be driven a distance in the AM to come up to proper ride height. If you don't have those - standard shocks have nothing to do with ride height - controlled by the springs. Worn out trailing arm bushings will alter the driveshaft angle to a degree (pun intended). - Dave

Nivomats should be the word you're looking for. Negative, I don't have those.

On shocks without any compressed gas (not even sure those exist anymore), they wouldn't alter the ride height. But the compressed gas in most modern shocks actually will increase your ride height. As it leaks out, the gas acts as less of a spring. Just think of the way new shocks expand if you make the mistake of cutting their straps before installing them.
I measured my Honda when I put 4 new struts in it, and the rear gained about 1 inch in the rear wheel well vs the ground. Putting the fronts in gained about 1/2 inch in the front. Same went for the volvo's rear.

I need to do the front struts on this 740, but I always hate starting that job. I don't think the 740s really have TABs in the same way that 240s do. There are some bushings, but they mount into the body near the rear jack points.

Hi Will,

How do you rule out wheel bearings/hubs (do 740's have hubs?)

Cheers, Bill

Hey, Bill.

I wouldn't think wheel bearings in this case. I just drove it to the store and wonder if it's the driveshaft output flange scraping. I shimmed it down about 1/4-3/8" (3x m8 washers) and had no real change. If it's the flange, it will need to be sleeved by a transmission shop.

For wheel bearings on this year of 740, I expect "sealed" hubs that are separate from the rotors and have a torque-to-yield (one use) hub nut. I added one of the diagrams for the FAQ on this model's hubs when I had the 2-piece internal race separate. The bearings are captive, but not really sealed. You can't remove them to look for signs of heat or wear, and you can't really see inside.

To check them, you really end up having to try driving at a fixed speed (30-50mph) on a curve to load each front hub with weight, then listening for a low thrumming noise that usually has rapid "beats" to it. It gets quieter and louder and quieter and louder as you drive with extra weight on it.

The only stationary way I finally found to test them was to put the hub in the air, remove the wheel, and use a hub wrench to spin the wheel by putting the hex wrench on the stud with no nut. I got it up to maybe 100rpm like that, removed the wrench, and could hear a definite thumping with every rotation that was not audible any other way. That was in like 2006, so a bit hard to recall the symptoms.


I'm going to spend the afternoon doing my girlfriend's spark plugs on a v6 fwd/awd lexus rx350, but I will try shimming the bearing up later. If it's the output flange, that might do it :)


Cheers,
Will

Hi Will,

"doing my girlfriends spark plugs'. That's cute. I don't think I've heard it described that way before.

Peter