BMW Z3 thumping noise


#1

A friend brought a '97 Z3 roadster by the other day for my opinion. He’s looking to buy it. Everybody seems to know that I’m a car nut, and know just enough to be dangerous. I’d never even sat in a two seater BMW before…

Cute little car with a nearly new top and tires, and supposedly a recent clutch. Peppy 2.8L DOHC I-6. Just over 100K miles.

The only thing I could really fault the car on was a thumping noise coming from somewhere in the drive line. It is only noticeable on starting from a dead stop. It doesn’t seem to matter whether you start out slow and easy, or like a jack rabbit, which it does well. You hear THUMP THUMP THUMP, and can almost feel it under you as you drive. The differential is VERY near both passenger’s backsides. If you start out hard it may be more like THUMP THUMP… THUMP thump THUMP before it quits making noise Of course the car has independent rear suspension. I’m thinking it may be a rear CV joint in need of lubrication. This car did sit for nearly a year recently as it was tied up in an estate. I don’t know if that’s part of it or not, but it might be.

Have any of you experienced this sort of issue?


#2

Those Z3’s had problems with the rear suspension mounts tearing out of the body - not good. He MUST have a very thorough pre-purchase inspection before buying it.


#3

Could be the tires, since it sat for over a year.


#4

@texases That’s not very encouraging. He’ll have to get it from the seller for a while before anyone would have time to get under it. It may well be me. Are you talking about where the suspension “cradle” bolts to the underside of the body? 3-Series BMWs have been known to do that too.

@knfenimore I think if it were tires, you’d keep hearing it after you got rolling. It quits thumping once you stop accelerating, even if you hold it at very low speed. Once you’re over 10 MPH or so, it quits thumping whether or not you’re accelerating.

Thanks guys.


#5

When I googled ‘Z3 rear suspension problem’ lots of links came up. Some point to failed rear differential mounting bracket spot welds. Here’s one of several videos showing the problems (there are several). It’s long, but you’ll see the problems in the first 2 minutes:


#6

My money is on an inner CV joint. But, without getting under the car that’s just a wild guess.


#7

If the sound goes away, then I’m with the inner CV joint too.


#8

Reports of a differential (mounting?) bolt breaking:

http://forums.bimmerforums.com/forum/showthread.php?1584960-Clunking-Thumping-Noise-From-Rear-End


#9

@insightful Of course that was a BMW M3, not a Z3. I s’pose a Z3 could do the same thing, but it is a completely different type of car.

@texases Now THAT’S scary. Looking at the California license plate on that car would make me think it was not a rust issue. This Z4 came here from Nebraska at some point, not exactly a rust belt state, but darned close.


#10

What’s the powertrain configuration for this car? Rear wheel drive with front side engine and transmission, driveshaft, rear differential?


#11

yep


#12

Longitudinally mounted front engine, rwd, with independent rear suspension. The rearend has a differential like a pickup that drives driveshafts with CV joints very much like a FWD’s front axles… except without the ability to steer. Like a Corvette rear suspension.


#13

Except the transmission is with the engine, not with the differential like it is with current Corvettes.


#14

Oops. I goofed. I forgot that 'Vettes have a transaxle in the rear. The BMW roadster has the tranny bolted to the engine.


#15

My Ford truck has a driveshaft/rear diff/rear axel shafts. No CV joints. It has gotten a clunk symptom before, usually most noticed just pulling away from a stop sign, “clunk … clunk … clunk …” increasing in frequency the faster you go. It always turned out to be one of the u-joints in the driveshaft between the engine and transmission (well xfer case in the truck’s case). Not sure if the BMW uses u-joints in the driveshaft, but if it does that’s something to consider. On my truck it is very easy to tell if it is a u-joint problem by crawling under the truck (after taking appropriate safety precautions) and twisting the drive shaft with my hands. If there’s any play at all in the driveshaft, there’s a u-joint problem. I can usually tell which u-joint it is — on my truck there are 4 or 5 – just by looking at what part is doing the moving.


#16

Check the condition of the guibo which is the flex coupler that takes the place of a front drive shaft u-joint found on other most other brand rear wheel drives. It’s not that difficult to replace except that you will probably have to remove most of the exhaust pipes to get to it.

As a side issue find out if the convertible top hydraulic motor has been replaced and how long ago. This is a known weakness due to poor design. It gets waterlogged, rusted and fails after awhile. I’ve replaced one on a Z4 and it was quite a job. The whole top has to be removed.

Also, the lower control arm rear bushing fails with regularity.