z3 1.9 rear end clunk when changing from 1st to 2nd gear or into reverse

[red314]

I can hear this clunk from the rear end every time I quickly tap the gas pedal while going from 1st to 2nd gear or into reverse. I also feel some sort of vibration when starting to move into reverse.

Rear diff bushing has been already replaced, so that's not the cause.

What's next to check? Rear subframe bushings?

[laptop4079]

I'm not well versed in the 1.9 but when I had a reverse/clunk in reverse it was engine mounts

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[saneesh8]

See if you can reproduce it on the ramps (not jack stands). From N, put it in R. Then you can pin point where it is coming from. May be from the drive shaft or related?

For me, it was various things. Outer CV joint have slight play, the differential carrier bearing, it have vertical play and the differential it self have some looseness in it.

[gmushial]

Saneesh pretty well's got it: the diff is effectively a large sounding surface, which will make noise/clunk, when there is looseness in the driveline, from the twin-mass flywheel, to an outer CV... and as he said, you need to locate the actual looseness and address it. And putting it up on ramps is a good way to do that.

[ItsQuik]

I'd suggest looking at your rear body cross channel. (aka "subframe failure")

[magnetchief]

I'm with the drivetrain. Check the shafts out from the diff. Worn cv joint inner or outer. If you can get the back end up off of the ground you should be able to rotate the wheel and detect any sloppiness.


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[Vintage42]

I'd suggest looking at your rear body cross channel. (aka "subframe failure")

Almost unheard of on the weak 1.9s that the OP and I have.

[ItsQuik]

I have a 1.9 body and it was separated.

[red314]

If it is a subframe failure I will be selling it without thinking twice LOL

[Vintage42]

I have a 1.9 body and it was separated.

All the bodies are 1.9, for that matter. What engine did you have in the body?
If you are saying you have a Z3 1.9 in which the rear trunk floor separated, I would be interested in hearing the car's history.
In reading the two main forums for a few years, I have heard of two 1.9 trunk floors that separated. One car belonged to a student who abused it. It takes a lot of repeated stress to separate the trunk floor, and that is hard to generate with a 1.9.

[red314]

Seems like spotwelds are ok

[GBPaterson]

Did you check the flex disc (giubo)?

If that goes you can get a kind of delayed clunk when you engage the clutch. I've found that replacing the flex disc immediately made the driveline tight again.

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If its really gone bad you can get a rattling caused by extreme flexing resulting in the nuts / bolts hitting off the body. If this is the case you want to change it pretty quick as it ends up shearing them which makes removal a major headache (trust me I know).

Easy to check if you raise the car up.

- - - Updated - - -

If its really gone bad you can get a rattling caused by extreme flexing resulting in the nuts / bolts hitting off the body. If this is the case you want to change it pretty quick as it ends up shearing them which makes removal a major headache (trust me I know).

Easy to check if you raise the car up.

BMW part# is

26111225624

[Vintage42]

Seems like spotwelds are ok...

Yes, but the trunk has rust from leaks. Hope those are fixed.

[kyrix1st]

I have clunk in all gears lol.

[deni2s]

It takes a lot of repeated stress to separate the trunk floor, and that is hard to generate with a 1.9.

With proper welds, yes, unfortunately that's not the case with z3. Most abused z3m can handle stress with proper welds. The other probably 5-15% (as someone already calculated) have bad welds.

I had seen several people on FB claiming subframe issues for their 4 cylinder cars.

For OP my guess is subframe bushings - especially if those had never been replaced.

[Vintage42]

... Most abused z3m can handle stress with proper welds. The other probably 5-15%... have bad welds... For OP my guess is subframe bushings - especially if those had never been replaced.

The OP titled Post #1 as "z3 1.9 rear end clunk when changing from 1st to 2nd gear or into reverse". I did not know that old rear subframe bushings could do that.
I also did not know that trunk floor separation was due to bad welds rather than weak design.

[s8ilver]

Have you inspected the drive shaft? I've got a clunk that's been attributed to u-joints, but just haven't cared enough yet to order up a new shaft. I'll get to it some day.

[deni2s]

The OP titled Post #1 as "z3 1.9 rear end clunk when changing from 1st to 2nd gear or into reverse". I did not know that old rear subframe bushings could do that.

Those are exact symptoms of really old subframe bushings (not trailing arm bushings).

I also did not know that trunk floor separation was due to bad welds rather than weak design.

Well we know that even some 4 cyl cars had the issue even when relatively new. If that would be bad design, I assume there would be more issues with 2.8, even more with 3.0 and probably most z3m would have that issue. And we know that majority of z3m don't have the issue (many z3m owners just put Randy's kit proactively). So I tend to think the issue was more due to bad welds rather than weak design. Probably design could be better too.

[Vintage42]

Those are exact symptoms of really old subframe bushings... we know that even some 4 cyl cars had the issue even when relatively new...

How can old subframe bushings cause clunking when shifting?
How do we know that any 4 cyl cars had trunk floor failures when relatively new?

[PhilPhil]

"It takes a lot of repeated stress to separate the trunk floor, and that is hard to generate with a 1.9."

While my mechanic was installing the Randy Forbes kit in my M Coupe, he explained to me that, having taken the rear end apart and having seen how it's designed, subframe failure on these cars is not caused by engine power or hard launches, etc. It's created by lateral loading from hard cornering. So, any of these chassis can have popped spot welds, regardless of engine type.

When I posted this interesting info in the Z3 Facebook group, Randy himself gave the post a thumbs up. I imagine he would have corrected that assessment if it were inaccurate.

[Vintage42]

"It takes a lot of repeated stress to separate the trunk floor, and that is hard to generate with a 1.9." ... subframe failure on these cars is not caused by engine power or hard launches, etc. It's created by lateral loading from hard cornering... When I posted this interesting info in the Z3 Facebook group, Randy himself gave the post a thumbs up. I imagine he would have corrected that assessment if it were inaccurate.

I had not heard that before, and it's a really important point. It would explain the importance of replacing rubber rear subframe bushings with urethane bushings, to limit the lateral stress transmitted to the differential mount on the trunk floor channel. Even for a 1.9.

But some have said that hard launches and engine braking transmit fore and aft stress through the drivetrain to the differential mount, rocking and twisting the trunk floor channel. Could that explain why Zs that are manual, powerful and tracked have more trunk floor failures? Or, is it all due to the hard cornering of tracking?

I think it is confusing to call the channel across the unibody's trunk floor a subframe. The rear subframe is the carrier beam to which are mounted the differential, the suspension and wheels. It is attached to the body by the the rear subframe bushings, originally rubber, replaced with green urethane shown here, and by the differential mount. All three points shown in white circles.
Most know all that, but some may not.

RSF Diff Carrier 1.jpg

[MORRIE]

Hey vintage, is that your rear end laying on the garage floor? If so, did you replace the differential and sub frame bushings yourself?

I had not heard that before, and it's a really important point. It would explain the importance of replacing rubber rear subframe bushings with urethane bushings, to limit the lateral stress transmitted to the differential mount on the trunk floor channel.

But some have said that hard launches and engine braking transmit fore and aft stress through the drivetrain to the differential mount, rocking and twisting the trunk floor channel. Could that explain why Zs that are manual, powerful and tracked have more trunk floor failures? Or, is it all due to the hard cornering of tracking?

I think it is confusing to call the channel across the unibody's trunk floor a subframe. The rear subframe is the carrier beam to which are mounted the differential, the suspension and wheels. It is attached to the body by the the rear subframe bushings, originally rubber, replaced with green urethane shown here, and by the differential mount. All three points shown in white circles.
Most know all that, but some may not.

RSF Diff Carrier 1.jpg

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[Vintage42]

Hey vintage, is that your rear end laying on the garage floor? If so, did you replace the differential and sub frame bushings yourself?...

No, I can't do that stuff. I reached my limitations installing struts and shocks myself.
I did buy a pair of green bushings from IE but it looked too hard for me and a shop quoted $400, so I sold them.
I think the photo may have been posted by Greg Mushial when he did his car years ago.

[MORRIE]

Shucks Vintage. I was ready to drive to Kentucky and we could tackle that DIY.

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[s8ilver]

Shucks Vintage. I was ready to drive to Kentucky and we could tackle that DIY.

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If you make it to CO I've got a crew that'd make quick work of it. They work for beer.

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