“I’m finding that the older I get, it’s
not that I learn new things, it’s more
like I find out how much of what I
know is common knowledge.”
–Sam Lipsyte
We’ve owned our trusty 1997 BMW M3 for more than a decade, and during that time we’ve learned most of the E36 chassis’ common problems. Fortunately, expertise on the …
Hey! I’m finally going to be tackling this job on my m3 sometime within the next month or two, and I was thinking about going with this same setup, but I’m a little nervous after reading about some of the issues people have had by running bushings with different stiffness ratings in the rear. Have you had any issues with yours? What’s it like on the street? Thanks!
Turbine said:Hey! I’m finally going to be tackling this job on my m3 sometime within the next month or two, and I was thinking about going with this same setup, but I’m a little nervous after reading about some of the issues people have had by running bushings with different stiffness ratings in the rear. Have you had any issues with yours? What’s it like on the street? Thanks!
I don't have an M3, but I somewhat recently rebuilt the entire rear subframe on my E34 touring. Now, I opted for Powerflex street (yellow) subframe bushings and OEM rubber for the differential and RTAB bushings, so it's not 100% comparable. I haven't noticed any negative effects of using harder bushing for subframe location in relation to their interaction with the rest of the rear bushings. I think a good rule of thumb is to keep parts of the same system a similar hardness. You don't want solid motor mounts with rubber transmission mounts, but I think its generally safe to run stiffer subframe bushings with softer differential bushings. Maybe someone with more experience will contradict me, but that's the assumption I work under and haven't had any bad results.
In reply to MTechnically :
Alright awesome! Thanks for the info
MTechnically said:You don't want solid motor mounts with rubber transmission mounts,
...Yes you do! Those mounts are 3 feet apart along the length of the car, across one of the main points of chassis twist and flex. If you don't have some give in the trans mounts, WHEN (not if) the chassis flexes and twists, it will stress the trans case and cause weird shifting at best and broken transmission cases at worst. The end of the transmission is not engineered to be a stressed member, the mounting point is just strong enough to hold the transmission off the ground and anything else is purely coincidental.
I have done this job in my home garage. It's do-able, but my advice to anyone is assume you'll be at it for a few days before it's all said and done. And always always go ahead and replace the BMW-specific mounting bolts that screw into the chassis before you re-mount the subframe. If they're old and you break one, the whole unit needs to come off the car to replace it.
Knurled. said:MTechnically said:You don't want solid motor mounts with rubber transmission mounts,
...Yes you do! Those mounts are 3 feet apart along the length of the car, across one of the main points of chassis twist and flex. If you don't have some give in the trans mounts, WHEN (not if) the chassis flexes and twists, it will stress the trans case and cause weird shifting at best and broken transmission cases at worst. The end of the transmission is not engineered to be a stressed member, the mounting point is just strong enough to hold the transmission off the ground and anything else is purely coincidental.
Fair point. I hadn't thought about the forces at play in that specific example. I've always heard that you do want to be careful using mounts of wildly different stiffness within the same system, because you will wear softer bushings much more quickly. Maybe I was misinformed about that.
Nice work! This job is in my M3's future. Every other bushing on the car is original, and surprisingly not as horrible. The subframe bushings look like crap, though. I'll probably go with poly subframe bushings and OE diff bushing.
One of these days, the car will be off jackstands. It's been in hovercraft mode for months. Hopefully done by the Mitty, as an arbitrary goal. We'll miss the GRM crew this year.
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