Rear End Refresh - Bushing Questions

[MR E30]

Morning all,

I am in the process of completely refreshing the rear end of my '97 M3.

The entire rear end has been removed and disassembled at this time.

I need to determine what each bushing should be upgraded to. I've done my research but haven't found all the answers, so I wanted to get it all in one place for convenience sake.

The build is a '97 M3 coupe with turboed LM7 and 6-speed T56 Magnum transmission. Car is currently, and will always be, on coilovers. Will be tracked occasionally, but is also being built to enjoy on the day to day and will be capable of long highway trips as well.

For the (4) subframe bushings I am going with 80a poly bushings.

I have read that in order to avoid diff whine you want to go with OEM rubber bushings for the diff. Is this correct?

What about the trailing arm bushings? Garagistic sells an offset version to help with toe-in/toe-out on lowered cars. My M3 will never be ultra low/slammed, but it will definitely be lower than factory. They also offer a centered version as well. All of these bushings are Delrin.

Does anyone do anything with the bushings for the upper wishbone, the component that houses the bottom of the rear spring?

I'll be purchasing new lower wishbones, as they don't appear to be serviceable based on how they are manufactured.

Thanks for your help!

- Mike

[Gene V]

I recently had the rear subframe and diff bushings replaced with OE stock and the ride has firmed up quite a bit...delrin would have been too firm for our crappy roads here in Honolulu...

[MR E30]

I recently had the rear subframe and diff bushings replaced with OE stock and the ride has firmed up quite a bit...delrin would have been too firm for our crappy roads here in Honolulu...

Thanks for that feedback. Brings up a good point; The M3 is not my DD. And I prefer a more 'rugged' approach to cars like this, as that helps immerse me in the experience the car creates.

[RRSperry]

Sorry to say, but I think you pretty much killed it as a street car...lol Since you are almost all the way down that road, might as well consider Spherical bearings..

as for the diff, you are REALLY going to have to support it. You will break the bolt, the mount, or the diff ears themselves. I’d also have the rtab pockets and roll bar mounts reinforced.

Next up are the 1/2 shafts and driveshaft.. lots of people have been down that road...

[blckstrm]

Sorry to say, but I think you pretty much killed it as a street car...lol Since you are almost all the way down that road, might as well consider Spherical bearings..

as for the diff, you are REALLY going to have to support it. You will break the bolt, the mount, or the diff ears themselves. I’d also have the rtab pockets and roll bar mounts reinforced.

Next up are the 1/2 shafts and driveshaft.. lots of people have been down that road...

I'll second the motion. Reinforce everything while you're in there (RTAB pockets and the roll / sway bar ears on the subframe). It's a million times easier while everything is out.

I refreshed my ear end a year or two ago. I was trying to get to 0 toe, and couldn't get there. I did the offset delrin, but it wasn't necessary - I would have been fine with the normal centered setup if I'd replaced my horribly worn ball joints first. I still had terrible tire wear and dynamic toe change until I refreshed the ball joints in the trailing arms.

Having done all that, I'll replace my offset RTABS with the spherical bearings at some point. For either, you'll want to reinforce the RTAB pocket. The delrin are worse, since they resist the arm's need to rotate as it pivots. But the lack of compliance is tough on the pocket for either option,
and if you reinforce the pocket they should be able to handle the delrin fine.

As for NVH, it's only bad when I hit some kind of slightly raised transition (like entering a driveway) at more than driveway speed. Other than that, you don't notice them. The spherical bearing may be worse in this regard, but I haven't tried them yet. But harder RTABs (the delrin or the spherical bearings) give you the ability to run zero toe, which is the best thing ever.

As for ball joints for the control arms (or wishbone, though they're not really wishbones). Only the inner bushings are in the control arms. The outer ball joints are housed in the rear trailing arm.

You'll want to replace both the ball joints in the trailing arm. They're the same top and bottom. If you have a 95 (for others reading this thread - OP has a 97) the bottom one originally was a bushing, not a ball joint - and you'll want to replace both with the ball joint like the 96+ cars.

As for the control arms, there are rubber bushings on the inside where they mount to the rear subframe. And yes, trying to replace the bushings in the lower arms is a fool's errand.

There are also ball joints that fit in the inner location of the control arms. I bought some adjustable lower camber arms to replace the stock arms, and they came with ball joints at the inner location, so three of my four are ball joints on each side (the uppers were relatively easy to replace the bushing on). I don't feel any downside and will change that last bushing to a ball joint next time it needs refreshing.

I did a lot of research and got Megan racing lower arms. They're reasonably priced and as robust as the best out there (and better than most). Some people told me that they're hard to adjust when installed - I didn't find that to be true. At all. They're easy to get to and I have plenty of clearance.

None of this should make it unpleasant to drive, but it should be a lot more responsive when you finish. The conventional wisdom is to keep the OEM rubber for the diff, which is what I've got as well (purple Powerflex in my subframe - I forget the durometer number) and I don't have any diff noise.

[MR E30]

Sorry to say, but I think you pretty much killed it as a street car...lol Since you are almost all the way down that road, might as well consider Spherical bearings..

as for the diff, you are REALLY going to have to support it. You will break the bolt, the mount, or the diff ears themselves. I’d also have the rtab pockets and roll bar mounts reinforced.

Next up are the 1/2 shafts and driveshaft.. lots of people have been down that road...

You know, you very well may be right.

I was previously one of those fellas: Back in 2010 I supercharged an S52 swapped 1991 318is. Went all the way to the Driveshaft Shops 1 piece driveshaft, among quite a lot of other upgrades to handle the powa.

I drove that thing everywhere! I certainly am not as young as I was back then, but I do enjoy a more visceral experience, even if I am just headed across town to a friends.

Josh shared a very informative post below, so I'll tackle the rest of your comments in my reply to his response.

- Mike

[MR E30]

I'll second the motion. Reinforce everything while you're in there (RTAB pockets and the roll / sway bar ears on the subframe). It's a million times easier while everything is out.

I refreshed my ear end a year or two ago. I was trying to get to 0 toe, and couldn't get there. I did the offset delrin, but it wasn't necessary - I would have been fine with the normal centered setup if I'd replaced my horribly worn ball joints first. I still had terrible tire wear and dynamic toe change until I refreshed the ball joints in the trailing arms.

Having done all that, I'll replace my offset RTABS with the spherical bearings at some point. For either, you'll want to reinforce the RTAB pocket. The delrin are worse, since they resist the arm's need to rotate as it pivots. But the lack of compliance is tough on the pocket for either option,
and if you reinforce the pocket they should be able to handle the delrin fine.

As for NVH, it's only bad when I hit some kind of slightly raised transition (like entering a driveway) at more than driveway speed. Other than that, you don't notice them. The spherical bearing may be worse in this regard, but I haven't tried them yet. But harder RTABs (the delrin or the spherical bearings) give you the ability to run zero toe, which is the best thing ever.

As for ball joints for the control arms (or wishbone, though they're not really wishbones). Only the inner bushings are in the control arms. The outer ball joints are housed in the rear trailing arm.

You'll want to replace both the ball joints in the trailing arm. They're the same top and bottom. If you have a 95 (for others reading this thread - OP has a 97) the bottom one originally was a bushing, not a ball joint - and you'll want to replace both with the ball joint like the 96+ cars.

As for the control arms, there are rubber bushings on the inside where they mount to the rear subframe. And yes, trying to replace the bushings in the lower arms is a fool's errand.

There are also ball joints that fit in the inner location of the control arms. I bought some adjustable lower camber arms to replace the stock arms, and they came with ball joints at the inner location, so three of my four are ball joints on each side (the uppers were relatively easy to replace the bushing on). I don't feel any downside and will change that last bushing to a ball joint next time it needs refreshing.

I did a lot of research and got Megan racing lower arms. They're reasonably priced and as robust as the best out there (and better than most). Some people told me that they're hard to adjust when installed - I didn't find that to be true. At all. They're easy to get to and I have plenty of clearance.

None of this should make it unpleasant to drive, but it should be a lot more responsive when you finish. The conventional wisdom is to keep the OEM rubber for the diff, which is what I've got as well (purple Powerflex in my subframe - I forget the durometer number) and I don't have any diff noise.

Josh, thanks for the very comprehensive post. I appreciate you taking the time to share this with me in one location.

I already have your first comment underway. RTAB reinforcement plates and swaybar reinforcement plates arrived in the mail yesterday, and a welder is coming to the garage I store the M3 in during the winter months to weld it all in place. I also had the front subframe motor mounting area reinforced last week as well.

Spherical bearings you say? I guess I have a new option that I hadn't thought about to research. Looks like AKG and Ground Control sell the ones for the trailing arms. Do you have a preference on which manufacturer you prefer?

With regards to zero toe, do I need trailing arm spherical bushings that are adjustable, like Ground Controls?

Alright, I will replace the two ball joints in the rear trailing arm as well. OEM is acceptable for this?

I'll snag the Megan racing lower arms as well, as I have heard positive things about them thus far also.

Great news on the (3) OEM diff bushings.

Thanks again for all of this. I feel much more equipped to tackle the rear end now.

Obligatory pic of the M3 and some recent work that has been done:

M3 Work - Round 2 by Michael Rickerd, on Flickr

M3 Work - Round 2 by Michael Rickerd, on Flickr

M3 Work - Round 2 by Michael Rickerd, on Flickr

2-6-2021 Work by Michael Rickerd, on Flickr

[MR E30]

The M3 has been registered in Maricopa County (Phoenix, AZ) since it was purchased new from from Camelback BMW. I'm the first owner (#7) to register it in any other county (Coconino County, still in AZ just north).

As a result, the chassis is in incredible shape. Not a hint of rust, and all structural areas of the chassis, albeit dirty, look brand new in terms of shape and condition.

Gives me confidence to run some serious power though it.

[BMWManiac]

What brake reservoir is that? It has the two barbs to connect to the ABS pump?

[MR E30]

What brake reservoir is that? It has the two barbs to connect to the ABS pump?

Chase Bays, boosterless MC.

No ABS.

[blckstrm]

Spherical bearings you say? I guess I have a new option that I hadn't thought about to research. Looks like AKG and Ground Control sell the ones for the trailing arms. Do you have a preference on which manufacturer you prefer?

With regards to zero toe, do I need trailing arm spherical bushings that are adjustable, like Ground Controls?

Alright, I will replace the two ball joints in the rear trailing arm as well. OEM is acceptable for this?

I haven't done enough research - I don't know which spherical bearing is the best. I have had a former race engineer tell me that most aftermarket spherical bearings are undersized because most guys aren't really doing the engineering on them and don't fully understand the forces at play. So I feel like it's something worth doing some healthy research on. Maybe someone else will have some feedback.

You shouldn't need anything special to get to zero toe - factory adjustability allows it.

[MR E30]

I haven't done enough research - I don't know which spherical bearing is the best. I have had a former race engineer tell me that most aftermarket spherical bearings are undersized because most guys aren't really doing the engineering on them and don't fully understand the forces at play. So I feel like it's something worth doing some healthy research on. Maybe someone else will have some feedback.

You shouldn't need anything special to get to zero toe - factory adjustability allows it.

Thanks for your post.

[aeronaut]

I'm a little confused on what the use of this car is, so read my recommendations with that understood.
- Don't use poly bushings in the RTAB. Use OEM w/limiters or spherical.
- Don't use spherical anything on a street car.
- If you buy sphericals from a quality supplier (BW, AKG, Rogue, etc.), there won't be any issues with them being "undersized", that is they won't catastrophically fail under hard use.
- And I'd personally never run 0 rear toe on a street car.

[RRSperry]

I'm a little confused on what the use of this car is, so read my recommendations with that understood.
- Don't use poly bushings in the RTAB. Use OEM w/limiters or spherical.
- Don't use spherical anything on a street car.
- If you buy sphericals from a quality supplier (BW, AKG, Rogue, etc.), there won't be any issues with them being "undersized", that is they won't catastrophically fail under hard use.
- And I'd personally never run 0 rear toe on a street car.

I thought the same thing? What's it for? A Turbo LS swap for track days I can see, but everything else is going to make it horrible on a highway...

Two diametrically opposed uses...

[E85STI]

Man your car is so clean. I am extremely jealous of the lack of rust!

The M3 has been registered in Maricopa County (Phoenix, AZ) since it was purchased new from from Camelback BMW. I'm the first owner (#7) to register it in any other county (Coconino County, still in AZ just north).

As a result, the chassis is in incredible shape. Not a hint of rust, and all structural areas of the chassis, albeit dirty, look brand new in terms of shape and condition.

Gives me confidence to run some serious power though it.

[blckstrm]

Thanks for your post.

I forgot about the "which ball joint" part of the question.

The Non-M cars have rubber bushings, and the 95 M3 only has a ball joint in one (I forget if it's top or bottom - I think it's the top). So even just having ball joints vs a rubber bushing was already an upgrade.

There are always arguments about which OEM supplier is better. I don't know how much it really matters. The Febi Bilstein ones are about half what the Lemforder ones cost ($17 vs $38). I got the Febi.

If you've gone this far down the rabbit hole, you could probably benefit from some poly bushings in your FLCA lollipops (which you may also have already).

...

I totally understand where some of these guys are coming from - my wife won't ride in my car anymore.

But I love it. It is super sharp and playful, and it is super reliable. It is a complete joy to drive.

[Carpy2]

A few notes I noticed when I redid my rear end last season as I was able to kind of experience each step of the way. Most of this has been said, just my notes on a few things.

1. I went solid subframe bushings, no need for that thing to move. Virtually no NVH added.
2. 95A Diff bushings. Diff whine increased substantially over new stock bushings. I run 75D engine, tranny, FCAB bushings/mounts which increase NVH the most out of anything. I kept the differential bushings at 95A to minimize whine (NA S52, drivetrain movement isn't really an issue).
3. OE RTABs with limiters still, spherical would be the next step, but haven't felt the need. You want these to be able to move, don't go solid here.
4. Camber arms to achieve -2.0 and more negative in the rear.
5. New OE ball joints everywhere else, makes a huge difference.
6. RTAB reinforcement and sway bar reinforcement if you run a rear swaybar.

This has been my only car for 10 years now, and the solid engine/tranny mounts are the single biggest contributor to considering a second car to date lol. However, the engine noise and feel you get is just incredible so I will continue to deal with it ^^. It's really only at idle that it's NVH'y.

[MR E30]

Man your car is so clean. I am extremely jealous of the lack of rust!

Thanks! It is certainly a tremendous benefit.

- - - Updated - - -

I forgot about the "which ball joint" part of the question.

The Non-M cars have rubber bushings, and the 95 M3 only has a ball joint in one (I forget if it's top or bottom - I think it's the top). So even just having ball joints vs a rubber bushing was already an upgrade.

There are always arguments about which OEM supplier is better. I don't know how much it really matters. The Febi Bilstein ones are about half what the Lemforder ones cost ($17 vs $38). I got the Febi.

If you've gone this far down the rabbit hole, you could probably benefit from some poly bushings in your FLCA lollipops (which you may also have already).

...

I totally understand where some of these guys are coming from - my wife won't ride in my car anymore.

But I love it. It is super sharp and playful, and it is super reliable. It is a complete joy to drive.

I happen to have (2) Lemforder ball joints for the trailing arms, so I will purchase (2) additional Lemforder units to swap all 4 in the rear. This is covered and solidified.

FLCA's received a set of Garagistic Lollipop 'bushings'. I did these on my SC'ed S52 E30 and they were an incredible upgrade, so it was an easy choice to do that with this car as well.

--------

I hear you there. I think I am looking for more of the 'enjoyable to drive' aspect, by the car really feeling like a machine on the road.

If I don't feel like dealing with the car that day I'll just take one of my much comfier Tacomas to the store or wherever.

Thanks again!

- - - Updated - - -

A few notes I noticed when I redid my rear end last season as I was able to kind of experience each step of the way. Most of this has been said, just my notes on a few things.

1. I went solid subframe bushings, no need for that thing to move. Virtually no NVH added.
2. 95A Diff bushings. Diff whine increased substantially over new stock bushings. I run 75D engine, tranny, FCAB bushings/mounts which increase NVH the most out of anything. I kept the differential bushings at 95A to minimize whine (NA S52, drivetrain movement isn't really an issue).
3. OE RTABs with limiters still, spherical would be the next step, but haven't felt the need. You want these to be able to move, don't go solid here.
4. Camber arms to achieve -2.0 and more negative in the rear.
5. New OE ball joints everywhere else, makes a huge difference.
6. RTAB reinforcement and sway bar reinforcement if you run a rear swaybar.

This has been my only car for 10 years now, and the solid engine/tranny mounts are the single biggest contributor to considering a second car to date lol. However, the engine noise and feel you get is just incredible so I will continue to deal with it ^^. It's really only at idle that it's NVH'y.

Thanks for this input!

1. Agreed on the solid subframe bushings and that piece of metal should be solid as can be.
2. Based on my research I will pass on upgraded diff bushings and instead stick with OEM for now.
3. Agreed on skipping the solid mounts. Heavily leaning towards the spherical bushings, but not fully decided yet.
4. Taking blkstrms advice and getting the Megan lower camber arm.
5. Agreed here as well.
6. Just spent the afternoon prepping the chassis for the pocket reinforcement plates to be welded in. Scheduled an on-site welder for 2 weeks from now to get those installed. Swaybar reinforcements will go in as well, though I am undecided on how the swaybars will be upgraded at this time.