e90 M3 4th Diff mount bushing prototype (lockdown alternative)

[rbryantaz]

Hi everyone, I was looking at a way to install a 4th mounting point to the e90 M3 rear differential and here is what I came up with.

This is similar one that I have seen for the e30 for the extension.

I am not aware of anyone that has done it for the e90 so I made one.

Back view:

(The center bolt is too close to the frame and will have to change to a countersunk flat bolt like the ones holding the bushing extension housing, the bushing extension housing bolts do have some room so those could be button head instead)

Front view:


This puts the bushing about 16mm from the frame so an aluminum spacer is used between the bushing and the subframe.

It requires a 9/16 bolt hole to be dilled through the rear subframe on the passenger side (nearly symetric to where the mount is on the driver side). This uses an e30/e36 bushing so they are readily available in pretty much any hardness that people desire. It could also be made as a solid mount with no bushing but that seems like overkill for most.

What does everyone think?

-Rich

[roastbeef]

The goal is to add rigidity? What is the purpose besides a solid mount for the single lateral diff mount?

[rbryantaz]

Originally Posted by roastbeef

The goal is to add rigidity? What is the purpose besides a solid mount for the single lateral diff mount?

The goal is more to prevent the diff from being able to rotate more than just adding rigidity.

The 4th mounting point can greatly reduce movement in the diff without having to go with solid mounts which add a lot of NVH.

It will also eliminate movement even more than the solid mounts alone. Kits like the DEFIV which I think is discontinued included both solid mounts and the 4th mount point.

-Rich

[Redd]

So the original 3 diff mount points are retained, and the bracket is bolted to the diff cover which adds the 4th mount point? Are the original mount points still using stock bushings? Any additional NVH or diff whine?

Some years back I enquired about the Defiv diff brace and was told it was discontinued because it didn't make much of a difference.

[Delete]

Does a sleeve get inserted into the hole that you drill ? So you dont crush the tube when tightening it down.

[SAMM3Y]

Very interesting and great fab work! Thanks for sharing.

[rbryantaz]

Originally Posted by Redd

So the original 3 diff mount points are retained, and the bracket is bolted to the diff cover which adds the 4th mount point? Are the original mount points still using stock bushings? Any additional NVH or diff whine?

Some years back I enquired about the Defiv diff brace and was told it was discontinued because it didn't make much of a difference.

The original 3 3 bushings are retained. I don't have the rear end installed yet to listen to thr NVH. I plan to start with stock bushings and see how it is with them and upgrade to poly on the original 3 if needed.

This is a different style than the defiv brace so I think it can make a difference and is not as involved.

Conceptually it is like the Turner F80 4th diff mount bracket but it puts the bushing in the bracket because there is nowhere to put it in thr frame without a lot of modification to the subframe. A bolt hole is much more reasonable for the average guy than welding in a bushing mount.

[rbryantaz]

Originally Posted by Mog-10

Does a sleeve get inserted into the hole that you drill ? So you dont crush the tube when tightening it down.

I haven't put a sleeve in yet but I was considering it. The tube is quite strong where it was added but it did seem to crush ever so slightly.

I am going to take a look at adding one. I also got my back side bolt hole just a little low when figuring how where/how to drill it a sleeve would let me correct that because it would enlarge the hole.

[Delete]

I would . If you can weld it in. To keep movement from egg shaping the hole over time.

[amrazM]

This is a nice piece of engineering you did here, you going to make more brackets? If so I would take one.

[rbryantaz]

Originally Posted by amrazM

This is a nice piece of engineering you did here, you going to make more brackets? If so I would take one.

I can make more.

I am looking into providing the weld in inserts. I think they are optional. The tube really doesn't crush much given that it is rounded on the back side and I use a 35mm spacer to distribute the stress on the front side.

I am talking to a machinist about hadding a 3.5" 3/4" OD, 9/16" ID spacer with a 1" OD step that is 16mm tall to replace the 35mm spacer that I used so that the bushing then connects directly to it and it can be welded in without having to grind it flat again.

Send me a PM and we can work out something on the prototype. I might have someone that is interested in testing the first prototype but I would like to have 2-3 people test it out and I can give a good discount for doing that and reporting back.

I have to see what the pricing looks like but I think it should be somewhere around $300 depending on if I include the poly bushing and if the steel weld in tube/spacer is included.

Adding the spacer does have the advantage of giving more margin of error when drilling. I did have to use a 90degree drill adapter with a step bit to start the hole on the front side.

Drilling the front side is pretty straight forward, I used a pick tool to scratch the paint in a circle through the mount hole so finding the drill point was easy.

I drilled from the front to back with a pilot hole to find the rear drill point. My pilot hole was a bit low once I reinstalled the diff and put the bolt through I could see that I needed to move it upward. That should be done BEFORE enlarging the hole to the full 9/16". Fortunately I did not need to go beyond the sleeve size so it will be fine. I will provide some measurements on where to drill from the back side for the pilot hole within the margin of error for hte OD of the bolt hole. Then if the diff is installed and the bolt pushed through from the front side it will be visible through the pilot hole and can be adjusted to be perfect.



https://www.harborfreight.com/38-in-...ent-69337.html



-Rich

[Bartledoo]

Yea, these cars should’ve come with another mounting point or something from the factory. Was so weak.

[rbryantaz]

Originally Posted by Mog-10

I would . If you can weld it in. To keep movement from egg shaping the hole over time.

As suggested:

I took my frame to a local welder who TIG welded in a 4130 chromoly sleeve that I bought which has a nice tight 14mm ID. It is a .0950 wall tube so chromoly is definitely overkill... I would have just bought it in mild steel but the mild steel version was backordered from my supplier. In order to get it done over the weekend I had to just bite the bullet and pay for the more expensive tubing even though it is definitely not needed in this application.

I will switch back to the M14 bolt instead of the 9/16" bolt I was going to use to keep everything tight. I also found that the powerflex bushing has more of a true 14mm inside diameter insert than the Nolathane which was closer to 9/16" The stock bushings have a hole large enough for the 9/16" bolt even though the stock bolt is 14mm. The purple powerflex bushing is also considerably softer than the black Nolathane (the powerflex bushing costs about twice as much).

Front Weld before paint:

We used a 1/4" steel spacer here so that less spacers are needed for the bushing. This also helps spread the load over a wider portion of the frame.


Front after primer and paint (always prime and paint welds or they will rust very quickly)

The bolt will really come through from the back but this test fitment shows that it still fits and doesn't have to be reamed out after the welding. The camera angle makes the washer look off center but in reality it isn't, the welding is just not perfectly round. The goal is just to get a nice flat surface for the poly bushing spacer to contact.


Back before Paint:



Back after paint:

This washer is only here to spread the load a bit on the frame. The bolt is just going to the end of the tube. It could have been done flat like the front side too. The welder just happened to do it this way.


I think it is possible to skip the welded tube given that there are 3 other mount points but it is definitely better to have it. If you have the frame off doing this just makes sense.

I have enough of the weld tubes to do more frames. If people are interested in a kit let me know. I will just need to make more of the aluminum pieces and some of the front and back weld on spacer/spreaders that go over the tubes.

-Rich

[rbryantaz]

I a M3 prototype 4th diff mount through with my anodizing run.

I did forget to countersink the middle bolt first so that is still bare but it will be covered by the flat head bolt anyway.

Back view:



Kit breakdown with anti-crush sleeve and a nolathane (same company as whiteline) e30 bushing installed:


Send me a PM if you are interested in purchasing one. I can offer it at a discount for someone that wants to beta test it!

-Rich

[rhyary]

PM sent

[Redd]

Originally Posted by rbryantaz

I a M3 prototype 4th diff mount through with my anodizing run.

I did forget to countersink the middle bolt first so that is still bare but it will be covered by the flat head bolt anyway.

Back view:
Attachment 2781836


Kit breakdown with anti-crush sleeve and a nolathane (same company as whiteline) e30 bushing installed:
Attachment 2781837

Send me a PM if you are interested in purchasing one. I can offer it at a discount for someone that wants to beta test it!

-Rich

Looks good! Any additional NVH or increased diff whine?

[rbryantaz]

Originally Posted by Redd

Looks good! Any additional NVH or increased diff whine?

I expect a small amount of whine but it should be less than the extra wine from adding 3 poly bushings and significantly less than solid bushings.

I plan on running a similar setup in my 335i in the next couple of weeks and I can report back. That setup will use a 335i diff with helical LSD with an M3 subframe with stock M3 diff mounts and a powerflex purple as the 4th mount. It is a different bracket but uses the same bushing in the same position.

-Rich

[Rajinders737]

Id be interested in purchasing one of those and mock up on my E60 M5(same diff bolt pattern). Can u email me at rajinders737@gmail.com?

Thanks,
Raj

[rbryantaz]

Originally Posted by Rajinders737

Id be interested in purchasing one of those and mock up on my E60 M5(same diff bolt pattern). Can u email me at rajinders737@gmail.com?

Thanks,
Raj

A lot of time has passed without a lot of interest in this so I have abandoned the project after making just the single prototype for my 335i.

If it were specifically for the M3 then I could probably have one made or share the plans but the M5 will have a different subframe so it probably wouldn't fit without a bunch of work and measurements.

-Rich

[Rajinders737]

Originally Posted by rbryantaz

A lot of time has passed without a lot of interest in this so I have abandoned the project after making just the single prototype for my 335i.

If it were specifically for the M3 then I could probably have one made or share the plans but the M5 will have a different subframe so it probably wouldn't fit without a bunch of work and measurements.

-Rich

Yeah, It's an E60 M5 W DCT from e92 m3. Will soon be throwing an M3 rear diff in due to the gearing. The stock rear differential cover is the same bolt pattern(confirmed) and I wouldn't mind purchasing it and then using that as the base to modify it to fit my car. The rear diff mounts are so weak that I snapped one. Had to get it re-welded so adding a 4th support would be ideal.

Please let me know if you can have one made or send the plans. We can definitely talk cost in regards having you make one for me.

Thanks,

[Redd]

Originally Posted by Rajinders737

Yeah, It's an E60 M5 W DCT from e92 m3. Will soon be throwing an M3 rear diff in due to the gearing.

Hi Rajinders737 - just tried to PM you but it did not go thru. If you don't mind can you email me pls, I'm keen to find out more about how you mated the DCT to the S85. Thanks.

[rbryantaz]

Originally Posted by Rajinders737

Yeah, It's an E60 M5 W DCT from e92 m3. Will soon be throwing an M3 rear diff in due to the gearing. The stock rear differential cover is the same bolt pattern(confirmed) and I wouldn't mind purchasing it and then using that as the base to modify it to fit my car. The rear diff mounts are so weak that I snapped one. Had to get it re-welded so adding a 4th support would be ideal.

Please let me know if you can have one made or send the plans. We can definitely talk cost in regards having you make one for me.

Thanks,

It looks like you need a couple of more posts before your PMs are enabled...

When you get them enabled send me a PM.

I would need to make a new mount either way. I scrapped and recycled the original M3 mount because I decided to use a smaller bushing in my setup. With the mount perfecty centered the mount clears the subframe just fine but was too close to the body of the car and could make contact.

So I revised the 188 diff mount to use a smaller bushing and never followed up on doing the same with the M3 diff version.

I still have the CAD files but we would need to do a bunch of measurements and revisions to make it work for an M5 and I probably won't have much time for a one off project for a while.

We can talk about me making a quick conversion to the smaller mount and you would then need to make the frame meet up with that.

-Rich