Diff bushings replace or not?

[VictorH]

Okay, I'm admitting defeat.
I have fiddled the past two days with the front subframe bushings. The rears are no issue, no problem, particularly given the flange that goes all the way around the bushing.

I was able to get the fronts started and advanced to within 3/4" of being seated (which is still a ways off). I stripped out 3 standard threaded rods. I Cut an inch off the cup so I could use some Grade 5 hardware I found, but the tabs on the flange plate bent from too much pressure and kept slipping off.

Next I invited my neighbor over who used to own and run a bunch of tire shops. We tried a chain around a 4 ton floor jack, but it just didn't work.

So, then I broke down and went to Northern Tool and got a 12 ton hydraulic press. Even with the press I couldn't get the bushing to more than flush with the end of the sub-frame flange. There's just no way to support the outside of the flange and the edge is just tiny and flared to the outside so your press plates just pop right out as soon as you apply some force. I don't have much in the way of metal pieces to try to fit in to support the inside of the flange.

What's crazy is the interference fit, at least in my sub-frame, is much tighter for the front bushings than the rear. I think they are at least a few 10 thousands too big. My neighbor says he would have measured the inside and outside diameters to see where we are but I had already started both bushings.

I'm really stuck at this point, which is a bit unusual for me. We'll work something out but the plans to start the installation of the subframe this weekend is not going to work out. That's life.

[SAMM3Y]

Get a bigger hammer... 30 ton press

[M43S7RO]

I had the same issue. Go to a local pipe supply shop and ask for about a 4-5 inch length of 3" inside diameter steel pipe. It's such a small length they may just give it to you if laying around. I payed about $5 for it.

See my pm.

Originally Posted by VictorH

Okay, I'm admitting defeat.
I have fiddled the past two days with the front subframe bushings. The rears are no issue, no problem, particularly given the flange that goes all the way around the bushing.

I was able to get the fronts started and advanced to within 3/4" of being seated (which is still a ways off). I stripped out 3 standard threaded rods. I Cut an inch off the cup so I could use some Grade 5 hardware I found, but the tabs on the flange plate bent from too much pressure and kept slipping off.

Next I invited my neighbor over who used to own and run a bunch of tire shops. We tried a chain around a 4 ton floor jack, but it just didn't work.

So, then I broke down and went to Northern Tool and got a 12 ton hydraulic press. Even with the press I couldn't get the bushing to more than flush with the end of the sub-frame flange. There's just no way to support the outside of the flange and the edge is just tiny and flared to the outside so your press plates just pop right out as soon as you apply some force. I don't have much in the way of metal pieces to try to fit in to support the inside of the flange.

What's crazy is the interference fit, at least in my sub-frame, is much tighter for the front bushings than the rear. I think they are at least a few 10 thousands too big. My neighbor says he would have measured the inside and outside diameters to see where we are but I had already started both bushings.

I'm really stuck at this point, which is a bit unusual for me. We'll work something out but the plans to start the installation of the subframe this weekend is not going to work out. That's life.

[pbonsalb]

20 ton press rather than 12 ton. Or higher quality threaded rod. Maybe even the kind with bigger threads you find in a bushing c clamp type tool.

[M43S7RO]

His problem isnt the power of the press and a 100 ton press wouldn't help his problem. A 12 ton will do just fine. He needs to support the rim of the subframe so that the bushing can be pressed.

[VictorH]

Originally Posted by M43S7RO

I had the same issue. Go to a local pipe supply shop and ask for about a 4-5 inch length of 3" inside diameter steel pipe. It's such a small length they may just give it to you if laying around. I payed about $5 for it.

See my pm.

Got it thank you. That's what I'm going to do. Appreciate your insights, experience matters.

[pbonsalb]

Yes, the 2 press plates that come with a press are not sufficient for many jobs. You need various other receivers, supports, etc. Over time as you do more work, you will accumulate more of what you need to get jobs done.

[VictorH]

Since I can't do anything until I get a 3" ID pipe I thought I'd go ahead and clean 140K miles of grime off the underside and finally install the two flex brake lines that I never installed because of the nuisance factor. Super easy with no sub-frame.

[VictorH]

Another question for those of you have done this bushing replacement.

How do you ensure you have the the sub-frame centered on the body before you tighten everything up? There is a ton of slop in the space between the M12 bolts and the bolt holes in the bushings (it's a bit over 1/2"), so it would be possible to install the sub-frame a ways off from center.

I did think about marking the subframe before I removed it but it wasn't obvious how to mark the sub-frame and body since the bushings create a gap between the two. Is it worth putting a sleeve between the bolt and the bushing?

[Bartledoo]

Originally Posted by VictorH

Another question for those of you have done this bushing replacement.

How do you ensure you have the the sub-frame centered on the body before you tighten everything up? There is a ton of slop in the space between the M12 bolts and the bolt holes in the bushings (it's a bit over 1/2"), so it would be possible to install the sub-frame a ways off from center.

I did think about marking the subframe before I removed it but it wasn't obvious how to mark the sub-frame and body since the bushings create a gap between the two. Is it worth putting a sleeve between the bolt and the bushing?

I always wonder about this as well. I remember Malek saying he made his own centering tool for the subframe because of this issue. Because of that and my limited set of tools I payed a shop to do it. But I always wonder how/whether they centered it properly.

[Mr_Reeves]

I personally wouldn't recommend doing this job yourself unless you've done it before and have all the tools to do so.

I've had the BW bushings installed recently by my shop and they have a jig to hold the subframe while the bushings are pressed into place. As they were, the bushings will not fit, they will need to be shaved down to get them in all the way.

[VictorH]

Busy week, just getting back to the car.
Found some thick-wall pipe but internal diameter was 2.935" which is just a touch small. Went to local machine shop and had it milled out to 3.05" ID which looks to be just about right. They were also good enough to also make sure, and machine, both ends to be sure they are completely square.

[Richbot]

This is the kind of thing I would farm out because I'm soft and weak and scared even though I could probably pull it off. Good on you for persevering/being stuck with your poor decisions and not burning the garage down for the insurance money

Did you buy new swaybar bracket bushes? Mine are looking a little sad lately at 120k miles, not totally worn out but clearly getting a bit distorted. Not sure there's any way to change those without dropping the subframe

[VictorH]

You can do it. It's not really all that difficult it's just a matter of being organized and sequential in terms of the process. I learn something new every time I do a project like this. Oddly, mostly because of work, this one is taking a lot longer than the rod bearings! I think I'm in the home stretch.

The "sway bar" bushings look fine. I'm replacing the diff bushings with the purple ones but they look pretty good too. However, it's looks only, no cracked rubber, no dry crusty stuff, but who knows maybe it's a lot softer and more compliant than new.

[VictorH]

Victory!!
So, the front bushings are now fully seated. As many have said and now I'm a believer you really need a press to install the front bushings. This might be only a BW product issue but clearly the interference fit for the front bushings is too tight for any other method to get the bushings seated. The rears are a different story and can be seated with threaded rod without using Grade 8 hardware.

A tubing spacer of pretty much exactly 3.0X" inside diameter is necessary for proper support of what is a really tiny flange. Also, you are not likely to be able to apply sufficient force to get the bushing seated without full support all the way around the flange. After they were seated I sprayed the bare metal spots (basically the flanges on both sides) with chassis black spray paint and looks good to go.

For those who are interested or maybe their car was involved in a rear-end accident the center to center measurements of the rear subframe bolts are as follows (these are tape measure measurements so not super accurate).
Front bolts side-to-side 41 3/8"
Rear Bolts side-to-side 32 3/8"
Front-to-back for both driver's side and passenger side was 21 5/8"

[wyatth]

Great work, Victor! Home stretch now. Anxious for your impressions!

[GORDON.M3]

Originally Posted by Redd

As someone who dailies solid subframe with stock diff bushings, I truly belive that this is how our M3s should have left the factory. Zero downsides, zero NVH, and the solid subframes makes the chassis feel one generation newer and tighter.

solid bushings are probably my next mod...

[VictorH]

Next step is to see how best to center the sub-frame on the body. I'll take some measurements of the amount of possible slop in the bushing to bolt hole.
I think it's really important to have the sub-frame as close to even and square with the body so that the driveshaft and diff line up as close as possible with no angle and also that the tire clearance is the same side-to-side.

I think I might have to have some insert bushings made to fit the bolt hole, in the subframe bushing, to ensure each is as centered as can be. I just don't see any way to find the true center-line of the car and be able to make accurate measurements to it from each side.

[VictorH]

As mentioned in previous posts there's about .185" of movement within the bushing bolt hole for the bolt to move around. If the right side of the subframe is all the way forwards and the left side is all the way rearwards then you could be as much as nearly 3/8 of an inch out of square. That's not going to be good for your driveshaft to diff alignment. The wheels of course can be aligned to fix the problem but it's really not ideal. Monday will be machine shop day for another, smaller set of bushing for the bolt holes.

Most folks should be able to get the subframe reasonably centered but it's still a bit of a guessing game. Bolt bushings will take some of the guesswork out of the re-mounting of the subframe.

[M43S7RO]

The mounting pins in the front chassis fill the gap you picture above pretty well, leaving less play than it seems. I shined a light through the holes and "eyeballed" that the bushing looked centered when seated over the pin by lifting the subframe pressed into position against the chassis for a test fitting.

Once front left and right are centered over and into the pins, this also aligns the rear holes.
Unless the subframe is bent, you can visually see through the holes that all four bushings are centered over the said chassis mount points and you can put the subframe bolts in.

I honestly dont think you can end up far off from where it should be. People mention special "jiggs" in subframe installation threads used by shops but I think this is just the supporting tool to raise and lower the subframe that allows for tilting and raising the subframe assembly and somewhat doubt there is something that perfectly centers the subframe into position as this would somehow require it to find the centerline of the chassis and exact position from some relative front or rear point of the car...

Maybe unnecessary but I used blue thread locker on new subframe bolts and marked the heads of the bolts with a Sharpie so that I can visually inspect that the bolts aren't moving (rotating) after installation.

[mtx450]

This is great! Looking forward to the finished product.

[MasterP]

My shop made index marks before removing the rear subframe. You're beyond that now.

I do not know for certain if someone makes "rigid collars" for the E92 but it's popular with the JDM crowd for this.