rear subframe bushings and differential mounts

[gwb72tii]

There's one thing about this job that I don't quite understand.
After you unbolt and lower the subframe, what is the reason for having to remove the two long splined bolts? Is it simply because without removing them, you don't have enough clearance between the subframe and the bottom of the car to R&R the bushings? 

I've tried ordering a pair of the splined bolts from several sources but have been told they're on some type of back order from BMW. I'd like to have replacements in case I bugger them up in the process of removing them.

However, I came across a creative method of getting them out that involves drilling and tapping into the heads of the bolts, then using a simple fabricated puller to extract them. Has anybody tried this?
https://www.forum5.co.uk/topic/47-rear- ... placement/

 

 

more than one person has suggested, including me that just performed this job, that you do not need to remove the pins. the subframe can be lowered enough to remove the bushings. I'm left wondering how thoroughly you read responses to your original question.

BTW - I tried the suggested big f**king hammer method and the pin just laughed at me.


 


 

[LarryM]

^^^^ I read the responses so thoroughly, in fact, that I decided to purchase the same tool you used. It seems robust enough to do the job, however I did notice that, included with the tool’s instructions, is a note that when installing the new bushings: “If the subframe is still in the car and room is limited you can always cut down the height of the [tool’s] tube to gain extra clearance”.  This tells me clearance may be tight, and is why I asked the question. There are just as many people saying the pins must be removed, as there are those saying they don’t. One factor (besides the tool or method used) may be whether poly or OEM bushings are installed as replacements.  Since you had no trouble using the FoRSVARA tool installing (what appear to be) OEM bushings without removing the pins, that’s good enough for me. But I’ll still be prepared to extract them if necessary.

Meanwhile, still waiting on parts....

[Mashford]

More than a month later, I am finally under the car. I had to put down footings and cinder blocks to get jack stands bases off the side of driveway to work around the car. 

Then, with all the rain here in DC region, I took the opportunity to put in French drains around the footings. Otherwise, I would have been on my back in the mud at least some of the time. 

“Give a mouse a cookie…. ”

So, starting now with diff mounts.  Subframe bushings after that. 

[Mashford]

Any suggestions here?  I can't remove the last bolt of the differential mount because the stabilizer bar is too tight up on the bolt.  Now I have my ratchet stuck in there between the bar and the mount/frame, too.

Should I jack up the subframe so the stabilizer bar tilts more, down away from the bolt?  If so, where should I place the jack?  

I have the differential on a jack stand and the car on jack stands on the side rails (standard points for jack stands).  I seemed to have some success on the other side of the differential mount by jacking up the subframe piece extending to the rear axle, but the car felt unsteady, so I got nervous being under it (the car came up off the side jack stands a bit.

Thanks.
 


 

 

[Mashford]

Got it out by raising right rear axle which tilted the bar away from bolt and stuck wrench. 

Trying to determine now if mount was installed backwards, perhaps. Looking for DIAgrams. 

[Mashford]

 

To clarify, the differential mount is offset, with two of the bolt holes slightly farther from the actual center holding the rubber and main bolt hole.  When I just pulled mine, the offset side was facing the front of the car, so the entire mount was pretty snug up against the stabilizer bar.   You can see that pretty clearly in this photo.  This is how it was installed when I removed it.  Is it backwards?

Thanks!

 

[Mashford]

 Bump!

[Mashford]

I found a picture of correct position here:

https://www.1988bmwm5.com/replace-rear- ... ial-mount/

[Mashford]

The old and the new, before installation of new.
 
  

 

[Mashford]

I got the diff mount in/replaced and put the four bolts holding the mount to the frame in then the 20mm bolt holding diff to the mount.  

Then I removed the subframe bushing nuts from the splined pins and the other two nuts holding in the plates (?) and without making any attempt at removing the pins, lowered the jack below that was supporting the subframe in the center and the subframe did not budge.  It wiggled a bit when I put a pry bar in there and levered against it, but did not slide down the pin at all.  

I realized at this point (and want to confirm), that it is not dropping with the bushing nuts off because the differential is still bolted to the rubber mount at the far end of the drive train assembly (and the differential is mounted to the subframe and the other end).  So I removed the main differential nut from the mount and lowered the differential and the whole subframe slid down the pins another inch or so and stopped again.  

So then I got the torch out and got the cylinders holding the subframe bushings smoking hot on both sides, with room for the subframe to "fall" a bit more before stopping on the jack under the center of the subframe (the differential is hanging free at that point).  

At smoking hot, the subframe did not "fall" any lower.  I thought I might be damaging the differential by letting it hang without that bolt in the rubber mount, so I put the jack under the diff and gave is some support.  

I tried levering the subframe again with a magic bar (small crow bar), but it won't budge.

I am pausing to check in here, ponder, and scratch my head. 

Do I just need to torch the bushing cylinders some more until the bushings really get liquid hot and drip out of the subframe and set it free?  Or am I not allowing the subframe to work with gravity to fall free (I don't see it being held back anywhere else now that I have removed the bushing mount bolt.

Thanks for any advice!!

[Mashford]

This where I am "stuck" and am not sure how to get the subframe to drop more. 
 


 

 

[LarryM]

I haven’t done this job but don’t you also have to remove the dog bones (pitman arms)? Also did you disconnect the muffler from the rearmost hangar? 

[///M]

You may have electrolytic corrosion on the mounting to the body. What can happen is that if you removed the bolts the subframe does not drop. The alloy of the mount fits to the metal of the car body and corrosion bonds them together. I have used a large bar and quite a lot of force before they broke free so make sure the subframe is well supported. You have the bolts in place which should make it more stable.

[Mashford]

You may have electrolytic corrosion on the mounting to the body. What can happen is that if you removed the bolts the subframe does not drop. The alloy of the mount fits to the metal of the car body and corrosion bonds them together. I have used a large bar and quite a lot of force before they broke free so make sure the subframe is well supported. You have the bolts in place which should make it more stable.

Thanks. Would I be able to see that, confirm that visually, before I start trying to force it?

[Mike W.]

This where I am "stuck" and am not sure how to get the subframe to drop more. 

IIRC the hub of the bushing is aluminum. Not like steel on steel, but steel and al can sometimes develop a relationship. My guess is that's what's holding it together. Take a sawzall and a can of WD40 and cut out around the hub thru the rubber. Once you get the rubber bushing cut thru it should no longer have anything to hold it in place. It'll be messy, spray the crap out of the blade while cutting thru the rubber, but if you get it cut thru it should drop. At that point you can put a pipe wrench or whatever on the hub of the bushing and start turning it. Again, with some sort of penetrating lube. I like Liquid Wrench for that, trying to get between the bolt and the hub, but everyone else likes PB Blaster. WD40 is not the right choice for that one.

[///M]

You may not see it but the subframe mount sticking to the body is common. Anyone living in a dry climate miss out on a lot of problems due to corrosion.
The subframe is held at three points, the two side mountings and the differential mount. If the three mounting bolts are removed then the subframe is free.
If the differential drops it puts a stress on the side mounts and they can bind on the bolts. Make sure that the subframe is level (leaving the differential mounting bolt in a couple of threads can help) and you should be able to lever the mount away from the body. It should move. If it does not move then it is stuck to the body. How badly is down to the amount of electrolytic corrosion.
Mild corrosion and it lets go easily. The worst I have seen is when with the subframe large bolts removed and a large lever the alloy of the mount broke leaving about 20mm  stuck in the steel of the car body. The remains had to be forcibly removed and did not come out in one piece it was completely bonded in. Using sprays had not effect.
Depends on where your car spent most of its life how yours now but worth trying some release spray first.
 

[Mashford]

Thanks everyone. 

The subframe does move slightly when I use a mini-crow bar to leverage it, so that says to me that the subframe alloy is not corroded onto the body of the car.   But then it must also mean the bushing rubber is adhering to the bolt (pin) and the inside of the cylinder holding the bushing.  That is the most common challenge with this job overall, right?

My best guess.

So I am going to try to melt it.  First, though, I am going to drill a bunch of holes vertically up into the bushing from below, into and through the rubber, to make it weaker overall.

I realize that there are a lot of posts on this and I am sometimes asking questions that have been answered in other posts, but it is very helpful to check in real time as I review them. 

Apologies for any redundancy. 

Back soon and thanks again.

[///M]

There are many ways to do that job. It depends on what you have available to you and like every job when finished you now a little more than when you started.
I have done it many times and getting the bolts out makes it some much easier. If you do not have the special tools and a ramp then working on your back it is hard to hit the bolts hard enough but it can be done.

[Mashford]

There are many ways to do that job. It depends on what you have available to you and like every job when finished you now a little more than when you started.
I have done it many times and getting the bolts out makes it some much easier. If you do not have the special tools and a ramp then working on your back it is hard to hit the bolts hard enough but it can be done.

 Thanks, ///M.

I will see if I can smack on the pins while under there, too.  

I enjoy the learning process and am patient about all this.

I wouldn't be able to do any of this without help of the forum.

[Blue Shadow]

Crap, I wrote a bit in response but I guess I forgot to post it.  

Read the bushing replacement guide onRod’s Automobile Pages and see how I did it. 

The bushing does not have rubber in it that will keep the bolt in place it is between the inner aluminum sleeve and outer steel can…pictures in the how to

Heat is only going to soften the thin rubber layer between the steel and subframe. Use heat to help the puller it won’t do much otherwise. 

There isn’t much room at the top of the bushing when the sf is dropped but you only need enough to put in the puller part which was about an inch thick in the tool I used. 

Protect the pin as you beat it out of the car.