Subframe Bushings
- Thread starter bavbob
- Start date
I can say without hesitation, that I put poly sub frame bushings into both my E24's. I have felt zero increase in harshness, only a much less wandering arse of the car. I wished they were available when I redid my E9 and E3.
Hi nosmonkey - As you may know from reading my posts, I am one of the few people here who is concerned about the transmission of noise, vibration and harshness into my car's body. I am running 15" wheels, which means I have wider sidewalls that most folks here, since 16" wheels seem to be preferred. I have a strut brace across the front shock towers, but have not otherwise done anything to stiffen up my car.
I've done polyurethane bushings in an e34 and in an e39; they make a distinct difference. In doing so, I know that the stresses that are not being absorbed by the rubber bushings don't disappear, they are instead transferred elsewhere into the structure of the vehicle. Those vehicles can handle the stresses.
My view is that the coupes flex a lot because of the way they were made. For this reason, the improvement that would be obtained by using polyurethane bushings in a coupe would be limited by the fact that other parts of the chassis of a couple will flex in response to the increased loads. And, we don't really know what effect these increased loads will have on the welds that hold the car together, and the sheet metal that comprises the structure of the car, before failures start to occur. Stevehose's thread on the rear shock tower tear, for example, had an influence on my thinking, as did the fact that folks have found structural issues around the emergency brake mount in the transmission tunnel and the fact that Coupe King sells a differential reinforcement kit to repair tears and/or fortify the metal around the dif mount.
If I had taken my car down to bare metal and had a metal wizard rework the welds and strengthen the door sills, I might look at this differently. And I think newer model cars can accommodate more stiffening because the metals and manufacturing processes were more consistent that those used by Karmann when building our cars.
All that said, I like the W&N solid rubber bushings, and would recommend them.
I've done polyurethane bushings in an e34 and in an e39; they make a distinct difference. In doing so, I know that the stresses that are not being absorbed by the rubber bushings don't disappear, they are instead transferred elsewhere into the structure of the vehicle. Those vehicles can handle the stresses.
My view is that the coupes flex a lot because of the way they were made. For this reason, the improvement that would be obtained by using polyurethane bushings in a coupe would be limited by the fact that other parts of the chassis of a couple will flex in response to the increased loads. And, we don't really know what effect these increased loads will have on the welds that hold the car together, and the sheet metal that comprises the structure of the car, before failures start to occur. Stevehose's thread on the rear shock tower tear, for example, had an influence on my thinking, as did the fact that folks have found structural issues around the emergency brake mount in the transmission tunnel and the fact that Coupe King sells a differential reinforcement kit to repair tears and/or fortify the metal around the dif mount.
If I had taken my car down to bare metal and had a metal wizard rework the welds and strengthen the door sills, I might look at this differently. And I think newer model cars can accommodate more stiffening because the metals and manufacturing processes were more consistent that those used by Karmann when building our cars.
All that said, I like the W&N solid rubber bushings, and would recommend them.
Am preparing for the subframe bushing replacement now. But where would you suspend the vehicle if the usual support location is coming apart to access the bushing you wish to replace? Have looked at old threads, trolley jacks offer options, but a lift, well where do they position the pads?
gazzol
Well-Known Member
Where you put the pads is a good question and the answer depends on how solid your car is. I recently renewed my rear subframe bushes at home and jacked the car up under the diff, I placed the axle stands on the rear sill (rocker) lip cushioned with a piece of wood to prevent damaging the paint. If you don't trust your sills then your only option is to place your stands under the floor about 1/3 of the way in using a piece of 3x2 wood which runs from one side of the car to the other to spread the load but this is less than ideal and you do so at your own risk. Having said that I have done this successfully in the past.
Yeah, this is rather a tough one, and the shop manuals I have merely say "support the body."
I am reluctant to use the factory jack points, which makes for a difficult time when seeking to remove the rear subframe. The first time I removed my subframe, I lifted the car using the differential, loosened the bolt holding the trailing arm to the subframe bushing, removed the two bolts holding the trailing arm to the body, swung the trailing arm out of the way and placed a pair of jack stands, with a 2x4 block of wood, where the trailing arms are mounted to the body. This is not ideal because this location is not flat. However, my car spent 40 years in CA and TX before I bought it, so the floors are rust free.
And just in case you think you might want to go down the path of removing the bushings with the subframe in the car, my experience was that it is impossible to access all of the bolts holding the bushing to the subframe with the subframe in the car.
I am reluctant to use the factory jack points, which makes for a difficult time when seeking to remove the rear subframe. The first time I removed my subframe, I lifted the car using the differential, loosened the bolt holding the trailing arm to the subframe bushing, removed the two bolts holding the trailing arm to the body, swung the trailing arm out of the way and placed a pair of jack stands, with a 2x4 block of wood, where the trailing arms are mounted to the body. This is not ideal because this location is not flat. However, my car spent 40 years in CA and TX before I bought it, so the floors are rust free.
And just in case you think you might want to go down the path of removing the bushings with the subframe in the car, my experience was that it is impossible to access all of the bolts holding the bushing to the subframe with the subframe in the car.
wilies13
Active Member
Dear all,
a few months ago I replaced #10 and #3 and I would like to share my experiencies.
I used for #10 the W&N part. The old one was really in a bad condition and this was not really visible, when installed.
In the german E9 forum I had a discussion about the "solidness" of the used screws #8.
Standard "solidness" is 8.8 and BMW delivers for this case 12.9. I do not know the good English terms for this.
For #3 I used parts from Febi/Bilstein shipped by a second source supplier. They are so cheap, that every discussion makes not really sense.
Alternatively for sure made of PU....thought that for the rear axle this is not so important (I´m more an cruiser)
In german forum there was add. a report about how to replace #10 without removing the whole subframe (in German...):
When I started the process, I thought that there is close to no rust. But it was again hidden.
So I had really a huge amount of work. At the end I believe, it was the right approach to revise the whole area.
Best Regards; Willy
a few months ago I replaced #10 and #3 and I would like to share my experiencies.
I used for #10 the W&N part. The old one was really in a bad condition and this was not really visible, when installed.
In the german E9 forum I had a discussion about the "solidness" of the used screws #8.
Standard "solidness" is 8.8 and BMW delivers for this case 12.9. I do not know the good English terms for this.
For #3 I used parts from Febi/Bilstein shipped by a second source supplier. They are so cheap, that every discussion makes not really sense.
Alternatively for sure made of PU....thought that for the rear axle this is not so important (I´m more an cruiser)
In german forum there was add. a report about how to replace #10 without removing the whole subframe (in German...):
When I started the process, I thought that there is close to no rust. But it was again hidden.
So I had really a huge amount of work. At the end I believe, it was the right approach to revise the whole area.
Best Regards; Willy
Attachments
The "solidness" is the strength property class according ISO standards. It defines the ultimate tensile strength at which it fails .
Yes, further to Willy's post, one of the reasons I concluded it was not possible to change the bushing with the subframe in the car is that I did not want to knock out the knurled bolt that is pressed into the body under the rear seat and that holds the bushing and subframe in place.
If you are willing to knock this bolt out, then it can be done. I had forgotten about this in my earlier post.
If you are willing to knock this bolt out, then it can be done. I had forgotten about this in my earlier post.
Thank you gazzol, Ohmess, wilies13, and all other mentions about this important service from past posts. I was under my car this past weekend and cleaned the area well, and to my surprise, every nut turned. Still applied penetrant, to prepare for the final assault, and have chosen my local indy mechanic carefully. He has been under my car a couple times over the decades, and I had a thorough discussion on where I feel the safe places are to lift up my car. He indulged my photos, pictorials and general excessive concerns about how to jack and support the rear end. I have just picked up all parts from dealer, and next week its finally gonna happen. BTW, deQ wrote an excellent step by step on this job in 2014, with great detail (like all of his other contributions) and was a great help as well. In his case, he used a trolley jack which provides some jack point flexibility. But still an onerous job. Mike
wilies13
Active Member
At least in my case it was surprisingly easy to knock out the knurled bolt. Mother; hammer and it went easily out.
Not to forget to remove the rear seats before...
Not to forget to remove the rear seats before...
When I removed the knurled bolts, I used the weight of the car. I had the car on the lift. I first sprayed penetrating oil (Kroil) in the bolt from the top. Let is sit. Then I used a timber on the floor of the garage to the bolt and gently lowered the car. It slid out rather effortlessly. This, of course, required a lift. But it was gentle.
Well I guess I went the hard route. I could not get the knurled bolt out despite PB blaster for 3 days, a torch and placing the nut on, and lifting the car by the bolt itself. Thus, I left it in and I don't recall exact details, but I lowered the diff, removed the brake lines and was able to elevate the rest of the car to clear the subframe for the knurled bolts.
I do not use poly bushings except at the subframe. Again, I think it stabilizes lateral and rotational motion to an extent that, unless you drive like you stole the car, is not such a strain on the chassis but does offer more stability. I would ask if people worry about using oversized ST swaybars.
I do not use poly bushings except at the subframe. Again, I think it stabilizes lateral and rotational motion to an extent that, unless you drive like you stole the car, is not such a strain on the chassis but does offer more stability. I would ask if people worry about using oversized ST swaybars.
Wish I could have seen that!
Would love to have captured it. But I just scanned my pics and I evidently didn't record it. However, now that I think about it I do recall that they didn't come out immediately. I let the weight rest on them to the point where the timber on the stud was lifting the car off the lift a bit. I then got in the car and added my weight and a little jiggling/bouncing to get it to comply. I'd forgotten about that part until just now...Wish I could have seen that!
@Ohmess thanks for the response. My concern too was also the trade off between ride compliancy/boatyness/ transferral of forces to the monocoque. Although mine's OK-ish in terms of rigidity compared to some coupes (fresh resto, stitch welded sills, increased spot welds, strut bars and some gusseting) I still feel like i'll wince every time I put my foot down round some twisties. I went polybush/solid mounted on my Mk1 Golf build and it is horrible to drive on anything but smooth roads but the sharpness is incredible.
With the direction i'm going with my Coupe perhaps a few choice items in PU and maybe a rear swaybar could be the answer i'm looking for.
@autokunst the correct mechanical term is "jiggery-pokery" I believe
With the direction i'm going with my Coupe perhaps a few choice items in PU and maybe a rear swaybar could be the answer i'm looking for.
@autokunst the correct mechanical term is "jiggery-pokery" I believe
Yeah, its tough to determine what is going to suit each of our particular likes and whatnot, and it is not easy taking parts for a test run because when you jump in someone else's car, they usually have done several things different from your car.
I must say, I am jealous of the stiffening you have done to your car. It would take me out of action for quite a while, but I may need to do that.
I must say, I am jealous of the stiffening you have done to your car. It would take me out of action for quite a while, but I may need to do that.
I would put poly bushings only in the sway bar links. Nothing else.
I put Poly everywhere on the front of my 2002. Handles superbly, but a bit noisy/bouncy; but most of that is due to the IE front coilover setup.
I put Poly everywhere on the front of my 2002. Handles superbly, but a bit noisy/bouncy; but most of that is due to the IE front coilover setup.
Update. I got 1 side done today. Wasn't that bad. Once I got over the trepidation of needing to support one side of the car by the seam part of the rocker, I thought, if i don't trust my rockers, then why worry about replacing subframe bushings at all? Pin popped out with a few hammer blows, but needed to remove bracket that holds armrest in position to get pin all the way up and out. On to the left side.
wilies13
Active Member
Great, that it works