Rear Control Arm Bushings

[Bill K.]

How can the rear control arm bushings be replaced and upgraded?

Ray mentioned replacement with two-piece flanged bushings made of glass filled delrin or mds nylon (click here).

Top view of right side outboard pivot (all 4 look like this):


Inboard end extends from control arm:


Outboard end is about flush with control arm:


Questions:
1. Has the pictured bushing slipped?
2. How to remove the stock bushings?
3. Would the flange of the replacement bushing be the same thickness on both sides (inboard/outboard)?
4. Is there need for steel washers between the bushing ends and the pivot brackets?
5. Is there need for a steel sleeve on the inner diameter?
6. Would mds nylon 6/6 work well? It's only about $9/ft for 1.5" extrude rod...
7. Would the replacement bushing be a press-fit to the arm?
8. Would the bushing ID be lubed with moly-grease on assembly?

Thank you,
Bill

[raygreenwood]

You asked all the right questions.
These are complex bushings. As designed, they are an active part of the suspension. See that "knurling" around the face at theend of the bushing? That is so the bushings "grip" the faces of the control arm pivot housing. These bushings are torsionally tension loaded. Sounds like a great design but its not.
This is what causes the inner sleeve bushing to tear loose from its bonding. It is frequently the fault of any wheel alignment specialist...that these bushings get torn up very eaqrly in their life. Here is what happens:

The alignment guy jacks up the car so the wheels are off the ground. The suspension goes to full travel. He loosens the eccentric bolt to adjust toe-in. The knurled edges come unlocked....while the supsension is at full travel. He adjusts toe-in...then locks the bolt up....and the knurls grip at full travel. Then when you put the car back on the ground.....it twist-loads the entire bushing...generally overloading it and tearing the rubber from the inner bushing or the outer metal shell that is bonded on.

Yes your bushing has slipped. Its very hard to tap it back over sometimes because the rubber that has torn loose unevenly blocks things from sliding.
Yes, you must have a steel sleeve on the inside. It is heavily loaded. You can actually use a hardened split bushing instead though...try Mcmaster carr.

6/6 or 6/12 nylon is not acceptable for suspension use. They do not work well with water and heat and it is too soft for use in this part.
Delrin or glass filled delrin....among other plastics...are just fine. The MDS delrin is rellay nice stuff...but the addition of MDS makes it too soft.
You need a hard, weatherproof, easily machinable plastic. The real bearing surface is the metal bushing.

The twist load characteristic is not an expecially useful feature so don't worry about losing it. Comnpared to the tension of the coil spring it does little.

When you machine your bushings...think about machining the hole for the bshing off-center...or eccentric. Over time, teh rear suspension takes a little bit of a set....giving excessive camber. Having the hole drilled offset...can correct for that.
To see how much to correct for...you generally have to install new straight bushings first and have an alignment shop tell you how much it is off. Then calculate how much lift at the inner bushing and/or how much drop at the outer bushing you need. Ray

[Bill K.]

Thank you Ray. To clarify:
1. Has the pictured bushing slipped? Ans: Yes
2. How to remove the stock bushings? Ans: Press out...
3. Would the flange of the replacement bushing be the same thickness on both sides (inboard/outboard)? Ans: Yes
4. Is there need for steel washers between the bushing ends and the pivot brackets? Ans: Optional, but use hardened steel sleeve that is clamped between brackets with through bolt to bear load. Sleeve ID is close fit to bolt, length is a little longer than space between brackets, OD is slight clearance for rotation in delrin bushings.
5. Is there need for a steel sleeve on the inner diameter? Ans: Yes
6. Would mds nylon 6/6 work well? It's only about $9/ft for 1.5" extrude rod... Ans: NO, use glass filled delrin
7. Would the replacement bushing be a press-fit to the arm? Ans: Yes, light press fit
8. Would the bushing ID be lubed with moly-grease on assembly? Ans: Yes, between steel sleeve delrin bushing

McMaster.com has glass filled delrin in 1.5" rod for $25/ft, p/n 8719K16(each pivot is about 2.5" long). It's Delrin 570. Right stuff?

I couldn't find a 2.5" long hardened steel sleeve with 15/32" ID at McMaster...Help...

Bill

[Bill K.]

I couldn't find a 2.5" long hardened steel sleeve with 15/32" ID at McMaster...Help...

I found the sleeve to use -- front control arm bushing sleeves. Just need some junk arms for another pair... I'm replacing the fronts with Golf/Jetta 1 urethane bushings that come with sleeves.

[Bill K.]

I'm going to use the crush sleeve from Rabbit/Porsche 944 front-front control arm bushing (L2030-17733) for the rear crush sleeves. I'll place grade 8 washers on the ends of the sleeves and use glass filled delrin bushings (custom flanged units). The bushings are just $3.36 at Paragon Products (p/n PP171.407.182D)...

[Bill K.]

Update-those Rabbit/944 rubber bushings are really stuck to the inner sleave. I couldn,t remove them... Also, the wall thickness of the delrin bushing flange would be a bit thin with the washers in place. So, we made custom sleaves from chromoly DOM tubing. Up next is to make more bushings.

[func412]

I'm replacing the fronts with Golf/Jetta 1 urethane bushings.

How did this upgrade work? Was it easy job?

[Bill K.]

I'm replacing the fronts with Golf/Jetta 1 urethane bushings.

How did this upgrade work? Was it easy job?

It didn't. The bushings were not even close for a match. Major reshaping with a sander would have been required. Instead I went with glass-filled delrin flanged bushings with the original crush tube. I'm staging all new suspension and brakes for a swap, so I haven't driven this.




more here vwbughead.com

I recently made bushing sleaves and crush tubes for the rears with a similar design.

More related info here http://www.shoptalkforums.com/viewtopic.php?t=112144

[raygreenwood]

Nicely done! Mine are a slight variant of exactly what what you have pictured. Except...instead of a two peice bushing....Mine is a one piece full length with a flange on one end and a free floating flange on the other. I have also come to the thought pattern....that as long as you have flanges on both outboard sides to "wedge" the trailing arm into its yokes....so it cannot slip either way...you could probably get away with a single piece bushing with a single flange.
Putting in new front and rear bushings is a major improvement. Ray

[herr_sparky]

i bought some delrin to make new control arm bushings and i noticed Bill K. removed the outer sleeve thats pressed into the front control arms... why not leave it? its so conveniently knurled... is there a good reason? wall thickness?

[Bill K.]

I didn't have a reason to remove them, I just did. When the sleeve is removed, the control arm bore is inconsistent enough that each bushing needs to be sized.

Check the roundness and size of the sleeve compared to the other side. They may be consistent enough to size the bushings for interchangeability. That would be a good reason to leave them in.

[raygreenwood]

The only really good reason to "keep" the knurled tube is that the knurled ends of the tube were a function of the torsionally loaded bonded rubber bushing. Once thats gone...the only function of the knurled tube is to let the arm pivot around the bolt instead of letting the bushing pivot in the mount wearing out the mount faces. But with slightly recessed bearing tube and delrin faces with or without bronze washers....it makes no difference. It will not wear the mount. Just be ar in mind for whatever you do...that the correct function is for the arm to pivot on tehe bolt. Ray

[herr_sparky]

thanks...i can only afford to to this job once, so i'm double checking everything. i measured them at each end and found some difference, but very little (0.004"), and that could just be my cheapo calipers. so i think i'll be able to make 4 identical bushings. i figure the knurling will help prevent the delrin from rotating inside the arm...

[raygreenwood]

Wait..lets think about that for a minute.
If you leave the knurled tube.....the tube will be locked to the bracket. That means that the delrin will rotate around the tube. Thats not good.

I had to look in my notebook (cause my car is not close by)...But what I used were the original tubes....ground off at each end. I have a 1/16th" bronze thrust washer at each end. So......the bronze washer is between the end of the tube and the bracket. Ray