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ChrisO

E36 rear trailing arm mounting point

Question

Did BMW ever do rear trailing arm mount reinforcements for later E36 M3's? I know 95 M3's had subframe mount problems but they corrected that for later years with reinforcements. I'm doing poly RTABs and I don't want added stress without reinforcement around the mount

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I had Condor RTAB's on my coupe and the passenger side rocker was completely rotted away right next to the pocket. I never had any cracking or other issues. You'll be fine haha. If you're really that worried there are a ton of places that sell weld in reinforcements.

https://www.akgmotorsport.com/product/rear-trailing-arm-reinforcement-plates-e36/

https://www.condorspeedshop.com/collections/e36-suspension/products/copy-of-reinforcement-plates-rear-shock-tower-e36-e46

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I have used AKG reinforcements.  They fit good, it's a lot of work to clean up the area to weld them in.  Also you have to go slow and let it cool so it doesn't get the area too hot.  Remove the back seat and move the wires along the sides so they don't melt.  

No preloading of poly because the insert sleeve rotates after install.  It slides rather than twisting like stock plastic.  Lube them or they will squeak.  Like Earl said the reinforcements aren't really necessary.  Just put the poly in and go.

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The E36 never came with reinforced RTAB pockets, but if you plan on driving the car hard or running stiff RTAB bushings it couldn't hurt. I was planning to reinforce mine at some point and have a set of AKG reinforcement plates sitting on my shelf, but since I am going to be selling the car soon I won't need them if you're interested. 

As far as pre-loading the bushings, the only ones you need to worry about pre-load are the OEM rubber ones. On those, the center sleeve is bonded into the rubber and the motion of the arm happens by twisting the rubber of the bushing. With poly bushings, the center sleeve that the carrier bolts onto is greased and allowed to pivot within the bushing, so no pre-load is necessary (or possible, the sleeve will just rotate as the car is lowered down). Make sure you grease them liberally with the appropriate grease or they can get really squeaky. I would stay away from "solid" RTAB bushings like delrin, UHMW, or Aluminum, as the RTAB is not a single axis pivot and a solid bushing can cause binding as the suspension moves. 

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I ordered 80A street/autox bushings from Garagistic, so hopefully those aren't too hard. I think for this summer and fall I'm going to skip out on doing the reinforcement plates, probably will do them in the future though!

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You also can't fully weld the reinforcements without removing the gas tank.  I live on the edge and just kept spraying it with water to keep it from getting too hot.  It would be best done with a full tank so the liquid keeps the plastic cool.  I have UUC poly, they don't specify durometer but they are in the middle I would say compared to other bushings I have used.  I would agree that solid ones are not good for that location because of the multi axis movement.  I see a few places offering a spherical ball joint.  I need to take some measurements but one I saw looks to be a machined part that uses the same outer lower ball joint from the rear control arm pressed into it.

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3 hours ago, jc43089 said:

You also can't fully weld the reinforcements without removing the gas tank.  I live on the edge and just kept spraying it with water to keep it from getting too hot.  It would be best done with a full tank so the liquid keeps the plastic cool. 

using more gas to absorb the heat to keep the gas tank cool while welding precariously next to it...😲!

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15 minutes ago, straight6pwr said:

using more gas to absorb the heat to keep the gas tank cool while welding precariously next to it...😲!

Yup, like 2 inches from the gas tank.  The plastic is pretty thick ;)

 

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They're much more expensive however. I really can't see you driving the car enough to wear out a spherical bearing but I would assume Nerptech would warranty them or have service parts at that point. 

Condor also has mono ball ones:

https://www.condorspeedshop.com/collections/e36-suspension/products/trailing-arm-monoball-bearings?variant=8067098017838

They appear to be a little nicer than the ones Turner offers.

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I think the non sealed ones whether from Nerptech or Turner would not last long on a daily driver, dirt gets in and wears the joint rapidly. 

Condor ones look like they use the same insert as Turner.  The ball joints can wear out, both of them on the control arms of my coupe were loose, it does have almost 300k on it and they are likely original though.  Replacement joints are cheap.  I saw the Turner ones and thought, hmm I should just machine my own housing and press in the Lemforder joint.  I need to measure and see if the length of the inner sleeve matches up with the ball joints.  i understand though not everyone can just machine their own parts.  

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