Backdraft - broken bolt on rear trailing arm bracket

[FlyingGumby]

Hi Everyone,

I have a problem on BDR #870. Discovered what I thought was a missing bolt on the passenger side rear trailing arm bracket. This is the bracket that holds the front of the trailing arm to the frame. It turns out to be a snapped bolt (1 of 3) that is welded onto the bracket. I assume this is not repairable and a new bracket is needed. Does anyone know where to get a replacement?

Any help would be appreciated.

[spdbrake]

Those studs appear to be soft metal, I'm guessing all thread. I wouldn't recommend replacing a stud with that material though.

Try calling Iconic parts and and ordering a set. Chances are they may be able to get them as they did build a build over 2000 BDRs in that configuration.

Baring that then find a Machine shop or a Welder to cutoff the old stud and attach a 10.9 (=grade 8) or a 12.9 rated bolt. Once welded on, lop off the bolt head.

[FlyingGumby]

Thanks. I’ll start the process with a call to Iconic.

[SBSerpent]

This is the first time that I have read on this forum of this type of damage. Has this happened to any other BDR owners? Just wondering since I'm a BDR owner (#983).

One things for sure, gonna go out to the garage and check those bolts.

[spdbrake]

I had mine shift outboard during heavy braking causing toe-out. Studs were fine. I finally noticed when I backed in to the garage and the rear started jacking up a bit and the cambers went to a positive angle.


I added small pieces if steel ground to the correct height and shaped to fit the gaps in the sides on the studs and slots. The washers under the nuts prevent them from dislodging. I haven't had an issue since, and don't have to smoke torque the nuts to prevent the trailing arms shifting.

[FlyingGumby]

Devin at Iconic is checking with the factory for availability and price of the brackets. Will hopefully know something next week.

Was told the Supercharged Roush crate engine puts out >550hp. Will replace both sides for peace of mind. Unfortunately looks like the arms need to come out to replace the mounts. What else should be replaced or upgraded while everything is apart? I use my Cobra on the street. No tracking. Likely no auto crossing either.

Thanks.

[spdbrake]

You can drop the trailing arms pretty quick.
Remove the axle bolt or nut (depends on build #), Remove calipers and hang with zipties or safety wire and not from the brake hose..
Remove the upper outboard swing arm bolt (near the spring) and lower outboard arm bolt.
Remove the lower shock bolt.
If you don't want to fiddle with parking brake shoes, remove the nuts from the emerg brake handle and pull the cables down. Disconnect the Adel clamp on the frame holding the cable.
Pull the trailing arm out off the axle splines and aft to remove.

While you have it apart you can replace some of the bushings with Polyurethane types if you desire.
This kit will do all the rear end bushings and rear hub bearings.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

If you are going that route ECS is easy to deal with and prices are good.
Fitment is BMW E36 325i.
https://www.ecstuning.com/BMW-E36-32...sion/Bushings/

[FlyingGumby]

Thanks, spdbrake. Hoping it is quick (and easy). Your metal filler hack is clever. Did that on a sagging frameless shower door once but never occurred to me for this application.

I can see yellow urethane bushings on the trailing arm. Not sure about others. Will check type and condition once in there.

[FlyingGumby]

With spdbrake's feedback I successfully removed the old bracket. Got the front bolt out of the bracket once everything was unbolted, and without having to completely remove the arm. Ended up being pretty simple.

Patiently waiting for replacement part info from Iconic...

[spdbrake]

Wow your brackets are a lot nicer than mine. Looks like you have bolts threaded thru the bracket and tack welded in place. Easy fix.

I have a very early car so several areas on mine appear to have been fabricated by Darrell and his other brother Darrell. Nothing radical, just body bolts too short with 1-3 threads engaged, etc...

[cycleguy55]

Originally Posted by FlyingGumby

With spdbrake's feedback I successfully removed the old bracket. Got the front bolt out of the bracket once everything was unbolted, and without having to completely remove the arm. Ended up being pretty simple.

Patiently waiting for replacement part info from Iconic...

Now that you have the bracket out, you can just remove that old bolt and have a new, stronger one (grade 8 or metric equivalent) tacked in place. Might want to replace all 3 with stronger bolts while you're at it. Head markings should indicate what you have now.

[FlyingGumby]

I like the idea of stronger bolts. What do you think a shop would charge to repair? It’s just grind out the old and tack weld in the new proper bolt, right?

[FlyingGumby]

Bolt head says 48 which I assume means 4.8. I think it's an M10 which implies 18 ft-lb max torque. That's not a very strong bolt.

Closest metric fit would be M10x30mm. It was suggested to go to 10.9 or 12.9 which implies 55 ft-lb or 63 ft-lb max torque. Does this match your charts?

I'm motivated to prep the brackets and ask a friend tack in some new bolts.

Thanks.

[SBSerpent]

Not to hijack this thread, but can someone please explain to me how that upper spring mount is attached to the frame? Where is the access to it in order to inspect?

[Mike_Gr]

While the trailing arm is out can also consider replacing trailing arm bushing. This is a weak spot in these cars keeping the rear end planted. I had this bushing replaced with a monoball I did subframe bushings at the same time so hard to tell how much each contributed to improvements.

[FlyingGumby]

Originally Posted by SBSerpent

Not to hijack this thread, but can someone please explain to me how that upper spring mount is attached to the frame? Where is the access to it in order to inspect?

SBSerpent, I don’t know but will look at mine tonight. You are referring to the rear upper spring adjuster posts, right?

[SBSerpent]

Originally Posted by FlyingGumby

SBSerpent, I don’t know but will look at mine tonight. You are referring to the rear upper spring adjuster posts, right?

Yes, that is correct

[FlyingGumby]

Originally Posted by SBSerpent

Not to hijack this thread, but can someone please explain to me how that upper spring mount is attached to the frame? Where is the access to it in order to inspect?

I still don't really know but venturing a guess after inspecting mine... it's likely threaded into the steel plate or into a collar welded onto the steel plate. And, butts into second plate.

Found a crappy picture of a BDR frame and it appears the threaded post does not go through the steel plate that the body sits on. I did not pull up my carpet to look.

https://www.pinterest.com/pin/545428204850191381/

[FlyingGumby]

Originally Posted by Mike_Gr

While the trailing arm is out can also consider replacing trailing arm bushing. This is a weak spot in these cars keeping the rear end planted. I had this bushing replaced with a monoball I did subframe bushings at the same time so hard to tell how much each contributed to improvements.

Thanks. I'm going down the rabbit hole... I mean researching different upgrades... bushings, camber arms, etc.

What's you experience with monoball bushings? I don't plan to track so a medium/hard poly might make more sense for me.

[spdbrake]

The 4.8 bolts are basically annealed steel.

https://www.engineeringtoolbox.com/s...es-d_1428.html

I buy from McMaster Carr a few times a month. Items are shipped same day ordered, up to 7:30pm EST.

https://www.mcmaster.com/fasteners/f...x-head-screws/
https://www.mcmaster.com/browse-fast...x-head-screws/