Backdraft - broken bolt on rear trailing arm bracket

[FlyingGumby]

Originally Posted by 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/

Thanks. Just placed an order. A friend agreed to cut the old bolts and weld the new ones.

[Mike_Gr]

Originally Posted by FlyingGumby

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.

If you ever get on the car hard from a stand still and have high hp, the RTAB upgrade will help keep the wheels planted and the tow from changing under acceleration.

[FlyingGumby]

The trailing arm mount bolts look over torqued. The drivers side didn't break but is surely weak. Do alignment shops know to torque only these nuts to ~18 ft-lb (based on the bolt spec site spdbrake shared)? Consider adding a bolt check to your maintenance routine.

My outer CV boots are torn and need replacement so off came the axles. One of the axle/spindle bolts required a pipe for leverage to remove. The other came off with a standard 1/2" ratchet. I estimate the torque on that one to be ~40-50 ft-lb. Spec is closer to 214 ft-lb. Consider checking these bolts too.

The diff is a little oily and leaves an occasional drop. Might as well replace 1 or more seals while everything is apart.

Will also replace the spring pads, trailing arm and control arm bushings, and add adjustable camber arms. Just need to decide which ones.

[FlyingGumby]

Thanks for info and guidance guys. Removed the offending bolts. The holes were not threaded. New 10.9 bolts and nyloc nuts arriving soon.

Down the rabbit hole. Now plan to install new subframe bushings since only a few more bolts to drop the subframe. Will be easier to install new camber arms, and change the side diff seals and oil (or at least loosen the drain/fill plugs).

[spdbrake]

Down the rabbit hole. Now plan to install new subframe bushings since only a few more bolts to drop the subframe. Will be easier to install new camber arms, and change the side diff seals and oil (or at least loosen the drain/fill plugs).

That's the way all my projects go. "The while I'm there". Starting to plan the next one now. My aft crank seal is starting to leave a blood trail.
So,,, New: seal, pilot bearing, flywheel, twin disc clutch, throwout, bellhousing, fresh seals on the TKO.

[FlyingGumby]

Originally Posted by spdbrake

That's the way all my projects go. "The while I'm there". Starting to plan the next one now. My aft crank seal is starting to leave a blood trail.
So,,, New: seal, pilot bearing, flywheel, twin disc clutch, throwout, bellhousing, fresh seals on the TKO.

Sounds fun.

I plan to change the differential mount bushings too. Any tool recommendations for subframe and diff mount bushing removal? I seen sketchy youtubes where people burn them out. Not going to do that.

[spdbrake]

On the diff bushings ensure you support the ear if you are knocking the old one out with a large socket or steel pipe. Penetrating oil and a heat gun on the Aluminum ear (not the bushing) also helps.
The carrier bushing can be chain drilled (multiple holes) then connect the holes with a narrow Sawzall blade.
https://www.homedepot.com/p/Milwauke...5161/203168541

Once the center is out cut the steel bushing outer band with a reg Sawzall blade. You don't need to cut all the way thru the band, just 90%. A good smack with chisel and the band with break and the bushing will fall out with very little effort.

[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.

Subframe and diff came out easily.

Going the monoball route for RTAB. What poly diff carrier bushings are recommended these days. Choices seem limited with 14mm front carrier bolt. Or, just drill the a 12mm bushing sleeve to accommodate 14mm bolt?

Saw on another thread that you did a major upgrade after using a DSB. I don't want to go that far but do you recommend a DSB? Is your used one still available.

Thanks.

[Mike_Gr]

Originally Posted by FlyingGumby

Subframe and diff came out easily.

Going the monoball route for RTAB. What poly diff carrier bushings are recommended these days. Choices seem limited with 14mm front carrier bolt. Or, just drill the a 12mm bushing sleeve to accommodate 14mm bolt?

Saw on another thread that you did a major upgrade after using a DSB. I don't want to go that far but do you recommend a DSB? Is your used one still available.

Thanks.

I would absolutely use a differential support bracket as piece of mind that the front of the diff wont twist under torque load. (My bracket is pending locally). I cant recommend any specific poly diff bushings. I used solid diff bushings and motor mounts.

For camber arms, I used SPC and have had good luck with them.

[FlyingGumby]

Originally Posted by Mike_Gr

I would absolutely use a differential support bracket as piece of mind that the front of the diff wont twist under torque load. (My bracket is pending locally). I cant recommend any specific poly diff bushings. I used solid diff bushings and motor mounts.

For camber arms, I used SPC and have had good luck with them.

Thanks. My car came with solid motor and tranny mounts. Will add a DSB.

My experience getting the bushings out…

Subframe - used the drill and heat gun method on 2 of the uppers. Used heat and the bushing tool that spdbrake recommended (once it arrived) on the other 3. The tool states it cannot be used on the subframe. It works and is easier than drill and heat.

Differential cover - drill and cut.

RTAB - cut 2 notches in old RTAB to clear bushing tool. Pulled right out.

Wheel carrier - bushing tool. They came out like butter.

Control arms upper inner - drill and cut method.


FYI... new mounting brackets are available from Iconic for $211/ea,; no torque specs given. Optimistic about repairing the old ones. New 10.9 bolts get welded in tomorrow. Now just waiting for other parts to arrive.

[FlyingGumby]

The old outer CV boot had BT-122 on the outside. It cross referenced to Beck Arnley 103-2628. It arrived and is a perfect match.

Anyone know the inside CV boot part number for the later “bigger” axles? Are these M3 sized? Standard e36 inner boot (the metal part) will not fit over axle spacer which is 4.43” diameter.

Thanks.

[spdbrake]

Sorry to say the later BDR axles are a secret part number. I'd contact the Driveshaft shop as they have upgraded those for some folks and may share the part number or application with you.
This thread has some details.
Broke a half shaft backdraft

These may work for you. The CVS-33 boot goes up to 125mm and your 4.43" = 122.522mm.
https://www.stretchcvboot.com/cv-boots/

[FlyingGumby]

Originally Posted by spdbrake

Sorry to say the later BDR axles are a secret part number. I'd contact the Driveshaft shop as they have upgraded those for some folks and may share the part number or application with you.
This thread has some details.
Broke a half shaft backdraft

These may work for you. The CVS-33 boot goes up to 125mm and your 4.43" = 122.522mm.
https://www.stretchcvboot.com/cv-boots/

Thanks. Interesting product. May come in handy on other projects.

Upon further inspection it appears the rubber boot is just clamped onto the metal end cap. The cap and boot come pre-assembled when purchased new. That's what confused me. Should be able to remove boot from e36 kit and install on existing cap. We'll see.

[FlyingGumby]

Things appear easy never having done it...

Me: Hey do you have 15 minutes to tack weld some bolts?

Buddy: Sure bring them over.

Me: Should only take 15 minutes, right?

Buddy: I budgeted 90 minutes. (Then proceeds to mill off old welds, sand off surrounding powder coating, sand bolt head edges, then clamps and tig welds them in place)

Took more than 15 minutes but they they look great and should work better than new!

[Kojack70]

Originally Posted by 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.

Another BRD owner here, thanks for posting this, just something else to keep an eye on.

[FlyingGumby]

Everything has been back together and aligned for a couple weeks. Noticeable improvement. Tracks straight on hard acceleration, and at low, med and high speeds. Steering is sharp, light and tight. I suspect the rear toe was off when the bracket bolt snapped making for a slightly vague steering feel. There is more noise adding poly bushings to already installed solid engine and transmission mounts. Do not notice any additional vibration or harshness. This is a great upgrade!

Trailing arm bracket repair with 10.9 bolts/nuts (torque is 48 ft lbs now versus 18) was $20. While “in there” added: monoball RTABs; adjustable lower camber arms; poly diff, subframe, wheel carrier and upper arm inner/outer bushings; new upper and lower spring pads; new axle seals; new diff speed sensor o-ring (it was missing); new gear oil; re-packed inner and outer CVs joints and replaced torn boots (pinch clamps hit a tab on the wheel carrier before switching to flat band clamps); and new power steering rack bellows (MOOG K150272 was a perfect fit). Should have installed a DSB when everything was apart. That’s next.

Anyone going to car week in Monterey? Doing a couple Classic Mini events but hope to get the BDR out for some fun.

[spdbrake]

Thank you for the follow-up and close on the repairs. It helps us all. Most of the time, folks seek help on this site, get it and never respond with their fix.

[AKA EDDY]

backdraft cobra wreacking at 130 mph

[spdbrake]

Yes that wreak was an early car like mine. The factory trailing arm mount gave way. BDR came out with a Service Bulletin kit (free) to beef up the frame mount, but I don't know the build #that the kit was factory installed.

Photo of the kit from Secret Squirrel's gallery dated 2010.

[FlyingGumby]

E36 trailing arm brackets bolt up into a pocket in the BMW 3-series body. Recommended torque is 57 ft lbs.

Backdraft brackets are custom, essentially flipped over and bolted down onto the frame with 18 ft lbs of torque each. Completely different stresses and load from OEM BMW mounting. Perhaps prior alignment shop saw E36 on my car and went to 57 ft lbs. Gussets on older builds seem like a must... and go for new bolts while in there.