I need to buy a new R56 right trailing arm. Mine broke and would like to know who is the cheapest.

Thanks.

 

BROKE? Wow. Bad news. Any details?

Darn big casting. What and how?

 

The thread you mount the shock on got stripped. I was gonna do a Helicoil, timesert or even considered JB welding it, but decided to buy a new one instead.

 

Great tip to watch out for. JB I would not do, but I did repair a lot of Al with the "Al solder" Of course, I melted a few parts too. You are probabbly wise to replace. If they are TOO expensive, might think about a good welding shop to tig it up.

I hate to pry, but was it stripped due to overstress in street use, or in race, or by cross-threading?

 

It was none of the above. It was stripped due to over torquing. The torque was set at the wrong setting. Was set at 100lbs. Just a really stupid mistake.

Has anyone done the swap? Do I need special tools and how hard is it to do? I can't find my TIS cd, when I need it the most. Arghhhhh.

 

You HAVE a CD! The rest of us just have to guess.
When you dig it out, I am about to get my Bilsteins, so what is the torque supposed to be, and what are the top bolts supposed to be?

 

Shocks to Rear Trailing Arm is 165nm
Strut support to body is 56nm

 

The new trailing arm would cost you $330. I would suggest using the Heli-Coil. Why ? because I was in your shoe. I tripped mine when I was installing a new set of coilovers. I fixed it with the Heli-coil. It's actually stronger than before because the thread is now steel instead of aluminum.
I still have the Heli-coil and am more than happy to sell it to you. Send me a pm if you're interested.

 

1. Remove the trailing arm.
2. Drill a new hole using drill bit size 14.25MM or 9/16.
3. Tap the hole with M14-1.5 size.
4. Install 2 Heli-Coil inserts into the newly tapped thread. Install the 1st insert then remove the tang then do the same for the 2nd insert.

Honestly, I'd suggest you bring it to a machine shop and have them drill the hole then tap it yourself. It would cost you $20-$50ish depends on the shops. Still, that is way less than buying a drill and the special drill bit size.

 

Does anyone know the original thread pattern of the bolt?

 

Thanks for the write up. Just a quick question? Shouldn't I be tapping it larger given the bolt size is M14.1.5?

 

The spec for the bolt state M14x1.5x101

 

take bolt and arm to a machine shop. They should have the heli-coils and tool.

I am surprised it is built that way. Usually suspension is through-bolted.

 

You could also just get a longer bolt and put a nut on it.

 

Maybe viable. I am not looking at one, but does it have enough meat in it? This is a bolt used in a cantilever ( bad design actually) and I would be very concerned with it pounding the hole oval and eventual failure. You would want to ream the hole to a snug fit of a proper long bolt so no threads were inside the arm. Helicoil is easier.

For those interested in how to, or not to, design a chassis, I recommend Carrol Smith's series of books. Build to win, Prepare to win, Tune to win. Yes, books, not internet.

 

Put my new rears on. I do see that the shock bolt is a through hole, lots of meat.

As the shear is taken by the shock conical bushing, a through bolt would not worry me as TS mentioned above.

The torque spec mentioned above scared me. Taking them out, they were at about 85 FtLb. I torqued them to 90, about 115 nm. 165 just seems really high.

 

The official BMW spec is 121 ft lb for shock to trailing arm and 45 ft lb for strut to chassis FOR THE REAR.