Thought that headline might get you. But I really do have something to point out to the unitiated about modding your suspension. I learned this the hard way as have a growing number of folks on this formum.

It has to do with the rear trailing arms and the M14x1.5x105 bolt that ties the bottom of your damper to the trailing arm. If you are going to change the rear suspension only one time and then change it back to stock before you sell you are probably all right. But if you do what I did and try out several spring/damper/coilover combinations you are heading for trouble.

The problem is that the trailing arm is aluminum and the bolt is a steel SELF-TAPPING bolt. If you take the bolt in out out more than a couple of times you are almost guaranteed to strip the threads. I don't care how careful you are, it is going to happen.

Now stripping the threads is bad, but there is actually a worse thing that has happened to a couple of folks. They didn't know their threads were stripped and they just kept tightening the bolt back up to the right torque. But the bolt didn't seat all the way and not too much later the bolt broke WHILE THEY WERE DRIVING. Now they had to get a really stuck broken bolt out of the trailing arm.

The fix for a stripped bolt hole is realitvely easy. You get a Helicoil kit (m 14 x 1.5) and a 9/16 in drill bit (a good drill bit helps), drill the hole out, tap the hole with the tap in the kit, and install one of the coils. The connection is now actually stronger than the original (more thread area). The trick here is to get a new m14x1.5x105 bolt (of the right grade) that is NOT SELF TAPPING. This means don't buy another bolt from Mini, go to a good hardware store and get a good, high grade stainless steel bolt.

How do I know the last bit, because the silly self tapping bolt cross threaded my helicoil and ruined the trailing arm and $350 later I have a new trailing arm.

There are several threads on this forum that talk about this (I started one) and at least two of our more mechanically inclined brothers, being machinist, said that the first thing they do on a track car with aluminum suspension parts is to drill out the part and install a helicoil. The machine shop foreman where I work used to work in the aircraft industry and said that they never trusted a steel bolt in a tapped hole in aluminum - they always used helicoils.

SO, how about one of our trusty after market parts vendors (Way? Out motoring? Detroit Tuned?) put together a kit for everyone who buys suspension mods so they have the right helicoil kit, drill bit, and bolt? An additional drill guide so that we drill straight holes would also be nice (my shop guy made one out a brass roundstock for me so I could drill the trailing arms while they were still on the car).

Sorry for the long blurb, but I talk for a living (actually I profess for a living).

Cheers,
Greg

 

great info,thank you!

 

Thanks for the info. I have changed springs a few times. Sounds like next time I should install a helicoil.
Vendors: A kit (with a drill guide) would be a great idea.

 

Just to reinforce the OP, this is what you can get into:

https://www.northamericanmotoring.co...-in-place.html

This problem is just now show up to be more prevalent. It happened to a friend at 70 mph and 2000 miles away from home.

Question to the OP - Do you think replacing the self tapping bolt with a regular bolt will save the threads? Just a thought

 

While not a Gen 2 owner I have been keeping an eye on threads (no pun) like this. I am a machinist by profession and my experience with Helicoils is pretty good. That said, removing and reinstalling bolts in a helicoil is dicey, way better than in the aluminum only of course. I've seen the actual coils of the insert pull out with repeated insertion and removal of bolts. So what we in our shop use are Keenserts in all fixtures where the bolts come in and out. IMHO, helicoils are for fixing and forgeting or where structure is critical.

http://www.acmeindustrial.com/keensert_comparison.html

Bryan

 

Have you or your shop repaired any MINIs?

I like that better than the helicoil. It would also seem that the Helicoil would deteriorate quickly here in the NE with all of the salt on the road.

There are actually several of this type of inserts on the market. Does anyone have experience with these:
http://www.ezlok.com/Home/index.html

 

You can also modify the trailing arm to accept a through bolt. Thats what I did, been that way for a couple years now, no problems.

 

Is this an issue on Gen 1 coopers too?

 

Can be for 2006 cars. The 2006 GP came with the alum arms. I also read that some of the very late 2006 cars might have come with alum arms.

 

Can you give some details of how you did it? Grinding, Size, length & grade of bolt. Also, what kind of nut you used. Also, did you do this right from the start or did something brake first?
Thanks for any input.

 

You can search my thread. I show a details description of how I made the trailing arm accept a through bolt. It involves an angle grinder, a drill, and strong drill bits, lots of patience too.

 

Thanks for the tip! Bookmark :-)

 

When I stripped the threads in mine, the stripped out hole size was correct for a 5/8-18 thread. I bought a tap at the hardward store, and a 4" long grade 8 bolt. I threaded the trailing arm all the way through, and needed to file the bottom bushing in the shock to fit the bolt (14 mm is about .550"). I felt better doing this than grinding a flat on the trailing arm and using a nut and bolt.

Also, you don't want to use a hardware store stainless steel bolt. Two reasons:

1. Stainless bolts are equivalent of SAE grade 4. This is generally not strong enough for critical bolts, like brakes or suspension. ARP makes high strength stainless bolts, if you want to mail order them (try totallystainless.com).
2. Helicoils are stainless, and stainless on stainless tends to gall. You can get away with it if you remember to use anti-seize. If you don't use anti-seize, you will pull the helicoil out if there is any galling.

Mike

 

Mike,
Good points about the SS...and for those who live in the rust belt...stainless steel is also susectable to chloride stress corrosion cracking. In otherwords, high stress (torque to 120 ft-lbs) and salt, the bolt fails on its own.

However, if you are going to be disassembling the shock to get at the top of an adjustable shock, then go the route that RedAndBlackMiniS went with putting the bolt through the trailing arm and holding the shock on with the nut. You could even do this before the threads are stripped and prevent the failures that have occurred to others. But that would require grinding the trailing arm, which seems to be less of a problem than the bolt failing out on the track at 120 mph.

 

Yeah, I guess if grinding the trailing arm was a problem, we would have heard about one or two breaking by now. Grinding just feels wrong to me, but it is probably OK.

Mike

 

I know what you mean. I hate to mess up a nice piece like that without knowing how it will last. It seems that a cutting tool could be done up and rented out that would do a nice job of machining that without it looking like a hack job and not taking too much material away. I just would worry that if I were to replace shocks that I would need to do something at that time to ensure the bolt doesn't fail later on, and I am not a big fan of the inserts, not that I have any real reason to not like them. Those just don't seem right either. It seems that it would be best to take advantage of the threads/design as it is, but make it better.

 

$30 angle-grinder at home depot worked like a charm, for anyone wanting to do this.

 

Are you planning to replace the bolt on the other side too, before it breaks?

 

So I was just installing coilovers and showed this thread to my mechanic. His opinion was this: wouldn't the danger be reduced significantly by first removing the top shock tower bolts, to remove the weight pull on the bolt in question - and when reassembling, do the reverse - first tighten this bolt to about 90%, then attach the top bolts, then finish up the job?

 

+1 Bryan

scott