2nd Gen R56 Cooper S Most liked posts in thread: Trailing Arm stripped bolt hole

Be careful what you get at the local hardware store. Suspension bolts on vehicles are rated at a much higher tensile strength (for obvious reasons) than whats available as a generic bolt for say putting a hinge on a gate door. This is an area where you don't want a failure.

 

Make sure it is a high quality bolt. Grade 5 or higher. In metric I believe it is an 8.8 grade.

American Fastener - ASTM, SAE, and ISO Grade Markings

 

Did the same thing on my R53. Longer bolt and nut works with no long term issues. Used blue loc-tite on it also.
Actually got new bolts from dealer and used nuts on end now that I think about it.

 

The 1st gens did use a nut and bolt there. When MINI when to the Al trailing arms on the 2nd gen and the GP the bolt became a self threading one for both ease of initial assembly and it's one less part to source and keep in inventory. While that seems silly on the face of things when you consider that is spread of 1/2 million cars or so it starts to make sense.

 

Lots of things were changed for the sake of easier assembly & add more profit in the companies pocket. Seems to me they must now stock trailing arms instead of bolts & nuts. Now that is progress.

Back on topic....

Using a longer bolt & nut seems like the correct fix for this.

 

^ + 1 & how!

You may be able to check the grade by looking at the markings on the original stripped bolt.

 

Just wondering if it was corrosion that got in between the aluminum and steel threads (I think so)? Then when originally removing (dry) the bolt and the aluminum threads were stripped. Perhaps spraying with a penetrant lubricant, sitting over night to let it traverse all the threads, would have prevented this? Then upon re-assembly, coat the threads with anti-seize?

 

Simple and professional way to prevent this is to apply anti seize on suspension fasteners to begin with and then torque the fasteners to the proper specs. Anti seize can be purchased at almost any of your local auto parts stores. 2cents

 

grodenglaive -

I have a couple of thoughts. Since that is a steel bolt going through aluminium I'd pull it out & coat it with anti-seize where it goes though the control arm & shock. The reason I'd do this is to prevent any corrosion you may get from the contact of aluminum & steel. While it is out I would also use threadlocker (blue) on the bolt & nut. Keep an eye on it, but my best guess is that you will be alright with your repair.

Good job....

 

Yeah...+2 on the blue locktite...

 

Lynn just suggested to me that you don't want to contaminate the two materials for obvious reasons. Yep the anti-seize will nullify the loctite if you contaminate the two. Sooooo, don't mix the two. Also, try and match the thread pitch to the original which looks to be a fine thread versus the coarse thread on the replacement bolt.

 

I'd keep the anti-seize on the shoulder of the bolt not the treads. The loctite on the treads will keep the moisture out & keep the threads from rusting. I agree cross pollinating chemicals can be bad ju-ju.... :wink:

 

Forget loctite and just use a nylock nut.

 

He has a nylock. It's been my experience that loctite keeps mosture out & thereby keeps corrosion at bay. Probably more important for a street driven car than a race car. I'd use both, just my .02.

 

Antiseize, loctight, nylock? Really? Just antiseize it with the nylock. Forget loctite.

 

It's not going to be that big of an issue for you in the future now that you made the change. You've eliminated the ability of the corrosion between the OEM aluminum threads and OEM bolt (since they don't exist anymore and don't intimately make contact with each other), so no more stripped aluminum threads. Your only issue now is to make sure you don't have a loose connection..... You'll always be able to get this fastener off in the future (even if you need to cut it off). The point is you didn't need to buy a new ($xpensive) trailing arm. And you did it yourself, versus a trip to the dealer.....

When you do the other side...... Spray the open side with liberal amounts of penetrating oil and let it sit so it can soak into the threads before you go at it with the wrench.....