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MG MGB Technical - U-Bolt Update

Sorry, I couldnt find my original thread on this subject but wanted to give some feedback....

The car was wandering side to side when power on / power off. After advise from this forum, I removed the U bolts and found that the bump stop pedestals were cracked, thus giving slack in the bolts. Anyway as the thread on one was stripped I replaced both bump stop pedestals, U bolts and nuts. I torqued all the bolts to 20 Ft/lbs. All seemed much tighter at the back end and the wandering has gone. Anyway after about 100 miles I went to retighten the bolts and was able to turn each bolt about 540 degrees before the same torque (20ft/lbs) was reached.

The rubber pads seem to be quite squashed and even the base plate for the damper seems bent! Is 20 ft lbs too much or is this normal.

Ta

Chris
C Briggs

Chris,

Glad youv'e solved your problem. The rubbers are quite soft so do squish out a bit but the bottom plate doesn't bend much. Some people have recommended 25ft/lbs but I think this is too tight. If you make it any less than 20ft/lbs the axle will continue to move so I think it's about right.

Iain
Iain MacKintosh

Great, thanks Iain, car is now ready with a secure axle and non squeaky brakes so it can be flogged around the track at Alford next Sunday!
C Briggs

One recommendation I have seen is that you retighten after 20 miles, then check it next day (having done some mileage in between). If it can be retightened again then repeat next day and so on. U-bolts are 3/8" diameter and the torque for those is given as a minimum of 30 ft lb for unplated in the Rover V8 manual, http://dodgeram.org/tech/specs/bolts/SAE_bolts.html and http://www.almabolt.com/pages/catalog/bolts/tighteningtorque.htm, FWIW.
Paul Hunt

Listed torque figures for the size of bolt don't apply in this instance as you are not bolting up solid components.

The nuts should either be nyloc or have locking nuts. In either case they should only be done up until the axle is firmly gripped - a good pull on a normal combination spanner is more than enough.

Chris at Octarine Services

Agreed torque figures go out of the window with Nylocs. "A good pull", now there's a scientific definition for Mr Puniverse and The Incredible Hulk :o) I probably do mine up tighter then, but I haven't had any problems of breakage or rear-wheel steering. The problem is knowing when to stop as they only tighten up very slowly, unlike a solid assembly that very rapidly tightens up, Nyloc or no.
Paul Hunt

Well the 20Ft lbs is probably a little more that a good pull but I doubt by much. I have used nyloc bolts.

Anyway, I have retightened the bolts once, I think its best to leave as is now and if I have problems with drifiting from side to side again, I will give them another nip up.

Thanks for the comments
Chris Briggs

My 80LE isn't off the jackstands, but I replaced the springs and a lot of other components also. Torque is misleading when using nylocs and soft components in between. I don't recall where I found the post when preparing to reinstall mine, but it suggesting watching the compression of the pads instead of relying on torgue readings. Tighten the U-bolt nuts a bit at a time to insure even pressure and make sure the rubber isn't squashed excessively and spread out. I did all of this with a simple 9/16 inch ratchet wrench using new nylocs. I installed Energy Suspension polyurethane pads and could see them "take up". I also used a non-nyloc standard nut below the nyloc to make sure that I had the same amount of threads exposed on each U-bolt below the nylocs.
Rick Penland

This thread was discussed between 09/08/2009 and 10/08/2009

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