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MG MGB Technical - Torque for rear shackle plate u-bolts?

My sister's 1970 GT just failed its WOF / MOT check because the guy said the u-bolt nuts were too loose.

On checking, the bolts are good and tight to my way of thinking, and well up in the u-bolts. I didn't have the torque wrench handy, but I'd estimate something in the order of mid-20's in terms of ft/lbs.

Any thoughts or official specs on how tight these nuts should be so I can show the guy at the testing station?
Curtis Walker

Curtis,
I've not seen a published figure for these. As the plates are tightened against the rubber cushion pad its a matter of visual inspection. They do need to be tight (enough), but should not over-compress the pad to a point of distortion.

Here we have two nuts on each thread. The first is mounted as above and the second properly tightened against the first. Mine have not moved in five years.
Regards
Roger
Roger T

25ft/lbs is about right and will cause a fair wind up of the nuts.
Iain MacKintosh

Having recently fitted new U-bolts and nuts to the V8 I found that you get the stiffness of the Nyloc, then gradually increasing stiffness as you start compressing the rubber pads, then rapidly increasing stiffness after that which is where I stop. By that time there is too much thread sticking out of the nut to get a socket on to use a torque wrench, although I suppose I could get a deep socket. Ordinarily if a specific torque figure isn't given (which it doesn't seem to be for these) a 'standard' torque figure is used for the size and material of the bolt, and 5/16" from one source is 18.5 ft lb. FWIW. I'd ask just what torque the guy was expecting, and if he can't say he shouldn't fail it. Sounds more searching than the UK MOT.
Paul Hunt 2

This guy says 10 to 15.

http://www.mgbmga.com/tech/mgb4(6).htm

mind you , composite springs.

Seems to be a matter of opinion.

Like Roger, I'm using pairs of nuts and locking them against one another. Nylox would be better.
Peter Sherman

One advantage of the two-nut method is that each 'locks' against the other. In Curtis' case this might provide sufficient nut security to pass the MOT - the nuts would be difficult to turn by an inspectors hand.
Regards
Roger
Roger T

Thanks for the input guys - the nuts certainly feel torqued into the low 20's by my hand, with what looks like a reasonable degree of compression of the rubber pad to me. The second nut idea sounds clever, and perhaps I'll give it a go!

I'd personally never heard of a WOF checker testing the torque of these bolts, and I do suspect he was taking things a bit far & unfair. I like the idea about him having to provide a stated torque figure :)
Curtis Walker

And, of course, if he does state a figure, the second question is, how is that achieved against a rubber pad without pinching the life (and purpose) out of it!
Regards
Roger
Roger T

Certainly a torque figure is not given for these bolts but I know from experience that 20ft/lbs allows the axle to move as I had problems with that setting. 25ft/lbs sorts the problem.
Iain MacKintosh

Iain - was that with Nylocs or double nuts?

With double nuts you could well have the nuts locked against each other and the U-bolt, but the spring and axle could still not be clamped adequately. There would be two torque measurements for these - on the first nuts for how tightly the spring and axle is held, and on the 2nd nuts for how tightly they are locked. Could well be the same figure, of course.
Paul Hunt 2

so between 20 & 25 sound good to me! I'll write in in my haynes manual (along with all the other additions).
I just did them up to the well known "I think thats about right..umm" figure.
Its that mysterious mark found on all torque wrenches.
Peter Sherman

Paul, my 25 ft/lbs was with nylocs. If they were any slacker the axle creaked in the rubbers and the car tended to turn one way during braking. 25 Ft/lbs solved the problem.
Iain MacKintosh

When they are new the rubber pads can "creep" a bit needing the nuts re-tightening to take it up. It is possible to overdo it though and actually start to crimp the axle tube. Mine have not needed attention for the past 10 years and the back axle has always passed its MoT.
Stan Best

Several years ago I replaced the rear springs on my 74B. I thought I tightened the bolts adaquitly, but I did not and the rear axel would drift on on side a bit during acceleration and braking. I went back in and tightened them a bit more and had no more trouble. I did not use a torque wrench as I don't have one. Replacing the springs was a pretty good job.
Bob Ekstrand

did this mechanic say i have failed your car because the axle u bolts are loose or did he say i have failed your car because the axle u bolt nuts are loose because they are two different things.if you are not sure go back and ask him and then get him to show you
andy tilney

Is it really worth the hassle. Why not not just tighten them up and take the car back and ask for an explanation if this is necessary. But of course all may become clear when you put the torque wrench on the nuts.
Iain MacKintosh

This thread was discussed between 05/12/2007 and 07/12/2007

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