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MG TD TF 1500 - Not to 'beat a dead horse', but....

While putting the rear axle U-bolts , back on the car, (see photos in my Moss thread), I am reading the WSM, and it says to be sure and make the bolts "quite tight"....
Would someone please tell me what the equivalent torque value is to "quite tight"?
Thankyou
Edward
E.B. Wesson

This came up a while ago - my experience is that you tighten them up as tight as you can without breaking the u-bolt. In other words, VERY tight, and re-check them after a thousand miles or so.

Tom
t lange

For 50 years I've been using a regular length 3/8 drive ratchet with a deep socket, and one hand no heroics, on thousands of BMC cars from 1950-1980. That would be around 25 lb-ft max, and probably more like 20. The entire point of the mounting is that it is meant to be flexible; if you over tighten you are invalidating that. As an absolute limit, you should not be bowing the bottom plate; I've had to hammer way too many out flat, in order to make them work correctly again. And yes, they have to be retightened periodically. Tighten progressively, in a cris-cross pattern, and use antiseize!
PS: If you didn't do it already, paint the area under the U-bolt saddle plates with very good paint or a Waxoyl type product - it is heart breaking to see holes rusted through the axle casing because of mud and water sitting between the plate and the housing.

FRM
FR Millmore

"This came up a while ago - my experience is that you tighten them up as tight as you can without breaking the u-bolt. In other words, VERY tight, and re-check them after a thousand miles or so."

Tom
That's exactly my point....Without torque specs, we are only guessing at where the legs will break off...
Tight to me is different than tight to a guy that lifts weights....
In any event, I will drive it this way for a while...
Test drove it today, and it was much improved....No
rear steering, going on.
Edward
E.B. Wesson

Most people don't have deep BS sockets, so a torque value is pretty meaningless to them - the factory didn't give and spec in the WSM. The quality of u-bolts today is so variable that I don't think I would care to venture a guess as to torque.

Sorry not to be more precise; perhaps one of our engineers can chime in.

Tom

t lange

with all due respect to all posters, i do not believe there should be any movement at the axle to spring attach point. 2o ft/lb looks right for a grade 5 5/16-24 bolt so that should be in the ball park. i can tell you from experience if it is not tight enough the rear axle moves and the car creaks and groans. regards, tom
tom peterson

There has to be some 'give' or movement in the rear axle/spring system. Just as there has to be some in the engine/gearbox system. Of course, too much movement results in axle tramp, juddering in reverse and possible rear wheel steering. Excessive tightness will bend the plates as Fletcher points out, and place the resulting loads in places where things will break.

It is very difficult to specify a torque when compressing soft materials (like the dual spring pads, etc) Torque is ususally associated with a slight stretch to the bolt and locking the nut against the threads. To get a real torque you wouild need to completely compress all the rubber in the system which would be counter productive to allowing the movmement needed to absorb the forces being applied by the driveline and the road.

The amount of tightening needed is enough to prevent judder in reverse. If you get some judder, tighten some more and use a second wrench to lock the lock nuts against the upper nuts. That's why the lock nuts are there, as a single nut in a soft installtion (rubber mounts) will never apply enough thread locking against the threads of the fastener if the rubber is allowed to absorb some movements. Eventually you will get a feel for the right amount of tightness. Follow Fletcher's instructions carefully and you will not be far off.

warmly,
dave
Dave Braun

I used brass nuts, (long or deep) & double nuts on each
Len Fanelli

Thanks all for the info....
I drove the car about 40 miles, a few days ago, and the car felt great....No rear steer, and no shuddering.
Re the painting of the installation, I am going to dis-assemble everything again this Winter, with the body off, and will be cleaning and painting everything.
I did POR15 the spring-center plates, while they were out.
The axle had been painted, so I think it will be o.k., for the few months, until cold weather sets in.
Edward
E.B. Wesson

Just to continue to "beat a dead horse",
I did put the car on the lift today, and checked the nuts again....
They had loosened slightly....
So I set my torque wrench to 18lbs, and , even at that low torque, the nuts could be run all the way up...(I didn't do that, though)....
So , evidently, the torque value is considerably lower than 20lbs, because of the rubber buffers....
My guess , now, is that "quite tight" , on these bolts, is probably more like 14 lbs. (Which is the value used on a 5/16" bolt , that would hold an aluminum manifold in place (as an example).
"Time will tell", I guess.

Edward
E.B. Wesson

you lost me edward...you found the nuts loose and you went with a lower torque? just saw the rear axle u bolt torque for the ford ranger is 76 ft lbs..not exactly apples to apples but the ranger is a small truck. regards, tom
tom peterson

another table..


http://www.engineershandbook.com/Tables/torque.htm

regards, tom
tom peterson

Ford Rangers and virtually everything else use a solid metal to metal axle to spring mounting. This is a completely different approach than the MG system of using a isolated mount. As far as I know, the system started with post war MG and was carried on to other BMC cars, but is otherwise unique. MG did not go to the trouble and expense of using all those special pieces for no reason. It's called engineering refinement, and is typical of MG design, and that is a large part of why MG are so much nicer than most of the contemporary cars. If that is beyond you, drive a Ranger, or a Triumph.

Ed- Now that you mention it, I tried many years ago to determine a torque spec, but came to the conclusion that the inherent variables of thread friction, rubber differences, etc made it not feasible. I went back to "mechanic's feel", now evidently another lost art.

One of the problems with over tightening such that the plate is bent is that then the load is taken only at the corners of the rubber. This causes the rubber to mush out, making the mounting sloppy well before it would be if the thing were correctly tightened to distribute the load - and friction - over the full face.

Once there were only torque specs for unusual or very critical fasteners; now it seems that every amateur in the world wants numbers, in the misguided belief that this will substitute for competence. Standard wrenches are made such that a normal person, with normal exertion, can correctly tighten a normal bolt. It might take more force to loosen one, and the experienced can use longer wrenches without breaking stuff, which is why professional tool suppliers offer "long series" wrenches. They make a long day a little easier.

FRM
FR Millmore

frm, i am not sure why you are taking a shot at a fellow poster who is just looking for some guidance. edward is just looking for some help.
i agree, good experience is invaluable, but i also believe there is a reason torque wrenches were invented. i've been a trained, licensed and practicing aviation mechanic with inspection authorization for over 30 years. can't say i've seen it all, but no where in the critical field of aviation would anyone refer to someone looking for correct torque specifications as an amateur and no where in the critical field of aviation is "mechanics feel" acceptable data.
i can still remember the demonstration one of our A&P instructors did in school. we were to equally tighten a row of identical fasteners. we were then given torque wrenches to check the accuracy of our "equally tightened fasteners" the torque wrench wins. why NOT apply the higher standard to critical fasteners? perhaps the beginner is looking for torque specs not in a "misguided belief that this will substitute for competence", but is looking to the old heads for guidance.
i did enjoy the comment about driving triumphs!
regards, tom
tom peterson

O.K., seems I've started something.....
First, I am not exactly an amateur....I've been building and wrenching on cars for 50 years....
I AM a newbie , when it comes to TD's...This is my first....(It is also , my sixth British car).
Regarding the reducing of torque, since the rubber buffers are relatively soft,(compared to the steel parts), starting with 18 lbs of torque would have resulted in completely crushing the rubber, and running the nuts of the new U-bolts, all the way to the end of the threads...Thus , once the rubber was a little worn, there would be no way to re-tighten them....
My feeling was that using the torque wrench , without
any real numbers, was a waste of time, since I would be guessing anyway, and the long handle, didn't give me the "feel" that I needed, so I abandoned the idea, and went to "King Dick"...
I tighened until the rubber just began to bulge, and then measured the 4 legs on each side, so that they were all exactly the same length, from the bottom edge of the nuts...I then added the locking nuts.
When I suggested 14lbs torque, it was based on intuition, rather than any fact...
I hope this makes sense.
In any event, thanks for all the input....I continue to learn as I go.
Edward
E.B. Wesson

Now you are going to make me get under the car and check my U-bolts that were installed earlier this year. Thanks.

Should this be done with the car sprung or unsprung.

Jim
James Neel

Both, Mike.

http://www.youtube.com/watch?v=7IU1bzZheWk
Mike Hart (52 TD 16378)

This thread was discussed between 04/08/2011 and 10/08/2011

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