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MG MGB Technical - Tranny driveshaft flange nut torque?

I just pulled my engine out today and noticed that the nut at the back of the transmission holding the driveshaft flange on was pretty loose. Does anyone know the torque spec for this nut, it doesn't appear anywhere in my workshop manual.
thanks
Bill
Bill Mertz

Bill,

If you want to go the extra step beyond just "tightening" and really want to use a torque wrench, you can follow the values given in tables of standard torques such as these:

http://www.zerofast.com/torque.htm

Notice the different values if lubricated/waxed.

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

I've got to ask if the "pretty loose" bolts were loose-loose or just didn't require much effort to undo. But you'll notice that a 5/16" bolt only takes 12ft.lb. That's not a lot. Also, in my experience, the automatic oiling/rustproofing system that seems to have been installed on most LBCs will have kept these fasteners well lubricated. Were the called for lockwashers present under the nuts? Every bolted joint should ideally have a locking device. That can be a lockwasher, a locknut, Loctite or safety wire. But how often to we finish a job and find "a few parts left over"! Or the DPO?

Good luck and keep your nuts tight!

TTFN

Derek Nicholson

I think Bill means the big nut holding the flange on, and the answer is PDT - pretty damn tight. I use my long handled 1/2 drive ratchet, est 120-130 lb-ft. On the 4synch especially, this nut clamping is all that drives the speedo gear, and endfloat of most of the 3rd motion shaft components is affected by any looseness here. Weird speedo slow readings after warm up (it tends to max out around 60 regardless of actual speed), and bizarro shifting troubles are the tell-tales, and it is another source of "the clunk".
The standard torques are useless on the propshaft nuts, they will come loose and damage the flanges, raising little lumps around the holes, which make it impossible to tighten correctly. These need to be as tight as you can get them with standard 5" half inch wrenches, or as tight as you can comfortably tighten with 7" long handled 1/2 wrenches.
FRM
FR Millmore

Varies quite a bit:

Manual without OD 150 ft lb.
Manual with D-type OD 100 to 130 ft lb.
Manual with LH-type OD 55 60 ft lb.
Automatic 55 to 60 ft lb.
Paul Hunt 2

Now that's a spread! Are these numbers buried somewhere in the shop manual, Paul?

Derek Nicholson

They are in the Haynes mgb manual in the transmission section.

Clifton
Clifton Gordon

Thanks for all the info guys. I was talking about the "big nut", and it was loose loose. Tranny shifted fine however and speedo didn't work (broken cable I suspect however I'll look into it).
-Bill
Bill Mertz

This thread was discussed on 28/08/2006

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