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MG MGB GT V8 Factory Originals Technical - Drive Shaft Loosening at Differential

I am in the process of giving the MG itís pre flight inspection and noticed the 4, 5/16Ē bolts connecting the drive shaft to the differential were loose. Anyone have any idea why this would happen. I am sure they were tight at one time. I am using grade 8 course thread bolts with a lock nuts. I question weather the lock nut is grade 8. Thinking of trying fine thread with a lock washer and a Loc-Tight adhesive.
Jim Miller

Jim, please don;t go lock tight. For YOUR own good later.. I had success with grade 5 hardware, but am also upgrading.

Fine or Course should be aceptable, the bolt itself is what you want grade 8, as it will take any torional stress. grade 8 bolt, lock washer AND nylock nut and you shuld not have a problem.
Larry Embrey

If you want to do it once and not look back, use airframe bolts.
Airframe bolts have the shank (unthreaded portion of bolt) pass through the shear area of the flanges and the threads are only long enough for the locknut and a couple of shim washers.
You order them by diameter (-5 in your case) and "grip length" (the combined thickness of the components you want to join). They come in length increments of 1/8"
You can go out to virtually any small airport using airport transfers sevenoaks and buy them or order them from Pegasus Racing (1-800-688-6946).

Do this, and you'll never have to worry about them again!

Larry's right about the locktight...
Randy Forbes

Randy, great find, I will file that info away for later use. Thanks!!

The only time locktight is used (and BLUE locktite ONLY) is with rears like the 8.8" where the pinion flange is threaded. The boltes used are hardened AND they heads are taller, so that your wrinch/socket does not slide off easily and put you in a real bind. The ones on my donor car were even 12pt, so you had to use a socket for better grip.
Larry Embrey

Had the same problem back in 1964 on a '63B. Had put the bolts in backwards by mistake. Turning them around was the cure. Don't know why it happened unless it has something to do with direction of rotation.
jim mindy

Are you chaps talking about what we call the propshaft?

I can't see how fitting the bolts either way round would make that much difference......I did notice however in the manual that one end of the shaft has bolts with spring washers, and the other doesn't.......I'm just about to refit mine (which previously didn't have washers ) and wonder if it makes a difference.

Michael barnfather


Yes, it is the propshaft they are talking about.

For the SD1 gearbox use metric bolts and nyloc nuts (to suit the metric flanges), it doesnít make any difference which way round but it is probably easier to hold the bolt and tighten the nuts if they are fitted on the gearbox side. Diff end use imperial bolts (AAA4039) and nyloc nuts (LNZ105), again it is probably easier to tighten with the nuts on the diff side. Use spring washers if the bolts are long enough but donít worry if they arenít - they are not essential.

Geoff King

I know this sounds crazy but I learned about it from an mg specialist with 60 years experience.
Properly tapered hardwood cylindical-wedge pins have been successfuly used to secure driveshaft flanges together since the earliest days of motoring. The corresponding holes must be cut with a tapered reamer of the same spec. as the wedge-pins.
Straight grained, red oak or ironwood pins give the best results. Wet weather driving will cause some swelling and possibly cracking but, applying waxol or 3M undercoating will reduce this tendancy.
Certainly not as strong as steel bolts, the use of wood taper pins will completly eliminate axle-shaft breakage, due to their inherrant torque-limiting feature.
Replacing broken or sheared-off pins can be easily accomplished with a punch and small hammer. In an emergency, replacements can be whittled from any suitable wood but, properly tapered hard-wood pins should be carried in your spares kit.
Enjoy this first day of April! Marc, (nobody's fool)
Marc Judson

This thread was discussed between 30/03/2003 and 02/04/2003

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