Rear Bearings

[december2013]

You recently helped me with the rack and pinion steering on my 1970 MGB-GT, which I greatly appreciated.  I have been hearing a slight growl in the rear that seems to be getting a little louder.  Put the car on jack stands and ran car in gear.  With all the motor noise really could not hear anything that is definitive.  With engine off when I grab the drivers side rear wheel at 12 and 6 there is no "play".  When I do the same thing to the passenger side there is a definite rock in and out.  

On other cars, not necessarily MG's I have had rear bearing go out and some I fixed, lots of years ago, and some I took to a repair shop.  I would like to change the rear bearings on both sides.  I looked at the exploded parts drawings in Moss catalog and sort of understand what's got to be done.  Wheels off - drums off - what's next is where I scratch my head.  I have MGB 1962 thru 1978 Haynes Owners Workshop Manual.  This has been a real help, except trying to read English - English has been a challenge (Bonnet, etc.)  There is info on how to remove and rebuild the whole rear end but no real help on just changing the bearing and necessary seals.

Are there any old Tech  tips from AMGBA that might help?

Tom Johnson

[Art]

The joy of owning an LBC (Little British Car).  Getting past the Queen's English, it's pretty straight forward.
 
The '70 has a tube axle, which, if you have experience with later model US made cars, it is very similar.
 
After you remove the road wheels and tyres (tires - ha, ha) and brakes (and yes, you need to disconnect the hydraulic line and remove the wheel cylinders to prevent breaking off the lines), you then need to remove the 4 bolts holding the backing plate and bearing to the axle housing.  Access to those is through the hole on the stud ring at the end of the shafts.
 
Being a tube axle, the shaft is a swedge or press fit, so really no need to even open the differential cover (though there is another item that should be checked that I'll come back to later).  Bearings are press-fit to the axle as well.

The hub will have to be removed. The cotter pin removed, the castleated nut may be easier loosened with the wheels on and even with the car on the ground.
 
The hub itself may take some doing to get off with a gear puller.  I've sometimes had to apply heat along with some gentle persuasion.
 
Again, that can also all be turned over to the machine shop once the half shaft is removed. The best way to extract the axle and bearing is with a slide hammer attached to the lug nut studs  (see sketch below.)
 
There are plenty of YouTube posts on this as well.  They're for American cars, but the assembly is very much the same.
 
Once the shafts are out, use a press to change the bearings or give them over to a shop to do.  Be sure to get the bearing kit (Moss part #125-850; 2 required) as it will have the seals needed with the bearings.  You might also want to get new collars and spacers just in case.
 
Installation is just the reverse of removal, with the last part being a light hit with a soft blow hammer to the end of the shaft to seat it.
 
Now, inside the differential are (2) thrust washers, which, when new, were made of a fiberous material and are notorious for wearing, cracking and falling out causing a noticeable "click" when you accelerate and decelerate.  Replacements are now bronze and more durable.  Installation requires removing both half shafts (which you are doing anyway) and taking out the diff to bench work it.  Still a bigger job than just the bearings, but if you need them, now's the opportunity to do this work.
 
I hope that helps you.  Let me know if you have any questions and how you make out.
 
Safety Fast!
 
Art

[Art]

Hey Tom,

I missed a minor, but obvious point (which you probably realized).  You do need to remove the hub and spacers first to be able press the old bearings off the axle. 

The castelated nut on the end of the shaft is probably easiest to loosen with the wheel in place (and on the ground with the brake set and car in gear).  With the cotter pin removed, it may still take some liquid wrench, significant leverage and possibly some heat to break the nut loose.  Much more easily done with the axle still in place than trying to hold and not damage it in a vice on the bench.

Same with the hub, which requires a gear puller to get off.  I've had to apply heat and some judicious "persuasion" with the puller in place to pop those loose.

Another thing, I did see that Moss offers a loop-on-nut for the end to axle shaft for slide hammer use.  It just replaces the castlelated nut on the end of the shaft and you can then hook  the end of the slide hammer into it.  It's Moss part no. 384-945 and about $28.

I hope that helps you.