Grinding from back end under heavy load?

[Moggie94]

It's a 1971 2 door.

Whenever I load up the car (or have multiple passengers) and pull away, there's a grinding noise coming from the rear end.
I haven't been able to isolate it (hard to do when it only occurs if moving)
It makes the noise over bumps or when accelerating, backing off the throttle silences it in both scenarios. Any ideas?

Unloaded and with just me in I can't get the noise to happen no matter how quickly I pull away or go over speed bumps

[bmcecosse]

Any problems with the rear springs? Has the suspension been lowered? Are the bump stops present and correct? What clearance do you see between the bump stops and the chassis bump pad? Is there any witness mark where the prop shaft(or inal drive pinion flange) hitting the floor?

[Moggie94]

Springs are decent and they look new-ish, no lowering and bump stops are there.

Had a look just before I posted this for any marks as somebody else suggested seat belt bolts coming through the floor and snagging when the suspension dips, there wasn't anything obvious but I suppose it can't hurt to have a proper look when it's light and I can get the car jacked up again.

[bmcecosse]

Yes -seat belt bolts are a possibility. And the gap between bump stop and pad??

[Moggie94]

Looks roughly 3 inches.

What's the "normal" distance?

[bmcecosse]

Sounds higher than most! So that's not the problem.....

[Moggie94]

Maybe I've got shorter bump stops than most, so the axle is able to travel higher up and potentially let the prop hit something?

[Tom and Maria]

Any old bits left in the boot by previous owners? It's happened before...

[bmcecosse]

It's quite 'standard' to hack about 1.5" off the rear bump stops - but with 3" clearance there shouldn't be a problem.

[DAVIDMCCULLOUGH]

Ive had a couple of different times when this has happened, first was as you have already mentioned seat belt bolts attached to the tunnel and when fully loaded they were touching the prop and scored a nice grove all the way round it. The noise was usually worse on cornering.

The next time it turned out to be the axle casing was rotten were it mounts to the springs, this caused the axle to try and turn in the U bolts because it wasnt held tightly enough. A repair section is available for the axle casing.

http://morrisminorspares.co.uk/shop/pro ... 141fa618fc

[bmcecosse]

Yes - I wasn't going to mention the 'perches' until all other possibilities had been explored......

[Moggie94]

Have had the car up and been under, no marks to evidence rubbing on anything...

Nothing rotten, I'd swear the previous owner must have replaced (or recon'd) the back axle and springs so I'm still stumped.

[Alex'n'Ane]

Is the axle twisted up? Whats the prop shaft to diff angle like?

[Declan_Burns]

It could be the diff.
Declan

[ASL642]

It may need it's oil topping up.

[kennatt]

have you got mud flaps on the back

[MarkyB]

Very surprised that there aren't any tell tale signs of a grinding noise, quite a small area will result in quite a lot of noise inside the car.
Might be worth taking the wheels off and looking inside the arches too, especially if bigger wheels have been fitted.

[lambrettalad]

I had a similar noise on a GT6,turned out to be a failing rear wheel bearing ,tho it was worse when going around tight bends,only ever there when a mate was curled up in the back

[mowogg]

I had a similar noise on mine -turned out to be due to the replacement spring hangers. The two piece were welded together along the lip on the undersideedge. This lip grated against the top of the spring under load, and caused quite a bit of noise -the solution was very simple -gring off lip around the rear spring shackle joint and the noise went away.

you may have something similar if they have been replaced?

[oddbod]

I had something similar on the rear of my saloon when I got it, a combination of having been lowered, and weak rear springs, causing the rear spring hanger to connect with the spring, but only when loaded at the rear.