Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) 3.7 differential

Whenever I have experienced those symptoms, I have removed the rear wheels, cleaned up the splines and bevelled seating areas and liberally applied copper slip. Always a success for me.
I wouldn’t worry about the backlash as others have said and if uj’s are clonking, then i would expect them to be past their best. Greasing can only effectively stop them from clonking in the first place.

I changed the diff oil to Red Line 75W90 Fully Synthetic Gear / Differential Oil in April '25 at 10500 miles. This has since been changed to Morris Lodexol XFS 80W-140 in late June '26 at 13250 miles.

First of all check the seating on the inner tapered mounting surface of the hub and the wheel, they need to be spotlessly clean. Inspect your splines on the hub and wheel, firstly dry without grease. They should be crisp and even and not look worn. Then fit the wheel dry and tighten the spinner by hand, handbrake on can you get any knock from the splines by trying to rotate the wheel? If so you do have some movement between the hub and wheel splines. This doesn't necessarily mean you have damage although you will have some wear, that's inevitable but they are not without some slop and often from brand new as well. Now start to tighten the spinner, can you remove any play you had when hand tight? How are you tightening the spinners. There has been a lot of gonads talked about tightening wheels. I remember my dad being told "you don't have to try too hard as they self tighten". Well yes they do hence the left and right rotation to tighten spinners! However this is what causes problems. Too loose and they will tighten but over tighten eventually and it's that period of effort that causes the spline damage. We have recently had a discussion post on here in some depth and gomog, Lorne, says that he tightens his Ferrari tight and that's FT. I'm not sure I go that far however tight is good and they tend to stay put and don't get any tighter. I originally had three legged spinners, look great but difficult to tighten adequately and a bugger to get off after self tightening! So I changed to euro octagonal which I have total control over. I have a socket and 600mm breaker bar which applies the correct torque by feel that I find works best.

Now greasing the splines. First keep both elements clean annually at least. I do use copper slip-on the splined area as the copper dust does cushion the contact areas but on the tapered seat at the rear of both hub and wheel I use a standard HT grease wiped very sparingly on these areas to corrosion protect only.... it is here that the wheel is locked tightly onto the hub and this friction protects the splines from getting knocked about. I apply the copper slip with a brush and don't slop it everywhere, rather apply it sparingly to hub and wheel. if you keep your wheels on the same hub, I do, use a front wheel on the rear to see haw it feels as they tend to suffer less wear. If it feels much tighter then all I have said here is the problem. put it back on the front and asses the wear to the rear wheels and remember a worn wheel will damage a new hub and vice versa.

With your wheels tight on the hubs there will be some play at the diff, it's a diff and you can't not have a small amount and 5mm at the tyre's perimeter doesn't seem excessive however if you have play throughout the drivetrain this will compound the issue so a good check from gearbox to half shafts is needed. Remember though Morgan have only ever used what are truck diffs and finesse is not a strong point, You will have the Australian pick up truck diff fitted in yours..... check the end float in the half shafts at the wheel. handbrake off and push the wheel in and out, you may be surprised! The manufacturers say 6mm is acceptable and without a complete rebuild it's not adjustable!!! Often people complain of the clucking going around corners, very often in fact. some can even feel the car move and its not been the springs!

The last thing you say is it feels like the handbrake is on sometimes when pulling away, This is probably a rear brake issue. I wouldn't be surprised if wheel cylinders are sticking. Many times I have seen the 'ease them off' technique tapping the pistons side to side until they move....."we've sorted your rear brakes sir". They won't last! and we all know they are notorious for gumming up! Also worn shoes can jam as do rear brakes adjusted without the handbrake being totally backed off. It's not impossible that you have a diff problem but I doubt it at your mileage. try adding some extra LSD additive as I have said before the ready to go doesn't always have enough in and quickly seems to have issues after changing. Both oils you used though are good quality products but it is a rough truck diff and might need some more help.

Of course it's impossible to reach a definitive solution without seeing the car so good luck in finding out the seat of the problem. One thing I have found is that there is no constancy in what's fitted to our cars, some better than others. New cars from the factory with issues are, or were hopefully common and individual items bought in with varying parameters too! Not a case of they all do that sir, more a quality control issue!

I haven't fully checked the specs above BUT I think only the Morris is LS, it's vital you use a high grade LS (limited slip) spec oil in a Roadster as the friction of the plates / cones within the diff depend on it

Thanks Sewin. I'll go through the procedure you have detailed to see if it improves the situation.

I'll report back when I have tried everything - probably a couple of weeks time as I am away next week.

Note Redline offer three differering synthetic oils in the 75W90 category.

GL5 is quoted on the bottle as being suitable for LSD axles as it has the necessary friction modifiers. I use this in my Roadsters axle.

NS (non slip) for situations where the LSD requires minimal/no slip so often used in race applications.

MT a GL4 spec oil for manual transmissions - it appears on back of bottle this is 75W80 grade though and the one I use in gearbox.

GL-5 was the one I used, however when it was drained out after a year and 3000 miles it was very dirty - silver grey colour. Which is making me think there could be a problem with the diff.