Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Changing diff oil

A few observations when changing the oil in my BTR LSD axle in the hope of curing noisy clutch slip when manouvering.

The drain plug is not obvious and appears to be one of the bolts securing rear diff cover to main body. Vaguely remember this being mentioned before. The lowest bolt is slightly larger though requiring a 15mm socket, and allows draining. You need to remove underseal first though or socket will not fit.

The filler/level plug requires a 10mm Allen key and is located in back plate. No clearance for socket keys or those that work through an angle. You need to use a simple L shaped key which in turn requires extra leverage. I used a long socket extension with socket attached that fitted comfortably over the longer shaft of key.

It was a very warm day so decided to drain without taking car for run first which worked fine after jacking up rear and putting stands in place on chassis. I did allow plenty of time for all oil to drip out though.

I have a hand pump fitted with one litre plastic bottle for topping up transmission oils on my Land Rover so filled that with 946ml contents of suitable Red Line oil. Emptying oil catch tray into empty bottle proved a tad over one litre had come out though as I couldn't squeeze it all in for disposal. Manual suggests approx one litre. Replaced drain plug with new copper sealing washer as it appears sealant alone was used on drain bolt previously.

The other issue was with hand pump, which has convenient goose neck on end of transfer tube, is that you can never get the last 50ml in from bottom of bottle. I'm guessing I'm at least 100-150ml short of what came out at present, which itself wasn't overflowing filler hole. Ordered another bottle therefore but it would have been handy to have at hand.

Hope this info helps others.

Won’t jacking it up give a false oil level ?

I did consider that Doug although DaveW makes no mention as far as I've seen. Remember that with car jacked up a modest amount, suspension is released offsetting the angle diff sits at. Will work on quantaties removed though.

Hopefully next time (if there is one) I do this job I will have a hydraulic lift and one of those fancy air assisted lube pumps.

This is the Draper one I use at present, which saves having to fill from above with long tube and funnel, not to mention all the spills that entails. Best avoid using this in winter though with oil like treacle and stiff pipe!



Cheap as chips as well

The only way to get the right level is to lower the back end to check. Having it high means a slight overfill, but lowering the rear allows the oil to drain to level.

It's a faff.

I've always filled my diffs from above, never had an issue with mess or trying to find the correct level as the car is on the flat and when the dribble comes out it is full. Seems a lot less kerfuffle.

The later cars have really tight access, and I always fill from above, but to get access to the drain plug, with short arms, my Morgans have to be lifted.

FWIW having just decanted the remaining old oil from diff for disposal, I'm measuring close to 1.3 litres! A little more than manual suggests and hopefully helpful to anyone preparing to do the same job.

Pumping oil from below is so much easier and more controllable with the right kit BTW. Especially given the point Dave makes for filler plug access.

Richard, that quantity sounds correct from last time I did mine

I also use the same little bottle pump

Just to round this thread off have now finished the job with 1.6 litres being required to filler hole (manual states 1 litre approx!). Would have saved a lot of jacking up and down if I'd known this in advance. I have updated my handbook though.

Thanks to Rchard for this post, I found it usefull as today I changed Monty's diff oil.

Having now done the job myself I can offer the following observations that may help others?

* The drain plug is 15mm as confirmed by Richard, but removing it in my case involves dropping Monty's Panhard rod, not difficult but worth noting for others with a PHR

* In my case the filler plug is 1 1/8" just like the BTR filler plug on my TVR Chimaera, so just a case of reaching for my 1 1/8" Kenedy combination spanner but it's worth noting as others may not have this large size

* When I removed the filler plug there was an inrush of air so the axle was under slight vacuum which is normal, the breather is the typical crude rear axle one way valve designed to only open under pressure

* I removed and stripped the breather valve, thoroughly cleaned it, reassembled ensuring the light barrel spring and rubber disc worked correctly after re-pinching the cap

* The drain measured 1.5 litres

* Monty's drain plug had a lot of Hylomar blue on it when it came out, Monty's file shows he enjoyed a diff oil change early in his life at just 5,000 miles which is good to know as the early running-in oil change is very important because that's when you need to clear any swarf. But in my opinion the mechanic who changed the oil 10 years ago used too much sealant on the threads so I cleaned it all off, cleaned the diff cover and fitted a copper washer this time

* I flushed the diff by pouring a slug of new oil through it with the drain plug still out

* With the drain plug back in and tightened, the diff took 1.6 litres to 'fill to spill', reassuringly identical to the oil volume reported by Richard

* The filler plug had no sealant on the threads or copper washer, it was also quite loose, I used one of the Rover V8 sump plug washers (hollow crushable type) that I hold in stock, to wind it onto the filler plug threads it just needed the inner diameter bringing out slightly with a file

* Monty's diff is definitely a LSD, so I bought 2 litres of 75w140 LSD Synthetic Gear Oil from Westway Oils for a very reasonable £32 including postage



* While what came out today had only done 15,000 miles, it was also 10 years old so definitely needed replacing



* Moving forward I will be changing Monty's diff oil every 20,000 miles or at 4 years, whichever comes soonest

I hope there's something within the above that someone will find helpful?