Asking for a client in Belgium who has a Northern General RM, he wants to fit a high speed diff. I'm sure the NG buses had a different axle to the standard London buses and the difs are not interchangeable.

Does anyone know if it's possible to change the ratio in the NG buses?

My bus number (if any): RML2532

Unless the bus has been fitted with a standard London-spec spiral bevel diff then it will have an underslung worm drive rear axle. I am uncertain whether this was an AEC - or possibly more accurately a Maudslay diff, or of Leyland manufacture. So the answer is no they are not interchangeable.

I have ex Northern General RCN701.

I am pretty sure it is Leyland.
I removed my diff 3-4 years ago to be sent of to Queensbridge PSV for rebuilding, when I did this I took a number of photos of it at the time. If you want/if it would be helpful; I can send them over when I get home from work.
If there was plate with a part number on it I would have taken a photo of it - I think.

My bus number (if any): RMF2771

Thanks, that's what I thought. another wannagofaster...that isn't going to.

My bus number (if any): RML2532

Northern General RM underslung worm final drives had a similar ratio as central London ones of about 5.2 to 1.They were similar in design to RT ones. Our chief engineer specified them for greater reliability and longivity in service.

My bus number (if any): RML2551

The NG specified Routmeasters had Leyland Engines with a traditional Leyland set up for the Drive train apart from the SCG Gearbox which set the Routemasters aside from other Front engined NG and Northern buses of the time.

The worm diff is actually better for speed as these buses ran long distance routes with less congestion and stop starting than in London.
Lots of LT specs were simply because of the traffic and operating patterns in London and to keep optimum continuity with overhaul lines, the same types were specified but with differing ratios for similar longer distance operations i.e. the RMC/Country buses and the Airline RMs.

The Worm drive diff is perfectly good and properly overhauled and in good condition along with all of the fittings & suspension bushes at the rear is a good option.

NG had a very good overhauling system as well so this made good pragmatic sense to go with that specification.

My contact in Belgium needs it to "go faster" as the Belgians are increasing the minimum speed on their motorways to 80km/h.

So the question is, what would be available to put in the back axle to make this possible?

My bus number (if any): RML2532

The minimum speed is 43mph now 70kph so he'd be pushing an RM to maintain that speed. It is only a draft idea to go up to 80kph. Best thing is to avoid motorways altogether and stick to main roads as we do, cheaper and safer.

My bus number (if any): RTL 960, RM 1585, RML 2667 and several RTs

The problem is that so many drivers, so-called professionals as well, are completely lost off the Motorway network. I think this man is going to really struggle, there were different ratio sets for the Leyland worm drive diff, however the only ones I have been able to find recorded so far are 6.5, 7.33 & 8.66 all of which will make the vehicle go more slowly. Apart from Foden the worm drive diff had been superseded for Lorries some 10 15 years before it was in PSV. There is an issue regarding the fact that as ratios become smaller numerically the size of the driven gear increases so the casing needs to be larger once a certain point has been reached. I suggest you contact Rush Green Motors Scrap Yard and let the customer do all the dealing at his risk.

Having looked up the proposed legislation in The Brussels Times, The draft wording is that the vehicle should be capable of achieving 80km/h on a flat level road. Not that is HAS to be driven at a minimum speed of 80km/h, otherwise there would be a lot of problems in Belgium once you get across to the Ardennes.

There's a section there heading south from Liege/Luik/Luttich on the E25 that climbs steadily for about 15km. We took BEA MLL738 up there in 2018 and it managed that at about 45km/h in 4th gear and didn't overheat. There aren't many heavies that go much quicker up that hill.

Looking at the figures roy quotes above for Leyland worm drive diffs, I'd suggest that the NG buses must have had similar ratios to the AEC diffs otherwise they'd have been remarkably slow on the road. I doubt there's much difference between the top revs of the AEC and Leyland engines.

My other advice to my client is maybe look at uprating the 11.3 engine t run at 2200 rpm if that engine is capable of running t hat sort of speed. I know the 760 is set to run that fast, but that has a balanced crank and front pulley dampers. Or as Brian says, keep off the motorways!

My bus number (if any): RML2532

It seems very sensible legislation. 50 mph is going to eliminate just about all old buses and some more modern ones as well. The Double deck bus is an urban or inter urban vehicle, it doesn't have a place on the Motorway network, so I think this owner just needs a reality check.