Morris Truck Wanted

Mrs Mac

Paul

You ruined my night as predicted. I have been sitting with a pencil and paper drawing differential drives and looking on all sorts of sites to get to grips with the various axle binding solutions.

It seems almost certain the problem can never be 100% resolved without some sort of power divider, centre diff or clutch system between axles. It can be brought within the realms of acceptable minor inefficiency as you allude to with your asymmetric wheel solution.

From what I can find out on various truck sites, including suspension manufacturers, your idea goes something like this:

By having both axles with a smaller wheel on one side forces the diff to naturally favour the small wheel side (least resistance).

If the small wheels were on the same side they would be reacting with the same load variations on very similar road surface. When the front axle reacted the back one would do the same almost instantaneously. No matter how accurate your measurement there will be some tiny difference in diameter and bind-up will happen. When it becomes large enough one of the axles will then spin or skid to take out the force. This happens constantly in the tiniest of movements but adds considerably to tyre wear and wasted power.

By placing the small wheels diagonally it means the two diff-action preferential small driving wheels are following a different path along the road with different load forces and instead of bouncing or loading up almost in unison are marching to their own tune making it much more likely their binding loads are being released at lower force and more regularly.

A genuine Mack bogie drive doesn't have a power divider like a normal bogie drive assembly

It has a sort of locking differential that doesn't actually lock or work like a diff

So the reason I mention this waffle is because if the tyres are to different in sizes the divider actually winds up and locks and axles jump and the tyres chirp as the skip

So some times you need to measure wheels as described

You can't just bung a new set of tyres on one axle, they need to be split the new tyres of each axle diagonally as I have already mentioned

Bogie drive Pomy trucks never had power dividers for many years and even the Yanky ones didn't until probably the 60's

Some lite reading

How a Mack Power-Divider works – Australian Roadtrains share.google/yoFMKYO85nkUU9wZ9

Paul

Here is a great movie of Michael Terry's expedition from Darwin to Broome in 1927 only a year from his Port Hedland to Melbourne Morris trip.A rare bit of Australian trucking history.

On this expedition he used Guy half tracks. As you can see from the second half the tracks were removeable to convert back to normal tyres.

Agree that in these circumstances 2wd is the way to go. The diff is worm drive so I think that your options are limited in that the rear diff is either part of the team or there is a way of taking the worm out of mesh so that it is not being constantly pushed in the absence of the jack shaft.

Interaxle differentials arent needed on light vehicles if rolling radius is matched within reasonable limits......Lots of big trucks never had them ...worm drive Fodens and Leylands ,and all the US WW2 military trucks ,even the tank transporters .......only NR Macks had them .