What makes a strong diff

[R Cubed]

Moving on a little from diesel engines in GMC's and air brakes got me thinking, yes I know that's a bad thing as I type stupid things but it gets people thinking which is a good thing.

 

Not considering the diff ratio, are there different types of diff, is the pinion in a slightly different position, are the gears cut at different angles are there bearing differences are there other options other than crown wheel and pinion ?

 

Which is stronger which will transmit more power or is it torque :nut: which allow faster speeds ?

 

How do modern diff's differ to war time or pre war diff's, does the quality of steel have an effect?

[gritineye]

To strengthen older diffs for more power off roaders of old used to put "buttons" threaded through the housing to the back of the crown-wheel from moving away from the pinion under extreme stress, not at all expensive to do just a bit of know how needed.

[Richard Farrant]

To strengthen older diffs for more power off roaders of old used to put "buttons" threaded through the housing to the back of the crown-wheel from moving away from the pinion under extreme stress, not at all expensive to do just a bit of know how needed.

 

 

Bedfords fitted these to their WW2 era, and onwards, lorries.

[R Cubed]

Yes seen that done on Land Rover for trialling comps.

 

More interested in the types of designs differences rather than mods on existing items.

[cosrec]

some heavy haulage trucks to day have relatively small diffs with planetry gearing built into the hubs so reducing strain on diffs and drive/ half shafts dont know if this helps with your question

Edited September 23, 2010 by cosrec

[cosrec]

Which is stronger which will transmit more power or is it torque :nut: which allow faster speeds ?

 

]

Niether it the ratio of the diff that dictates the the speed

[Degsy]

some heavy haulage trucks to day have relatively small diffs with planetry gearing built into the hubs so reducing strain on diffs and drive/ half shafts dont know if this helps with your question

 

These have been common on trucks since at least the 1930's

[Stormin]

Not considering the diff ratio, are there different types of diff, is the pinion in a slightly different position, are the gears cut at different angles are there bearing differences are there other options other than crown wheel and pinion ?

 

 

There are other options than crown wheel and pinion. Don't forget the very heavy duty vehicles of WWII the Pacifics used a chain drive to the rear axles. Also in use on Sentinel steam wagons until the 1950's. A chain is a very efficient method of transmitting power with little losses.

 

An entire transmission system is a chain of torque multipliers from the engine to the wheels. With few exceptions, every link, gearbox, transfer box, differential, hub reductions increase the torque to the driven wheel. Each link induces some loss is power through friction. The size and reduction ratio of each link governs how strong the next link down the chain must be.

[R Cubed]

some heavy haulage trucks to day have relatively small diffs with planetary gearing built into the hubs so reducing strain on diffs and drive/ half shafts don't know if this helps with your question

 

Yes ok did know about that type. More of an interest is the make up of the crown wheel and pinion arrangement, are there different heights between the pinion shaft and half shafts, are there different types of meshing gears and the benefits can some turn faster and stay cooler ?

[R Cubed]

Which is stronger which will transmit more power or is it torque :nut: which allow faster speeds ?

 

]

Niether it the ratio of the diff that dictates the the speed

 

Sorry I have not explained myself very well. What I am trying to get at is, how does one diff differ from another, are there different designs of meshing of the gears to enable the diff to transmit more torque ? Are there some designs which cant turn at higher RPM due to certain constraints ?

[R Cubed]

There are other options than crown wheel and pinion. Don't forget the very heavy duty vehicles of WWII the Pacific used a chain drive to the rear axles. Also in use on Sentinel steam wagons until the 1950's. A chain is a very efficient method of transmitting power with little losses.

 

Are chain drives limited by speed, what about reliability, are they high maintenance ? why are they not in use today ?

[R Cubed]

An entire transmission system is a chain of torque multipliers from the engine to the wheels. With few exceptions, every link, gearbox, transfer box, differential, hub reductions increase the torque to the driven wheel. Each link induces some loss is power through friction. The size and reduction ratio of each link governs how strong the next link down the chain must be.

 

So if you were considering an engine up grade and the vehicle in question had a high/low transfer box would it be reasonable to regard the diffs in the axles to be strong enough due to the fact it was designed to be used in low range and with that type of gear reduction the increase in torque must be quite considerable ? so would that be a reasonable thought that the old engine in low range produces x amount of torque so if you were to fit a more powerful engine but used it in high range the drive train still gets x amount of torque. This is not taking into consideration the transfer box of gear box as these will be having more put through them directly from the engine.

[fesm_ndt]

just going on the simple side, Land Rovers fitted with big 6's and V8's in Australia used to destroy gear boxes and axles

 

Mind you a lot of this has to do with your right foot, as if you are careful and don't drop the clutch and bang down your foot on the accelerator the drivetrain can handle it

[zoltan]

So if you were considering an engine up grade and the vehicle in question had a high/low transfer box would it be reasonable to regard the diffs in the axles to be strong enough due to the fact it was designed to be used in low range and with that type of gear reduction the increase in torque must be quite considerable ? so would that be a reasonable thought that the old engine in low range produces x amount of torque so if you were to fit a more powerful engine but used it in high range the drive train still gets x amount of torque. This is not taking into consideration the transfer box of gear box as these will be having more put through them directly from the engine.

 

I have a Gaz 66 and on that you must move into 4WD before you can select low ratio through the transfer box so that the increased torque from low ratio is split between the two axles

 

Would you be only using high range post engine upgrade?

[N.O.S.]

And - if the lady wants a GMC - split or banjo axle? As has been discussed on here before.

[Sean N]

If you look at (older) truck final drives there are three main types (as far as I can remember!).

 

A lot of very old heavy trucks will have worm drives. These tend to be quite strong and you can achieve big ratios easily with a worm, but the mechanical efficiency isn't great (50% - 90%) due to the sliding contact between the driving and driven gears, which can lead to rapid overheating and failure particularly if overloaded or if lubrication is poor.

 

Many vehicles use spiral bevel drives, which are highly efficient (99%), but it's quite difficult to arrange big ratios in a spiral bevel. You can spot a spiral bevel axle as the axes of the propshaft and axle shafts will intersect.

 

Also common is the hypoid axle, where the teeth mesh in what's called a hyperboloid. In a hypoid axle the propshaft and axle shaft axes do not intersect - the prop will normally enter the axle casing below the centreline. The teeth in hypoid gears have a sliding contact which is less efficient (95% - 99%) than a spiral bevel, but more efficient than a worm. The greater tooth contact area makes up for the poorer efficiency by increasing durability, though they can be hard on oil due to the high pressure shear between the teeth; Hypoid (extreme pressure) gear oil was devised to cope with the peculiar sliding contact between hypoid gear teeth. Hypoid axles tend to be quieter and smoother than spiral bevel axles and bigger ratios can be achieved. In some installations the ability to get a low prop centreline can be useful as well.

 

Bedford used at least two of these designs, having light duty spiral bevel axles in small trucks, heavy duty spiral bevels in big trucks, and hypoids in the ones in between!

Edited September 27, 2010 by Sean N

[Sean N]

In some ways, that doesn't really help with what makes a strong final drive though. A badly designed or overstressed drive of a theoretically more efficient design could be worse than a well designed 'poor' type.

 

Driving style makes a big difference too; put 200 bhp through an axle designed for 150 but go gently with the right hand pedal and you'll be fine, put 150 bhp through an axle designed for 200 and wheelspin off wet grass onto dry tar and you'll break a halfshaft.

 

My own feeling, having done many engine conversions without axle issues, is that you can worry too much about these things! In practice you're unlikely to have much choice with final drive types particularly on medium trucks and particularly if trying to retain the same axle casing.

 

As others have said, what affects speed is the final drive ratio (at least until frictional losses and air resistance approach engine power output) but either a spiral bevel or hypoid axle will put up with speed increases better than an (old style) worm drive.

Edited September 27, 2010 by Sean N

[gritineye]

 

Driving style makes a big difference too; put 200 bhp through an axle designed for 150 but go gently with the right hand pedal and you'll be fine,

 

Quite so, as I have more than doubled the torks available to wreck the drive train in Forceful, I have taken a lot of trouble to set the accelerator linkage in such a way that my foot is comfortable at half throttle, and at cruising speed this is perfect.

 

This means it is quite uncomfortable to use full power for long, which helps to prevent me getting used to the power and abusing things too much.

 

Remember that you will most likely be unladen and on smooth roads, and off road wheel spin will act as a safety valve.

 

Tuned Rover V8, in Series one 86", 2A gbox life span never more than 5,000 miles, overnight rebuilds used to be done in my sleep!!

[antarmike]

There are other options than crown wheel and pinion. Don't forget the very heavy duty vehicles of WWII the Pacifics used a chain drive to the rear axles. Also in use on Sentinel steam wagons until the 1950's. A chain is a very efficient method of transmitting power with little losses.

 

An entire transmission system is a chain of torque multipliers from the engine to the wheels. With few exceptions, every link, gearbox, transfer box, differential, hub reductions increase the torque to the driven wheel. Each link induces some loss is power through friction. The size and reduction ratio of each link governs how strong the next link down the chain must be.

 

If I recall correctly,the chain drive on a Pacific comes after the diff, it does not replace it. A prop drives back to a bevel gear diff. The two half shafts that form the output from the diff do not carry the road wheels, rather they carry Sprockets, and it is from these that the road wheels are chain driven.

 

I seem to remember that each half shaft coming from the diff actually carries two sprockets, one driving forward to the leading bogey axle wheel, the other driving back to the rear bogey axle wheel.

 

The Pacific rear diff therefore acts similarly to the Explorer rear diff in as far as one diff drives four axles.

[R Cubed]

And - if the lady wants a GMC - split or banjo axle? As has been discussed on here before.

 

I think, given the choice knowing now what I do, it would have to be Banjo axle, as the transfer box is also a much better design in terms of strength issues, I have herd that split axles if over loaded or used over harsh terrain can literally split at the join of the diff casings, not good...