I've been applying my limited brain power to this and reckon I might be onto something.

This is for front engined cars mounted longitudinally like most non midis.

Anyway, the theory.

Take one small diff - like this midget one. Mount it in the transmission tunne with the output shafts facing the engine and the rear of the car. Power goes in one and out the other. No crown wheel, no pinion.




As we all know, the two output shafts are linked via the spider gears and rotate either in tandem or in opposite directions.

So (stick with me here).

Engine power is applied to the output flange on the left, the diff cage is allowed to rotate freely, therefore power is transmitted unaltered to the other output shaft. The fact that the diff cage rotates means that the spider gears simply operate in a stationary fashion.

Reverse ?

Lock the diff cage to prevent it from rotating by means of either mechanical lock or small hydraulic caliper.
The power which enters the assembly cannot rotate the diff cage, so the spider gears transmit the power to the other output shaft - in reverse direction.

Bingo - reverse gear.

Discuss ?

(An oil can, and pillow blocks a la chain diff would of course be required, but that's relaitvely simple. )

Doesn't seem like terribly difficult engineering.

[Edited on 26/7/08 by zilspeed]

EDITED TO ADD THAT THE ABOVE WILL NOT WORK WITHOUT A LOCKING DIFF FOR FORWARD MOTION. HOW I COULDN'T SEE THAT, HEAVEN ONLY KNOWS.
THREAD STILL WORTH READING THOUGH

[Edited on 27/7/08 by zilspeed]

[Edited on 27/7/08 by zilspeed]

[Edited on 27/7/08 by zilspeed]

good idea but i think you will have to lock the planet gears to go forward and unlock/lock the casing to go in reverse?only one way to find out

Remember what happens when you have one wheel spining in the mud?

When you let the clutch out the cage would just spin (very fast) and you'd not move. You'd have to be able to lock the planet wheels in order to move forward.

adrian

Locking and unlocking the casing is a doddle.

Machine it down to resemble a brake disc and use a caliper.

Job done.

But I completely take your point on the forward motion bit. It will 100% work in reverse, that's not in doubt. But, I guess forward motion is sort of important as well.

Regarding the reverse function, I already have a very very elegant solution worked out involving nothing more than a hydraulic line lock and the car's existing brake pedal.

No mechanical linkages whatsoever.

quote:

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Originally posted by adithorp
Remember what happens when you have one wheel spining in the mud?

When you let the clutch out the cage would just spin (very fast) and you'd not move. You'd have to be able to lock the planet wheels in order to move forward.

adrian

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"One difference though. In your example, you are applying power to the ring gear via the pinion gear"

It's no diffrent if you applaying power to ring gear or drive shaft.

quote:

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Originally posted by Gerhard
"One difference though. In your example, you are applying power to the ring gear via the pinion gear"

It's no diffrent if you applaying power to ring gear or drive shaft.

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"I can see that I'm going to have to demonstrate this. :-) "

Just keep your fingers clear of the cage. I predict it will spin at twice the shaft speed (once there's load on the other shaft).

adrian

And I predict that everyting will rotate at exactly the same speed and in the same direction.
When I lock the cage, the output shaft will rotate in the opposite direction to the input shaft, at the same speed.

(It's a good job I'm not a betting man )

consider what happens if you have your car in gear, jack one wheel off the ground and leave the other on the deck, you can turn the wheel. it won't work

I thought about this and have the perfect donor, just lost interest really.

Range rover transfer box diff, nice tidy package already, especially if you can find an old 4 speed box as these are smaller.

Already has an option for locking the diff, for reverse you just clamp the outer with diff lock out.

As they come in a machined tail unit on the transfer box in so you already have a housing, just need to machine an end plate with bearing to replace the lump that the transfer gearbox sits in.

Here's a pic of the diff, about 3" across if mt memory serves me well.



regards Mark
Rescued attachment 220199297253_1.jpeg

an lsd might do it, right enough...

but an lsd doesn't have planet gears does it? so would that just burn the clutches out if you try to lock the diff case?

quote:

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Originally posted by mark chandler
I thought about this and have the perfect donor, just lost interest really.

Range rover transfer box diff, nice tidy package already, especially if you can find an old 4 speed box as these are smaller.

Already has an option for locking the diff, for reverse you just clamp the outer with diff lock out.

As they come in a machined tail unit on the transfer box in so you already have a housing, just need to machine an end plate with bearing to replace the lump that the transfer gearbox sits in.

Here's a pic of the diff, about 3" across if mt memory serves me well.



regards Mark

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quote:

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Originally posted by blakep82
consider what happens if you have your car in gear, jack one wheel off the ground and leave the other on the deck, you can turn the wheel. it won't work

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quote:

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Originally posted by daviep

quote:

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Originally posted by blakep82
consider what happens if you have your car in gear, jack one wheel off the ground and leave the other on the deck, you can turn the wheel. it won't work

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No you can't!!!!

However I still don't think it will work either, the cage will spin, you need to be able to lock the gears to the cage.

Just my tuppence worth
Davie

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Classic range rovers up to about 93 with an lt230 transfer box have open diffs with diff locks, later ones have viscous diffs.

The picture is of an open diff, they are made from a machined lump or metal which all bolts together, just because you cannot see the gears does not mean they are not there !
If you machined a couple of oil seals each end then it would be a self contained unit.

The output shafts slip in either side with spline that locates in the planet gears within. The diff lock simply locks one of the output shafts to the housing with dog teeth.
Rescued attachment Gbox_diff_in_bits.jpeg

Nearly bolted up
Rescued attachment Gbox_diff_part_assem.jpeg

where it all lives! left hand housing, the gears live in the bit to the right.

The 3 bolt plate is the diff lock level, the open hole goes across to the transfer box proper to operate the hig/low gears. but these all unbolt so can be discarded.

You can tell the size of the diff by the size of the prop flange, this is the same size as a sierra diff flange, PCD on bolts may even be the same.

Regards Mark



[Edited on 26/7/08 by mark chandler]
Rescued attachment gbox_diff_housing.jpeg

quote:

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Originally posted by daviep

quote:

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Originally posted by blakep82
consider what happens if you have your car in gear, jack one wheel off the ground and leave the other on the deck, you can turn the wheel. it won't work

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No you can't!!!!

Davie

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Mark Chandler is right.
I'm loving the range rover locking diff idea & have a suggestion to take it further..... get this:
1)diff unlocked, cage loose = no drive
2)diff unlocked cage clamped = reverse
3) diff locked cage loose = normal forward drive
4) diff locked cage clamped = parking brake!!!
Yes it's a combined reverse and handbrake, allowing the use of lightweight hydraulic- only calipers on the rear wheels!

quote:

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Originally posted by Bob C
Mark Chandler is right.
I'm loving the range rover locking diff idea & have a suggestion to take it further..... get this:
1)diff unlocked, cage loose = no drive
2)diff unlocked cage clamped = reverse
3) diff locked cage loose = normal forward drive
4) diff locked cage clamped = parking brake!!!
Yes it's a combined reverse and handbrake, allowing the use of lightweight hydraulic- only calipers on the rear wheels!

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Zil your idea will work, was something i was mulling over ages ago.

[Edited on 27/7/08 by blue2cv]

quote:

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Originally posted by blue2cv
Zil your idea will work, was something i was mulling over ages ago.

[Edited on 27/7/08 by blue2cv]

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Watching with interest...lots of it!

Been researching choices of diff.

First choice was going to be something which originally was used in RWD config, which meant Sierra probably.

But there's no real supply of those left.

For the point of view of suitable output flanges, It seems that anything with bolt on cv joints in a FWD transaxle might be suitable. Remember, we're chucking away everything except the bare diff and output shafts.

So, first observations of suitable donor boxes.

VW Golf MK2 / MK3.

Anything else ?

Trying to come up with easily available choices here.

OK, I'm going to say this one final time. IT WON'T WORK! It will with a diff lock (not lsd).

Theres a simple (if dodgy) way to try it. Jack up one rear wheel with a trolly jack on a flat, hard floor, so that the car and jack is free to roll forward on 3 wheels and the jack (the dodgy bit). Now leave the car in neutral so the diff cage is free to rotate. Now turn the lifted wheel (your input shaft) and see if the diff drives the other wheel forward (your output shaft).

Guess what... IT DOESN'T WORK! The prop shaft spins (driven by the spining cage) and thats where the power goes; Into the spining cage...and without the input flange and gears it'll have less weight to drive.

adrian

'fraid Adrian's right zil, dunno how to explain further - there are 3 things, cage & 2 output shafts all geared together & if you let go of any one there is no torque on any other. The power doesn't go anywhere, there is no power because there is no torque

It will work, the range rover diff does this already.

So jack up one side of a range rover, diff lock out car in gear engine off, the external part of th Xfer diff is now locked solid as the gears from the engine are meshed, turn a front wheel forward and the rear will spin backwards (planet gears in Xfer diff reverse the rotation).

Now take the car out of gear and engage diff lock, essentially jamming the xfer diff planet gears, now when you turn the front wheel forwards the rear also goes forward the whole xfer diff is spinning.

Stick the car in gear and its all wedged against the engine.

Regards Mark

I did say it would work with a diff lock and I like the idea of a transmission lock thrown in as Bob surgested.

But it won't work with an open diff as Zil is proposing.

adrian

And you're absolutely right Adi - I do have my head around it now.

I'm definitely glad we have had the discussion.

So, as Mark says, use an already available locking diff.

Or, devise a method for locking an existing diff for direct drive.

Thanks for all input so far lads, it has helped me to understand things more clearly.

This is something I also once considered and came to the conclusion it wouldnt work when I had the car jacked up and turned the wheel in gear and in neutral .
The 4x4 diff sounds feasible but I think the problem would be lubrication as this was the main fault with early reverse boxes as they contained so little oil it soon overheated.
I had considered trying to dismantle an auto box and see if it is possible to use some of the sun and planet gears from it.
Paul.

I think I may have it sussed.

The diff needs to be a locker to provide forward drive.

Ideally it will be already in a housing which can be modified to suit.

It should be robust to prevent overheating.


The diff we need is from the 2nd generation of the Audi Quattro system.
That;s the manually lockable diff from everything up to the mid 90s.

Currently searching ebay Germany.

I believe that this diff will give us forward drive and reverse drive.

Keep watching

What Marck Chandler said about a fornight ago, further up the thread.

He's dead right, no question about it.

Ignore anything else I may have said about Audi diffs etc. Way too big and cumbersome. Don't ask me how I know....

Anyway, Landy centre diff is already meant to live in the tranny tunnel and can handle the torque of a V8 crawling over rocks or pulling a horsebox. Has diff lock for forward drive. Can easily have the cage locked for reverse.

As before, you may or may not choose to keep watching.