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Old 13-01-2011   #1
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4x4 Gearbox internals.

Hi

I am considering changing the internals of my Sisley box for those from a Cinq/Sei, (or 2wd Panda) for 2 reasons:-
1 - its easier to get hold of low milage box
2 - ratios are more practical for road use

I have examined the main & lay shafts and the change rods/forks and they look compatable - the bearings certianly are.

Has anyone tried this in the past and has any words of wisdom?
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Old 17-01-2011   #2
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Re: 4x4 Gearbox internals.

Hi, I can only offer words of support and no wisdom. I didn't know you could do this but would be really interested to find out how you get on. Think it's a great idea. Good luck with it!

David
Quote Originally Posted by C.McMorran View Post
Hi

I am considering changing the internals of my Sisley box for those from a Cinq/Sei, (or 2wd Panda) for 2 reasons:-
1 - its easier to get hold of low milage box
2 - ratios are more practical for road use

I have examined the main & lay shafts and the change rods/forks and they look compatable - the bearings certianly are.

Has anyone tried this in the past and has any words of wisdom?
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Old 17-01-2011   #3
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Re: 4x4 Gearbox internals.

Very interesting idea, the 4x4 would definately benfit from some taller gearing. Two things that I can think of are would you keep the extra low first gear for off road use and also would having longer ratio gears cause any problem with the rear diff?
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Old 17-01-2011   #4
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Re: 4x4 Gearbox internals.

Would have thought the best that could be achieved here would be to simply use the 2WD ratios to end up with a normal 1st and tall 5th. There isn't a huge variation in suitable gear ratios for the box and you can't change the differential because of the rear differential ratio being non-adjustable.
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Old 18-01-2011   #5
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Re: 4x4 Gearbox internals.

I looked into this a couple of years back, and it'll be extremely hard to do. The trouble is not the ratios in the gearbox itself (before the final drive); the 5th gear ratio is something like 0.837:1 for a 2wd and 0.780:1 for 4wd cars (so before the final drive the 4x4s actually have a higher top gear!).

The final drive is why the 4x4s are very short on the road, it's 5.46:1 on 4x4s and 3.78:1 on 2wds, the 2wd pandas have much longer gearing as a result. It'd seem simple to swap final drives and put 3.78:1 on a 4x4, but the drive to the rear propshaft comes from the final drive crownwheel, and the gearing is matched to the 5.46:1 ratio (as well as complicated things like the gear tooth profiles, pitch circles etc. being fixed for that particular setup).

So in short, unless you fit a 2wd gearbox to a 4x4 and ditch having the 4x4 completely, its stuck as it is.... Of course there's always the option of getting a one-off full final drive gearset and rear propshaft pinion machined up, but it would cost 1000s!

You could try slightly wider tyres which will increase the overall tyre diameter; going from the standard 145/80 R13 to 155/80 R13 gives around 2.8% higher gearing and fit OK without fouling bodywork, fuel pipes etc...
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Old 18-01-2011   #6
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Re: 4x4 Gearbox internals.

Didn't realise the FD was so low! As you say, it pretty much rules out any modification for higher gearing.
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Old 18-01-2011   #7
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Re: 4x4 Gearbox internals.

If one rev of diff = 1 rev of front wheels, then surely the rear wheels should go round 1 rev as well? So if I changed the crown wheel (& associated main shaft) the rotatation rate would change but the relationship between front & rear wheels would not............or am I crazy?
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Old 19-01-2011   #8
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Re: 4x4 Gearbox internals.

5.5 revs of the diff = one turn of wheels is what we're saying. The rear prop is moving at layshaft speed via the transfer box. You will need to have a new crownwheel and pinion (whole layshaft as it's integrated) made for the main box and the same for the rear differential to match. This would be 1000s.
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Old 01-08-2012   #9
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Re: 4x4 Gearbox internals.

Quick update on this, its been a while.... Have finally taken a 4x4 gearbox to bits; the old blue panda Haynes manual is useful for this, as well as some pics on flickr by uk_senator.
Looks like I might have told a bit of a porky having now seen the crownwheel/diff and 4wd takeoff, the crownwheel can be removed separately and it might be possible to change the final drive without affecting the 4x4 side of things. I've got a 2wd gearbox which I might nick the final drive from and try changing the whole thing. I'll try and do a better write up when I've tried this out and have some time, it will involve splitting the mainshaft gearset as the final drive pinion is on the mainshaft itself and will need changing (I need to replace the 3rd gear synchro ring anyway).

So things to do are:
1. Strip 2wd gearbox, check bits will fit the 4x4 box, remove mainshaft (for pinion) and crownwheel.

2. Fit 2wd crownwheel and rebuild 4x4 gearset to 2wd mainshaft (inc. new synchro rings).

3. Replace all 4 gearbox bearings and maybe both final drive bearings (looks like about 200 for the lot, can supply part no.s when I know for sure!).

4. Stick it all back together. I might change the 4x4 5th gear (0.78:1) for the lower 2wd 5th gear (0.837:1) as the final drive change is a big jump and it might not pull the taller top gear (can be done later with box still in car).

5. Put in car and hope it all works.............optimistic eh?! Have attached a couple of pics of it all in bits so you can laugh at me!

cheers,
Mike
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Old 04-08-2012   #10
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Re: 4x4 Gearbox internals.

Tis I, uk_senator (lifting moustache)

All I`m gonna say is, make sure you put the 3rd gear selector ring in the right way up, I`ve been deficient of 3rd gear since I rebuilt it last summer because I made that fateful (& very embarrassing) mistake!

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Old 04-08-2012   #11
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Re: 4x4 Gearbox internals.

I'm still pretty impressed with a level of knowledge of members inhere. Looks like some of you guys could easly improve design side of pandas if only time machine were available.
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Old 04-08-2012   #12
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Re: 4x4 Gearbox internals.

I was thinking of going down this route with Barbara's 4x4 as it would be used 99% of the time on normal roads where the 2wd final drive ratio would be a big plus, 4wd would probably only be used if we had snow.

Because the 4x4 doesn't have a central diff 4wd can only be used on surfaces that are slippery enough to let each wheel turn at its own speed. If you change the final drive ratio for the front wheels but keep the rear diff the same won't it make a slippery surface even more essential? If you select 4wd and the surface is not allowing the wheels to slip the transmission will lock up.

Correct me if I'm wrong, but this is my understanding of it.
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Old 05-08-2012   #13
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Re: 4x4 Gearbox internals.

Quote Originally Posted by VmanC View Post
Because the 4x4 doesn't have a central diff 4wd can only be used on surfaces that are slippery enough to let each wheel turn at its own speed. If you change the final drive ratio for the front wheels but keep the rear diff the same won't it make a slippery surface even more essential? If you select 4wd and the surface is not allowing the wheels to slip the transmission will lock up.

Correct me if I'm wrong, but this is my understanding of it.
This is what I was saying in post #8. You will need to change the rear diff ratio to match perfectly or you will break the gearbox (at least) in 4WD. It isn't worth doing at all without the rear diff modification. Even off-road and on "slippy" ground the chances of wind-up seem very high to me.
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Old 05-08-2012   #14
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Re: 4x4 Gearbox internals.

Could possibly have a viscous clutch system to buffer it for short term use, but it`d probably overheat it on the road if left on.
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Old 05-08-2012   #15
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Re: 4x4 Gearbox internals.

Quote Originally Posted by lewey View Post
This is what I was saying in post #8. You will need to change the rear diff ratio to match perfectly or you will break the gearbox (at least) in 4WD. It isn't worth doing at all without the rear diff modification. Even off-road and on "slippy" ground the chances of wind-up seem very high to me.
Nope, the 4x4 take off is after the final drive, so the rear wheels will always go the same speed as the fronts regardless of the final drive ratio(I didn't realise this at first). The spiral bevel gear that takes drive to the propshaft hasn't been changed. Anyway the 3.78 final drive is now fitted to the 4x4 diff ok having drilled the holes at work, it's hardened steel so needed a carbide drill bit. Just need to get the rest back in now, a couple of new bearings and shove it in the car sometime.
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