Technical 4x4 Gearbox internals.

[C.McMorran]

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?

 

[aquamarine]

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

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?

 

[panda1408]

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?

 

[lewey]

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.

 

[totnesmonster]

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...

 

[lewey]

Didn't realise the FD was so low! As you say, it pretty much rules out any modification for higher gearing.

 

[C.McMorran]

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?

 

[lewey]

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.

 

[totnesmonster]

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

 

[a73uk]

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!

 

[kolza]

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.

 

[VmanC]

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.

 

[lewey]

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.

 

[a73uk]

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.

 

[totnesmonster]

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.

 

[VmanC]

Ah ok, this does change things and I am watching with even greater interest.

 

[lewey]

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.

I read your earlier post more carefully and realise that you had covered this actually. I get it now! Good luck.

 

[C.McMorran]

I started this thread a while ago but have been away a while. I have done the gear box mod using Cinq main shaft & crown wheel, going from 4x4 60/11 to Cing 57/14. I works. trouble was with my attempt is that for some unconnected reason the selection od 1st /2nd was nigh on impossible so I put my standard box back in. I can however verify that I have driven the 4x4 with Cinq rations and it does appears to work.
I've recently tacked down some new synchro rings so I'll rebuild another box this winter. Lets see what happens.

 

[totnesmonster]

Good to hear you've had at least some success with this! My gearbox is all back together now, all gears seem to select fine so fingers crossed....

With the 15/58 final drive and 0.837 5th gear i should be seeing about 19.8 mph/1000 rpm. Can't see that I will need it at the moment, and it would probably make the gearing too high but I also have 0.780 and 0.731 ratio 5th gears to make the gearing longer still if needed.

Out of interest where have you got the synchro rings from? Mine are a little worn, but OK for now, might be worth getting some in. As far as I can work out on eper, just the 3rd and 4th rings and corresponding collar look like they will total over £100!

 

[C.McMorran]

There is a little place near me that is one of those old fashioned 100 year old chipbord counter/dexion racking/greasy cardboard/curling vinyl on floor (& walls) kinda places that has probably got everything but no idea where abouts. I got a ns panda door skin for £25. he sold me a bum track rod end a couple of weeks ago & let me have the synchro rings "to try". If they are right I'll give him £20 each.
My road ratio box changed fine on the bench. All slotted in nicely, but when in the car.........nada. Ended up doing 3 gearbox "rotations" in 1 weekend. 4 hours is my gold medal!
When it comes to bearings I changed mine using skf quality bearings from the internet. 3 of them cost no more that £5 each. The only one that is a Fiat only part is the roller bearing on the inboard end of main shaft. I paid £38 from Fiat for this. Running them now & all fine. No one needs to pay oem prices for bearings. Just look at the numbering on the bearing & do a search. Im restoring and old AP50 Suzuki & got all the bearings for about a third of the Suzuki price.
Back to Panda box - could I use Cinq 5th gear cogs to bring the ration back down a bit?