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Sierra diff upside down
genevive51 - 6/7/10 at 11:54 PM

I am mounting a Kwak ZX9R engine at the back of my car with the differential in front of it. In its standard form I will have six reverse gears, so I need to turn the diff upside down. Can anyone see any problem in doing this apart from the fact that I won't be able to check the oil level, without first taking the diff out. Another question, I will end up with a propshaft about 300mm long, I am concerned that no matter how well the diff is mounted it will be putting some sideways pressure on the bike output shaft. Should I put a donut into the drive to cushion this to a degree? This would mean that I would then also only need one UJ in the drive. Any thoughts would be appreciated, thanks Nigel

blakep82 - 7/7/10 at 12:06 AM

the oil breather would be an issue too, but could be modded easy enough i'd say

Dan. - 7/7/10 at 12:12 AM

I am pretty sure this will effect the longevity of the diff as they are designed to run one particular way for most their life.

Simon - 7/7/10 at 12:21 AM

The alternative might be to use the front diff from a 4x4 Sierra as this might go the right way round, and give you the right number of forward gears

Sure someone in the know will confirm or otherwise!

ATB

Simon

Alan B - 7/7/10 at 12:41 AM

quote:
Originally posted by Dan.
I am pretty sure this will effect the longevity of the diff as they are designed to run one particular way for most their life.


So long as lubrication and breathing is addressed it will be fine...providing that it is running the same direction it was intended to run....they are built to handle the majority of the thrust load in a given direction and running them the opposite is not good for them long term ...

turbodisplay - 7/7/10 at 06:56 AM

Some honda engines rotate the wrong way, so the diff might as well in a rwd setup?

Darren

tony-devon - 7/7/10 at 07:40 AM

sierra diffs are quite happy running upside down, I have done this many times and there are many many bike trikes running them this way

for any shaft drive bike engine with the shaft on the left, we have to flip the axle/diff

I drill and tap the breather then fit a bolt with some sealant and a copper washer

then just drill and tap a new breather on the "new" top

if you are that worried about oil level then 2 right angled fittings in the cover and some clear tube will provide an external level indication and set your mind at rest

mangogrooveworkshop - 7/7/10 at 09:31 AM

MK have done that many times with some dutch sevens

Liam - 7/7/10 at 10:53 AM

quote:
Originally posted by Alan B

So long as lubrication and breathing is addressed it will be fine...providing that it is running the same direction it was intended to run....they are built to handle the majority of the thrust load in a given direction and running them the opposite is not good for them long term ...


If it's still in the back of a car, but has to be up-side-down, then obviously it's going backwards . But given the car's light weight, low torque, low intended mileage and the fact it has been done before, I'd say suck it and see. Sierra diffs are cheap enough to experiment on.

As suggested above, a sierra 4x4 front diff could be used. It'd still have to be up-side-down, but at least you'd be running it in its intended direction. A lot lighter too compared to a rear diff. It's not so easy to mount though, and you would have to modify the oil seal if you want to plug a driveshaft straight in the side that is usually attached to the sump (this is what Dax do on their 4WD Rush), or fit the intermediate shaft and bearing from the sump as well as the diff (see my photo archive for what that looks like).

Liam

Minicooper - 7/7/10 at 11:09 AM

quote:
Originally posted by Dan.
I am pretty sure this will effect the longevity of the diff as they are designed to run one particular way for most their life.


The diff is still running the correct way but as the engine is now behind the diff instead of in front like a normal lotus 7 type car the diff needs to be turned upside down to go forwards.

I borrowed a picture from imp pauls gallery

http://www.locostbuilders.co.uk/photos.php?action=showphoto&photo=CIMG0930%20(Custom)%20(Small).JPG

Cheers
David

JoelP - 7/7/10 at 11:39 AM

i cant imagine what the car is going to look like, with 30cms of prop and a zx9 engine behind the rear axle? Id sooner put it above the axle and chain drive it. Or even better, in the passenger seat with a normal prop setup.

Minicooper - 7/7/10 at 11:40 AM

quote:
Originally posted by genevive51
I am mounting a Kwak ZX9R engine at the back of my car with the differential in front of it. In its standard form I will have six reverse gears, so I need to turn the diff upside down. Can anyone see any problem in doing this apart from the fact that I won't be able to check the oil level, without first taking the diff out. Another question, I will end up with a propshaft about 300mm long, I am concerned that no matter how well the diff is mounted it will be putting some sideways pressure on the bike output shaft. Should I put a donut into the drive to cushion this to a degree? This would mean that I would then also only need one UJ in the drive. Any thoughts would be appreciated, thanks Nigel


There is no problem having a small prop of the sprocket adapter, when they are chain driven in the original bike they have massive side loadings. I would be surprised if you would have room to get a 300mm propshaft in, if you look at imp paul gallery you will see the engine is nearly touching the back panel with a what looks like a 75mm propshaft.

I think your main problem will be getting good sump clearance with good driveshaft angles and maybe the gearing if your using smallish wheels

Cheers
David

genevive51 - 7/7/10 at 12:30 PM

Thanks for the replies folks, some good ones there are too. Looking at that photo of Imp Pauls, the drive will be much shorter than I thought. I was forgetting just how long the diff is from the centreline of the wheels to the propshaft flange and I want to try and shoe horn in a starter motor for reverse in as well!!!
First job will be to get the old imp unit out and go from there. as you have said David ground clearance is a major concern for me. The car will be used on the road and I don't fancy ripping the bike sump off on a car park kerb somewhere. Thanks for the sight tube idea Tony, hadn't thought of that. Cheers Nigel

imp paul - 7/7/10 at 03:20 PM

hi i don't use that set-up now but it will work i have still got the frame out of my imp and the small prop shaft we made to fit zx to ford lsd upside down with modded diff it mounted from the gear box mounts and then in to left and right legs it should be a easy fit for you as your fitting a small engine hope you get it to fit all the best paul

genevive51 - 7/7/10 at 09:30 PM

Thanks Paul, I have been doing a bit of measuring tonight, I had thought I would have a propshaft about 300mm long - I wish!! What I think I will actually have is a coupling as short as I can make it between the bike engine and diff. I dunno how I'm going to sort out a reverse gear! I haven't worked that one out yet! What length was the connection shaft that you used Paul? Many thanks Nigel

genevive51 - 7/7/10 at 11:34 PM

Sorry Paul, I have found the answer to my question re the length of the prop on your car. This photos in your gallery show what I had come to realize this evening which is that I won't have a prop, just a coupling instead, many thanks and sorry for asking silly questions! Nigel

violentblue - 8/7/10 at 04:43 AM

quote:
Originally posted by genevive51
I am mounting a Kwak ZX9R engine at the back of my car with the differential in front of it.


if your engine is behind the axle. then flipping the axle over to get it moving in the right direction sould be fine. not the same issue as having an engine spinning the wrong way and compensating by flipping the diff.

diff should be spinning in the correct direction, so all is well once you have the breather and oil level sorted.