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Newbie Q - Sierra LSD - How can identify
dpnomad - 11/5/05 at 11:34 PM

Hi,

I would appreciate some help....

Are all sierra 4x4 fitted with LSD even the 2 litre versions ?

How can I tell if a diff is actually a LSD

Many Thanks

jacobeon - 12/5/05 at 12:26 AM

Hello and welcome,
Cant help with the LSD, but Im in Stockingford, where are you ?

Noodle - 12/5/05 at 07:00 AM

quote:
Originally posted by dpnomad
Hi,

I would appreciate some help....

Are all sierra 4x4 fitted with LSD even the 2 litre versions ?

How can I tell if a diff is actually a LSD

Many Thanks


To test for LSD's, jack up the back of the car and rotate a wheel. If the opposite wheel rotates in the same direction, it's an LSD. An open diff will counter-rotate.

Whether or not the fronts need to be up too on a 4x4 is another matter.

Cheers,

Neil

JoelP - 12/5/05 at 07:22 AM

all 4x4s are LSD, unless some locostbuilder has already pinched it... since the centre diff is another viscous diff , not only the back wheels need to be in the air

[Edited on 15/5/05 by JoelP]

dpnomad - 12/5/05 at 10:29 PM

Thanks for the info !

NS Dev - 13/5/05 at 07:41 AM

another local!!!

I am in Barwell just up the road!

Do you folks come to the nuneaton pub meet (at the former Ansty Arms, now the Raven, I may have met you already if you do!)

wilkingj - 13/5/05 at 11:09 PM

I believe LSD has two "A"'s in the middle set of numbers.

Do a search on the forum, as there are some good links to the exact info.

4x4's have LSD.
Two sets of LSD, 7" and 7.5" measures across the back mounting bolt.
7.5"'s are usually granadas or possibly cossies.

search it out, its on the forum,

Liam - 14/5/05 at 10:43 PM

quote:
Originally posted by JoelP
since the centre diff is open,


Another viscous LSD actually And unless it's porked you might need a front wheel off the ground too for this test to work properly on a 4x4.

Liam

JoelP - 15/5/05 at 08:48 AM

shoulda gone to specsavers....

NS Dev - 15/5/05 at 09:07 AM

quote:
Originally posted by Liam
quote:
Originally posted by JoelP
since the centre diff is open,


Another viscous LSD actually And unless it's porked you might need a front wheel off the ground too for this test to work properly on a 4x4.

Liam


Liam, as I see you are a knowledgeable sort on Sierra LSD's, I have a feeling I have heard this before, but when the centre diff "becomes porked" does it lock up solid or almost solid???

Just wonder because at MOT time my XR4x4 showed a worrying characteristic, when the tester was fiddling with one of the back wheels, he asked if the brake was on, which it wasn't and then we realised that turning one back wheel was turning all the other wheels on the car! I know both rears will turn but I thought there was enough slip in the centre diff to allow the rears to turn on their own at very slow speed. I just don't remember all 4 wheels turning when I turned one rear before, but then again it's not very often that the car has all 4 wheels in the air! (unless it's when I'm driving it!!!!)

clbarclay - 15/5/05 at 12:50 PM

If the sierra 4x4 viscous diff is anthing like viscous centre diff from latter range rovers, then as I understand it the, diff is effectively a normal diff, but sealed with a viscouls fluid (a bit like water and corn flour) inside that thickens when sudden force is applied to it, like the diff gears turning. The quiker the gears turn the thicker the fluid becomes.

NS Dev - 16/5/05 at 12:04 PM

That's exactly right, and in fact the sierra centre diff/stepoff drive arrangement is borg warner chain very similar to the later Range rover system, BUT............mine seems to be seized to the point where turning one back wheel turns all other wheels on the car. Locking the fronts by dropping them onto the ground and then turning one rear just turns the other rear, but it is then almst impossible to move the rear wheels at all!! (two people job to turn it at all!) no dodgy noises or anything though!

tks - 16/5/05 at 08:34 PM

Didn't it worked like

an orange cut in half (and take the fruit out)

then put some fluid in them seal them togetther

and turn on then the fluid with more revs will push the other also..

???

like clutches is guess

TKS

Liam - 16/5/05 at 09:01 PM

quote:
Originally posted by clbarclay
If the sierra 4x4 viscous diff is anthing like viscous centre diff from latter range rovers, then as I understand it the, diff is effectively a normal diff, but sealed with a viscouls fluid (a bit like water and corn flour) inside that thickens when sudden force is applied to it, like the diff gears turning. The quiker the gears turn the thicker the fluid becomes.


Not quite like that but similar! The diffs are mechanical and live in normal oil. The viscous couplings are separate and consist of sets of plates (very much like a bike engine clutch) that rotate against each other when there is slip in the diff. The plates are not in contact but live in a silicon fluid that behaves very much like water and cornflower as you say. So with sudden slip the viscosity of the fluid ramps up and tries to lock the plates together.

Any wear of these plates, or catastrophic failure (eg lack of drive to one set of plates or leaking of the silicon fluid) would lead to a tendancy towards an open diff rather than siezing of the coupling. I suppose contamination of the fluid by outside crap may cause the coupling to tighten but in my experience, high mileage lsds are usually loose. I have a high mileage lsd from a 2.8 and it is quite easy to turn the diff flanges against each other, whereas it's very difficult in my nice low mileage lsd that has had only 50,000 miles behind a piddly 2 litre engine.

With all the wheels off the ground on a 4x4, a good centre diff should be tight enough that turning a rear wheel turns the fronts too.

I have the original ford workshop stuff for the 4x4 system. I could scan stuff if you want but here is roughly what it says...

To test the rear viscous coupling you jack up the rear wheels and leave the fronts on the floor. Then turn a rear wheel with a torque wrench 1/2 a turn in 1 second. Should take about 70nm +- 30.

The other rear wheel should rotate in the opposite direction and the prop shaft shouldn't move (this suggests the centre diff should be tight enough that the rear diff slips first - but it also says if the prop shaft does move try and lock it).

Checking the centre lsd is less technical cos I suppose theres not quite the direct access to it unless you remove bits. It just says put the rear wheels on rollers and jack up the fronts. In nuetral roll the rears up to 5km/h and the fronts should rotate too.

Sounds like you are needing huge torque to slip the rear diff but I cant be sure. When you have the front wheels on the ground and turn a rear, what direction is the other going in and is the propshaft moving? If you can lock the propshaft (if it is moving that is) you can test the rear diff in isolation.

Sounds like your rear is overly tight. If it's just the centre it shouldn't be a two man job to turn the rears - even if the centre is siezed solid it should only take the above 70nm to turn the rears against the rear coupling.

Hope that helps. Suppose i tight diff is better than an open one! I know a guy with an escort cossy rally car in tarmac setup. The diffs are so tight that when pushing the car, as soon as you steer it at all the tiny speed differences in the wheels lock up all the diffs and you can't move it! Needs to be towed!

Liam

[Edited on 16/5/05 by Liam]

zetec - 17/5/05 at 03:04 AM

Just checked my MK (LSD from a 4x4) and I'm in luck, turn the rear wheels and no movement from the fronts!

Liam - 17/5/05 at 12:15 PM

NS Dev - 17/5/05 at 12:32 PM

Cheers Liam!

That all makes sense. I think there is nothing wrong really then. Yes, when you finally persuade a rear wheel to move, it's opposite number on the back does go the other way with the fronts on the ground.

I think I am somehow subconsciously comparing the XR I have now to my old one which was on it's 3rd time round the clock and evidently the centre diff wasn't working very well!

As an aside, the XR I have now is actually a pretty good car. I love it as a car but it's just a practical workhorse these days, rather used and abused but it's a 1990 Flint Grey one, and all original except the ruddy noisy fecking exhaust (Ashley system, cheap, but you need earplugs, only got it as it was 1/2 the price of a Bosal std system!)

I keep looking at alternatives but I won't spend more than £1500 on a daily driving towcar (much better to spend the money on the 7 and the grasser!) and I just can't find anything better than the £600 XR at the mo.........................and it seems to be going up in value, the grey ones are pretty sought after, and it has just gone through it's 3rd MOT in my possession with 0 defects, same as the last 2 years!! The XR's are the only cars I have had that consistently do that!!

Cheers

Nat