Ford Diff Identification

[Guest 2b cruising]

There are many varied diffs out these days, and they all work in different ways.

i have just been informed by a well learned colleague that Sierra diffs all lock out even without resistance felt on the opposite wheel.

If true, this means the opposite wheel will turn in the same direction.

I will remove my backplate tomorrow or Monday to identify the type and report further.

 

[brumster]

Sure, and just to qualify - it depends what you're turning. If you're turning the prop, yes, the wheels should both turn the same direction but this doesn't really tell you whether it's a slipper or not. Putting it in gear then turning one of the wheels, the wheel on the opposite side will turn in the opposite direction if it's an open diff (as has been said) - just clarifying as your colleague saying "all Sierra diffs lock out" is not right, of course.... I assume he/you meant all Sierra locking diffs lock out, even if they're viscous... which is cool, as I didn't know myself, so I can't confirm or deny one way or t'other!

 

edit: just had a thought. It's my understanding from other reports that much of the old Ford viscous diffs are pretty tired now, and knackered, and the viscous fluid within them has generally seen better days and is no longer at it's best. There is apparently Ford test figures (from my internet searching) :

 

"Does your existing differential still meet the OEM spec limit of 70Nm+-30 for 1/2 turn in 1 second?"

 

So torque wrench on the wheel hub nut, one side of the car on the ground, and crank the wheel round and you should be getting at least 40Nm of resistance. If so, your viscous coupling is in-spec.

Edited April 26, 2015 by brumster

[Guest 2b cruising]

Won't be able to carry this test out as my diff not fitted and nowhere to hold it and two of the flanges.

However, I will take the back plate off shortly and take a look what type it is.

[Snapperpaul]

Viscous diffs

The viscous differential also has interleaved plates, and in fact works because of the viscosity (internal friction) of the silicone fluid that fills the gaps between the plates. The plates therefore do not actually touch one another. The percentage of torque transfer varies with the difference in speed between the two wheels, partly as a result of the plate design and spacing, and partly because of a physical property of silicone fluid that it experiences virtually no change in viscosity when heated. If one wheel is rotating only a little faster than the other, only a little torque transfer occurs, when there is a big difference between the speeds of the two wheels, the viscous differential will transfer up to 95 percent of the torque to the wheel with traction. Because of the difficulties in handling the silicone fluid, servicing a viscous differential can be accomplished only with special equipment. The silicone fluid is under pressure, and there is an air bubble of known (and controlled) volume included in the differential casing. Any deviation from the correct amount of pressure or air bubble volume can radically change the characteristics of the differential.

[Snapperpaul]

Sierra Viscous diff is the one on the left

Notice the raised centre

Open on the right

 

[tractor]

paul I have a 3.91 lsd can I take the guts out and put it in my 3.62 cos I want to change the 3.62 to a lsd is the lsd part interchangeable

[Guest 2b cruising]

Sierra Viscous diff is the one on the left

Notice the raised centre

Open on the right

 

Hi Paul.

Have you got a picture of these from a lower angle.

Regards Ken.

[Snapperpaul]

Yes you can strip out the crown wheel and pinion ( they are a matched pair)

But I question why you would go to that much trouble, perhaps it's worth it for a 3.38 or 3.14 but 3.6 LSD's are the most common and you will get at least what you paid for it by selling your 3.9LSD

That's the only photo I have, the difference is the raised centre section and the radial ribs which on an LSD go to the edge but don't on the open diff

[tractor]

the 3.62 lsd is rare and expensive a lot more money than I paid for the 3.91

[Snapperpaul]

The LSD bit is on the top face you can see, there is no difference to the planet gear arrangment

[tractor]

cheers paul another little job when I have five minutes

[Snapperpaul]

Tractor, the only Sierra fitted with a 3.9LSD was the 2.0L DOHC 4x4 all the V6 4x4's many 2WD V6 and the Sierra Saphire Cosworths had the 3.6 7" LSD so in my experience I found it difficult to find the 3.9LSD so much so that I ended up with a push fit 3.9 Quaife

We have half a dozen 3.6 LSD's in the barn, 1 converted 3.38LSD and if I could have found a 3.9LSD I would have had that away

There may be a geographical bias the there location who knows

 

[Guest janis]

I measure ratio tomorrow..what ratio woud suit better for kit car..as higher ratio faster it goes and better mpg..lower ratio give u more speed up..is thats right?

Its doing bothing at the moment so i coud open ot up..check and put new oil in..what oil shoud i use?how u see level?is there some screw u take out and fill till oil coming out?

[brumster]

I measure ratio tomorrow..what ratio woud suit better for kit car..as higher ratio faster it goes and better mpg..lower ratio give u more speed up..is thats right?

 

Have a fiddle with this : http://www.tremec.com/calculadora.php

 

Pop your wheel and tyre size in first, to get the wheel height.

The key difference for many of our style of cars is the engine rpm. What does your lump run out to? An old Pinto doesn't have the revs of a modern-day 16 valve lump (well, generally speaking), so people tend to prefer a taller diff in a less revvy engine to make it more comfortable on the motorway - but at the expense of a bit of acceleration.

For your gear ratios, assuming a standard 5-speed box, put in :-

1st = 3.65

2nd = 1.97

3rd = 1.37

4th = 1

5th = 0.82

 

The number you can play with is the "axle ratio". Stick 3.62 or 3.9 in there and see the differences.

 

My personal preference, would be to have the engine max RPM's in top gear equating to around 120 to 130mph, and there's no standard gearbox/diff setup that would deliver that! I've got a BGH gearset that tightens things up a bit with a shorter fifth, but even then it's technically geared for 147mph at redline :-S

 

It all depends on whether you want to be doing 2000rpm on the motorway, or 4000, really. Personally, with these cars I don't have one for economy or low NVH, so I'd rather the latter - it seems more in spirit with the car - but each to their own. That's the beauty of kit cars - make it your way

Edited April 28, 2015 by brumster

[Guest Ian & Carole]

Good point well made Dan.

 

Each to their own,.

 

I prefare the long legged cruising that the 3.6 gives me.

 

But our car was built with long distance cruising and not for track or high speed laneing.(new word)