V8s diff. How to test?

[Top Gear TVR]

I understand the v8 has a differential in the differential dept. It's a hydrodoodar and not a plate diff.

How does one test such a thing?

[Alan Whitaker]

Is the hydrodoodar left or right rotation

[GreenV8S]

If it behaves pretty much like an open diff and seems pretty *cking useless as an LSD, that's how it came out of the factory.

Where a completely open diff would be a little unpredictable accelerating out of a tight corner and might spin the inner wheel only, or both wheels together, depending on surface, bumps etc, the hydro-cking-useless diff will spin up the inside wheel (tossing all your traction away in the process) and then transfer the excess power to the outer wheel. It's predictable, but predictably useless.

The person who specced this for a powerful rwd sports car is IMO a complete idiot, and that's putting it politely.

Going to a conventional friction plate diff makes this car *much* better to drive.

[Top Gear TVR]

And a better answer is what?

[DamianS3]

I think mr V8s is being a bit harsh here sounds like he is describing an open diff with spinning inner wheels mine does none of that and locks so both wheels spin if anything.

I have driven 2 different viscous diffs including my current one and they are a good improvement over standard imho.

I have also owned a quaiffe ATB which was better at maintaining traction yes but probably not as much fun. The quaiffe is £1200 a viscous circa £300 plate maybe a little more at £500 new.

I've not had a plate diff on the S but hear they can feel harsh and wear out eventually unlike ATB or viscous.

If you have an open diff any LSD will be a major upgrade after that it's just more money for diminishing returns.

Bara motorsport can upgrade / reduikd your open or viscous diff if needed.

Just my thoughts

Damian S3

[GreenV8S]

Top Gear TVR said:

And a better answer is what?

The friction plate diff commonly used in Fords fitted with this diff. The hydro-cking-useless diff was only used in a few applications and is harder to find.

[jesfirth]

Green v8S is spot on. I had a hyrdatrac in my cerb (amazingly is was an extra cost option) It was utterly crap so I got rid of it and put a BTR plate diff in which worked properly... much much better grip and predictable because you know what its going to do.

[GreenV8S]

DamianS3 said:

sounds like he is describing an open diff with spinning inner wheels

That's how it drives. I was convinced my hydro-cking-useless clutch pack was worn out and had it replaced the first time I had my diff rebuilt, and the brand new one was identically useless. The behaviour is consistent in all hydro-cking-useless equipped the cars I've driven and seen driven. The clutch pack contains some flexible plates that are shaped to produce a side force when the diff slips - the more torque it needs to transfer, the more absolute speed differential (slip) it needs to transfer it. At high road speeds there is relatively little torque to transfer and the differential speed is small compared to the road speed. It works OK under these conditions, but note that these are the conditions where you need the LSD the least.

At low speeds and lower gears where you need the torque transfer the most, it doesn't transfer torque until you get to a higher differential speed and that differential speed is a much higher percentage of the road speed. In other words when you boot it out of tight corners it just sits there smoking the inside wheel and wasting the potential traction.

[Top Gear TVR]

I've got a Ford plate LSD on my S2, it's great.

The V8S hydro less do. Time to hunt a plate diff I think

[DamianS3]

Top Gear TVR said:

I've got a Ford plate LSD on my S2, it's great.

The V8S hydro less do. Time to hunt a plate diff I think

What car is your plate diff from?

Thanks

Damian

[Top Gear TVR]

Sierra

[DamianS3]

Top Gear TVR said:

Sierra

Odd without going aftermarket i.e. TranX or something I was under the impression all the sierra LSD s were viscous in design. Even the mighty cosworth. So I guess you have either upgraded or you kind off made my point that the viscous really isn't that bad after all (if in good condition).

[zombeh]

Top Gear TVR said:

How does one test such a thing?

You jam one side solid and stick a torque wrench on the other and measure how much force it takes to rotate it.

it should take 70NM +/- 30 to turn it at a rate of half a turn in a second.

[Top Gear TVR]

So is V8 different to V6?

[DamianS3]

I dunno I'm very confused now.. maybe the V8s torque is too much? Maybe the fluid is goosed ? I did note on my rebuild sheet that mine is an updated viscous type. This is mentioned a bit on the ford sites too. That said I thought the 2nd Granada cosworth one i started with was good to, but admittedly not as good as the quaiffe or probably a plate type. Cheaper though

[zombeh]

Mine I think is pretty well buggered, when I snapped a shaft the car just stopped. If it doesn't lock up in the most extreme sort of slip possible then it's not doing a lot in normal conditions.

At some point it'll get replaced with a quaife but that's £900 I'd rather spend on other things at the moment.

[magpies]

I rallied a Sapphire Cosworth 4x4 15 years ago and had the rear viscous LSD 'uprated' by Mike Taylor Developments (who built semi-works cars at the time) and that rebuild cost £500. Worked a treat

photo of me on my way to 9th o/a out of 90 at Manby

Edited by magpies on Sunday 10th September 23:39

[Kitchski]

Not completely sure what you mean by 'test', but if both rear wheels are off the ground, both sides of the axle will spin the same direction with the input on one side. On the open diff, they counter-rotate.

As far as testing how much it loads up....not sure. Find an empty quiet road, 5000rpm, sidestep the clutch and see if you leave a number 1 or a number 11!

[magpies]

Kitchski said:

Not completely sure what you mean by 'test', but if both rear wheels are off the ground, both sides of the axle will spin the same direction with the input on one side. On the open diff, they counter-rotate.

As far as testing how much it loads up....not sure. Find an empty quiet road, 5000rpm, sidestep the clutch and see if you leave a number 1 or a number 11!

Not sure about the first part but definitely leaves 11 or better still try a U turn and that should swing the backend around with both wheels spinning

I'm sure (was a while ago and I am old) that when checking the diff before fitting that (needing 2 people) when turning one output shaft the oter turns in the opposite direction and the input shaft turns even with an LSD. With the LSD the difference is when holding one output and the input still, the other output shaft is impossible to turn

[Top Gear TVR]

I can get 11's but on a bend it's not as effective as my 2.9 which is positively predictable