looking for a sierra style 7" ZF diff

[CNHSS1]

as above, im looking to try a 'plated'diff (not viscous) back to back with my quaife, to see which i prefer. anyone know of a plated diff for sale at reasonable money?
also was the ZF diff available OEM in a car? or just as an aftermarket item?

[stevieturbo]

All OEM had the crappy viscous diffs.

Not sure if yours is the same fitment. But a local guy bought an expensive LSD and never used it.

http://www.jon44w.co.uk/forum/viewthread.php?tid=1...

Edited by stevieturbo on Monday 21st January 18:31

[CNHSS1]

Cheers Stevie, have dropped him an email is he someone you know?
thanks again, CNH

[stevieturbo]

CNHSS1 said:

Cheers Stevie, have dropped him an email is he someone you know?
thanks again, CNH

I dont know him personally. I just seen his ad recently on that local forum.

[CNHSS1]

the guys never answered that ad, so anyone else? been quoted 850 quid by ATM sport which is a no-go, tran-x do them for circa £575ish new not fitted. anyone got one s/hand? cheers CNH

Edited by CNHSS1 on Friday 1st February 16:20

[GavinPearson]

You probably ought to consider a Gripper plate diff.

Personally having tested everything I'd say I'd rate diffs from best to worst as follows:
Active plate
BTR hydratrak
Viscous
Plate with unlock on overrun (Salisbury, Gripper)
Pump action plate opening on overrun
Pump action plate
Torsen
Quaife
Plate with Belleville washers
Open

But this is assuning it can be tuned for the application, not "you get what you get".

[CNHSS1]

thanks for the reply, but has intrigued me somewhat (Ok more confused, but it makes me sound brighter lol).Few Qs for you if you dont mind...
by active plate i assume you mean electronically controled plated diff?
i notice a viscous comes pretty high up your list, why so? it seems to me that as they have little adjustment in their action, (save for recharging the fluid cartridge with differing grade fluid) and having the same characteristics both on and off (trailing throttle) and can have a fair amount of static preload/drag/stiction call it what you will, they arent as 'clever' as others tyles.
as for Gripper, yes i am considering both Gripper and Tran-x plated. i do like the idea of what the japanese call 1 way (locking on throttle only) or 1.5 way (partial locking under braking/throttle off)
whats the principle of the BTR hydratrack (used in some TVRs i believe).
what vehicles have you used them in? my application is circa 750kg RWD car for sprints/hillclimbs.
any help/insight much appreciated.

Edited by CNHSS1 on Wednesday 6th February 15:52

[stevieturbo]

GavinPearson said:

You probably ought to consider a Gripper plate diff.

Personally having tested everything I'd say I'd rate diffs from best to worst as follows:
Active plate
BTR hydratrak
Viscous
Plate with unlock on overrun (Salisbury, Gripper)
Pump action plate opening on overrun
Pump action plate
Torsen
Quaife
Plate with Belleville washers
Open

But this is assuning it can be tuned for the application, not "you get what you get".

You seem to rate viscous quite highly ??

Im sure most would say they are crap. Ive a Torsen in the rear of my car, and I think its great.

[GavinPearson]

CNHSS1 said:

thanks for the reply, but has intrigued me somewhat (Ok more confused, but it makes me sound brighter lol).Few Qs for you if you dont mind...
by active plate i assume you mean electronically controled plated diff?

Yes. A motor applies varying amounts of pre-load to the plates in a diff to provide any amount of rpm difference between the rear wheels up to full rear wheel torque.

CNHSS1 said:

i notice a viscous comes pretty high up your list, why so? it seems to me that as they have little adjustment in their action, (save for recharging the fluid cartridge with differing grade fluid) and having the same characteristics both on and off (trailing throttle) and can have a fair amount of static preload/drag/stiction call it what you will, they arent as 'clever' as others tyles.

Well firstly, when you are engineering a diff for OE use you can size the components and their action to the application. Secondly, the VC provides good torque transfer to the slower wheel so with one wheel on ice, the other on something grippier you can actually move the car. But it is torque dependent.

CNHSS1 said:

as for Gripper, yes i am considering both Gripper and Tran-x plated. i do like the idea of what the japanese call 1 way (locking on throttle only) or 1.5 way (partial locking under braking/throttle off)

You'll find that this principle is used in a lot of Salisbury diffs, all you need to do is change the ramp angles and you get the desired characteristics. Remember that a car needs to reverse, so 1 way is not necessarily that clever.

CNHSS1 said:

whats the principle of the BTR hydratrack (used in some TVRs i believe).

It basically is a fluid pump that locks up when speed differential is above a certain limit. So it is a speed limiter between the two sides of the diff, sized for the torque of the application.

CNHSS1 said:

what vehicles have you used them in? my application is circa 750kg RWD car for sprints/hillclimbs.
any help/insight much appreciated.

These were evaluated in a 1750 kg 370 bhp road car.

[CNHSS1]

thanks for the reply, helpful.
the 1 way refers to the diffs locking ability not its diff action ability. just means that the ramps only operate when the laod is accelerative, not on over-run or braking when it just operates as an open diff. not to be confused with one way overun hubs on some 4x4s.
cheers CNH

[GavinPearson]

CNHSS1 said:

thanks for the reply, helpful.
the 1 way refers to the diffs locking ability not its diff action ability. just means that the ramps only operate when the laod is accelerative, not on over-run or braking when it just operates as an open diff. not to be confused with one way overun hubs on some 4x4s.
cheers CNH

Yes I understand what you are saying but you need to understand that the ramps need to match the application.

What you are saying will match the demands of a racing car very well.

BUT it would be useless in a rally car.

If a rally car misses a turn and needs to reverse having a one way diff will make it go open and that's no good if the car has one wheel in something very slippery.

One thing I would strongly recommend is that you look at brazing the differential gears to the carrier and create a cheap spool diff. For your application it may actually be the most effective but you need to drive the car like a kart.

[CNHSS1]

yes, i see what you meant now. not a rally car but sprints/hillclimbs, so if i end up on the grass my run is spoilt anyway . as for a welded diff, thats too agricutural for me im afraid. time and effort spent on making the car grip is undone (at least to some extent) by the fact that the car has to be drifted around corners. also doesnt seem to work as well on lightweight cars (karts arent a car imho). i had a bit to do with some Legend cars a few years ago(albeit not in a mechanical capacity) and when the grip is good they tramp around the corners and makes them unnecessarily hard work to drive (again imho).

[sharkie]

In your application I would use the Quaffe in the Ford 7" unit. The Quaffe is forgiving when you get all crosseed up as its Torque transfer is progressive and the Ford final drive unit is about 25Kg if you up graded to the BTR unit which is much stronger then you are looking at 36kg and I don't see you need to lug this weight arounfd unless you are running massive power and torque.

[CNHSS1]

i do run a 7" quaife currently, just not convinced its the best for my application. agreed the quaife is a great all rounder, but looking for max performance in the dry with good grip (cars useless in low grip/wet due to high power/low weight and stiff setup). as you say, plenty of choice for diff types (ATB, plated, viscous) in the larger 7.5" which also benefit from better ratios (4.27+) but they are a heavy old beast. as for power not too high 280+bhp at the mo on slicks

[sharkie]

I think you have hit the nail on the head when you say about the stiff setup. I am a great beleiver in a soft spring settup is going to give you best traction. running the twin sping system works well with the soft spring nearly coil bound, as this system gives great grip and a stiff set-up in the corners

[GavinPearson]

CNHSS1 said:

i do run a 7" quaife currently, just not convinced its the best for my application. agreed the quaife is a great all rounder, but looking for max performance in the dry with good grip (cars useless in low grip/wet due to high power/low weight and stiff setup). as you say, plenty of choice for diff types (ATB, plated, viscous) in the larger 7.5" which also benefit from better ratios (4.27+) but they are a heavy old beast. as for power not too high 280+bhp at the mo on slicks

For the application I would go for a Gripper plate diff, stack the plates to get maximum locking and have it tight on drive, semi-loose on overrun.

I would still not discount the spool idea, get a secondhand diff, clean it out, weld the side and pinion gears and see how it goes.

It sounds like a crazy idea at first but it actually works very well, and I am speaking from the perspective of having actually done it.