Winter Jobs and LSD's

[PhilKent]

Hello all,
So, since my move in the late spring I have a lovely garage to do some of the jobs on the car over the winter months. On the cards is a brake service including full re-build of the calipers, plus the rear anti roll bar bushes.
While I'm in there! I've been thinking about having the gearbox and diff reconditioned for a while. 3rd has been a bit notchy for a good few years and I'm sure the backlash in the diff is getting worse. Does anyone have any recommendations for gearbox specialists? I'm in the South/ South East.
Should I get an LSD? I've been looking for a std lsd box for years, but never find any. Having a modified turbo I'm now putting quite a bit of power through the back wheels on a factory std non lsd box. Has anyone fitted the Quaife LSD available via D911?

Happy spannering!

 

[blade7]

Doesn't VEMS have traction control capability?

 

[scam75]

The Quaife is surely the way to go if funds permit. Any second hand LSD box will have a 30 odd year plate diff inside it, and as you say, they are hens teeth, usually about a grand for one you would most likely need to rebuild. After having scrabbled about for parts to rebuild my LSD box I would not recommend anybody to follow suit. Most of the internals in a non LSD box are then same (exceptions being hardened 1st and 2nd gears and shot peened shafts), externally you have an oil cooler which you won't have currently but the original oil cooler snapping is the main reason good, working 2nd hand LSD boxes are extremely rare. If, and a big if, you could secure a 2nd hand LSD box, have it rebuilt, put in a Quaife, and sort out a better oil cooler solution, then that would give you the best end result but I'd think you'd be near £3k to do that, assuming you found a box.

In your shoes I'd buy a Quaife and get it put in during your overhaul. New bearings and whatever else it needs. Be aware though many parts are NLA. Good luck.

Stuart

 

[blade7]

If I was lobbing £3k at a gearbox, I'd want it to have 6 gears.

 

[CarreraRSR]

You will not know the Quaife is installed on regular road driving. More traction available when you need it. I have one in my 924 turbo with 944 turbo bhp used on road and hillclimbs. Try DSD Motorworks for supply and fit.

 

[PhilKent]

So, I currently have a std early turbo gearbox which has the cooler. I've modified this to replace the std finned coil of pipe with a small matrix heat exchanger (radiator).
I can't utilise VEMS traction control if it has it (and I'm not sure of the top of my head if it does) as I don't have ABS.
The Quaife is about £1k and you can't even get std turbo lsd boxes for that anyway, so I like Stuarts idea, refurb my box as/if required and fit the quaife. I'll try and take a look at DSD Steve, thanks for the tip...
Stuart, did you recon your own box? If so how hard was it and do you have any tips and part numbers to help? I've got all winter and a warm garage to play in now!

 

[scam75]

Hi Phil. No I didn't. I used a local gearbox chap. I don't have part numbers, sorry. I ended up getting the box rebuilt using a combination of bits from my original box, a standard non LSD/non oil cooler box, and a box of AOR (code for LSD box) bits kindly sent to me from Simon SGL on this forum. It was a total nightmare from start to finish as we re-used my cleaned up crown and pinion first time round which proved noisy. Then I discovered all turbo crown and pinions were the same so we used the one from the non LSD box which was in good nick despite the box being noisy (was just bearing noise it turned out). So its all back together and working well now but I never want to repeat that carry on!

Stuart

 

[924Srr27l]

Doesn't VEMS have traction control capability?

TC will limit / reduce the power to the spinning wheel by (electronically cutting the engine) but it won't stop one wheel spinning which a mechanical locked differential will do.

R

 

[924Srr27l]

So, I currently have a std early turbo gearbox which has the cooler. I've modified this to replace the std finned coil of pipe with a small matrix heat exchanger (radiator).
I can't utilise VEMS traction control if it has it (and I'm not sure of the top of my head if it does) as I don't have ABS.
The Quaife is about £1k and you can't even get std turbo lsd boxes for that anyway, so I like Stuarts idea, refurb my box as/if required and fit the quaife. I'll try and take a look at DSD Steve, thanks for the tip...
Stuart, did you recon your own box? If so how hard was it and do you have any tips and part numbers to help? I've got all winter and a warm garage to play in now!

Another LSD alternative is the WAVETRAC unit from the US.
I've used this on road, trackdays and full race use and it's never been any trouble (aggressive locking) but if anything has given brilliant traction out of slow corners on 800lbs rear springs etc..
It requires no adjustment and I got it from EMC, who I'm sure can supply an fit for you.

http://www.wavetrac.eu/index.php?route=information/information&information_id=7


R

 

[blade7]

I can't utilise VEMS traction control if it has it (and I'm not sure of the top of my head if it does) as I don't have ABS.

I think it can be linked to boost control.

 

[Waylander]

Doesn't VEMS have traction control capability?

Hi Blade

the only way that would be possible is if the VEMS system used the signals from the ABS system, as that's how modern TC works, just by the rotational signals from each wheel, No ABS no Traction control unless you fit individual sensors to each wheel

even mid corner applied braking by an on board computer is done by a combination of wheel speed and lateral force sensors

 

[blade7]

Yes I understand how ABS/traction control works, though I think you only need the wheel sensors to be able modulate fuel supply/boost or cut ignition. And with no LSD only on the 2 rear wheels.

 

[924Srr27l]

Yes I understand how ABS/traction control works, though I think you only need the wheel sensors to be able modulate fuel supply/boost or cut ignition. And with no LSD only on the 2 rear wheels.

Yes no doubt something (ABS trailing arms or another sensor) could be made as you suggest just on the rear wheels, but a mechanical torque biasing differential will provide better performance.
The ultimate is an electronically controlled mechanical LSD, which can vary the torque to individual wheels either 2 or 4 like the 4WD Mitsi Evo's.

R

 

[TTM]

I would only use a clutch-type LSD on a tail-heavy car such as a 944, as this is what will prevent the rear from going the way it wants when cornering under heavy braking. Ask me how I know.
The ATB from Quaife will not help with as just like with any Torsen-type LSD it will lock up only under acceleration.

 

[924Srr27l]

I would only use a clutch-type LSD on a tail-heavy car such as a 944, as this is what will prevent the rear from going the way it wants when cornering under heavy braking. Ask me how I know.
The ATB from Quaife will not help with as just like with any Torsen-type LSD it will lock up only under acceleration.

Tail Happy car such as the 944???
This car has a big reputation for being one of the most neutral balanced sportscars, and I've never experienced oversteer on road / track day or race use so something must be up for you
to be thinking this?

Has your car got wider rear tyres than the fronts? or old / worn dampers?

R

 

[TTM]

Yes, TAIL HAPPY
If you have never exprienced this yourself then either you are not driving fast enough or your brakes do not perform well enough, or your car is too slow, or perhaps a bit off all of this mixed together.

 

[924Srr27l]

Yes, TAIL HAPPY
If you have never exprienced this yourself then either you are not driving fast enough or your brakes do not perform well enough, or your car is too slow, or perhaps a bit off all of this mixed together.

This is not a tail happy car, you're doing something wrong or expecting too much of physics?

"when cornering under heavy braking" this will be it then !!! you need some tuition to stop this, it's not a good idea.

Porsche got this transaxle chassis to 6th place at Le mans (1980) in the wet!

Too slow and the brakes not performing well enough are not the attributes of my 2.7 924 Racecar at all,
There are many reasons you've experienced Oversteer when braking, most probably will be your driving technique, but it could also
be an issue with your brakes, suspension or tyres too..

R

 

[TTM]

Whatever.

 

[924Srr27l]

Whatever.

Your welcome to your own opinions as anyone on this car forum is, however is far more adult / professional and fruitional if you, we, and all of us
can learn and understand new things, although there will always be some that prefer not to.

Comments and replies with one word are not much good to anyone! often rude and insulting.

If you're braking really hard and cornering at the same time your not only tipping all the vehicle weight on the front axle, but also a bigger percentage on the outside
wheel, not to mention putting the car in a high yaw (pivotal) position where the moment of inertia and the pendulum effect will lend itself to (kicking out the rear of the car)

If you Brake HARD when the car is straight, you can still continue braking if you wish (Trail braking) whilst turning in but with much less pressure.

Here's how to trail brake:
Brake in a straight line at maximum force.Slightly before the turn in point begin to ease off the brakes.Begin to turn into the corner.As you increase steering angle, reduce braking pressure.Use appropriate amount of braking to keep a well-balanced car through the corner entry phase.[/LIST]
Or you can do all your braking in a straight line, and then get earlier on the throttle (Trail - 1/4) from the turn in point to the apex and out the turn....

Both methods will eradicate the car being put into any kind of state (By you) where the rear will overtake you!

Usually the term "Tail happy" is used when a car has power oversteer coming out of turns, the good old 1970's designed Transaxle does not deserve this title at all!


R

 

[vitesse]

Here endeth the lesson! On sprint days at Curborough ,the modest power of my 924S will still allow my tailend to attempt to overtake when powering through the top hairpin.[]