Tayloring an ZF-LSD into a Fiat 132 axle

Non-engine, eg: aerodynamics, gearboxes, brakes, suspension
ricardoblack
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LSD

Post by ricardoblack »

Hi Thomas
Wow you have done a lot of work very impressive.
I have a couple of questions for you.

The large slots machined into the LSD case ,are these to lighten or allow better oil flow?Also the holes drilled into the outside toothed clutch plates I was curious about.Also curious about the Porche clutch plates did these have to be modified or are they the same other than thickness.

I am also using a ZF diff but would like to lighten what I can, so far I was just going to rifle drill out the drive shafts.
Any tipps as to where material can be removed greatly appreciated.
TR-Spider
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Re: Tayloring an ZF-LSD into a Fiat 132 axle

Post by TR-Spider »

Hi Ricardo

I think the large slots are primarily for the oil flow, secondarily for the weight.
All modern ZF housings I have seen have similar large slots (instead of the earlier type single holes).
In my case the casing could easily be modified because it is made of steel and not casted, I would be cautious modifiyng a casted one, it could break.

The holes drilled into the outside toothed clutch plates are genuine Porsche design as the sintermetall clutchplates, but they fit into the ZF diff because ZF makes them (I think).

I would first clarify the body's material (steel or cast), and if steel I would consider drilling some holes in areas which do not transmit much torque like the side flanges.
But before drilling I would calculate the amount of mass you can actually remove, to see if it is worth the efford. The original BMW outer casing, as example weights aproximately 4-5 times as much as the inner diff-body.

Or are you after reducing the rotating mass?
What car/pupose is it for?

Thomas
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ricardoblack
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Re: Tayloring an ZF-LSD into a Fiat 132 axle

Post by ricardoblack »

Hi Thomas
Thanks for the info. I have taken a different approach.
My car is a Fiat 124 spider with a 130 Abarth motor and 131 sport gearbox and I am fitting an Alfa 2 litre ZF LSD axle.
The plan is to mount it with an adjustable 4link and watts linkage and anti roll bar.This axle can be uprated to 45% lock with additional plates from 25% .
The Alfa race boys recon the 2litre diff is a bit heavy and tend to use the 1600/1750 axles as it has lighter drive shafts and diff.For my purposes the 2litre diff has better gearing so I think there is some room to remove some weight.

Rick
2000 Alfa lsd diff.jpg
2000 Alfa lsd diff.jpg (33.35 KiB) Viewed 9878 times
alfa lsd.JPG
alfa lsd.JPG (31.09 KiB) Viewed 9455 times
TR-Spider
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Re: Tayloring an ZF-LSD into a Fiat 132 axle

Post by TR-Spider »

Hi Rick

nice axle this Alfa one. Presumably the aluminium casing saves a lot weight already. The Alfa Montreal used the same axle, but had a extended oil pan underneath for increased oil volume and cooling, very nice detail.

Axle weigth general... I drove with the 1600/1800 axle before, which was certainly a lot lighter. With the new one I did notice some reduction in comfort, as the back end reacts somewhat slower/lazier on bumps. However I did not really notice a reduction of roadholding capabilities. Its just at some point it starts sliding and I enjoy that...

However there is some example with hints what can be done to reduce weight (remember the material question!):

Thomas
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ZF modified by Drexler motorsport.jpg
ZF modified by Drexler motorsport.jpg (15.36 KiB) Viewed 9411 times
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ricardoblack
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Re: Tayloring an ZF-LSD into a Fiat 132 axle

Post by ricardoblack »

Hi Thomas
Many thanks for that.
I think I will limit myself to rifle drilling the driveshafts like the Alfa GTA and slotting the outside diff case as per your photo.

I was wondering if you have experienced any nervousness under breaking .I was warned that this can sometimes happen if you go above 45 lock up but can be cured with machining of the ramp angles.
I think you mentioned ramp angles previously.If you do any mods on them please let me know.I understand they are very tough to machine properly and then need rehardening.
Did you end up using the Porche plates in your final spec? and did they require any mods to fit?

Regards

Rick
TR-Spider
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Re: Tayloring an ZF-LSD into a Fiat 132 axle

Post by TR-Spider »

Hi Rick

No problems with a "nervous" rear under braking with 45% lock, contrary I would say the LSD prevents the lockup of 1 rear wheel.
Ramp angles are standard 45° in my setup, I am satisfied with the locking. Changing the ram angle is done by EDM (wire erosion), my specialized workshop says the material is extremely difficult to cut otherwise.
In your case I would also stick with the 45° ramp and go for 2 clutchplates each side (=45% lock).
As far as I know the Porsche sintermetal clutchplates are only available in 48mm ID 88mm OD, (which is the medium size BMW diff). For that size no modification is necessary.

What diameter do you plan to "rifledrill" your drifeshafts?

Thomas
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ricardoblack
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Re: Tayloring an ZF-LSD into a Fiat 132 axle

Post by ricardoblack »

Hi Thomas
Sorry for the delay getting back.
I agree for my purposes just putting in two additional clutch plates will do.
I did find some info on changing ramp angles:For those that wish to change ramp angles:
modify diff ramp.jpg
modify diff ramp.jpg (83.17 KiB) Viewed 9534 times
Rampmachining.jpg
Rampmachining.jpg (27.22 KiB) Viewed 9540 times
I have not managed to find any info so far on the diameter of the rifle drilling on the Alfa GTA's so far but will let you know.

Regards

Rick
Mats
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Re: Tayloring an ZF-LSD into a Fiat 132 axle

Post by Mats »

The above drawing makes it clear that you cannot modify the ramps, new ones must be machined or you will have enormous problems with lash/play (9.24mm vs 7.17mm measurement).
More LSD engagement during braking also helps to stabilize the rear (just as TR-Spider mentions above) but you will only use the braking torque from the engine, if you press down the clutch only the preload in the LSD has an effect.

Now, about preload. If you have it set up with a lot of preload you will always have that as a breaking torque over the diff, this means you will always have a yaw-damping effect (i.e.understeer). If you need some preload to keep the car steady during transition between over run and throttle on, fine, but unless you need that I would try to keep preload low.

There is actually one loadcase where braking torque over the diff can induce oversteer and that is when you break traction during acceleration in a turn but that is not always good either. Use braking torque with moderation.
/Mats Strandberg
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