When to use LSD friction modifier additive?

[martyn]

What is the best course of action if I dont know what LSD I have?  I know there is lots of content on this in the archives, but it mostly discusses specific types of LSDs.   The diff is a ford unit as supplied by caterham in 2008.

If I use a LSD specific oil such as LS80w90 does this still need additive?

Thanks.

[gileshudson]

Martyn,
Some way down this page is a means of telling exactly what LSD you have fitted to your Caterham.
I've just installed a Quaife ATB and used Fuchs Titan Race SYN 5 75W-90 Fully Synthetic Gear Oil (was Silkolene SYN 5 75w-90).
Hope this helps.

[martyn]

Thanks Giles,

Yes I've seen that page before, however I'm not really prepared to dismantle the rear of the car just for a simple service drain and refill.  Really I'm looking for some cover-all advice for someone who simply doesn't know what LSD they have.  Is it better to use friction modifier additive or not..

I note that the oil you've chosen doesn't have any friction modifiers so is the correct type for your non-plate type LSD - The power of knowledge I guess! 

[7 wonders of the world]

Jack both rear wheels off the ground a plate lsd will.rotate both wheels in the same direction when one is turned.

Pate lsd needs modifier only if using normal.final.drive oil the one ypu mentioned is a specific lsd oil and wil have friction modifiers already added.

The quaife is not an lsd merely a torque bias final.drive with mot plates and therefore runs without additional friction modifiers.

[martyn]

Thanks, I've performed that test many times.  When I rotate either wheel, the other does not move at all.  However I do have quite a lot of drag, sticky brakes etc that may mess up that test.  I'll try later with the brake pads removed.

I've just tried it with the car in gear, and in this case the wheels move in opposite directions.  Not really sure what that signifies.

The car does drive like it has a LSD, and I have the original order form and invoices showing it as a paid for option..

[John Vine]

Hi Martyn,

My R400D is the same vintage as your car, and has a Quaife LSD.  I suppose it's possible that yours might therefore have the same.  I guess the only way you're going to find out is either to remove both driveshafts and peep through the diff, or ask CC themselves.

7WotW's comment above re Quaife's not needing a friction modifier puzzles me, though.  My last service (carried out by CC Crawley) included a dose (4 fl oz) of Lubeguard. 

JV

[martyn]

Ok, bit of an update..

I've removed the brake pads and tried again...   If I smoothly rotate the wheel at a slow pace, the opposite moves in the same direction and the prop shaft spins.  However, if I turn it faster or with more force then the other wheel switches to move in the opposite direction although seemingly a bit slower. The prop shaft also spins while I do this.

To me that seems to be the behaviour of an open diff.

However I'm not sure of the validity of this test because it is putting the power through the diff the wrong way.  It will therefore rely on the diff having some off power / coast ramp angle in order to cause any locking in this configuration.  I bet the OEM supplied caterham LSDs have very little to no coast ramp at all.

John, from what I've read of the owner’s manual and assembly guides, Caterham seems to suggest putting Lubeguard in everything with a LSD and no mention of the various types.  I guess this saves the confusion and Caterham service technicians probably follow a similar practice.

[gileshudson]

When I fitted my Quaife last June, I checked with Quaife and they said no extra lube necessary as below. I therefore bought the oil they recommended. FWIW, my new diff is absolutely whisper quiet and performs like a dream.

Quaife Technical Support page says:

"When running a Quaife ATB helical gear limited slip Differential in a standard transaxle gearbox, we recommend that you use whatever your vehicle’s manufacturer recommends.

The Quaife ATB Differential does not require any special lubricants.

When running Quaife gearbox internals and a Quaife ATB differential – we recommend FuchsTitan SYN5 75W90.

For a Quaife ATB differential, running in a rear axle – use a hypoid 90 or 75W90, as above.

For those applications that will accept a GL5 or SAE75W90 gear oil, we recommend and sell Silkolene SYN5 75W90 gear oil. We use Silkolene in all our own Quaife racing transmissions"

[DJ.]

My understanding is that with a plate type lsd, the opposite wheel will never move in the opposite direction. They will either turn together or if there is a binding brake or the diff isn't gripping just the one wheel will move.

Sounds like you have a Quaife torsen diff to me.

[martyn]

My understanding is that with a plate type lsd, the opposite wheel will never move in the opposite direction.

Never?  What about when the diff isn't "locked" and there is no pressure forcing the plates together?   I suppose there could be some latent friction in the clutch pack that would cause the behaviour you describe (is this the definition of preload?), but thats now getting beyond my understanding.

[simonpa]

You only need to remove 1 driveshaft and look inside with a torch.

It only takes a few minutes - certainly less than you've already spent discussing it :)

1. ​undo 2 bolts on the caliper and tie it up to the spring - no need to detach hose or cable
2. undo 2 rear bolts holding rear of ear to dedion tube
3. undo 2 bolts/nuts holding front of ear to dedion
4. pull out complete driveshaft/hub/disc assembly - carefully

Simples!

Another test you can do without dissembly is:

1. sit rear of car on axle stands so wheels are off the ground
2. handbrake off , gearbox in 1st, start the engine - the wheels will both turn forwards
3. using a pair of thick gloves - try and prevent 1 wheel from turning

If there is an LSD, you shouldn't be able to stop the wheel manually.

Simon

[martyn]

Thanks Simon.  I did consider removing the hub, carrier and ear as one unit, but was reluctant to because it felt like a bit of a bodge.  I'm more comfortable with it now that you've suggested it as well.

The rear discs will need replacing next year so it makes more sense to do it then. I'm tempted to just put some LS spec oil in for now and forget about it till next year.

[John Vine]

You only need to remove 1 driveshaft and look inside with a torch.

Yes, of course!  And, as you say, it's very straightforward.

 

Martyn, re rear brake discs, I've just replaced mine, so if you need any tips etc just say.

JV

[7 wonders of the world]

The lube gaurd is for plate lsds only to make the oil.more slipppery which reduces plate judder quaife has no plates only gears.

With a plate lsd assuming brakes are not binding both wheels will rotate togather due to the preload on the clutch plate pack.

[John Vine]

7WotW - rhat's helpful, thanks. 

Is it actually harmful to add Lubeguard to a Quaife LSD, or is it simply unnecessary and therefore a waste of money?  From a personal point of view, should I drain and refill to remove the Lubeguard from my diff?

JV

[7 wonders of the world]

Cant see why it would harm a quaife at all its only gears in yours and it causes no problem to the normal crown wheel and pinion in a plate set up.

 

[martyn]

Quaife seem pretty relaxed about what oil spec is needed.  It is fairly common for a Quaife ATB to be fitted inside the gearbox case of a front wheel drive car.  In these cases Quaife recommend that you use "whatever oil the gearbox manufacturer recommends". Based on that advice, I can't imagine a bit of Lubeguard is going to cause any problems.

[John Vine]

Thanks, chaps.

JV