R33 Gtst Active-Lsd Information

[PM-R33]

Updated July 2011

Why this sticky about the A-LSD?

The problem with this has been that there is little technical information on the Active-Limited Slip Differential (A-LSD) even though it is now over a decade later since they were made. There is information about however the information is scattered all over SAU over a dozen threads. The purpose of this sticky is to have all the information in one place to save people time searching all over the place for hours on end.

What is an A-LSD?

For people's information reading this that aren't aware of what an A-LSD is, it's a rare factory option on certain model R33 GTSTs of having a R33 GTR V-Spec diff. The diff is controlled via an ECU in the boot next to the HICAS ECU. The ECU triggers a hydraulic pump that pumps a hydraulic fluid into the diff to lock it up when required. It does this by observing the behaviour of the wheels and when it detects that one wheel has broken traction it will send power to the other wheel to compensate and keep maximum traction. So in theory it is ment to behave like an open wheeled diff all the time and behave like a locked diff when needed. In theory this is great however it doesn't always go according to plan.

The problem is the response time. When a wheel starts losing traction the diff should instantly recognise it and go into action instantly without you even noticing. This would give perfect traction. The thing is this doesn't happen. The single wheel will break loose and in certain situations the diff will take ages to send power to the other wheel - sometimes not at all. This causes very unpredictable "tank slaps" when trying to go straight or when trying to slide.

How do I know if I have an A-LSD?

The way to spot whether a vehicle has an A-LSD is as follows:

Cooling fins on the diff itself (and a large hydraulic line going to it)

Hydraulic pumps and wiring underneath back rear of vehicle

Hydraluic fluid resevoir in boot on right hand side

Two ECU's next to battery in the boot (one is HICAS, the other ALSD)

A-LSD and SLIP wording inside tacho on dash

Resevoir in Boot

The resevoir in the boot holds the hydraulic fluid required by the A-LSD. The original Nissan fluid is called Matic D however it is expensive and hard to get. Instead Castrol Transmax Z can be used due to it being an equivalent fluid.

A-LSD Fluid

The diff itself has "USE LSD OIL ONLY" stamped onto it so something like Castrol LSX90, Motul LSD oil or similar shall be fine. Some people have used non LSD oil it the diffs however I would do what Nissan says.

The following thread showed the main discussions about what fluid to use.

 

Next we shall go into the problems that arrise with the tricky A-LSD.

Aftermarket ECU Problems

The first problem that arrises with the A-LSD is aftermarket ECU’s are not made with it in mind. This causes the A-LSD to go into instant failure mode as soon as the factory ECU is removed and something aftermarket is put into its place. The A-LSD light on the dash will illuminate to indicate a failure. Luckily this is a fairly simple fix but took a long time to find by some of the people here on SAU.

The following thread shows how to overcome this problem. Basically a TPS signal needs to be rewired to go the the A-LSD ECU in the boot.

 

Thanks go out to T04GTR, Moanie and PaulR33 for this.

Diff Lock Problems - Bleeding

So now going onto the main problems with the diff, the delay. One main reason that adds to the delay is air being trapped in the lines that the hydraulic fluid flows through. This air needs to be bled - just like in brake lines.

On page 3, PaulR33 wrote a bleeding method for the diff.

 

The main thing is to use the bleed nipple on the top of the diff, which most people never knew about and the bleed nipple near the pumps.

Diff Lock Problems - Full Control with Aftermarket ECU

Here is my DIY write up on how to get full control of the A-LSD with an aftermarket ECU. This means that you can setup the diff to function the way you want and have it locking up when you choose.

 

 

Once again, great thanks to everyone involved in those threads, especially PaulR33 for all his hard work and posts regarding the A-LSD. Hopefully this sticky can continue to be a good information source regarding the A-LSD.

Cheers

Phi

Edited July 11, 2020 by PranK
Fixing links

[joeyjoejoejuniorshabadoo]

is this the same diff that came in gtt's?

and how does it compare to a mech? (feel wise)

[PM-R33]

Nah i believe the diff only ever came out on the R33 GTR V-Spec and as a factory option on the R33 GTST Series II's. However that's only because i've never seen/read about one elsewhere.

Feel wise i can only compare it to a normal R33 GTST diff since i've never driven a R33 with a 1.5-way/2-way mechanical diff. To me it feels completely normal, only times it is annoying is when it doesn't lock the wheels properly and single spins one, usually the left one and causes the car to kick out quite badly when coming onto power. It's been doing it more often lately hence why im going to service the fluids.

[joeyjoejoejuniorshabadoo]

yeah i hated that with my old stock diff, but at least it threw the car out to the same side every time so the 3rd gear crabwalk was at least "predictable"

[FineLine]

Ok. Just to add my 2 cents worth to this. I have never seen an ALSD in a series 2. I have seen several in series 1's Including my own.

To correctly bleed the system one must remember there are 2 bleed nipples. One at the pump under the boot and one on top of the diff on the left hand side.

If you look at the lid to the reservoir there is a tube protruding from it when you remove it.

Insert the tube on top of the cap, screw the cap back on and apply compressed air via the tube to bleed the system.

You can gravity bleed the pump nipple first but you must apply air pressure to the system to bleed the diff nipple.Be it because of their age or not i do not know but they require regular bleeding to keep them in top working order. Lack of maintainence renders them a useless single pegger but regular bleeding sees them working damn fine.

They really shine in high speed sweeping corners in conjunction with hicas (Ilove that too).

Once the car reaches its grip level the hicas and alsd work in unison to keep correcting the rear slip.

It can be a pain in the arse to maintain but i have no plans to swap mine out simply because its the best damn diff on the planet when it works correctly. That and the fact that it is a way bigger stronger diff than anything else in the skyline range.

[PM-R33]

Cheers for that buddy, ill make sure I bleed mine properly. I've got some Motul FF-LSD oil for it and the Castrol Transmax Z oil aswell.

Hmmm i thought it was only the Series II's that had them since all the ones i've read about have been Series II's, but there you go, was the Series I aswell.

Edited May 12, 2009 by PM-R33

[jarrod83]

fineline i think you may be the man!!! Ive tried so many things to fix this diff, i was ready to rip it out.. Gave it a bleed using a tyre pump as the pressure source which only managed 14psi.. didnt have much faith in it working..gave the diff nipple a good bleed... took it for a quick spin and it either always lit up 2 wheels nice and evenly or it died in the ass(big laggy turbo)... I'm not going to hold my breathe just yet but i think it may be fixed, its definately performing alot better than it has for a long time. I'll know for sure next time i go for a drift... maybe this should be added to the top post as the method for bleeding?

It's funny ive looked at that lid a 1000 times and never noticed the little hose connecter on top until you mentioned it

[FineLine]

fineline i think you may be the man!!! Ive tried so many things to fix this diff, i was ready to rip it out.. Gave it a bleed using a tyre pump as the pressure source which only managed 14psi.. didnt have much faith in it working..gave the diff nipple a good bleed... took it for a quick spin and it either always lit up 2 wheels nice and evenly or it died in the ass(big laggy turbo)... I'm not going to hold my breathe just yet but i think it may be fixed, its definately performing alot better than it has for a long time. I'll know for sure next time i go for a drift... maybe this should be added to the top post as the method for bleeding?

It's funny ive looked at that lid a 1000 times and never noticed the little hose connecter on top until you mentioned it

Good to hear Jarrod. Just remember, if your experience is anything the same as mine you will need to bleed it regularly to keep it in tip top working order.

Big thanks to Dan at Elite racing developments for putting us on to the pressure bleed technique. It made all the diff. (pun intended)

[PM-R33]

Thought i would quickly update this.

Changed the fluid in the boot and bled it properly with the nipple underneath the pump and the nipple ontop of the diff a month ago(most annoying position to put a nipple, no wonder people never knew about it). After a couple of days topped it up and checked over it again.

I also wired some LED's into my dash for the ALSD light and SLIP light as mine got covered up with my white faced dials I put in years ago.

My god, what a difference. Diff locks very nicely now and is very controllable in a slide with the slip light coming on when it is supposed to and the ALSD light not coming on to indicate a failure. The car also no longer kicks to the side violentely when coming onto boost in lower gears, holds traction nicely or just lights up both wheels. Very happy with the results

I think i will bleed the diff every 5000km when i do all my other services to keep it operating well.

Edited July 19, 2009 by PM-R33

[PLYNX]

Great thread man ! I am looking at buying one of these diffs and retro fitting it to my R33 S1 ! Has anyone done this and whats involved in fitting the extra ecu in the boot electrics wise ?

[jarrod83]

PLYNX - i wouldn't bother installing one, they are great when they are working properly but can be very troublesome requiring alot of maintence.. they add an extra 30-40kilos at the back end and its a fairly complicated system

has anyone got any ideas to why they work fine for many years then all of a sudden require bleeding every few months? maybe leaking seals or lines? anyone got any ideas? ive had a look at the lines and cant really see much that you could replace..

[PM-R33]

Yeah don't retrofit it man, more hassels than anything. If i could just have a nismo 1.5 way or something i probably would.

[PLYNX]

Hmmm ! Found a complete wiring harness now and Im still thinking of going a head !

Not to concerned about the weight factor. Ive seen the size of these diffs and as I have a fairly heavy duty 25/30 set up ready to go, strength is what Im after. As to the bleeding situation, the industry I work in uses machinery that has a similar oil pumping pressure seal system on them. They have a auto bleeding set up to bleed air out of the seals or they fail. When you hit the start botton the air is automatically bled out for abut 30 second and then it shuts off. Cant see why the same set up wont work on the diff.

[PM-R33]

Yeah fair enough, but that's making an allready complicated diff even more complicated Your choice man, i just don't think it is worth all the dramas with what you would have to go to to install it.

[openking89]

as with any other internal combustion engine that liquid cooled, yes you can run it without a thermostat, but your heater will not be very hot and the vehicle will run at a cooler operating temperature so the oxygen sensors will probably take longer to heat up, thereby you may need to start the car 10 minutes before you drive it when it gets below say 40 degrees fahrenheit outside. other than that it should still work fine.

Thanks

Jimmy

[PM-R33]

Ummm......what the hell does that have to do with an A-LSD?

[Ultimategtr]

Isnt it so that only the 40th Anniversary editions have the ALSD?

[PM-R33]

Nah, it was a factory option. I used to think it was only on 95 models onwards, but people have them on series I 93 models so must have been available on all R33's.

[TriniGT]

All this is missing is some pics and it will be golden.

[Brokenz]

I just bought a R33 off ebay. Series 1 94 Model and was pretty happy to see it has A-LSD and still has hicas installed. Also has dual airbags which was a suprise for a series 1. The seller never mentioned any of these things and didnt know anything about A-lsd. My plan is to use the car at queenland raceway for timeattack series so I will be interested to see how the diff performs on the track compared to my 180sx with the stock LSD and no hicas