Changed Diff Oil, Car Now Pushes Very Wide?

[sonicz]

A few months ago I Bought 2x 1L of LS90 diff oil from repco. I took it to my mechanic to change the diff oil for the first time since owning the car sicne I figured its in need of it.

The mechanic Gave me back one full 1L bottle, and the second used bottle still had about 200ml left. In other words the mechanic said all it took was 800ml. I was dubious but I went with it as he said he filled proplerly.

After a short while I noticed a drastic change in the way the car turns especially under acceleration. It heavily pushes wide whereas previously it used to tuck itself into the apex very easily.

The green line is how the car used to behave before the fluid change, and the red line is after.

If I accelerate in the rain in a straight line on a flat road the car begins to spin out by turning right. Ditto under engine braking in the rain.

The diff has many Ks on it, but I wonder, why did it seem to be working better for me before the fluid change? I did not use any additives.

Almost forgot, the car is a 1993 R33 GTS-T, as far as I know it does not have the A-LSD.

Edited February 13, 2014 by sonicz

[MatthewT85]

ummm i cant explain how its driving like that, but i changed mine last month, same reason have nfi when/if mines been changed, plus it began a slow leak out of the drain plug, i used castrol 80w 90 and i just checked the 4L bottle i had and ive used approx 1.5L.

i do remember when i drained it, i had driven it, so warm, also after i let most drain out, i put my finger in there and actually managed to get a fair bit more oil out, sort of sticking to all the surfaces i could feel

do know what diff it has, does it have fins on the cover?

[sonicz]

Damn 1.5L. Thanks for confirming. Time to go back to him. How could he only used 800ml? Maybe he filled it using the middle bolt instead of higher up.

No it doesn't have the fins so its not an A-LSD.

Is the diff permanently damage now?

[MatthewT85]

it could be a little less but thats an approx,i doubt you'd get even 800ml using the drain plug

i cant really see how a mechanic would balls up something like that

is it the correct weight of oil? i cant tell from the picture it just says ls90

i dont know heaps about cars ect, sort of learning by doing, and reading heaps here before doing...

whether there's damage, im not sure, im sure by tomorrow some of the more knowledgeable guys will have some ideas i was mainly just letting you know how much i had used

i think you have the right oil, cause i think its roughly 90wish

Edited February 13, 2014 by MatthewT85

[sonicz]

The only thing I can think of is he didn't remove all the old fluid. How did you remove the old oil anyway? I don't see a drain bolt looking at the diff from the back. Only the one in the middle of the diff.

[MrStabby]

There's always two plugs. One right at the bottom to drain it, and one around half way up to fill. Its best to open the filler first, because its a bummer if you open drain and drop the oil then find the filler is stuck... Anyways, when you fill it you keep going until the level is up to the filler. I just keep pumping still it starts leaking out.

If you can, open the filler and put your finger in to see if its right up to the filler level. If not you can get $20 hand pumps from supercheap etc. Its a bit crude, but you can just use a half inch drive without a socket to open it if its not too tight. Or post up in your state's forum and see if anyone will check it for you - its a 5 minute job.

With the different driving - the oil could potentially make the LSD tighter or looser, but im not sure which would make the car drive the way you describe.

[PN-Mad]

The tighter the LSD the more understeer it will push as my understanding.

Forgive my ignorance with the R chassis cars, but of what variety is the LSD? Viscous? In which case you don't need to use a LSD type oil.

First thing is to check tyre pressure, as a Pesky mechanic might have pumped them up thinking he was doing the right thing.

[MatthewT85]

also with the location of the plugs, the one on on the back is the drain, the filler is on the left side of the diff, inline with the exhaust, can be a pain in the arse to see without getting under the car

and yeah its viscous

[sonicz]

Thankyou guys. I just got under the car and saw the big bolt with box pattern at the bottom. Thats easy to get to but wont be needing that one.. Will I be able to just as easily get to the left side filler bolt without needing any special equipment? Just a car jack and stands?

Can anyone recommend an oil that will make the car easier to change direction, if thats even a thing people do with old Viscous diffs...

[MatthewT85]

basically i just jacked the car up high. cause i used my breaker bar to undo the filler plug, its in a difficult position with the exhaust ect, but had the breaker and some other 1/2 tools depending on the position of the plug, its more fidly than anything... and a bit of swearing...

you might want to go to supercheap and get a hand pump that can lift the oil from the bottle to the filler plug too, just keep pumping till it start spilling a bit out of the filler and then stop, do it up and youre done...

as for oil, like i said above i used that castrol and its been fine.

also there is a diy i used somewhere cant find it right now, so ill have a look later and post the link

[GTSBoy]

What has almost certainly happened is that someone in the past has "shimmed" your viscous diff. So whilst a VLSD doesn't need LSD oil, once you "shim" the diff you introduce some friction surfaces outside the viscous cartridge and turn it into a hybrid VLSD and plate LSD. At least until the plates wear again.

So if that has happened, then the diff will respond differently to different oils.

Now, putting LSD oil into it (which has fewer friction modifiers in it) will definitely make the plates ("shims") grab more, so the change in behaviour makes sense.

[MrStabby]

Thankyou guys. I just got under the car and saw the big bolt with box pattern at the bottom. Thats easy to get to but wont be needing that one.. Will I be able to just as easily get to the left side filler bolt without needing any special equipment? Just a car jack and stands?

Can anyone recommend an oil that will make the car easier to change direction, if thats even a thing people do with old Viscous diffs...

No special tools required.

Having a tighter diff should help get the power down. If i were you, i'd check the level and top up if necessary. Then just drive it for a few weeks so you can get used to it, then decide if you like it or not. It might grow on you.

[Ben C34]

I thought everyone wanted a tight diff? !

[GTSBoy]

Not one that causes understeer if it can be avoided. I'll take a helical any day of the week.

[sonicz]

I parked the car on a kerb with one wheel and street on another and managed to barely get under the car. It was easier to find and undo the bolt than I expected, thought it was scary having my head mm away from the subframe bolts. I did not need to use a breaker bar as you said MatthewT85 or any swearing or special tools. This is all I used

Yup just a generic socket wrench. It fit in the square hole easily. The bolt was not tight.

The diff took about 200ml to it before It started leaking out. This time I used light castrol manual transmission fluid 75w-80. End result is car now tucks into corners again so I'm happy.

One thing I found odd was that I could not tighten the nut all the way when closing it, there was about 2-4 threads left visible and the bolt was very tight. But thats how I found it.

Edited March 2, 2014 by sonicz

[MatthewT85]

fair enough i assume mine was on tight probably cause its never come off before....

but yeah easy job in the end...

im wondering if the reason for it taking more oil on is cause you had it on an angle... obviously making the oil fall below the filler hole but higher on the other...

either way if its fixed your problem. all should be good...

[MrStabby]

The diff took about 200ml to it before It started leaking out. This time I used light castrol manual transmission fluid 75w-80. End result is car now tucks into corners again so I'm happy.

One thing I found odd was that I could not tighten the nut all the way when closing it, there was about 2-4 threads left visible and the bolt was very tight. But thats how I found it.

Thats normal - its a tapered thread. You dont need to tighten it up hard, just firm.