Confirmation Of 4.2 Rear Lsd?

[rpaterson]

Hi Folks.

In recent snow-related threads, there have been some excellent write-ups of the various 4x4 transmissions fitted to the various RAVs. Anchorman posted that the earlier 4.2s with square front fogs had a rear LSD. I changed all my fluids last year (or sometime?) in my wifes '02 plated 4.2 and I didn't use an LSD oil in my rear diff. I'm sure that I've had one rear wheel jacked off the ground in the past (prior to the fluid change) and I've been able to turn the wheel by hand numerous times. I thought that an LSD would prevent me from doing that?

I'm confused.

[pmb]

According to my brochure that I still sadly retain the NRG and the VX of 2002 have an LSD.

[shcm]

Yep, see this thread:

http://toyotaownersclub.com/forums/index.p...st&p=828772

[anchorman]

In true 4.2 fashion, simplicity is king and unlike some lsd's with complicated multi-plate clutches (not to be confused with a 4.3 drive clutch) the lsd is no more than a belleville washer which loads the diff against the casing and reduces the risk of slip. It is a compromise but for a "soft roader" it often made the difference between being stuck or not. It isn't tough enough to stop you turning a wheel and it doesn't require special oil.

[rpaterson]

Cheers folks.

anchorman - I looked on wikipedia for 'belleville washer' and I kind of see how it works. In my mind the preload creates a kind of locked diff, but still allows it to slip open??? Looks to be a simlar idea to a spring washer, but without any sharp edges.

[anchorman]

Yes, thats right - they are just dished or cone shaped washers that are capable of exerting a spring side force. Its hard to describe how a diff works without you actually seeing one but a series of gears allows the drive from the engine to turn the rear wheels - simple! However, if the vehicle goes around a bend one wheel has to travel much further than the other and the gears then start to climb over each other. This lovely old film shows it quite nicely;

Now imagine that the gears have spring washers on the side of them that just makes them stiff to turn. Instead of one wheel spinning freely if you get stuck in the snow, it has the same effect as you rubbing your foot against that spinning wheel which transfers the same amount of resistance you exert back to the non spinning wheel and encourages it to turn. A true torque sensing LSD will lock up and apply the same torque to both wheels but the RAV LSD is a compromise and makes it less easy for one wheel to spin unimpeded.

I hope that makes at least a little bit of sense!!!

[rpaterson]

Cool, I get how a diff works with regards to wheel speed when cornering etc and the scrub/transmission wind-up involved with locked diffs. I was just worried that I'd used the wrong diff oil last year when you helped me with my fluids change :)

On the same topic, I wonder if the RAV set-up mean that you could tweak the spring to get a different reaction? Not that I'm planning to, just nosiness.

[anchorman]

Cool, I get how a diff works with regards to wheel speed when cornering etc and the scrub/transmission wind-up involved with locked diffs. I was just worried that I'd used the wrong diff oil last year when you helped me with my fluids change :)

On the same topic, I wonder if the RAV set-up mean that you could tweak the spring to get a different reaction? Not that I'm planning to, just nosiness.

You mean the spring washer? I guess you could keep going in stiffness but in doing so are going to make the diff more reluctant and that will begin to affect tyre wear, economy and eventually start to bind up on tight cornering. It would be a case of trial and error.

[rpaterson]

Cool - nosiness satisfied :)

There used to be guy in Ayr that had a 3.0 Capri that just welded his diff up instead of getting an LSD for it. Apparently he was good friends with a tyre fitter...