Sj brakes vs grand vitara

[Fwb2700]

What's the differences??? Might be able to get the vitara front diff really cheap but need to get in quick if the brakes are comparable for a rear disk conversion on my sj.

I hope a expert answers quickly

[twiss]

You can get grand vitara calipers to fit but I think they may require some modification.... and you might need 16" wheels to fit them in but I'm not sure on that one!

[donkeychomp]

I'd hold out for SJ ones if you are putting them on the rear...the discs are bloody massive for such a tiny car!

[Anton]

"Normal" vit callipers (tokico) are slightly smaller than Aisin SJ ones (48.1mm vs 51mm), so they'd be a bit better suited, but Grand Vit (GV) ones are bigger than SJ ones - depending on which GV they're off, some are a bit bigger and some are a lot bigger. Some are 57.2mm and some are 60mm. I *think* the 57's will fit 15" wheels, but I'm not sure - the 60's need 16" rims for sure.

SJ Aisin's are 51mm and Girlings are 48mm.

Don't put GV callipers on the back. Really, just don't. You'll lock up the rear in the wet under relatively "normal" braking, and then the rear will want to overtake the front of your vehicle.

I went with Rover rear callipers, because the surface area of their callipers was right about the same as the standard drum brake pistons, meaning they would provide about the same level of clamping force as the drum brake pistons at roughly the same distance from the axle centreline, thereby maintaining the total overall braking force at more or less equal to factory.

However, SJ's have kind of weak rear brakes compared to other manufacturers - there's usually a 1:0.5 ratio between fronts and rears, SJ's have closer to 1:0.3 (from memory). I'm happy with that because I'm SPOA, and that shifts even more weight forward under braking (meaning the rear goes even lighter, and will lock up sooner).

Many people run SJ front callipers on the back, and that results in a 1:1 ratio - that can be dangerous in the wet. Sorry to those running that setup, but it can be. Running GV callipers on the back would be even worse - please just don't do it!

If anything, put the GV calipers up front and either run standard vit callipers on the back, or girling type SJ callipers on the back (they're a wee bit smaller than Aisin's) so you have about 1:0.8 ratio. Still not ideal, but better than 1:1.2(ish) that you're talking about here.

Also, don't try to compare directly. 57mm doesn't sound much bigger than 51, but it is (pi times radius squared) quite a bit bigger. My 51mm front pistons are 3 times the size of my 30.2mm rears. Yes, 51mm is 3 times the size of 30.2mm (2042.82mm sq vs 716.31mm sq).

57.2mm is 2569.69mm sq, or 25% bigger than 51mm,

Ideally what you want is a piston that is double the size on the front, or maybe a bit less (between a third and a half the size on the back is where manufacturers tend to go, I just matched what Suzuki did, which is roughly a third)

For Aisins on the front (51mm), that means between 30mm and 36mm on the back.
For Girlings or Tokico's on the front (48/48.1mm) that means between 27.7mm and 33mm on the back.

If you can find a 2:1 brake bias valve you could fit identical brakes front and rear, and just use the bias valve to lower the pressure in the rears. That should do the same thing. You would also be ok to use slightly smaller callipers on the rear (48's for example) as you'd still be in the sweet spot of between 33% and 50%.

But whatever you do, don't drive "earnestly" with your new brakes until you've had a chance to test them properly! I went to a nearby road that is always deserted (it leads to a sewage processing plant and nowhere else) made sure there were no other cars around and tested my braking. I did one round of tests in the dry, and then again while it was raining, so I knew whether or not the rears would lock up too soon. They didn't, my fronts locked up first in the wet, neither locked up in the dry (31x10.5 rubber for the win! I may get bigger callipers front and rear when I finally switch to 33x12.5's).

HTH.