Subaru brat rear differential question

[Atteblo]

Hi I am wondering why does my rear differential in my 1988 brat act just like an LSD when I put it in 4wd, I read on forum that no brat had LSD. 

When its not in 4wd it acts like open diff. In 4wd it spins both rear tires and is choppy when doing sharp turns just like a welded diff is. So anyone know why its like that? 

Edited October 25, 2019 by Atteblo

[el_freddo]

You’re talking about 4wd bind. 

Since there’s no centre diff to allow differences in front and rear axle rotation, the gearbox and pinion shafts are effectively working against each other. 

With all four wheels on the ground the inside wheels will try to spin to reduce the stresses on the drive train. 

If you try to drive up an obsticale that compresses the suspension ina diagonal fashion - eg: front left and rear right, the front right and rear left will loose traction and both wheels will spin, losing much of not all of the vehicle’s momentum.

This is due to two open diffs and a locked centre between the two axles. If you have an LSD in the rear, you’re more likely to power over the obsticale until a rear wheel is lifted, at which point the LSD won’t be useful. 

Cheers 

Bennie

[Steptoe]

Put it in neutral, fwd and Jack up the rear wheels off the ground, spin one wheel by hand

what direction does the other wheel turn?

[DaveT]

Are all 4 tires the same brand and model and close in miles?   If they are not, you will bet that on dry pavement,  because there is no center diff.   Even with identical  tires,  it will do it some.

Edited October 25, 2019 by DaveT