Re: [DML] Rear Calipers on Ebay

[Steve Stankiewicz <protodelorean@xxxxxxxxx>]

Thanks Marc.  I was wondering that myself.  Since we've already calculated the difference between the rear calipers, we now need to understand the difference between the master cylinders. (Feel free to scroll to the bottom for results if you're not interested in the calculations.)

The original Delorean MC is a "68/32" and the Saab unit is a "50/50".  On the surface it would seam like the difference in the rear is only the difference bewteen 50 and 32 or the Saab unit is 18% more pressure in the rear.  This is NOT correct.  Automotive braking systems give full pressure to the front wheels, then use an internal or external proportioning valve to reduce pressure to the rear wheels.  If the proportioning is done internal to the mastercylinder, you see a value like the Delorean and "68/32".  If the proportioning valve is separate from the matercylinder, then no proportioning is done inside the master cylinder and it puts out equal pressure to the front and rear, "50/50" like the Saab unit.

So, the Saab unit puts full pressure (100%) to both the front and rear, while the Delorean puts full 100% to the front and only (32/68) or only 47% to the rear.  So the while both units put full pressure to the front, the Saab unit will put 100% also to the rear where the Delorean only put 47%, resulting in (100%/47%) or 2.12 times the pressure designed to go to the rears.  By sending more than twice the original pressure to the rears, it's obvious why people with saab mastercylinders report the car's "tails wanting to come around" on hard braking.

The jaguar calipers will help this condition, but not fully correct it.  If the Saab MC is putting 2.12 times the pressure it should to the rears, and the jaguar calipers reducing clamping force by 20%, then a car with both the Saab MC and the Jaguar calipers would have 2.12 x (1-.20)=1.70 times or 70% more than the designed braking force to the rear wheels.  Better, than the Saab MC alone, but still a significant deviation from design and definite safety concern.

**********************************************************************

In summary, here's what the combinations produce:

Master Cylinder/Rear Calipers: Results

Delorean/Delorean: Rear braking as designed
Delorean/Jaguar: Rear braking reduced by 20%
Saab/Delorean: Rear braking increased by a factor 2.12 times the design
Saab/Jaguar: Rear braking increased by a factor of 1.70 times the design

So none of the alternate parts produce results in very close proximity to the original design.  Also keep in mind ANY increase in rear braking will increase the tendency for the rear of the car to come around and swap ends with the front in a panic situation.

 
Steve

VIN 2650 ("Project Delorean")
www.projectdelorean.com


 
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