exodus82

I am changing my 81 GS rear end to a 85 GSL rear end. I was wondering if i need the master cylinder off of the GSL as well as the proportioning valve.

1984special

I'm not sure, but I think you will need the new master because drum brakes require more fluid to work (IIRC!).

btw you're not daddy...

exodus82

I know IM not, im asking daddy to answer, its an joke. Ever seen Happy Gilmore???

Siraniko

iTrader: (13)

You can get away by just changing the rear disk assembly.

rx-7ames

iTrader: (1)

i went from an 84 gs rear end to an 85 gsl rear end. i don't know if the 84 and 81 uses the same master cylinder but it has worked fine for me. i stop a lot better with the rear disk brakes. a must for all gs owners.

jorx81@aol.com

iTrader: (6)

no problems here, but I can't say I've ever really noticed better braking with the disc.
anyone?

Gregs

i have definatley noticed a difference

when i swapped my gsl-se rearend in
all i did was swap the rear
the master and proportioning valve in my 81 with drums and the one from me se parts cae were identicle including the numbers on them

rxtasy3

iTrader: (2)

I'm sure there's more of a difference in the proportioning valves than there is in the master cylinders. The valve for disc rear will have different springs allowing more braking in the rear than drum brakes do.

exodus82

Dont drum brakes take more power to work though?? So it would allow less power to the rear brake.

Rx7carl

Itll work with the drum MC PV. But the correct one will be better, but not noticably in my experience. I took apart a drum PV looking for the residual pressure valve (that would cause a problem in a disc brake system) but was unable to locate it so I dunno for sure if Mazda even used it in the drum cars, although it should be in there.

Keaponlaffen

yeah, residual check valve would be a problem.... but they didn't use one? weird, couldn't that eventually cause the cups in the wheel cylinders to collapse and allow air entry in the system?

Oh, and discs actually take more pressure to activate, as drums are self-energizing through a servo action of the shoes jamming up against the rotating drum and pivoting out on the anchor pins. Disc pads have to be manually forced out onto the disc to apply the brakes. It also takes slightly more fluid to operate disc brakes, so make sure you check your fluid levels on the back side of the reservoir as your pads wear down and the caliper self-adjusts... or you could wind up with air entering the system.

Seems weird that mazda would use the same master cyl. for both systems, as drums need different requirements than discs... but hey, if it works, it works I suppose

Rx7carl

No, thay are definately different MC's. Look at them side by side. I suspect that the residual pressure valve may be tucked in the MC. I didnt see it in the PV. AFAIK there HAS to be one in the system somewhere. But I dunno where.

Bruceman

iTrader: (5)

There is a small difference between the master cylinders.
The drum brake master has the residual valve behind the large nut where the rear brake line screws into the cylinder body. You can just undo this large nut, remove the valve and spring, screw the large nut back on, and reattach the brake line. It will then work like perfect for rear discs.
The rear disc brake master cylinder doesn't have this large nut, instead it has a threaded boss.
Leaving the residual valve on with rear disc brakes could cause the pads to drag on the rotor a little.