Re: Drum/disc master cylinder??

[farna@xxxxxxx]

NOT NECESSARILY! You are correct in what you mention about drum brake master cylinders and the residual check valve. But the check valve is easily removed! So you CAN use a drum brake MC, but only if you remove the check valve AND match the bore size to the brakes. 1977+ Gremlin/Hornet/Concord/Spirit/Pacer/Eagle calipers use a 2.6" bore caliper and can use the drum MC. All 71-76 models used 3.1" bore calipers and need a larger MC -- I think it's 1-1/16" bore, may be 1-1/8". 77-78 Matadors continued to use the big calipers and MCs. 

Around 77 the residual check valve moved to the combination valve, but that's about the time that all AMCs started using front discs as standard. 

--
Frank Swygert
Publisher, "American Independent 
Magazine" (AIM)
For all AMC enthusiasts
http://farna.home.att.net/AIM.html
(free download available!)
			

 -------------- Original message ----------------------

> From: ortfamily@xxxxxxx
> Date:  Mon, 20 Dec 2004 21:30:51 -0500
> 
> >Whatever you do, you need a master cylinder for disc/drum if you are running a 
> disc/drum setup. Drum brake master cylinders hold residual pressure to overcome 
> the springs in the drum brakes, and discs do not. A disc master cylinder on drum 
> brakes will not stop the car even if you push the pedal with both feet (I tried 
> it). A drum master cylinder on disc brakes will keep the brakes slightly 
> applied, due to the residual pressure valve in the master cylinder. I have mixed 
> boosters and cylinders with great luck, providing they are the correct disc/drum 
> master cylinder. I would order a master cylinder for the year/model of booster 
> you have and adjust the push rod to have a very small amount of slack when the 
> brakes are not applied. I have even elongated the holes for mounting the master 
> cylinder and used grade 8 washers to reinforce the holes. You can find all sorts 
> of boosters, cylinders, and combo units on Rockauto.com. Happy motoring and 
> stopping.

>