Upgrade to aluminum/plastic master cylinder
 

The cast iron master cylinder on my truck keeps leaking all the fluid out. The gasket is in good shape but the machined sealing surface keeps rusting for some reason.

Will the plastic/aluminum master cylinder from an 80's truck bolt in place and do the lines have the same thread? I think these look a little better and I always hated how even the littlest spill ate the paint off the cast iron one.

Re: Upgrade to aluminum/plastic master cylinder
 

IIRC the lines are the same but it will only fit if you have the booster to go along with it becouse where the fit together is different.

Re: Upgrade to aluminum/plastic master cylinder
 

on mine the lines were different sizes...

Re: Upgrade to aluminum/plastic master cylinder
 

the lines on mine was the same but the master cylinder didnt fit the brake booster

Re: Upgrade to aluminum/plastic master cylinder
 

Make sure the lines go to the right end as well....

that is, on some cast iron units the front reservoir is for the front system and the rear supplies the rear; whereas on the aluminum/plastic the front is for the rear/ rear is for the front.

K

Re: Upgrade to aluminum/plastic master cylinder
 

this is probly why mine didnt match up.. and why i didnt do it..

Re: Upgrade to aluminum/plastic master cylinder
 

For an 90 suburban with the plastic tanks, Raybestos makes 1", 1 1/8" and 1 1/4" bore master cylinders. Shows Ports=2 Primary Outlet Size=9/16x18 Secondary Outlet Size=1/2x20

Re: Upgrade to aluminum/plastic master cylinder
 

Thanks guys! I did notice looking through parts catalogs that the reservoir sizes looked a little odd but I guess I know why now.

What didn't match up when you guys tried to bolt up the newer MC? Was the center hole in the booster too small or was the mounting bolt spacing/location wrong?

Re: Upgrade to aluminum/plastic master cylinder
 

It's the center hole size (not the mounting stud/spacing).

Some of the aluminum master cylinders have the "quick take up" feature, which allows less drag on the front discs for better rolling resistance and improved fuel economy. These are larger in the rear where they fit into the booster.

So - you can put a "non QTU" master in any booster, but you can't put a QTU master in a "non QTU" booster.

K

Re: Upgrade to aluminum/plastic master cylinder
 

Thanks Keith. I looked up part numbers for boosters and there are different part numbers for 1973-1980 and 1981+ and like you say I can see in the pictures where the hole in the later models are larger. Too bad, the booster I'm running is pretty new so it'll have to stay a long with the cast iron master cylinder. Guess I'll just order a new lid and gasket and hope it seals.