Recently purchased a 58 Chevy Apache pickup that has had a camaro front clip and rear installed (believe its from 70s or 80s?). I would like to replace the master cylinder but not sure what to get as a replacement. I've never seen the one that is currently in it (see pic) so could use some input on what to get. Right now the fronts are doing all the stopping (front disc, rear drum). Any info or suggestions would be appreciated. Thanks Scott
the ones from GMC vans(1990~) look just like that. I would make sure the fittings are the same as well as the bore first though. Cesar
Cesar, thanks so much for iding the MC. At least now I know my suspicions that it doesnt match up to the rest of the braking system was correct. Guess I will go with a MC for a 2nd gen camaro and see how that works out.
I use a univeral GM corvette style with a 1 in bore. If you like your pedal feel just measure yours first. These come with a 3/8 - 24 inverted flare
Thanks. I'm just looking into this but from what I've found specs show 1" for non-power, 1 1/8" for power.....sound right, or r we splitting hairs here? Also was thinking of using this MC, and getting a matching proportioning valve (since I have no idea where the one on the truck came from):
That looks a lot like one that GM used on some S 10 chassis, late 80's, into early / mid 90's. Our fleet of delivery vehicles were S 10 based, and used that m/cyl. Ugly plastic reservoirs.......I used the 1" Corvette type, for my under floor installation (40 Ford) 4TTRUK
The 1 1/8 inch will produce higher volume but lower pressure. Good volume for disc brakes but vaccum assist is needed to multiple the peadl pressure. Using a large vacuum booster like you have it would probably be fine. My suggestion is if you like the pedal feel and you can get the brakes to lock up with what you have take the existing master cylinder off and measure the size. You mentioned that the front brakes are doing most of the work. Do you think the brake bias needs to be adjusted front to rear? If so the proportioning valve would help or an adjustable prop valve on the rear line can be used. I ask because a friend of mine recently had issues with his 47 and replaced the master, prop valve etc but still had low pressure at the rear. He later found that the rubber flex line at the rear had partly collapsed and that was the real issue. After spending a few Benjamin's he really only needed a $25 hose.
For good general brake info check out 911brakes.com. Their parts are pricey, but they have good tech info on their site like a pressure chart, trouble shooting guide, etc.
Thanks MrForty, I appreciate the info. My problem is I really dont know what the pedal feels like currently. I recently purchased the truck and during the test drive I noticed the brakes worked fine but did not stop as well as I would have liked. Figured I would look at it better once I got it home. After it arrived I looked closer to the brakes and found that the front reservoir was pretty much empty. Apparently the front line was leaking for some time and PO didnt notice it. This explains why it didnt have much stopping power during test drive. So I filled it up and tried in the the driveway, only to almost go thru the windshield. I'm kinda hoping that if everything is the same from the donor (big assumption, PO didnt know), and I get the correct MC, then I shouldnt need an adjustable prop valve, the "stock" prop valve should be enough. So if it the current MC is 1" bore and I go with the larger size, would it make it less touchy? I'll check on the rear line. Thanks again. Scott
Whatever you get, make sure it plays with your power booster. Match up the rear of the new master with the old one and make sure it takes the rod from the booster. Bob
If you go to a larger bore size you create less pressure so it will be less "touchy". Just to put it in perspective if you had a pedal ratio of 6:1 and applied 100 lbs of pressure to the pedal a single 1 inch piston can create 764 psi with no vacuum assist. A 1 1/8 piston creates 603 psi. Remember the stroke is the same so you get more volume but less pressure. Like bobss396 said be sure the new master fits your booster and the rod is long enough to engage the master cylinder piston. It shoudl but not actully push on it once it is installed. You want to make sure that the vacuum booster rod has a small amount of clearance between it and the master piston so it does not push the piston in at rest. Some boosters have an adjustable end so set this. Maybe I can post some pictures if that does not make sense.
Finally had a chance to pull MC. There is a difference between the center section (piston?) that mounted against the booster. Can anyone shed some light if the new MC can be used or do I need to get one the same size center as the old? Old = 2", new = 1.5" Any help or info is appreciated. Thanks Scott
I dont think the rod in the booster will adjust enough to take up the space on your new mc. Youre gonna a have to fab up a spacer on the deep piston to make it match the one you removed. What mc did you end up getting? The "vette" one with 1" bore? It might be less trouble to find a master that would better match what you got. The mc you removed looks like a "quick take up" type with dual bore diameters.
The new MC comes with a spacer to use with a booster, should have mentioned that (wasnt shown in pic). It was advertised as 67-77 camaro, firebird, etc., has a 1 1/8" bore. My concern is the center section diameter difference. Thanks Scott
The difference in the housing diameter will make no difference. The 1 1/8 bore is a good start since you are using a booster. Let us know how it turns out or if a smaller bore will be needed if the pedal is too stiff.
Maybe you need a delay valve like gm used. Mid fifties chev trucks had a brass Block mounted on the front cross member, 1 line in, 2 lines out that delayed front brake actuation so the rears react slightly first to prevent going through the windshield as you put it. Later 60's/ early 70's cars had them mounted next to the master cyl. The brake booster going over center will also put you through the windshield.
To the OP , the orignal MC looks like one for the low drag calipers. If so you will need to replace it with the same kind/style.
As long as it ; 1 bolts up tight, 2, only the rod moves out of the booster 3, the rod engages the MC with the spacer IT should be fine as far as the master and booster are concerned.
Maybe you need a delay valve like gm used. Mid fifties trucks used a brass block with 1 line in and 2 out, mounted on the front crossmember to delay front brake actuation slightly so the rears could apply slightly avoiding sending you through the winshield as you put it. Some later gm cars had them mounted next to the master cyl. Puting an adjustable valve in the rear will only reduce pressure to the rear, making the problem worse.
I would take your old master and have a sharp parts counter guy match it up for you. If the clip you have is from a Camaro, the master might be from the same donor car as well. I wouldn't try to adapt the other master to your power booster. Bob
The Jalopy Journal
