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  • GM master cylinder question

    The power master cylinder in the ventura (1977) has started to weep between the bore seals, so the pedal is gettin' soft. I currently have a cylinder that is for a '79 trans am with the ws6 disc brakes and worked great untill this...

    My question is this - Is there a bolt-on replacement master cylinder that is aluminum and with a plastic resevior, that will bolt up in my application? I have seen a couple on mid eighties buick GN's but I don't think they had disc brakes on the back... I have a stock type front disc set-up and 1999 ford explorer disc brakes on the 9" at the rear, with a mopar adjustable proportioning valve mounted under the dash. Money is (as always) extremely tight right now, so I am lookin for something I can buy cheap. No billet pls.....

    anybody got any experience with this application and have a suggestion? I would be eternally greatfull for any help you could send my way... thanks!
    Mike in Southwest Ohio

  • #2

    Re: GM master cylinder question

    GM masters are pretty much interchangeable. At least, in that they bolt on boosters the same. If you have four wheel disc, make sure you get a master designed for that. I'd get one with a 1 1/8 bore.

    Oh yeah, is your master/booster pointed up at angle or straight out from the firewall, level?
    BS'er formally known as Rebeldryver

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    • #3

      Re: GM master cylinder question

      If it's angled slightly up a B-body unit will work (generic between the disc and drum rears) but there are modifications that will alter the balance to a more disc rear friendly ratio. Search for "Stealth Bolt" on www.impalassforum.com for info. I have a spare prop valve, though I cut it's bracket off, if it would cost extra from the yard. F-bodies and Y-bodies are the only other rear disc applications I'm aware of for RWD till the 99+ trucks.
      Central TEXAS Sleeper
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      ROA# 9790

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      • #4

        Re: GM master cylinder question

        You mean like this......



        http://www.ebay.com/itm/Wilwood-260-...ht_1998wt_1163

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        • #5

          Re: GM master cylinder question

          yep, like that. and my master is pointed slightly upwards. I've heard that there is a difference in the bore diameter and pushrod length amongst all the GM style masters and I got no clue as to what's right or wrong.
          Mike in Southwest Ohio

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          • #6

            Re: GM master cylinder question

            yep, like that. and my master is pointed slightly upwards. I've heard that there is a difference in the bore diameter and pushrod length amongst all the GM style masters and I got no clue as to what's right or wrong.
            Bore diameter is not that big of an issue as we've discussed before here on the forum......Basically if you have manual brakes you want a smaller diameter bore and if you have power brakes you go with the larger diameter bores........This kit seems like it has an adjustable pushrod, so that might not be an issue.......

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            • #7

              Re: GM master cylinder question

              There are deep and shallow master cylinder bores. you'll need a longer pushrod if you are using a deep master on a shallow booster. I'm doing that now with my hydroboost setup. It's kinda hinky, but it works for now until I get a new master.
              BS'er formally known as Rebeldryver

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              • #8

                Re: GM master cylinder question

                Bore diameter is not that big of an issue as we've discussed before here on the forum......Basically if you have manual brakes you want a smaller diameter bore and if you have power brakes you go with the larger diameter bores........This kit seems like it has an adjustable pushrod, so that might not be an issue.......
                Uh... yeah, it is, unless you want a rock hard pedal and / or a MC setup that won't stop you. That's kind of like saying the pushrod ratio is not that big of an issue when you go from Power to Manual. It is.

                Mike, you can get a rebuild kit for the original MC for about 20.00, if you can run a brake hone through it and install new seals it fixes a ton of problems. On the other hand, I went onto RockAuto and a rebuilt master cylinder is 20.00 plus or minus a buck or two for a 79 Trans Am with 4 wheel discs. I'd replace the one you have if you are satisfied with it.

                The plastic resovoir deals are maybe 4 pounds lighter, I'm not sure it's worth the hassle, and it won't be anywhere near 20.00 by the time you are done. A lot of them use Metric fittings, something to be aware of if you go that route. THe conversion nipples are 5-11 dollars apiece from when I looked a few weeks ago. I know that didn't answer your specific question, but it speaks loudly to the cost.

                I haven't checked it out completely yet, but I bought a 1" bore aluminum MC for a 85 Lincoln Town Car (4 wheel disc) for 20.00 from Autozone and I'll space it out so I can use the same pushrod after doing the "Stiney mod" on my pedal for a 5:1 ratio (manual, 4wheel discs). I thought about going with a V6 Mustang MC (4wheel disc, no ABS) and resovoir, but cost becomes an issue when you start "modifying" this junk unless you have a nearby yard that will let you pull little parts for cheap. The high dollar part on mine will be the adjustable proportioning valve. Since mine had early ABS it didn't have a traditional block on it.

                http://www.pirate4x4.com/tech/billavista/Brakes/ This is a really good "manifesto" on brakes. Plenty of math in here to tell you what you need. Happy reading!!
                Last edited by Beagle; April 15th, 2012, 06:27 AM.
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                • #9

                  Re: GM master cylinder question

                  difference between aluminum and steel is you need to cut the fittings off your current setup, and put the metric fittings on for the master cylinder.

                  why not use a Corvette master cylinder? they're pretty cheap, even for new ones.
                  It only takes one aweshit to erase a dozen attaboys

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                  • #10

                    Re: GM master cylinder question

                    That's why I went with the '85 Town Car. Aluminum, 1" bore, already setup for four wheel discs, "Mercun" fittings. Spend some time on Rock Auto, they'll give you a lot of the specs if you want to research it.

                    The tubing size is the same for either fitting - you could hack the ends off of something modern at a yard if they're into dollar parts selling. Some guys would just steal them, but that is wrong and Karma is a bitch. This is why I love having parts cars.

                    I'd like to take a MC for a Ford and Chevy and see how close they are on mounting. Hydraulic fluid doesn't much care what brand of car it's getting pushed through. Ford has been using a plastic resovoir and either cast or aluminum cylinder for a loooonnnnngggg time, making it really cheap. Not as cheap as replacing the one that's on it, but cheap nonetheless.
                    Last edited by Beagle; April 15th, 2012, 07:55 AM.
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                    • #11

                      Re: GM master cylinder question

                      Mike, you can get a rebuild kit for the original MC for about 20.00, if you can run a brake hone through it and install new seals it fixes a ton of problems. On the other hand, I went onto RockAuto and a rebuilt master cylinder is 20.00 plus or minus a buck or two for a 79 Trans Am with 4 wheel discs. I'd replace the one you have if you are satisfied with it.

                      !
                      OK - I found out this morning that I can get a newly rebuilt master for a 79 T/A w/discs for all of $17.99 (lifetime guaranteed).... I also found that the weight I would be saving is about 3.5 pounds and all of the aluminum masters have the metric fittings... someone else mentioned to me that they have seen allot of the plastic resevuiors (did i skell that rong?) that weep fluid, but the cast iron jobs - obviously - cannot... and a rebuild kit here is almost $22.00...?......

                      I am seriously bummed about my monetary situation (working hard to change that) because I've always had the mantra that any part that wore out should be upgraded at that time... but not this one. I'm gonna get the stock replacement and be done with it... but I may be posting in a few months asking for more advice on that covette cylinder... ..They want $66.00 for one, and its also metric. I really like the look of the aluminum and the weight savings, but for now... its gonna be cast iron.... Thanks for all the responses.... it's very much appreciated.
                      Mike in Southwest Ohio

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                      • #12

                        Re: GM master cylinder question

                        Uh... yeah, it is, unless you want a rock hard pedal and / or a MC setup that won't stop you. That's kind of like saying the pushrod ratio is not that big of an issue when you go from Power to Manual. It is.
                        I already played that argument when this came up the last time and you guys all shot me down for saying what you just said......

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                        • #13

                          Re: GM master cylinder question

                          nun unh ^^ did not did not neener neener... I stayed out of that one.

                          Mike, on the Fords at least, it's just the fittings that are metric. The brake line tubing is still in inches. If you can get the flaring tools, you can put the metric ends on it easy enough. I think your choice is wise.
                          .

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                          • #14

                            Re: GM master cylinder question

                            nun unh ^^ did not did not neener neener... I stayed out of that one.

                            Mike, on the Fords at least, it's just the fittings that are metric. The brake line tubing is still in inches. If you can get the flaring tools, you can put the metric ends on it easy enough. I think your choice is wise.
                            Speaking of Flaring Tools, I'll be throwing down some how to plumb a fuel system tech here in the next few weeks.......

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                            • #15

                              Re: GM master cylinder question

                              Speaking of Flaring Tools, I'll be throwing down some how to plumb a fuel system tech here in the next few weeks.......
                              A good quality flaring tool is important...the cheap ones will make leaker fittings... I spent the dough for a decent set years ago and it has paid for itself several times now... I got my replacement master installed and didn't have to change a fitting ( i should have though, they are rusty and look bad). I now have good solid brakes that don't slowly fall to the floor.....


                              ed- and i spent less than $25 including a can of brake fluid
                              Last edited by oldsman496; April 19th, 2012, 05:28 AM.
                              Mike in Southwest Ohio

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                              • #16

                                Re: GM master cylinder question

                                I think it was Freiburger and / or Dulcich... minimum requirements for driving a car with risky or dysfunctional MC (choose 2):

                                a) manual transmission
                                b) working emergency brake
                                c) working horn

                                man I hate that sinking pedal feeling. Good call!
                                Last edited by Beagle; April 21st, 2012, 02:22 AM.
                                .

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                                • #17

                                  Re: GM master cylinder question

                                  I think it was Freiburger and / or Dulcich... minimum requirements for driving a car with risky or dysfunctional MC (choose 2):

                                  a) manual transmission
                                  b) working emergency brake
                                  c) working horn

                                  man I hate that sinking pedal feeling. Good call!



                                  Uh - i uh.... well... i uh....stammer, stammer....... I actually drove a 75 ventura (when i was 21 or so...) for 4 months every day to work about 15 miles a day with no brakes. I mean none, nada, zip.... and the clutch linkage was broken also... to start from a stop, you just hit the key and it would jerk and go.... and to stop, you did the reverse. turn off the key. i never claimed to be real bright... One day I misjudged the stopping distance and it was either a big bush to stop me or a new fiat convertible. I chose the bush. ate the steering wheel, loosened my front teeth real good and shattered the windshield with my forehead. i was doing all of about 10 miles an hour and i thought i could stop myself from smacking the windshield by grabbing the wheel real hard. broke my wrist too.

                                  from that day forward i never drove without a seatbelt on... I fixed the brakes a week later and the clutch a few days after that

                                  young n dumb
                                  Mike in Southwest Ohio

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