I took my truck ('64 Chevy C10) in to a local mechanic for a good once over and to fix a bunch of minor problems. No **** about not doing it myself, please. I need it done quickly and done right the first time. I have to choose one or the other if I do my own work. Anyway, one of the things I wanted done was to swap in a two-pot master cylinder. Manual, drums all around. (Swapping in discs later, but that's later.) I brought him a bolt-in replacement master cylinder and a couple of 10 pound residual pressure valves, which is what MP Brakes recommended. He said he'd feel a lot more comfortable with a combination valve or proportioning valve and a switch connected to a dashboard light that would tell you if your brakes were failing. Problem is, he's having trouble finding what he's looking for. So on one hand, I have a very reputable, by-the-book mechanic. On the other hand, I have MP Brakes, who I've had mixed luck with, but works with custom applications. Anybody know what I should be looking for?
when I did my 66 suburban, I just put in a dual m/c for a 68 pickup, and plumbed separage lines to front/rear. No valves or idiot lights of any kind. Worked fine. Most drum/drum master cylinders have the residual pressure valves built in...they hide under the br*** inserts that the lines seat against.
Yeah, I should clarify that I'm not worried about the idiot lights and I know most people just run new lines, skip the combination valve, and have no problems. Problem is, I don't know enough about brakes to contradict my mechanic (whose reputation is on the line) with any degree of certainty. I guess what I'm really looking for is information on GM's factory setup. When did they add the combination valves? Which cars/trucks did they come on? Was it just on the disc/drum cars or did the drum/drum setups have it? How do I know if the MC I just bought includes the residual pressure valves? Anything official to move it out of the realm of "my cousin did this once and it worked fine," know what I mean?
If its all drum, why would it need a proportioning valve? If anything, it just needs a distrabution block. A p-valve is needed for disc brum setups since disc and drums both use different pressures.
You would also be able to tell right away if you have a problem in one of the front or rear circuits as the brake pedal will be different height, as in lower to the floor.
I agree with that. Sounds like a case of upward delegation, in the rodding world. You want a certain setup, your mechanic doesn't want to do it that way. He doesn't have a solution but will do it if you do all the legwork and find the solution (if one exists to his satisfaction). You might have better luck taking it to a reputable rod shop. Your mechanic may be too worried about liability issues. Another reason why so many HAMBer's do their own work.
I have had good luck over the years with your set up, but the front and rear will have different pressures and volume. It may be necessary to run different size tubing to the rear. As stated before, you won't need a proportioning valve with drums at all four corners.
My thoughts exactly, but like I said, I'm still new at this and don't want to dismiss what he's saying without considering it. Back to the combination valve, let me see if I've got my **** straight before I try to talk to him. The more times I change my story, the less likely he'll be to believe me. My understanding is that the combination valve keeps the front brakes from applying until the rear brakes have had a chance to kick in (metering), keeps the rear wheels from locking up under heavy braking (proportioning), and keeps the shoes close to the drums (residual pressure). Now, I understand why the different pressures in a disc/drum setup would force you to use these valves. Otherwise, the discs would activate at very low pressure before the drums even kicked in, right? So I get why that wouldn't be an issue if front and back worked at the same pressures. What I don't get is why weight transfer doesn't affect rear wheel lockup with a drum/drum setup. I mean, the rear is going to unload a little during a panic stop no matter what, so why don't the rear wheels lock first? Or do they, and it's just not noticeable enough to be a problem?
The bores of the front wheel cylinder are larger than the bores of the rear wheel cylinders. Resulting in less force being applied to the rear brakes than the front.
MP recommends the 10lb valves because most hot rods use an under floor MC, where you need the valve to keep fluid from running back into the MC. You should be fine just running the lines.
as for when/why the valves came into being, check the federal new vehicle regulations for 1968/69 cars, you'll see they specified an idiot light and a dual master cylinder (separate front/rear brake systems). Combination valves were just the cost effective way to get the idiot light to work, and do all the other stuff that was needed. To see if the m/c has residual valves, poke in the tube seats with a paperclip and see if you feel a rubber valve in there.
What's up this is your buddy in cisco. The dirty bum that sold you the front end for your chevy. I don't know alot about brakes either other than that is what the middle pedal is for. i do know that if you do ron the proportioning valve up on the booster you have to be carefull about which one you use. If your getting it out of a yard it has to be from a vehicle with compareable size to your truck like a 1/2 ton truck. If you want to or need to go that route I think I have one for a 77 chevy scottsdale with the switch right on it. You can have it if you want it. If you want to totally ignore what I just said that's cool to. Don't hesitate to ask if you need any original part for the chevy( i.e. motormounts!). If your not doing anything on Sunday come down to Plowboys he's having some Hambers over. Haven't seen you around in awhile.
Hey! I remember you! Check it out: old crossmember's out and the new one's in. Just need to run new brake lines. Yeah, I'm getting better about asking if people have parts. Not sure if the 77 MC and switch would work, though. I forget the exact year, but I know GM had switched to disc/drum by '72, and mine's all drum. I'm going in to talk to him this afternoon. I'll probably take another crack at getting him to skip the switch. I'll be there.
They're all bagged up and ready to go. Just to follow up, I stopped by the mechanic's today to figure out what the hell we were going to do. First thing he told me was that I have a little lizard living somewhere in my truck. Must have followed me back from Florida. Anyway, it looks like we had a difference in terminology more than anything else. I sketched what I was thinking, he sketched what he was thinking, and they were pretty similar. He agreed to do it my way if I'd agree to give his way a shot first. I picked a valve out of an old GMC 4000 for a couple of dollars. Only manual drum setup in the whole yard. Might work, might not, but it made him a lot more comfortable to try it.
Noting the incredibly high readership of this dry post, we're on to your subliminal tricks: "**** master"?
The Jalopy Journal
