I'm trying to make my Buick safe to drive, now that I have it running well. If I had built this car, it would have broken down every time I drove it. I don't see how people get away with some of the stuff they do. It has a front disc brake conversion on it and it is plumbed so badly that I'm afraid to drive it. Also, when you get on the brakes, it nosedives big time. It's kind of scary. It also has a 10 bolt rear with decent sized drums It has a proportioning valve that may not be working. I know it needs residual pressure valves and I'm going to try it without a proportioning valve until I decide it needs that. My question is, does it need a hold off valve? If you have the residual pressure valves, can the hold off valve actually make a difference? What's your experience? Thanks!
Been building hot rods professionally for almost 40 years but I've never heard of a hold off valve (?). Little more info needed. What type of master and where is it mounted, firewall or under floor? The proportioning valve, is it adjustable and if it is, I assume you've tried adjusting with no change? Since it's nose diving it sounds like your front brakes are doing all the work. Does it still dive if you do a gental stop or only on hard braking? On all our cars we set up with a adjustable proportioning valve in the rear line as well as a 10lb residue in line for drum brakes. Disc brakes don't get a residue unless the master in under the floor (lower the the calipers), then it get a 2lb to keep the calipers from bleeding back to the master. Should be able to adjust the proportioning valve to balance the front to rear. Of course I'm assuming everything is in good working order to start with.
Check this link. http://www.ecihotrodbrakes.com/discbrake_kit_components.html EC-526. Says it allows the rear brakes to actuate first.
When you have something someone else built, and its questionable, redo what you can to make it safe. Then, have a helper wet down the driveway and try to see if one end always locks up first. That will answer your questions. Keep the kids and dogs away when you do this.
When I did my dodge, I installed a proportion valve and duel master cylinder. It should be plumbed just like a newer car with new lines, if needed. I got 2 bad master cylinders in a row when I did it, but the third worked great. I'd check the work of the other guy, then test the parts. Proportioning valve go bad as well. Good luck Posted using the Full Custom H.A.M.B. App!
My question is in regards to the hold off valve. Is that the reason I'm experiencing so much nosedive under braking? Would that help? Or is that just the way that old 49 Buick suspension is.
Like was said before, what is a hold off valve? Could you describe what it is suppose to do? I have been into cars for 55 years and never heard of a hold off valve! If the front shocks on your 49 Buick are original, they are probably bad and that can cause the front end to nose dive. Have you checked to see if they have fluid in them?
Hold off, or metering valves, were used on and off through the late '60s-'90s on disc/drum systems. They "hold off" pressure to the front discs until the rear drum brakes receive around 100 psi line pressure, overcoming the shoe return springs. The idea is to have all 4 brakes apply at the same time. I would NOT use a metering valve on a non-stock system not designed for it, as they could cause early rear slide, something that you really want to avoid. You stated the plumbing needs rework, so that's where you want to start. As already stated, you want a 2 lb residual to any discs ONLY if the master is below the floor, and a 10 lb to drums, regardless of master location. (Check for any internal residuals in your master) Only use an adjustable proportioning valve in custom systems, not any factory/aftermarket fixed value valve. Make sure your front suspension is intact and in good condition, as that could also cause excessive nose diving.
I think everyone knows them as metering valve. Everything V8 Bob said is completely correct. There's your answer. Posted using the Full Custom H.A.M.B. App!
Thanks. My MC IS below the floor, so I will put in the residual valves. I may experiment with the hold off valve and see if I can tell the difference.
Darn. After totally re plumbing the car and installing new MC and new calipers, I cannot get a good pedal. I did install the hold off valve in the system and I have pressure bled it several times. Actually, I tried to bleed it with the original MC and couldn't get a firm pedal. So, I changed the MC and pressure bled it again. Still no pedal? I didn't have any pedal before I re plumbed it either. Suggestions? I'm thinking about getting a momma to pump the pedal tomorrow but I don't think that will change anything. Oh yeah, I did bench bleed the new MC.
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