Hot Rod Brake Question

Old 05-05-2008, 07:12 AM
  #1  
Scorpion1110
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Default Hot Rod Brake Question

Thought I'd fish for some info from the experts.

The car is a 46 Chevy 2-door coupe with a 327 and TH400.

Received the car from a less than honest gentlemen in Texas-a story for a different day.

Car was not running, but had a late model GM brake master and booster, with a proportioning valve (probably an F-body set-up). Car had brakes when we pushed it into the garage. Never driven as it didnt run (though it was supposed to.)

Current:

Brake pedal assembly from 69-72 GM A-body with a camaro brake pedal and actuator rod. Standard late 60's GM two bale master cylinder (new) and a metering block from a late 60's Corvair (used). New brake hoses in the front, custom formed brake lines (1/4 inch all way round), no residual valve as master is higher than pedal on the firewall. Drum brakes all the way round too.

Got the old piece of junk running yesterday and am trying to get brakes.

Bled fronts and got decent pressure. Rears are giving me problems as I can seem to get suitable pressure on trying to bleed master. Checked pressure at fitting on axle (central hose that feeds both sides), and on pumping brake the rear pressure was less than expected. Bleeding the brakes gives me just a trickle of fluid after the master is pumped up. I would have expected to see it shoot out when I pumped up the master and let my thumb off the line end.

What I know-

* The master is new,
*The metering block is clean and the master cylinder connections through the block to the master are correct,
*The brakes were not rebuilt save for front hoses.

The actuator rod was adjusted fully out but am wondering if its not long enough. Or could it be the need for a residual valve? Or should I be looking at new rear wheel cylinders?

I just cant get pedal and I cant get the fluid up at the rears.

Any suggestions would be appreciated.

later-
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Old 05-05-2008, 05:08 PM
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olds48
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My 48 Olds had the master underneath when I got it.Put residual valves on it(Wilwood,junked the factory piece) and worked fine.Got tired of having to lift the hatch in the floorboard to check the fluid so I put it on the firewall.Being the master IS higher I figured,like you,that I wouldn't need the residual valves anymore.WRONG.Never could get a really good pedal.Decent but not great.Read somewhere that the seals on the wheel cylinders require the constant pressure that a residual provides to keep enough pressure on them to keep from leaking.Now,I don't know if that is true or not,but I do know that when I put them (res. valves)back on that the pedal instantly improved :shock: Don't know if I just got lucky or not,but was a definite improvement.Hope you get it figured out and let us know what happens.BTW,can I have your grill??The Chevy's were 10 times nicer looking than the plain ol' Olds'.
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Old 05-06-2008, 04:44 PM
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olds48
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!/4" lines may be too big.Mine are 3/16 and m/c has 1 1/8 bore.Just a suggestion.
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Old 05-07-2008, 04:37 AM
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Scorpion1110
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Thanks Olds, and no you cant have my grill

I ordered a residual valve (wilwood) yesterday from Summitt and will plumb that this weekend-Also, becuase of the possibility of an airloc in the lines, I left the bleeders open overnight to try and gravity bleed the system. MC rear bale was down about an inch, so I replaced the bleeders, put a vacuum pump on the wheel cylinders and finally was able to pull fluid through. I have some pedal know. Hopefully with the residual valve in place and another round of bleeding that old boat will be running and driving this weekend.

The master is 68 camaro and should be the right bore for 1/4" lines. Hopefully I wont have to change them out but thats a good tip and I'll do it this weekend if I cant get firm brakes.

Fired up the motor last weekend and it sounded pretty good-chased a few leaks, changed a gas tank fitting, and it sounds fairly strong-suprise since everything on that car was a slam job from my "Favorite Texan". Its actually halfway decent now.

Funny think is I just found and bought a cherry 1931 Model A with a 250 Chevy six and some vintage speed equipment so the 46 might be for sale.

keep me in mind if you know any buyers.

Later
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Old 05-07-2008, 05:11 PM
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fla1976
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Default 46 brakes

I would bleed the system with a low pressure bleeder. That would keep any air in the system from being compressed and getting lodged somewhere. You can build one if you have a compressor, a pressure regulator, some flat 1/4 inch thick rubber material, some flat 1/4 inch steel and a quick connect fitting and a large "C" clamp. Cut the steel to a size that would cover the top of the master cylinder. Then cut a piece of flat rubber to the same dimensions. Glue the rubber to the steel plate. After it has cured, drill and tap a hole to accomodate the fitting. Install the fitting using teflon tape. Remove the master cylinder cover and fill the reservoir. Place the plate over the master cylinder, and clamp it it place with the clamp. Connect the regulator to the compressor and connect the regulator to the fitting on the master cylinder. Bring the pressure up to where the gauge on the low side of the reg just barely moves. Then bleed the system. Start with the wheel furthest from the master cylinder. After bleeding each wheel, remove the plate and refill the master cylinder. You don't want to introduce any air into the system. Be sure to crank the pressure down before removing the plate from the master cylinder. This will remove any air from your system and you will have a bleeder for future use. I got the design from a car magazine (don't remember which one) and it works great.
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Old 05-08-2008, 06:29 AM
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Default Cool Idea

Thanks Fla1976-Awesome idea! Will give it a try this weekend.

later.
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Old 05-08-2008, 10:17 AM
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That is a cool idea.Makes sense,too.Thanks!
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