Hi Gang..Have a question about brakes. I have a willys coupe that I am doing a brake system from scratch. Utilizing a speedway rotor and metric caliper kit. I have made a mounting under the car for the master cylinder and am using an 70-80's ford master like a granada , fairlane etc. with a 1" bore . I have a 9" truck rear big bearing style with tapered roller bearings. that I bought rear wheel cylinders for with 15/16 bore. I need a combination valve and have wondered if the 60-70 ford stock one would work for this. Granada wheel cylinders I think are 1"8 less bore than 15/16 size. I am assuming the metering valves are in a master cylinder as well as the proportioning valve but just if these would work or not with my other choices . I can add the metering valve as well as an adjustable proportioning valve as seperate units but then do you need to add the combination valve also? rear drums are 11 X 2-1/4" thanks for any tips
I've got a hot rod with a similar master cylinder and it runs 15/16" rear wheel cylinders with no extra inline stuff. I'd just set yours up and not worry about extras for now and see how it performs. I was under the impression smaller rear wheel cylinder diameter was used as a means to prevent rear wheel lock up on cars with not so much rear weight. The famous Ford Falcon GTHO in Australia from what I was told used a similar setup and that size rear wheel cylinders to prevent rear wheel lockup at high speed during racing at the Bathurst track.
If the metric calipers are GM G body they could require a quick take up master cylinder. G bodies were made from 78-88 (monte carlo, regal, grand prix, cutlass) but somewhere in there the quick take up castings showed up. Wrong master will mean you will never get a firm pedal feel. Just something to be aware of.
Some brake system clarification. A combination valve can include one or more of the following 3 valves: Pressure differential valve-triggers a warning light in the dash when there is a primary/secondary pressure difference of a few hundred psi. Metering valve-holds off front axle disc pressure about 100 psi to allow rear drum shoes to overcome their return springs. Proportioning valve-Controls rear brake pressure in percentage of master cylinder pressure to prevent early rear slide. Residual valves- Located in production drum brake master cylinders until the mid-'70s to prevent air entering the wheel cylinders. These are needed on older drum brakes, but are beneficial on any drum brake system. Factory combo valves are designed and tested for particular vehicles and really should not be used on any custom non-stock system. Best to simply use an adjustable prop valve with a disc/drum system, along with a needed residual, internal or inline 10# aftermarket. Drptop70ss gave good advice on the metric calipers.
A quick "rule of thumb" is if the bleed screws are metric (10mm) ,then the calipers are the low drag variety . You can cheat around the quick take up M/C issue by using pressure residual valves to stop the low drag callipers retracting too much.(not reccomended) Some people with the M/C below the floor don't even notice the difference in callipers because of the need for the valves
Right there may be the answer to countless "I just put disk brakes on and now have a mushy pedal threads. I got out and away from doing brake jobs on a daily basis just about the time those came out. Then what rigs with those brakes I did work on were stock units that weren't an issue because I replaced the parts with correct parts that matched the old parts. A search to see what he was writing/talking about brought up this page that explains it very clearly. https://www.freeasestudyguides.com/brakes-quick-take-up-master-cylinder.html I'll be bookmarking that page.
I've been trying to educate myself a bit on brakes and coming to the conclusion that there might be a bunch of unsafe street rods out there? Yikes! Would you rule out a factory combo valve even if it were being used on a similar wheelbase and weighted vehicle? And, all the components (master cylinder, front disc / bore diameters and rear wheel cylinders where the same as the donor vehicle? Seems like it might be OK?
It might be OK, but there are other factors that also have to be included, like CG, tire type and size, F/R weight bias, suspension design etc. Proportioning is the big variable in a combo valve, and can controlled better with an adjustable valve in a custom system, imo.
I don't use modern proportioning valves at all. I have a CPP distribution block in my Ford and it works well. Mine is black anodized. I'm using a Ford style dual master from Speedway, 1" bore. Very simplar to a '72 Mustang disc-drum master. Probably well under $30 at places like Rock Auto. https://www.ebay.com/itm/CPP-PROPOR...ON-BLOCK-CHROME-SWITCH-AND-WIRE-/262771374225
Yes, I'm sure you are correct. My father was an aircraft hydraulics mechanic on the carrier Midway during WW2 and after the war he started an auto repair shop which he successfully operated for 45 years. He used to tell me to keep in mind how much engineering went into producing vehicles and changing things could be risky business. Seems like some companies trying to sell their aftermarket brake products don't know or don't care that they may be putting peoples lives at risk. Anyhow, does keeping the combo valve in my transplanted Jeep system and adding a adjustable proportioning valve for fine tuning make sense?
Best to remove the proportioning portion from the combo valve while adding the adjustable prop valve.
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