I have a 48 Ford sedan that has really touchy brakes. The car is a new build with all new brake parts, including drums. It has the stock Ford pedal, and if stepped on too quickly will lock up the front tires. It has F100 Ford internal expanding brakes in the front, and Ford truck (9") in the back. The master cylinder is a 1" bore 1967 Mustang dual chamber drum/drum, with a Chassis engineering power brake booster. This is all pretty common stuff, I'm wondering if I should put a proporating valve to the front brakes and reduce the line pressure. I hate to discard the booster. Have any of you guys had this experiance? Thanks
I don't think using a proportioning valve on the front is a good idea. The brakes would probably be fine without the booster. Is it a remote unit or mounted with the master cylinder? I would either try running without the booster or try with a slightly larger master cylinder. 1-1/16" or 1-1/8". Or just get used to pussy footing the brakes. Mart.
As already mentioned, your pedal ratio is probably too low for power assist, especially if you're using the stock '48 6:1 pedal, ...and...Do NOT proportion the fronts. Are the front brakes assembled correctly, with short linings to the front and adjusted properly? You mentioned the 9" rear, but what size are the brakes? Do you know the wheel cylinder sizes?
Thanks guys. The wheel cylinder size in the front is 1 1/16. I don't remember the rear size. It's a Chassis Engineering booster that is attached to the master cylinder. This car is a new build. I removed the 4 door body from the frame, and saved the Earl Shieb paint, and original interior. I built a chassis using mostly Chassis Engineering parts, and a Okie Joe dropped axle. I drive it everywhere, but I have to do something with these brakes....
You don't really need the booster with the drums. If you had discs, then, yes, it would be a good idea. Either rework it without the booster or make the master cylinder diameter bigger. Mart.
i have basically the same brake setup on my `36 except they are not boosted, brakes work great. ditch your power booster
It's not the booster. Sounds like you just have more brake in front than the puny 9" ones in the back. Put bigger diameter wheel cylinders in the back for a better % gain and it might even out. It's NOT the booster!
Do you know for a fact that the outlets from the m/cyl are plumbed correctly for the front and rear brakes? Could having them reversed cause the problem you're describing?
Just for clairification when I said 9" I meant a 9 inch Ford pick-up rear end with 5 on 5 1/2 lug pattern. I rear brakes are intended for a big pick-up or van. It seems like I have way too much brake on the front. Of coarse like most hot rods I have big tires on the back, and smaller ones on the front. The smaller ones provide less traction which makes the problem worse. Sounds like I need to ditch the booster. I hate modern stuff, and am being stubborn on the disk brake idea. Thanks
I have the same problem with my 67 camaro .it has power brakes , front tires will lock up with little effort. it is dangerous not sure what to do
Actually the brakes are pretty much the same at 11" diameter...F100 fronts are maybe 1/4" wider than the rear..The rear brakes wheel cylinders are probably around 15/16" but brake parts listing will show other sizes available, I would put larger ones in...As in previous post check plumbing to MC [not that I am conviced it really matters] as it might react different with boost...
The front to rear weight bias of a 48 sedan is probably quite a bit different to a F100. The truck is probably underbraked on the rear to prevent rear wheel lockup when unladen. You may be able to get some 1" cylinders for the rear which would improve the front locking problem by making the rears do more work. You can still ditch the booster though. Lots of guesswork, but as yours is a not standard application, you will need to experiment until you hit on a combination that works. Mart.
Sometimes we have issues with the brakes on a rig if they don't work like the brakes on our daily or the other rigs we drive. Watch a guy climb out of his four wheel disk Audi into a Model A V8 running 40 drums on all four corners and that becomes quite obvious but it can work the other way too. On the booster it's learning the feel of the booster and knowing how it affects the brake feel. That shouldn't be a big issue and should come with time. On the brakes not hooking up evenly, Somewhere in the system it isn't balanced front to rear. A search shows that most mid 60's full size Ford Sedans run 1-3/32 front wheel cylinders and 7/8 or 15/16 rears and that most Ford pickups run the 15/16 rears. As some said, are all the shoes on correctly with the smaller shoe in front and the one with more contact area in the back? Primary/Secondary just like a carb the secondary almost always is the larger of the two. Are the rear brakes adjusted correctly? The lining may have to move too far before it contacts the drums. Are the brake lines the correct size front and rear for the application? The wrong size may cause reduced pressure to the rear brakes.
I hate guessing- First - check your pedal ratio If you use a manual brake pedal with a booster you'll likely put yourself into the windshield or ditch. If you use a power brake pedal with manual brakes you'll likely not stop, hit a object then go into the windshield. The idea is to avoid hitting the windshield. For 50.00 you can eliminate a lot of guess work and trial and error parts accumulation.
I put custom pedals/arms in my '42 pickup and found out that I didn't do enough homework on the pedal ratio and booster, good brakes but "touchy". My fix was a cheap adjustable regulator spliced in the vacuum line between the manifold and booster and dialed it in to what I wanted. Its been working great for over a year.
Change the MC to a 1-1/8 or remove the booster. The bigger MC will have less line pressure for a givin input force making less touchy brakes.
Thanks for the response. I keep my parts boxs so I can refer to the part number of the suspect pieces in the future. I discovered the rear wheel cylinders are 13/16. I'll go to the auto parts store in the morning and see if i can get 7/8 or 15/16. I have suspected all along the rear brakes wern't doing much. Now I know why. Thanks again, and keep the ideas comming.
If you want to try a bigger master ,I used one from a full size ford van it has 1 1/8bore. Let us know how this works out. Were all just guessing and we all need knowledge Russ
This is a pedal swing ratio problem, without a doubt. I have experienced this very same issue in the past after adding a vacuum booster to a 4 drum setup.
Front brake lockup is always tough to diagnose as it can have so many causes In your case you have Lockheed style non-self energising 11 x 1 3/4 on the front and self energizing 11 x 2 on the rear. That should give you significantly more rear brake than front You then have more leverage on the rear (larger tires), which reduces brake effectivness at the rear You then have different wheel cylinder sizes. If it was my car, I would fit bigger wheel cylinders in the rear AND then install an adjustable proportioning valve in the rear circuit and adjust it so the car stops right
The rear brakes have 13/16 wheel cylinders now, I just bought 15/16, but haven't installed them yet. Maybe the first of the week. I'll keep you guys informed. thanks
I spoke to a nice guy that runs a front end, and alignment shop about the touchy brakes on my sedan. He said F1 or F100 brakes were not intended to be power boosted, and I had an "over active braking condition" He said to reduce the wheel cylinder size on the front brakes. I had 1 1/16 and I reduced the size to 15/16. I used rear wheel cylinders intended for a Ford pick up with a 9" rear end. The wheel cylinder bolted on the F1 backing plate, but I had to grind or relieve the top area of the spindle for hose clearance. I tried the new brakes out this morning, and what a difference!! The brakes still work well, but now they don't skid the front tires, and try to launch you through the windshield. The rear brake wheel cylinders are 13/16. I have always thought the rear brakes wern't being fully activated, so I am going up in wheel cylinder size on those to 15/16 to bring the braking action up a little. I'll keep you informed. So far, so good...
You might want to leave the rears alone. By reducing the fronts you have increased the rears, if you see my logic. If they're working ok now leave them alone. Mart.
I had F100 brakes on the front of my avatar with pickup rears servo assist. They would put you through the windshield - worse than air brakes. Without the servo perfect. Just take the vac off the servo and drive it - you will be surprised! F100 brakes and vacuum booster will not work.
I had the exact problem as the OP. I called Master Power Brakes and they told me I needed a hold-off valve. All of your parts are the correct size, but the hold off valve does not apply pressure to the front until the rear reaches ((I think) 125 pounds of pressure. You want the rear brakes to come on first so the car doesnt swap ends when you hit the brakes
wade-a-minit! Of course you can add a booster to F100 brakes. I did it to my 1960 F100 several years ago and have been driving it every day
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