Trouble Shooting Brakes

[masonjarz]

Hi,

I have a 1967 Caliente with a SSBC front disc conversion and rear drums from a larger Ford installed by the owner about 15 years ago (not a ton of miles since and the rear shoes were replaced 1000 miles ago). There is no power assist.

The pedal pressure is very high and the braking effect is poor. I can get the front end to dive a little if I jab the brakes at low speed. In a panic stop, none of the wheels lock up, the car goes straight but it takes about twice the distance it should to stop. The pedal pressure just to keep the car stopped at idle is ridiculous.

The master cylinder (1" bore) and rear brake proportioning valve were included in the SSBC kit. I don't know about the distribution block but I suspect it, too, was part of the kit as the car was originally drum/drum.

As you can see from the photo, from what I can tell, the system seems to be properly plumbed with a 2 reservoir master with the large plumbed to the discs and the small plumbed to the rear wheels through an adjustable proportioning valve.

The brakes have been checked out by a local shop. There were no leaks and everything looked good. The front pads are good. The shop was able to get a slight improvement because the PO had put the primary shoes on one drum and the secondary shoes on the other. They also got the front end of the car to dive on braking whereas before, it simply stayed level. They took some time with the proportioning valve and think they got the right setting. This is a good little independent performance shop.

The car had previously passed a provincial safety inspection when I imported it into Canada and that's where they noticed the problem with the brake shoes but found no other issues.

I'm wondering if I need a residual pressure valve for the rear circuit or whether the distribution block already has one.

I'd appreciate any help whatsoever.

[Lou's Comet]

Do you know if the car originally had power brakes?

Power brake and manual brakes have different pedal ratios. If the car originally had power brakes and someone converted it to manual with out changing the pedal to a manual pedal might be your problem.

Some of the fords have both holes drilled into pedal arm and you would just have to move the pin to get the correct ratio.

Power brakes the ratio is around 4 to 1 and manual brakes the ratio is around 6 to 1.

So if you have the power brake ratio, going to the manual brake ratio would help a lot.

Lou

[Jims65cyclone]

Check this page about half way down. It shows the difference in pin location between manual and power brake pedals.

http://www.cometcentral.com/forum/viewt ... 472#p91472

Jim

[masonjarz]

Thanks guys!
I got excited and ran out to the garage...I definitely have a manual pedal.

[A/FX]

The first thing I noticed is that you have a combination valve AND a proportioning valve. I see no reason for the duplication, the combination valve has a proportioning circuit built in so the other valve is redundant and could be the problem. Also if the front disc installation is not factory there may still be a residual check valve in the port of the master cylinder that was for the drum system. I would suggest you gather all the info on what you have, (bore sizes of each caliper and wheel cylinder, line size, master cyl. bore size,) and submit it to a company like Master Power Brakes. They will recommend what you will need to make your existing brakes work correctly. ( you may need to replace your master cylinder and the combination valve.)
The braking system is the one system on your car that you want done the right way.
Jim

[poboyjo65]

The first thing I noticed is that you have a combination valve AND a proportioning valve. I see no reason for the duplication, the combination valve has a proportioning circuit built in so the other valve is redundant and could be the problem. Also if the front disc installation is not factory there may still be a residual check valve in the port of the master cylinder that was for the drum system. I would suggest you gather all the info on what you have, (bore sizes of each caliper and wheel cylinder, line size, master cyl. bore size,) and submit it to a company like Master Power Brakes. They will recommend what you will need to make your existing brakes work correctly. ( you may need to replace your master cylinder and the combination valve.)
The braking system is the one system on your car that you want done the right way.
Jim

Damn good advice right there!

[masonjarz]

The first thing I noticed is that you have a combination valve AND a proportioning valve. I see no reason for the duplication, the combination valve has a proportioning circuit built in so the other valve is redundant and could be the problem. Also if the front disc installation is not factory there may still be a residual check valve in the port of the master cylinder that was for the drum system. I would suggest you gather all the info on what you have, (bore sizes of each caliper and wheel cylinder, line size, master cyl. bore size,) and submit it to a company like Master Power Brakes. They will recommend what you will need to make your existing brakes work correctly. ( you may need to replace your master cylinder and the combination valve.)
The braking system is the one system on your car that you want done the right way.
Jim

That is damn good advice! Thank you very much!

[62Cometman]

I know 1 inch is a lot of companies go to for a manual system, but honestly i like to go smaller. If you look at a company like wilwood their manual master units are 1" and smaller they have a 15/16" and a 7/8" the smaller the bore of the master cylinder the more pressure produced at the caliper,this usually means that your pedal takes less input to stop, it will still be hard but this is the case on any manual brake system and only seems worse with disc brakes. What a lot of people dont realize is that in a perfect condition a drum brake system brakes better than disc brakes. There is more friction surface area and due to the lever action of the shoes it will "help" apply. Disc brakes systems are asking you to clamp the rotor as it rotates which requires much more pressure to produce the same amount of stopping force. The pedal on my car is rock solid pretty much all the time and it does take some input to make it stop quickly. My suggestion is if you arent running too large of a caliper on the front to switch to a 15/16 or 7/8 master. The pedal will likely still be rock solid but it will take less input to get more stopping power.

[masonjarz]

Great advice! Thanks.
I think a smaller bore master, deleting the adjustable proportioning valve, getting a new distribution block with an adjustable proportioning valve built in and installing 2 residual pressure valves in the rear circuit Is my best strategy. Thanks for all the input!