Thread: Brake troubles

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In my case the discs are very close to the same size, so no advantage. The point I was trying to make is that in many cases, street rods are built using what parts are available or will fit. That doesn't mean they are going to work together.

In the case of GM metric calipers, typically they have a 2.496 bore in the front. The rears can range from about 1.88 to over 2". Choose the wrong bore and you can wind up with a situation that has the front brakes stopping the car, while the rears never do much of anything. If the fronts are too much larger than the rears, the line pressure required to allow the fronts to stop the car will be too low to allow the rears to offer much clamping force. In most cases, you're never going to want more braking on the rear that the front, but you do want a relationship that allows complimentary action. Bore size, for me, is just a convenient way to compare.

My Ford calipers are actually closer in bore size than some combinations of GM parts. I agree that area is a probably a better description, but bore size will work as long as you understand that bore size will determine area.

Originally Posted by Hotrod46

. If the fronts are too much larger than the rears, the line pressure required to allow the fronts to stop the car will be too low to allow the rears to offer much clamping force.

1st thing to check!

My Wilwood MC sends 2x the volume to the front and equal pressure to both ends. It might be worthwhile to see what the Corvette MC does.

Originally Posted by Henry Rifle

My Wilwood MC sends 2x the volume to the front and equal pressure to both ends. It might be worthwhile to see what the Corvette MC does.

There's a test I can do with ease !

I started pulling the front caliper to do some measuring tonight but got pulled away, should have some results from more testing measuring etc tomorrow.

Thanks again everybody.

Originally Posted by Henry Rifle

My Wilwood MC sends 2x the volume to the front and equal pressure to both ends. It might be worthwhile to see what the Corvette MC does.

Looks to be 2 to 1

I tried to find the specs on the Corvette MC, but had no luck.

Here's some pictures and some measurements

rear brake line to caliper, small hole is aprox .080" large is 3/16"


rear caliper


front caliper


inside front caliper


inside measurement of front caliper


I tried to put the front caliper on the rear today but due to line connection location on the caliper I couldn't, the axle was to close or the medal hard line part was to long however you want to look at it.
I tested the rear calipers by them self's using a recirculating line back to the MC from the unused side. I swapped lines on the MC to the rear and had just a bit better braking from the front side which is putting out more volume. Still it took way to much foot pressure to stop the rotating axles.
When I look at the caliper brake lines and see the hole size I wonder how the small hole effects things or doesn't effect things.
11 " rotors on front and back.

Tire diameter, rotor diameter, brake pad/shoe area, caliper bore/volume, MC volume/pressure, brake pedal ratio, vehicle weight . . . with all of those variables, which are almost always different fore & aft, it's a wonder than any of the cars we build actually stop. I know that's belaboring the obvious, but I'm out of answers.

Hmmm. I can't help but think two things, one being twice the volume going to the front would be a issue, the rears never would get enough volume to fully collapse, two the banjo fitting on the rear with the small orfice would do nothing to pressure I wouldn't think but would provide a hard pedal until the volume is moved (very slowly) until woops maybe the fronts are already collapsed and the pedal will not move any further...and would equal no rear brakes! I would think you need the same type of lines and fitings front and rear (or very similar) and the unequal master cylinder (at least that much inbalance) would be for either a larger difference in size calipers front to back than you have or rear drums. Just my first thoughts. You now have enough info to give to someone like Master Power brakes and get it solved!

Looks like crud on the calipers-are these old used units??? does the spraque even work?

Are you doing anything with the Ford parts?

and did you bench bleed the master cylinder??

If this was my system I would check each caliper to see that the piston wasn't stuck-would move easily with a little compressed air into the line-----I would bench bleed master----I would get a stock OEM type combo valve---------2 lines from combo vale to front calipers and a 1/4 line to rear housing where splits to 3/16 to each side caliper

What I don't understand is just how are you turning the discs???? running the engine in gear??
Make sure the combo valve is centered----when OEM started using them it was to prevent lost of front and rear brakes with a failure in one half of system-------this seems as though the valve isn't centered in the system shutting off flow to the rear, but I don't like the CPP valve so don't have any idea on it----it seems according to the description that it is basicly just a junction for the brake lines and has a brake lite pressure switch built in--in other words-doesn't have function of the OEM type combo valve which delays front brakes while rears are engaged and then porportion fluid pressure flow to the rears to prevent lockup and allow the fronts to be primary braking.

Originally Posted by jerry clayton

Looks like crud on the calipers-are these old used units??? does the spraque even work?
Its just paint off the pads. The spraque works just fine, these are new units.
Are you doing anything with the Ford parts?
Tried the ford parts and they acted the same
and did you bench bleed the master cylinder??
If I bench or any other kind of bleeding on the the MC again I think I'm going to puke

If this was my system I would check each caliper to see that the piston wasn't stuck-would move easily with a little compressed air into the line-----I would bench bleed master----I would get a stock OEM type combo valve---------2 lines from combo vale to front calipers and a 1/4 line to rear housing where splits to 3/16 to each side caliperGot one off a car at the junk yard and will try it

What I don't understand is just how are you turning the discs???? running the engine in gear?? Yes with the engine running at idle
Make sure the combo valve is centered----when OEM started using them it was to prevent lost of front and rear brakes with a failure in one half of system-------this seems as though the valve isn't centered in the system shutting off flow to the rear, but I don't like the CPP valve so don't have any idea on it----it seems according to the description that it is basicly just a junction for the brake lines and has a brake lite pressure switch built in--in other words-doesn't have function of the OEM type combo valve which delays front brakes while rears are engaged and then porportion fluid pressure flow to the rears to prevent lockup and allow the fronts to be primary braking.

I bypassed all valves during testing

At this point I'm so frustrated that any body with the right amt. of cash could take it off my hands.

thanks for the help guys.

2200 $nz an can you arrange shipping?
feel sorry for you mate - been watching this thread for awhile an hoping that someone can help.
I've done a few brake systems now, an (touchwood) have had no issues. Can't help with any ideas sorry.
I've certainly been frustrated with a lot of other different parts of building a hotrod/street machine tho, so can definitely identify what your going thru.
keep your chin up !
mark

Navy, sitting this morning and your problem popped into my head. I'm wondering if you don't have a bad master cylinder. Looking at the Pete & Jake's catalog they have a MC for "Corvette Dual", and then three models of their GM Generic - 1) disc/disc, 2) disc/drum 7/8", and 3) disc/drum 1" that happens to be the chrome model. I think I'd be tempted to buy one of the GM Generic's for disc/disc and see if that might fix your problem. Also questioning that banjo fitting with the very small port.

Originally Posted by rspears

Navy, sitting this morning and your problem popped into my head. I'm wondering if you don't have a bad master cylinder. Looking at the Pete & Jake's catalog they have a MC for "Corvette Dual", and then three models of their GM Generic - 1) disc/disc, 2) disc/drum 7/8", and 3) disc/drum 1" that happens to be the chrome model. I think I'd be tempted to buy one of the GM Generic's for disc/disc and see if that might fix your problem. Also questioning that banjo fitting with the very small port.

I have 2 new ones, 1.125" and a 1", corvette types . I wonder if the out put is different on the Generic type as in equal amt of out put fluid ? The ones I have have a 2 to 1 out put, the 2 going to the front.

With all my testing including the last one with a proportioning valve from the junk yard I believe some how I have to increase the pressure to the rear caliper.

Originally Posted by Navy7797

I believe some how I have to increase the pressure to the rear caliper.

Navy, I believe you need to increase the volume to the rear, just my thoughts. I know its frustrating in a situation like this but volume and pressure are different and on brakes pressure can be held off but the mc determines volume not the valves assocciated with pressure. If there is anything to gain its you now know as i mentioned in the first of this thread there are many rods running around with no rear brakes.