The Weekly H-Boost/Chevy disk Discussion!

[SaddleUp]

I hate to call you on this, but it is absolutely wrong. Most of the Chevy's are opposite of ford, including the popular corvette master. This is why everyone is always having a problem with rear wheel lockup.

This is a good website for looking up master cylinder bore sizes. They also include pics of many of the parts. http://www.discountautoparts.com/

Just to pick at random, here is a '78 blazer 4x4, and a 76 camaro. Note the smaller reservoir is to the rear.

76 camaro

By all means correct me if I am wrong. Even better when you have documentation to support it which you have. I can't argue with the pictures you have displayed.

72Sport, even if the brakes are disk/disk the master cylinder should be hooked up in the right direction. The disks may not be the same size to start with (rear disks are often smaller than front ones) and even if they are not the front brakes still need to have the most braking power. I'll concede that GM couldn't make up their mind (I figured that as soon as I posted someone would prove me wrong) but they still should be mounted as designed.

FWIW, My disk/disk master cylinder doesn't have matching revervior sizes. They are both large for sure but the one closest to the firewall is still a little larger than the other.

 

[72Sport]

Fully understand that things should be hooked up correctly. 68 Bronco was reversing lines to correct a problem that wasn't or isn't related to having lines reversed.

 

[BG's 68 Bronco]

Is Madguyver the only one using a corvette MC? I'm still in limbo, as to whether the res closest to the firewall would be for the front brakes. From what I've learned it would be, but there is a lingering question in my mind as to whether this is correct or not. NAPA can't even tell me.

I don't know really anything about Proportioning valves, but if I only have what I guesstimate to be 20% pedal pressure what would PV do? I could see it doing more if I actually had some significant resistance in the brake pedal. I have bleed my fair share of brakes and these ones are not working correctly!

After bleeding them I could pump the brake until the cows come home and there is no difference in pedal pressure... the thing should get hard as a rock right. I should barely even move the pedal after pumping it 10 times.

thanks for your help guys this one is really eating at me... I mean brake systems are not all that complicated!! I'm probably doing something really stupid, but haven't noticed it!

 

[Kansas Corey]

I use a 2 liter plastic soda bottle and some windshield washer tubing. Put brake fluid in the bottle to cover the tubing,
connect the other end to the bleeder nipple with a loop higher than the bleeder nipple, no air will be drawn back into system if a snug fit at nipple. can be used solo less than 5 bucks and you get to drink the soda

Wes - thanks for the suggestion - will give it a try this weekend. Corey

 

[Madgyver]

I'm going to PM Mad, as he uses the corvette MC's he should be able to clarify.

I have T-Bird calipers up front and Caddy rear discs using a disc/disc Corvette MC on the Yellow77.
For the disc/drum set-up on the other 77 w/H-boost I'll use the same MC and add an adjustable proportioning valve on the rear lines.

 

[BG's 68 Bronco]

Yes Mad!

Okay I have a 78 corvette MC disk/drum. Which reservior feeds front brakes just to clarify? Maybe I should say how do you have your MC plumbed?

 

[SaddleUp]

Is Madguyver the only one using a corvette MC? I'm still in limbo, as to whether the res closest to the firewall would be for the front brakes. From what I've learned it would be, but there is a lingering question in my mind as to whether this is correct or not. NAPA can't even tell me.

I don't know really anything about Proportioning valves, but if I only have what I guesstimate to be 20% pedal pressure what would PV do? I could see it doing more if I actually had some significant resistance in the brake pedal. I have bleed my fair share of brakes and these ones are not working correctly!

After bleeding them I could pump the brake until the cows come home and there is no difference in pedal pressure... the thing should get hard as a rock right. I should barely even move the pedal after pumping it 10 times.

thanks for your help guys this one is really eating at me... I mean brake systems are not all that complicated!! I'm probably doing something really stupid, but haven't noticed it!

If one reservior is larger than the other then it will be the one for the front brakes. (Which is how I know I was wrong above)
If I am hearing correctly you tried it both ways and the result was the same? If so then try the proportioning valve as was suggested above. Trying them reversed essentially eliminated any other cause unless it is in the front disks. I.E. It isn't in the booster or master cylinder.

 

[BG's 68 Bronco]

If one reservior is larger than the other then it will be the one for the front brakes. (Which is how I know I was wrong above)
If I am hearing correctly you tried it both ways and the result was the same? If so then try the proportioning valve as was suggested above. Trying them reversed essentially eliminated any other cause unless it is in the front disks. I.E. It isn't in the booster or master cylinder.

Which line would I put the PV on? Rear! I have the stock Astro PV would this one work or should I try an adjustable one? Sorry for all the questions I know dick about PV's.

 

[toddz69]

Which line would I put the PV on? Rear! I have the stock Astro PV would this one work or should I try an adjustable one? Sorry for all the questions I know dick about PV's.

Proportioning valve goes in the rear. I would use an adjustable one. Summit/Jeg's, etc. sell the cheapest versions - usually about $30-$40.

Todd Z.

 

[Madgyver]

Yes Mad!

Okay I have a 78 corvette MC disk/drum. Which reservior feeds front brakes just to clarify? Maybe I should say how do you have your MC plumbed?

I'm not sure how I ran it because both reserviors were the same. I kept it simple and may have done it with the front res for the front discs and the rear res for the rear discs. I had problems with rear discs locking up with stock front calipers and thought of restricting the line with a proportion valve but why reduce line pressure?
So I did the upgrade to T-Bird front calipers and now my brakes is pretty close to balanced without having to use a proportioning valve.

 

[toddz69]

Yes Mad!

Okay I have a 78 corvette MC disk/drum. Which reservior feeds front brakes just to clarify? Maybe I should say how do you have your MC plumbed?

I don't think this is really part of your problem, but I don't think there were any '78 Corvettes with rear drums. Most years, if not all, from the mid '60s on, had 4 wheel discs. Since you have disc/drums, I'd use a '78 Camaro master cylinder instead since it should have the RPV in it for the rear brakes.

Todd Z.

 

[Madgyver]

After bleeding them I could pump the brake until the cows come home and there is no difference in pedal pressure... the thing should get hard as a rock right. I should barely even move the pedal after pumping it 10 times.

thanks for your help guys this one is really eating at me... I mean brake systems are not all that complicated!! I'm probably doing something really stupid, but haven't noticed it!

It could be that you got a bad MC... Auto parts stores around here have done it to me but they are just the vendor. Counter people don't know too much anyway..."Was that a Chevy Ford Bronco?"%)

 

[BG's 68 Bronco]

I don't think this is really part of your problem, but I don't think there were any '78 Corvettes with rear drums. Most years, if not all, from the mid '60s on, had 4 wheel discs. Since you have disc/drums, I'd use a '78 Camaro master cylinder instead since it should have the RPV in it for the rear brakes.

Todd Z.

I'll double check w/ NAPA, but the guy told me the MC was for disk/drum Hmmm! I think the MC is correct because the the rear brakes work fine... I don't have to pump them up to build pressure!
Rear brakes feel the same as when I had my manual MC on.

 

[BG's 68 Bronco]

It could be that you got a bad MC... Auto parts stores around here have done it to me but they are just the vendor. Counter people don't know too much anyway..."Was that a Chevy Ford Bronco?"%)

I was questioning the MC. I'm going to try a couple things to narrow down what my issue could be. Maybe I should start with swapping MC's.

 

[BG's 68 Bronco]

Alright... I'm getting somewhere;D I clamped the flexible lines for the front brakes starting from the MC. I get normal, meaning a firm pedal, which is what I'm looking for. That rules out anything with the MC. Next I clamped the line which stops on top of the front axle... firm brake, good! Now I move onto the new 1/8" flexible hoses connected to the calipers. I clamped the one side first and I have medium brake feel then I clamp the other and I have firm brakes.

So, I guess what I am wondering is... will a proportioning valve, as suggested previously, give me a firm pedal and increase the amount of pressure the calipers are putting on the rotor? if so where do I mount the PV, as it is the front brakes giving me the havoc.

Could It mean something else with the calipers?? they are brand new 70's Blazer single piston style calipers.

One other thing what size are the stock brake lines on the Bronco? Would going from a smaller dia. line to a larger dia. cause the lack of pedal pressure symptom I am experiencing? because I think my new flexible hoses connected to the calipers are a larger dia.


I've got a good feeling we're going to solve this one soon!

Thanks again!

Barret

 

[72Sport]

Pro Valve has nothing to do with front brakes even if you had one. It only affects the rear.

Sounds like air in the caliper or calipers. Some have had to remove the calipers one at a time and bleed them to get the air out. I have never had to do it. I believe they stick of wood or two between the piston and housing of the caliper to keep the piston from popping out and point the bleed screw straight up and bleed out the air.

Since brake fluid can't be compressed what you put in at the MC comes out at the caliper no matter what the line size. If there is air in the system it will give you a soft pedal.

 

[BG's 68 Bronco]

Pro Valve has nothing to do with front brakes even if you had one. It only affects the rear.

Sounds like air in the caliper or calipers. Some have had to remove the calipers one at a time and bleed them to get the air out. I have never had to do it. I believe they stick of wood or two between the piston and housing of the caliper to keep the piston from popping out and point the bleed screw straight up and bleed out the air.

Since brake fluid can't be compressed what you put in at the MC comes out at the caliper no matter what the line size. If there is air in the system it will give you a soft pedal.

I got to thinking last night and I believe you are correct. I should be more positive... I know you are correct. Thanks again all that helped. I will let you know how it turns out this afternoon!

 

[bludorbronc]

Make sure when you bleed the front calipers that the bleeder screw is at the highest point so no air is trapped above it.A friend of mine put chevy discs on and we had to take the caliper off and hold it so the bleeder was at the highest.

 

[SaddleUp]

Make sure when you bleed the front calipers that the bleeder screw is at the highest point so no air is trapped above it.A friend of mine put chevy discs on and we had to take the caliper off and hold it so the bleeder was at the highest.

I've seen people put them on upside down as well. (bleeder at the bottom) Not sure if the Chevy setup can be done this way or not but it's a pretty common mistake.

 

[ET]

I've seen people put them on upside down as well. (bleeder at the bottom) Not sure if the Chevy setup can be done this way or not but it's a pretty common mistake.

Uh yeah. You can put the cheby caliper on with bleeder on the bottom. Ask me how I know. Second thought dont ask.

Eugene