No Brakes

[hunter1]

Drove this build for the first time today. Cobra Hydroboost (I think), GM based front and rear disc. Just installed ElDorado brakes on the rear axle and have very little pedal. Previously had drums on the back with disc on the front and had good pedal. Had a GM based universal aftermarket master cylinder that said it was good for Disc/drum or Disc/disc. Evidently not enough for the front and rear disc. Which Master cylinder do I need? Also using a Wilwood adjustable proportional valve.

 

[ksagis]

Passing on what I have learned through research on forum, trial / error, and feedback from various gurus on forum. I think you need at least a 1.125" MC and likely happier with a 1.25" MC. And make sure the bleeder screw on the Caddy rear brakes caliper is horizontal when bleeding.

Edit: and make sure parking brake is properly adjusted too. Should have less than 0.125" of clearance between parking brake lever and stop when the parking brake is toggled.

 

[Yeller]

ksagis hit what I think the biggest issue is, the parking brake adjustment on the rear calipers. If the master cylinder bore is too small the pedal will be low but it will stop, probably very well, just have more travel than you want.

 

[Torkman66]

Had similar issue. Adjusted rear parking brake lever per video and solved the low pedal.

 

[Broncobowsher]

Have you cycled the park brake to ratchet the piston out? I always understood that the parking brake was an issue with those calipers if they didn't get used enough to keep them adjusted. In this case, initial adjustment.

 

[ntsqd]

Also need to get in the habit of using those p-brakes every single time you park it. You want to keep that adjuster mechanism working or it will seize up. Should also flush the brake fluid annually, without fail. Any moisture that gets into those calipers is death to the adjuster mechanism.

 

[ksagis]

Also need to get in the habit of using those p-brakes every single time you park it. You want to keep that adjuster mechanism working or it will seize up. Should also flush the brake fluid annually, without fail. Any moisture that gets into those calipers is death to the adjuster mechanism.

Thanks for these tips on the Caddy brakes! I had not heard previously about the moisture concern specifically related to the adjuster mechanism.

I'm assuming the moisture leads to rusting of adjuster mechanism and a subsequent inability for it to adjust to keep the pad gap small. And that then results in more pedal travel needed? Or is it something else?

 

[ntsqd]

From what I've seen of those adjusters most of them don't work at all. Given that most people do not flush brake systems any moisture in the fluid eventually finds itself in the calipers. Where it goes to work on that adjuster mechanism. The calipers get rebuilt, but the rebuilders don't have the parts to fix the adjusters. So if you have some that are working you definitely want to do everything that you can to keep them working.

 

[hunter1]

Passing on what I have learned through research on forum, trial / error, and feedback from various gurus on forum. I think you need at least a 1.125" MC and likely happier with a 1.25" MC. And make sure the bleeder screw on the Caddy rear brakes caliper is horizontal when bleeding.

Edit: and make sure parking brake is properly adjusted too. Should have less than 0.125" of clearance between parking brake lever and stop when the parking brake is toggled.

Thanks for the information. Adjusted the parking brake on both sides per youtube. Got good brake now but pedal is still a little lower than I like. Will bigger bore MC take care of that?

 

[hunter1]

ksagis hit what I think the biggest issue is, the parking brake adjustment on the rear calipers. If the master cylinder bore is too small the pedal will be low but it will stop, probably very well, just have more travel than you want.

You're right definitely stops better after adjusting the PB. I Guess I need a bigger bore MC? I need one with passenger side ports to match the lines I already have made. Any suggestions?

 

[hunter1]

Also need to get in the habit of using those p-brakes every single time you park it. You want to keep that adjuster mechanism working or it will seize up. Should also flush the brake fluid annually, without fail. Any moisture that gets into those calipers is death to the adjuster mechanism.

Thanks for the information!

 

[hunter1]

Have you cycled the park brake to ratchet the piston out? I always understood that the parking brake was an issue with those calipers if they didn't get used enough to keep them adjusted. In this case, initial adjustment.

No I did not. Didn't realize this was needed until I watched a video about the caddy brakes. Thanks.

 

[hunter1]

Brake pedal still returns very slowly. I have checked the return line from the HB and it is working fine. Do not see any air bubbles in the reservoir and believe I have cycled the steering wheel about a thousand times, Ha. I have two separate return lines, not using a tee. Is this a HB issue or is it in the brakes?

 

[ntsqd]

Thanks for the information. Adjusted the parking brake on both sides per youtube. Got good brake now but pedal is still a little lower than I like. Will bigger bore MC take care of that?

Any idea what bore size you have now? What front brakes do you have?

 

[ksagis]

Thanks for the information. Adjusted the parking brake on both sides per youtube. Got good brake now but pedal is still a little lower than I like. Will bigger bore MC take care of that?

It will help with travel but not until all the other things that eat up travel have been addressed. In order from pedal to MC

1. Manual pedal’s ratio isn’t optimally tuned for power brakes. Especially hydro. I made a 5:1 pedal but haven’t installed yet
2. Make sure you have bushing in pedal pin or can be introducing slop that needs taking up
3. Try to minimize gap between hydro pushrod and cup of MC
4. MC takeup distance isn’t easily addressed other than picking one that you know doesn’t have a lot

After all the above are addressed, a bigger MC will move more fluid and help with travel. But keep in mind that 0.125” across the first three items is already 0.75” of “wasted” pedal travel and coupling with maybe another 0.125” in MC takeup ports could result in 1.5” of pedal travel before fluid flows.

Going with too big of a MC can result in super touchy brakes, particularly with hydro forces. I *think* going bigger is goodness for pedal force since pressure at caliper will be reduced with bigger bore, but seems if flow is more, the pedal sensitivity will be touchy. I’m getting smarter in this area so take with grain of salt and listen to others.

My two cents, sure others have good input to add.

P.S. don’t discount having bleeder screw horizontal when bleeding. Super easy to pull a pin and rotate it slightly as needed. Was a bigger deal for me since my pinion is rotated a fair bit with my suspension lift and driveshaft alignment.

(editted my comment about MC size)

 

[ntsqd]

Closing the m/c transfer port off takes very little m/c piston displacement. Really only needs to travel the hole diameter or a little less. Those are usually way less than Ø.10" and more likely to be in the Ø.03" range. This is something that m/c designers pay a lot of attention to. I was taught when rebuilding m/c's to inspect this. the piston seal's lip want to be *right* at the edge of the hole if not occluding it just a tiny bit. If it isn't located like that then something is wrong and it needs to be fixed before putting it into service.

 

[Yeller]

Before we can really make a suggestion for MC bore size, really need to know what you currently have. One of my trucks has a 1-7/16” bore with very close to your brake set up minus the rear disc the pedal only moves about 3/4” and is extremely firm but extremely powerful. So what is acceptable good or bad is often up to the individual interpreters feeling.

 

[ksagis]

Closing the m/c transfer port off takes very little m/c piston displacement. Really only needs to travel the hole diameter or a little less. Those are usually way less than Ø.10" and more likely to be in the Ø.03" range. This is something that m/c designers pay a lot of attention to. I was taught when rebuilding m/c's to inspect this. the piston seal's lip want to be *right* at the edge of the hole if not occluding it just a tiny bit. If it isn't located like that then something is wrong and it needs to be fixed before putting it into service.

Good point, the 0.125” for MC takeup quoted above is too high. When I bled my MC with the plugged port method, I maybe got 0.030” to 0.050” of travel.

 

[hunter1]

Any idea what bore size you have now? What front brakes do you have?

1 inch bore. Front brakes are some GM based caliper that comes with disc conversion kit from most of the vendors on here. Not really sure what the application is.

 

[hunter1]

Before we can really make a suggestion for MC bore size, really need to know what you currently have. One of my trucks has a 1-7/16” bore with very close to your brake set up minus the rear disc the pedal only moves about 3/4” and is extremely firm but extremely powerful. So what is acceptable good or bad is often up to the individual interpreters feeling.

I’m used to a lot more pedal driving my truck. The piston in my MC is one inch. It is some type of GM based design but with a screw down aluminum cover.