Front disk brake conversion, now brakes wont stop

[sasaeger]

I bought the Chevy disk brake conversion and put it on the front of my 74 bronco without issues. After the conversion was complete the brake would go to the floor. I bought a new master cylinder, (I did bench bleed it. OEM for a 1974 Bronco) and still very loose brakes. If I pump them very quickly while driving, it will stop better, but still does not bring the truck to a stop like it should. I did bleed the brakes (starting with the back passenger first), and a ton of fluid comes out with no air in it. I went through 3 large bottles of DOT3 thinking that I was doing something wrong. I need help!!! Any thoughts?

I am really looking for a shop in Houston (Katy perferred) that I could get to do some work for me.

 

[Viperwolf1]

Sounds like air. Did you mount the calipers with the bleed screws at the top?

 

[sasaeger]

Yes they are on top.

 

[baglock]

Could it be that you are using a drum/drum master cyl. instead of a disc/drum set up?

 

[sasaeger]

Not sure Do you think I should be a master cylinder from a 76 that has disk/drum?

 

[baglock]

I'm not sharp on the subject and don't know if that is the sole problem. You should be using a disc/drum master cyl. It could also be a proportioning valve issue. Did the kit come witha new prop.valve?

 

[Moon's74]

You don't require a proportioning valve for a solid pedal. The stock H valve works fine.

Did the kit come with a master cylinder, or are you using the original?

 

[raleigh_bronco]

Did you pull the brass jets out of the MC? Run a screw into them and pull them out.

 

[sasaeger]

The MC that I got didnt have brass jets in them. My lines screw right inside the MC. When I bleed the lines the Front wheel bleed screws shoot all the way to the firewall.

 

[broncnaz]

If theres no air in the system then you may need a MC with a larger bore stock bronco drum brake and disc brake MC's both have 1in bores. You may need a 1 1/8" bore MC. Check out the writeups in the links section. On a side note the GM MC that was used with those brakes were either 1 1/8" or 1 1/4". A lot of people have tried the 1 1/4in bore MC but the pedal becaome to hard. ! 1/8" usually works.

 

[ol gray mare]

Did you grind the knuckles to clear the calipers?

 

[Broncobowsher]

You did grind the knuckles for caliper clearance? Without that you will have less then half your possible front brakes.

 

[sasaeger]

I did grind the knuckles. While I was bleeding the system I was watching to make sure that it was able to move. The brakes slow down the vehile, but the pedal goes all the way to the floor. If I pump the brakes quickly it slows the truck faster, but still does not have any braking power.

What type of master cylinder do you think I should buy? Do you think that the larger MC will help that much?

 

[broncnaz]

Pedal going to the floor say not enough volumne so you need a bigger bore again check out the links some give part numbers for the bigger MC's

 

[sasaeger]

when I put the calipers on I didnt have to grind much at all. Although there is not a lot of clerance between the knuckle and the caliper, there is room. Do I need a certain amount to clearance? I will look at a larger MC, and see if that helps. Brakes are not my strong skill set, so I really need help

 

[broncnaz]

If the calipers needed more clearnace then I doubt your pedal would hit the floor. The only other thing it could be is that your new MC has bad seals and is leaking which is why it requires the second pump the second pump.

 

[DirtDonk]

Just out of curiosity, did you do anything else to the system at the same time, like adding a power booster?
Just checking, since incorrect pedal rod clearances can cause the soft pedal issue.

Paul

 

[Jonboy69]

You might try the ford camper special MC. I think some are 1 1/4" bore but that is usually too big. I have a 1 1/16th" bore. I picked one up @ Napa Item#: UP 39368 & it works good. I think it was about $45 or $50.

 

[DirtDonk]

Did you pull the brass jets out of the MC? Run a screw into them and pull them out.

You're right to mention that raleigh, but leaving one in would have the opposite effect of what he's got now. It would make for a good stiff pedal, but might let the pads drag on the rotors.

sasaeger, when using the Ford brakes at least, even an original '74 master should give you a good pedal feel if all is well. Lots of us running that setup with good results.
The GM brakes have slightly larger pistons though, so that might be just enough to cause the problem. I would at least try the larger master like the others have recommended. Probably not wasted money, even if it doesn't fix the problem. If not, when you do find the culprit, at least you'll have a more appropriate master to use.

Have you done a search here too? Might come up with some similar threads talking about the pros-and-cons of the different master cylinders with the GM calipers.

Good luck. I know it's not fun to have mushy brakes!

Paul

 

[LouB]

You said pumping the breaks gives better stopping. That would usually indicate air in the system. I can never get mine purrged without power bleeding. If you decide to power bleed and don't haveaccess to a power bleeder, Firestone or goodyear tire will usually do it reasonably. Also, if you change MC don't go bigger than 1 1/8". It Will take King Kong to apply enough pressure on anything bigger than 1 1/8. I bought true 1 1/8, new from O'Rileys for about $45 with lifetime guarntee.