Dual Master Cylinders

[matth_85]

Whats everyone running on their buggy? Chevy Tons. 1 Ton front calipers and 3/4 ton rear calipers. Currently have dual 1" MC's and the front will not bleed out right. It looses it's pressure over time. No leaks and it was bled the same way as the rear. I'm thinking from what I have read I need to go down to a 7/8 bore for the front. Opinions?? Was gonna just order one and try it out when it goes back together but would rather have a more educated/opinionated guesstimate.

 

[Elliott]

Have you tried a residual valve .

 

[civicmindedex79]

I had 1" and now down to 3/4". I like them much better but if I had to reorder I would prob go 7/8". The pedal was very hard with 1" but wouldnt lock up wheels. 3/4" are soft but locks up wheels well. So I think 7/8" or 3/4" would be fine in my opinion.

 

[matth_85]

No residual. That's what I wa thinking also. My problem is backwards though. I never have luck with brakes.


Sent from my iPhone while sitting on the crapper

 

[Elliott]

Does any part of your lines run higher than you mc?

 

[blzrgb]

^^^^What he said^^^^
I had this problem a little while back with a sand rail. I thought I wasn't getting all the air out. Stood it on both ends with a loader trying
to get all the air out. Didn't work. My problem was runout/deflection in the rotors. Rotors would push pads back into the calipers. Then you'd have to pump yer pedal a few times to get a good firm pedal. Residual valves fixed it. Kept the pads up against the rotor just a little bit. I think the ones I used were 3lb's.
It could still be air though. But this fixed my junk.

 

[REVELATION]

I opened my bleeders and filled the cylinder full of fluid and let it bleed itself. I didn't have any problem aftef that!

 

[John Galbreath Jr.]

Are you bleeding BOTH the front AND rear at the same time?

Requires three people, but the only way to do it right on dual master cylinders.

 

[Elliott]

That would only matter if it was a single pedal tho wouldn't it?

 

[matth_85]

I have dual pedals so that wouldn't apply.

No lines are higher. They run down the "fire wall" and down the driver side upper. then split to each caliper.

 

[matth_85]

^^^^What he said^^^^
I had this problem a little while back with a sand rail. I thought I wasn't getting all the air out. Stood it on both ends with a loader trying
to get all the air out. Didn't work. My problem was runout/deflection in the rotors. Rotors would push pads back into the calipers. Then you'd have to pump yer pedal a few times to get a good firm pedal. Residual valves fixed it. Kept the pads up against the rotor just a little bit. I think the ones I used were 3lb's.
It could still be air though. But this fixed my junk.

I had this same issue in my 4runner years ago and never got it fixed.... Tried everything.

I will prob. order a residual and a smaller MC and if the residual fixes it I will send the MC back. Just runnin on borrowed time as it is to have it back together. Takin it to powdercoat tomorrow. Been ridin it a year nekkid so I figured i'd get the last little kink out while it's torn down.

 

[John Galbreath Jr.]

That would only matter if it was a single pedal tho wouldn't it?

Correct.

Are the bleeders pointed straight up, if not you may can rotate them a little while bleeding. If new master cylinder, was it bench bled before putting it in service?

 

[Elliott]

I fought the brakes on my last Buggie till I got rid of it i do feel your pain, But why I was asking about the lines is on my new Buggie my braided lines came out of the mc and had a little rise to go over the bar my orbital is mounted on , and I mean a little rise not much, but it was enough that it would let the pedal come up and then it would get back soft.Once we stuffed it under that bar you could see air run out of the mc. We bleed it a few more times and now it's a rock hard pedal.If you bleed the mc first and then bleed the calipers and the residuals doesn't fix it then I would be lost.. I had my old Buggie with the mc mounted in the floor like you do a drag car. And every spring, line, pad I mean everything was replaced, even had bleeders mounted it the lines at the highest spots and could never keep the pedal hard, when I sold it we put residuals on it and bam, Decent pedal. And the mc was higher than the calipers so by the book you shouldn't have needed them?????

 

[matth_85]

Bench bled yes. On the bleeders, I am not sure honestly. I'll have to look next time I am in the shop. I'll check that. I will probably order the stuff to add/replace/test just so it will be here when it's going back together. Headed to powdercoat tomorrow. No more wiping down w/ WD-40 after every ride....but it sure was a lot of work.

 

[BigCountry]

I have been running a one ton Chevy master cylinder. Have had issues with my rear calipers busting (3/4 ton Chevy) because those MC's are built for rear drum brakes they have a check valve in them and would not allow the fluid to come all the way back from the caliper after each time you pressed the pedal. Ordered an aftermarket replacement MC from Summit built specifically for disk brakes. I haven't installed it yet but hopefully it will fix my issue.

 

[wizzo]

do yourself a favor and get a 7/8 mc for the front and 3/4 for the rear. also get residual valves for each, it'll be alot better.

i had 1" and 7/8" with the same brake setup. the brakes felt spongy and it was like you had to pump them all the time. the residuals helped the spongy but the mc swap helped the brake performance.

 

[matth_85]

To be honest I have no complaints with the rear. They are money. But...that could be the fact that the front ones piss me off so badly I think the rear is good...haha

 

[krayjeeps]

To be honest I have no complaints with the rear. They are money. But...that could be the fact that the front ones piss me off so badly I think the rear is good...haha

I have been fighitng the front brakes also , I had 1 inch in front and 3/4 in back . Back were fine but never could get any pedal worth a **** on the front. I finally gave up and took the Wilwoods off and put a 1-5/16 bore MC from a 1 ton truck on, ita a huge beast but it bled out great the first time and I can lock all four up now with no prob..