Front Disc Brake Tutorial

[eldoradojim]

 

[eldoradojim]

What are you using for a stop light switch and how are the flex lines? Are your caliper brackets bent?

inline stoplight switch, the original one...all new stainless braided flex lines, one at each caliper and the rear one from frame to axle

 

[eldoradojim]

Just a thought from the “ignorance is bliss” camp. I’ve been researching this topic a bit having just converted to front discs, just haven’t got this far due to rain every weekend.

The point of the residual pressure valve is to keep a little bit of pressure in the calipers since they use more fluid to move than a wheel cylinder right?

I didn’t go back to re read your whole thread but I think you used a 2# residual valve?
Could you use a bit heavier valve to assuage the “2 stage” pedal, 3 or 4-5#?
I really don’t know, just spitballing.

everything ive read said to use the 2lb residual valve for the disc brakes, its a wilwood so would think its a good one? maybe its not good? you dont want a heavier residual valve for disc brakes 10 lb for drum brakes, MC has built in ones for drum brakes, I removed the rear one,installed the inline 2lb one

 

[Jw60]

Just a thought from the “ignorance is bliss” camp. I’ve been researching this topic a bit having just converted to front discs, just haven’t got this far due to rain every weekend.

The point of the residual pressure valve is to keep a little bit of pressure in the calipers since they use more fluid to move than a wheel cylinder right?

I didn’t go back to re read your whole thread but I think you used a 2# residual valve?
Could you use a bit heavier valve to assuage the “2 stage” pedal, 3 or 4-5#?
I really don’t know, just spitballing.

Yes residual pressure valves hold a little pressure back but not too much. Drum brakes use a 10lb valve to counter the springs and all.
It's kinda like a hydraulic self adjuster. 10lb valves will cause a disk setup to drag.

inline stoplight switch, the original one...all new stainless braided flex lines, one at each caliper and the rear one from frame to axle

On mine with k10 calipers I used the K10 hose from caliper to frame one per corner. Nothing across the axle

How does the pushrod length look?

We need to start breaking down the system.
Front / rear
Calipers pads rotors brackets,
lines switch and hoses,
master cylinder and pushrod

I'm also using the wilwood valve, no issues.

 

[Fireball]

Yes residual pressure valves hold a little pressure back but not too much. Drum brakes use a 10lb valve to counter the springs and all.
It's kinda like a hydraulic self adjuster. 10lb valves will cause a disk setup to drag.

This is incorrect. The shoes always retract against the adjusters 10lb isn't enough to prevent that. The 10lb valve is to keep pressure on the lip seals so they are forced into the bore and don't leak.

Disk brake pistons use a different kind of seal that doesn't need that pressure. The 2lb valves for disks are to prevent drain back to low mounted master cylinders which could cause the pistons to retract too far and require excessive pedal travel. You don't need them for high-mounted master cylinders.

 

[eldoradojim]

I forgot to mention that I installed a adjustable proportioning valve in the rear brake line....i have it wide open now had it turned in a couple turns when i first tried the brakes....this shouldnt matter at all because the front and back are using separate reservoirs , correct? the MC just isnt moving enough fluid is what im seeing....and the rotors are not warped and caliper bracket is not bent like some have mentioned

 

[eldoradojim]

Yes residual pressure valves hold a little pressure back but not too much. Drum brakes use a 10lb valve to counter the springs and all.
It's kinda like a hydraulic self adjuster. 10lb valves will cause a disk setup to drag.



On mine with k10 calipers I used the K10 hose from caliper to frame one per corner. Nothing across the axle

How does the pushrod length look?

We need to start breaking down the system.
Front / rear
Calipers pads rotors brackets,
lines switch and hoses,
master cylinder and pushrod

I'm also using the wilwood valve, no issues.

I didnt change anything with the MC push rod,all i did was remove the 10 lb residual valve in the rear port of the MC ,the rear brakes used to come out of this port, I am running the front brake line from this port now, I installed the 2lb inline wilwood residual valve right next to the MC....I moved the rear brake line to the front port of the MC, didnt remove the residual valve in that port.....there are 2 switches in line , guess they are both for the brake light switch, one is in the front line, one in the rear line, they were already installed ....the calipers, rotors,look fine , nothing out of the ordinary, I put new pads on the front, new shoes in the rear, new wheel cylinders in the rear....new stainless steel braided lines in the front and the one in the rear from axle to frame.....the brakes were 11" drums on the old axles, upgrade my dad did years ago, they worked perfectly when i removed the axles a few months ago....also, I did add a adjustable proportioning valve in line on the rear brake line, its open all the way ,i had it turned down a couple turns at first, no change either way....I converted my old toyota pickup to 4 wheel drive nine years ago, put a adjustable prop valve inline in the rear brake line, it helps to keep from locking up the rear brakes first, this shouldnt have anything to do with the fronts not working....this is driving me crazy......the MC is a dual reservoir MC just to be clear, I know a couple years before mine they still used single reservoir MC's

 

[Fireball]

I forgot to mention that I installed a adjustable proportioning valve in the rear brake line....i have it wide open now had it turned in a couple turns when i first tried the brakes....this shouldnt matter at all because the front and back are using separate reservoirs , correct? the MC just isnt moving enough fluid is what im seeing....and the rotors are not warped and caliper bracket is not bent like some have mentioned

It's hard to say in your case. It's possible you've got mechanical slop or air in the system somewhere. It's also possible your pedal ratio, master cylinder size, caliper piston size are mismatched.

 

[45es]

I didnt change anything with the MC push rod,all i did was remove the 10 lb residual valve in the rear port of the MC ,the rear brakes used to come out of this port, I am running the front brake line from this port now, I installed the 2lb inline wilwood residual valve right next to the MC....I moved the rear brake line to the front port of the MC, didnt remove the residual valve in that port..

I asked in your other thread if you ever install a 10 lb residual valve into the rear brake circuit. I see here, it looks as though you did not.

I moved the rear brake line to the front port of the MC, didnt remove the residual valve in that port.

Why didn't you remove this residual valve? I sure you know it isn't a 10 lb valve and also know a 10 lb valve is needed for the rear brake circuit based on your above comment.

 

[Fireball]

I didnt change anything with the MC push rod,all i did was remove the 10 lb residual valve in the rear port of the MC ,the rear brakes used to come out of this port, I am running the front brake line from this port now, I installed the 2lb inline wilwood residual valve right next to the MC....I moved the rear brake line to the front port of the MC, didnt remove the residual valve in that port.....there are 2 switches in line , guess they are both for the brake light switch, one is in the front line, one in the rear line, they were already installed ....the calipers, rotors,look fine , nothing out of the ordinary, I put new pads on the front, new shoes in the rear, new wheel cylinders in the rear....new stainless steel braided lines in the front and the one in the rear from axle to frame.....the brakes were 11" drums on the old axles, upgrade my dad did years ago, they worked perfectly when i removed the axles a few months ago....also, I did add a adjustable proportioning valve in line on the rear brake line, its open all the way ,i had it turned down a couple turns at first, no change either way....I converted my old toyota pickup to 4 wheel drive nine years ago, put a adjustable prop valve inline in the rear brake line, it helps to keep from locking up the rear brakes first, this shouldnt have anything to do with the fronts not working....this is driving me crazy......the MC is a dual reservoir MC just to be clear, I know a couple years before mine they still used single reservoir MC's

Another item of note. The original master cylinder has stepped bore sizes. I think it's a 7/8" bore in the front where the original front brakes were connected and a 1" bore where the rear brakes connected.

You can see the size difference in this picture from when I had the master cylinder apart on my '68. Smaller piston for the front brakes to the left and large piston for the rear brakes to the right:

This means you need to be careful when swapping which master cylinder port is connected to which end of the Jeep.

In your case I'm not sure switching them back would help. A smaller master cylinder bore makes more pressure for a given pedal force but takes more travel to move the the caliper piston the same amount. It seems like you're having a travel problem so switching ports back would make it worse.

Have you verified the rear brakes are adjusted out all the way? Although it sounds like they were fine before and you haven't changed anything.

I looked up a manual disk brake Blazer master cylinder diameter and it's about 0.827" so you're in the ballpark for master cylinder size. In fact the 1" port you are using should move the caliper pistons faster. The one thing we don't know is the pedal ratio of the blazer compared to your Jeep.

It still seems like you have air in the system somewhere.

 

[jeepstar]

Are all of your bleeders pointed up/ at the top when you are bleeding the system when its all together on the jeep?

 

[eldoradojim]

I asked in your other thread if you ever install a 10 lb residual valve into the rear brake circuit. I see here, it looks as though you did not.



Why didn't you remove this residual valve? I sure you know it isn't a 10 lb valve and also know a 10 lb valve is needed for the rear brake circuit based on your above comment.

drum brakes require a 10 lb residual valve, thats why i left the one in the port that now feeds my rear brakes....MC is original to jeep, had drum brakes both axles before i swapped axles...I removed the 10 lb residual valve and added the 2 lb inline valve for the front brakes,,,,,there has to be a 10 lb residual valve in the port im using for the rear brakes, it worked before with drum brakes

 

[eldoradojim]

Are all of your bleeders pointed up/ at the top when you are bleeding the system when its all together on the jeep?

yes they are

 

[eldoradojim]

Another item of note. The original master cylinder has stepped bore sizes. I think it's a 7/8" bore in the front where the original front brakes were connected and a 1" bore where the rear brakes connected.

You can see the size difference in this picture from when I had the master cylinder apart on my '68. Smaller piston for the front brakes to the left and large piston for the rear brakes to the right:

This means you need to be careful when swapping which master cylinder port is connected to which end of the Jeep.

In your case I'm not sure switching them back would help. A smaller master cylinder bore makes more pressure for a given pedal force but takes more travel to move the the caliper piston the same amount. It seems like you're having a travel problem so switching ports back would make it worse.

Have you verified the rear brakes are adjusted out all the way? Although it sounds like they were fine before and you haven't changed anything.

I looked up a manual disk brake Blazer master cylinder diameter and it's about 0.827" so you're in the ballpark for master cylinder size. In fact the 1" port you are using should move the caliper pistons faster. The one thing we don't know is the pedal ratio of the blazer compared to your Jeep.

It still seems like you have air in the system somewhere.

thanks for helping, i verified the rear brakes are out all the way, every article i read said to use the rear port for the front disc brakes...especially this thread here...the original poster even has a pic of this in one of his posts....cant believe i could still have air in the system , maybe ill try and do the MC bleed again....also, i see in the picture that there is definitely two residual valves in your master cylinder, the little springs and cups that were behind the big nuts ....so i definitely still have a residual valve in the front port

 

[eldoradojim]

update......I still had air in the system i guess, I pressure bled it again today, must have gotten more out because now the brakes are working like they should!! thank you guys for all your input, this is an amazing group!!!! I almost gave up and was going to go with a different style MC, that would have been a pain to modify the bracket,etc

 

[Jw60]

update......I still had air in the system i guess, I pressure bled it again today, must have gotten more out because now the brakes are working like they should!! thank you guys for all your input, this is an amazing group!!!! I almost gave up and was going to go with a different style MC, that would have been a pain to modify the bracket,etc

 

[eldoradojim]

lol, yeah i definitely need a beer now!!!

 

[eldoradojim]

I came to the conclusion that the MC couldn't push the air out while bleeding by pedal. But once I got it, they worked fine. Here is my crude bleed plate. I used an angle fitting with the saddle over it, so I could C-clamp it over the fitting to the cylinder. I used some rubber to create a seal underneath. I used about 20 lbs air to move the bubbles out, it goes fast so watch the fluid level.

thanks for your suggestion to use the pressure bleeder, I couldnt have gotten all the air out without making a plate and using the pressure bleeder....the brakes are working good now!!

 

[timsresort]

lol, yeah i definitely need a beer now!!!

Definitely a few. I was about to suggest sleeping on it and bleeding once more, but you got it, good.

 

[givemethewillys]

So glad you got it figured out!