Rear disc conversion and master cylinder

[homemade87]

Update, I put the master from the 2001 silverado on ( 13-2881) and I did not see much if any improvement . The peddle has a soft spot at the top and when pressing down harder it comes to a hard spot you have to bare down on to get any additional braking . The peddle has at least a 1" travel before it starts to brake. I had just did a 4 corner vacuum bleed to eliminate air.

I understand my 82 had a quick take up master on it to accommodate the front quick take up calipers. I am not real familiar with this. I just wonder if the 1" travel could be from this. Does anyone now if there is a reg caliper that would fit my 82 that's not quick take up. Does anyone know more about this than I do. Any opinions on this would be helpful .

[y5mgisi]

Im not of much help to you, but for what its worth, i did a rear disc swap on my 78 k10 suburban. I used 3/4 ton calipers front and rear and used a stock 78 k10 master. The brakes werent terribly firm, but they sure did stop good!

[homemade87]

Originally Posted by y5mgisi

Im not of much help to you, but for what its worth, i did a rear disc swap on my 78 k10 suburban. I used 3/4 ton calipers front and rear and used a stock 78 k10 master. The brakes werent terribly firm, but they sure did stop good!

Thanks for the input. I just wonder if that caliper will fit my 82. I don't think they started the quick take up calipers until the 80's. I am still leaning on this being part of the problem. I may pick up a caliper at the local parts store and check the fitment of the 70's 1/2 and 3/4 ton on the 82

Justcallmesean may be right also . May have to change booster to get it to work with the bigger bore master cylinder.

Still looking for anyone that may have any input, Thanks for everyone's help.

[y5mgisi]

What's a quick take up caliper?

[laidlow91]

im no expert at disc brake conversions so im only adding this as
food for thought.

on any of the drum to disc conversions ive ever done, the master cylinder never got touched.
as far as i know, and have been told, its all in the proportioning valve.

theres kits ive used to modify the existing valve that came on the vehicle.
like this kit http://www.summitracing.com/parts/pof-112-10001
to get the correct fluid to the rear.

and ive used manual proportioning valves that have to be plumbed into the brake system.
these have turn knobs to adjust the fluid proportion and can be a little tricky to adjust.

hope this helps

[homemade87]

Originally Posted by y5mgisi

What's a quick take up caliper?

As I have learned gm had developed a caliper that retracts from the rotor to reduce drag when the brakes are not applied . The stepped large bore master cylinder is designed to take this slack up quickly .

In my case I have changed the master to a disc/disc one. The master had to move the piston in the caliper to take that slack up before the brakes start to works. I think this is contributing to my soft peddle. I am looking for some calipers that dont have this feature that wont brake the bank. Willwoods are expensive.

[homemade87]

Originally Posted by laidlow91

im no expert at disc brake conversions so im only adding this as
food for thought.

on any of the drum to disc conversions ive ever done, the master cylinder never got touched.
as far as i know, and have been told, its all in the proportioning valve.

theres kits ive used to modify the existing valve that came on the vehicle.
like this kit http://www.summitracing.com/parts/pof-112-10001
to get the correct fluid to the rear.

and ive used manual proportioning valves that have to be plumbed into the brake system.
these have turn knobs to adjust the fluid proportion and can be a little tricky to adjust.

hope this helps

Laidlow, This is one of the other things I will address after I try the caliliper change. I have removed the rubber check valve from the stock 82 proportioning valve. I tried it before I removed it and after I removed it and there was no change. Thanks for the heads up on the kit for the prop valve. I did not know they had something like that.

I am still plugging away at it and will figure it out at sum point . I am not one to give up easy.

[homemade87]

Update, I did install the 2001 silverado master and did not like the feel that I had mentioned in a previous post. When I pushed the pedal it would drop some and it felt like it hit something in the stroke an was hard to press at that point with not as much braking control as I would like. So it came off.

Did a little more research and found a 1981 trans am master was a disc/disc and was a alum quick take up type. So I picked one up and did a install. It feels much better and feels like it had a lot better control. I had to use my reservoir on my original . The one it came with was made to much of an angle. I am much happier with this one.

The one thing I need to point out about these alum masters is it takes a lot to bench bleed. I worked with it about and hour to be sure it was bleed. I used the plugs it comes with and pump , tap , bang , put it at and angle and tap , pump , wait , pump some more. And even after all that. I would work it some more and to my surprise I would still get a burp. So don't give up on bleeding to soon. When you think you got it do some more.

So as it stands right now I am going to run it a few days to be sure how it feels. I will also do some testing to see how the front /rear balance is. Don't know if I need a prop valve or a dist block or maybe a 2lb residual valve for the rear at this time until I do some more driving.

Note, I did not change the front calipers. They are still oem type

['68 Newtricks]

Oh boy. I might ramble a little during this. Here's hoping it helps.

Here is my fun. Ignore the title, it addresses the exact same thing you're deal with now.
http://coloradok5.com/forums/showthr...ghlight=brakes

I landed on a 1 ton master and booster set up from another member. This is because I'm running a D60 front and 1/2 ton rear calipers. The combo also has that larger booster hole. My original K5 booster had the smaller hole. No, I would not mix the smaller master with the larger booster.

The 1/2 rear calipers take less volume to extend and actually helps create pedal pressure if the larger 3/4 ton calipers give you a soggy feeling. (not the OP, but others that mentioned the 3/4 ton calipers)

I used to use a Corvette MC, but it was small. To aid in power, I used 2lb check valves on each end. Later, I found out my front check valve broke inside, making my fronts worthless. The rear check valve looks good inside, but doesn't seem to help with braking. I have a 10lb check valve awaiting a test. I'm fighting the rear "take up" calipers right now. (never heard this term till now) I can easily watch the piston move in and back out. If it moves out 3/16" for each stroke (disc missing of course) they will retract 1/8" when the pedal is released. This is where the soft pedal comes from.

It has to move a massive amount of volume EACH TIME the pedal is pressed BEFORE the fronts can aid in stopping. (especially if you use a prop valve, which checks rear pressure against front pressure and modulates. No, or late, rear pressure can mess with front pressure) Each pedal push should only need to move enough volume to clamp the pads against the rotor, not move the piston 1/8" and then apply pressure.

I also tried the 99 3500 and had the same results. I tried a 2003 Tahoe with matching prop valve but at the time my front check valve was bad, so my result my be off. The pedal always felt the same, no mater which MC I tried. (other than '99) It has to be the "take up" of the rear calipers. My fronts don't do that.

Also, as long as the rod length in the booster is the right size, it will work. A booster is just a vacuum assist. If you push on the pedal and it goes down without effort, doesn't hissssss with a leak, and holds vacuum....it works. Don't waste money on boosters, they are expensive. As long as the rod bottoms out inside the booster AND touches the MC when installing, it should be good. As long as it's not applying pressure on it's own AND the stroke doesn't bottom out the MC or leave it short, it's good.

['68 Newtricks]

Also, in my research, the mid 90s caprice cop cars and SS impallas have a 4wdb MC with 1 5/16" bore, similar stroke. Never got around to trying one though.


Luckily my truck isn't daily driven. It can handle itself on the street fine, even with the crappy pedal. It will lock up the 38s in the front with a panic stop and holds the truck at some really nasty Moab angles. Just imagine if my rears worked lol.

[craig113]

ok, Maybe a stupid question... all I have seen was about the MC and boosters, what rear calipers are you using? 76-78 Caddy with park brake? If you you need to ratchet them 30-40 times to take out the pad to rotor play then bleed them.

['68 Newtricks]

If they are using 1/2 and 3/4 ton truck calipers than no, they are not caddy calipers. Unfortunately that means no parking brake. I would use whatever year the truck is, just to make sure banjo bolts and SAE/MM stay the same.

[homemade87]

Originally Posted by craig113

ok, Maybe a stupid question... all I have seen was about the MC and boosters, what rear calipers are you using? 76-78 Caddy with park brake? If you you need to ratchet them 30-40 times to take out the pad to rotor play then bleed them.

Heres what I used. I think these are the same as the caddy calipers w/brake.The fronts are the oem calipers . They are the 1/2 ton 1" rotors

http://www.autocityclassic.com/chevy...-rearc105ltrk/

All of the proper ratcheting of the park brake and bleeding has been addressed.

[homemade87]

Originally Posted by '68 Newtricks

Also, in my research, the mid 90s caprice cop cars and SS impallas have a 4wdb MC with 1 5/16" bore, similar stroke. Never got around to trying one though.


Luckily my truck isn't daily driven. It can handle itself on the street fine, even with the crappy pedal. It will lock up the 38s in the front with a panic stop and holds the truck at some really nasty Moab angles. Just imagine if my rears worked lol.

Newtrick, Thanks for your input. The 81 trans am master looks just like the oem on on the 82. I may not have mentioned but it is also the quick take up type for the front calipers just like it came with except it is for rear disc.(stepped bore ) . The straight bores seemed to be to much of a hard peddle. I think the straight bores required a dual diaphragm booster.

I am going to drive it today to see how it does. In the gravel driveway I locked the front but not the rears. I do know they are working. Its possible I may have to have a 2lb residual valve to take up some slack . I will do some road tests. But the peddle does feel pretty good and responsive compared to the others.

Also I did find a company that had the non quick take up type caliper for the 1/2-3/4 ton . 1" or 1-1/4" rotors. If need I can find it again.

['68 Newtricks]

What's the update? Also, whats the name of that company and how much $$$ are they asking? Thanks

[homemade87]

Originally Posted by '68 Newtricks

What's the update? Also, whats the name of that company and how much $$$ are they asking? Thanks

Newtricks, The company I found was Performanceonline.com Here's the caliper I was looking at They are for 1" rotors $49.99 https://www.performanceonline.com/19...lacement-Type/ . The email they sent me said they are the standard type . Not the quick type. I think you would benefit from this caliper to get rid of the retract feature of the oem ones.

(Update on performance 82 2wd 1/2ton), After driving it for a few days I do like the peddle feel with the 81 trans am disc/disc master cylinder I got from oreilleys. The peddle does feel more normal when driving. When I drive now I never notice the pedal like I used to. I have not had any rear lockup issue . I do have a rather wide tire in the rear ( 295/45/18). I think this aids with rear wheel lockup . There is just a lot of tire on the ground. If you had a stock tire you may have to address rear lockup with a proportioning valve . But in the end for me it took the rear Cadillac calipers w/ebrake , used the stock 82 booster , 81 master from trans am disc/disc , removed the check valve from the rear distribution valve .This made a braking system not just livable but pretty good for me. I can not stress enough bleed , bleed , bleed these step bore master cylinders. They are very hard to get all the air out.

One other note on the Cadillac rear calipers if you have ebrake . If you do not get them installed and adjusted proper you will have problems. Also you have to use ebrake pretty frequently so they stay adjusted . As the pads wear the ebrake ratchets the pad closer to take up for wear. If you don't the rear's have less and less braking power as time goes on. Just remember to use the ebrake from time to time.

['68 Newtricks]

Hey Homemade:

Do you happen to know a way to check my rear calipers, to see if they are the "take up" type? I have no idea what year they are. Just that they are front 1/2 ton calipers

Oh, my front is an '85 D60, which has a different size bleeder than the rears. I can't remember which is which though

[homemade87]

Originally Posted by '68 Newtricks

Hey Homemade:

Do you happen to know a way to check my rear calipers, to see if they are the "take up" type? I have no idea what year they are. Just that they are front 1/2 ton calipers

Oh, my front is an '85 D60, which has a different size bleeder than the rears. I can't remember which is which though

I am not sure about a way to identify the quick type calipers . I do know the difference is in the boot around the piston. The boot is designed somehow to pull the piston back when the pressure is released . I have never had one apart. They started this in the early 80's and were all the 1" rotors. This feature was not on the earlier 1-1/4" rotors . Its possible you may be able to change your rear rotors to 1-1/4" and get the earlier calipers to match . They called this the heavy duty brakes.

I do believe your problem is there is to much volume difference between the front and rear and the stepped bore masters cant handle it .The 1-1/4 hd calipers are a larger volume . You could try this with a larger master ( disc/disc not stepped ) to get more fluid to the rear. Possible a dual booster as well to help with peddle feel with the larger master. The larger bores m/c makes for a hard peddle if to large.

If you still have it I would put the 2lb residual valve back in the rear and see what happens.

Also the other option would be to convert back to rear drums. I did read that your buddy converted his front axle and had problems . Changed the prop valve and fixed. The one thing that you may not have realized is that he still had rear drums. That's the difference. That master was designed for that. Rear drums are a pretty good brake system . Its just that they don't like heat. That's the biggest reason towing and high performance people change to them . Disc are more forgiving to heat. It sounds like heat may not be that bid of a deal for you.

Anyway I will get off this long rambling reply and hope some of this helps . I do know what it is to fight brake conversions.