Rear disc conversion and master cylinder

[homemade87]

I did rear disc to my 82 truck and was going to change the master cylinder to a disc/disc to try to get a little better peddle . I did a little research and seen where some was using the corvette master so I ordered one . When I pulled the oem one off the bore opening was much larger that the corvette master. The one I ordered was for a 70 something to a 82 corvette. The booster has a much larger hole so the vette master will not fit like it should . Is this what some of you are using and just bolting it up.I did not know if this would affect the rubber seal in the booster. Heres a picture of what I am talking about. If anyone has a better solution I would like to here it.

[Just call me Sean]

Might have to use the Corvette booster too.

[homemade87]

Originally Posted by Just call me Sean

Might have to use the Corvette booster too.

Just wonder what booster will fit the 82. I will have to do some looking into the booster and call some of the brake people . I called a couple online people on the master cylinder with not much success. Thanks for the input Sean

Still looking for input if any one has any ideas.

[homemade87]

Update, After looking at a forum that was mostly k and big trucks I had seen they were using a master cylinder from a 99 c3500hd with disc/disc brakes. It also has the big bore that will fit my booster. I am picking it up today at the local parts store. It is a cardone 10-2754. Dorman has one also but no one had it in stock. It is a part # m630028. The dorman one is new and the cardone on is rebuilt. I wanted to find one local just in case it did not work.

I will keep you posted for those that are interested ( keep in mine that my booster has the large 40mm hole ) . I do not know if all 80's trucks had the 40mm bore that fit the booster. This master cylinder is plenty large enough for a rear disc brake swap. I am hoping to get rid of the soft peddle that most everyone has problems with after the swap.

[lolife99]

What proportioning valve are you using?

[homemade87]

Originally Posted by lolife99

What proportioning valve are you using?

Right now I am using the stock disc/drum valve. I have removed the rubber check devise in the rear part of the valve to allow for the rear disc.

Here is what I did in page # 4 . http://67-72chevytrucks.com/vboard/s...ight=rear+disc.

Don't know if I will have to do anything else. I will try it first to see how it does. I may have to put a adjustable proportion valve in the rear but I will wait and see. I have some wide tires in the rear that may may help with rear tire lock up. I will have to do some testing.

[Rich84]

Can you give some information on the parts you used for the swap? Brackets, rotors etc...

[homemade87]

Originally Posted by Rich84

Can you give some information on the parts you used for the swap? Brackets, rotors etc...

I ordered it from here as a kit.http://www.autocityclassic.com/chevy...-rearc105ltrk/

[homemade87]

Well I do have a update on the master cylinder. The size fit perfect . I did have to swap the Reservoir because it hit the hood. I did manage to get rid of the soft peddle. Now I have to stand on it to get it to brake hard. The 1.5" bore is to much for the brake peddle ratio it seems. But I do have a good solid peddle. So I am going the right direction just need to find the right master cylinder . It seems to be the problem. The rest of the system is working fine. One other thing I had to do was swap the lines . I think this made the rear brake line be in the front brakes spot. I may put some new fittings on the lines and move then back to the proper place. I think they are reverse to what they need to be. This could be the reason for the hard peddle. Heres a couple pictures.

[homemade87]

Another update. I did find some adapters to move the brake lines to the correct port on the master cylinder. It did not change anything. The peddle is real firm. You would have to stand on the peddle with both feet for a panic stop. I would say this in not a good master for the 1/2 ton trucks. So my quest continues to find a master cylinder for the 1/2 ton rear wheel disc conversion.

[Just call me Sean]

Still going to say that the matching booster may help.

[burban nate]

The large bore size of that master is designed for the hydroboost booster. I would convert over to hydroboost if I were in your position. You can find the pedals in most pull-a-parts.

Nate

[cadillac_al]

Two of my 70's Caddys (77 Fleetwood 78 Seville) have rear discs and the master cylinder looks just like a normal disc/drum master cylinder. I don't know why one of those Masters wouldn't work for you. I have never liked hydroboost (at least the 80's version) and that would never be an option for me. Just some food for thought.

[greg64]

I had similar problems on my 64 when I converted to rear discs. The usual "corvette" master had too small a bore and didn't displace enough fluid, so the pedal dropped to the floor. I ended up switching to a mid 70s (75 iirc) 1 ton master, which has a 1-5/16" bore. Worked perfect. I have a vacuum booster, not a hydro boost. My calipers are all 3/4 ton, which have larger diameter pistons then 1/2 ton.

[homemade87]

Thanks for the input everyone. Right now I am going to try a 2001 master for a silverado . I think most trucks and Tahoes and maybe some others had disc/disc brakes. The bore size on these are 1.3xx something. Right now I am trying to find a master to fit the stock big bore booster . I think theses are from 81 to 87 on the squares . I have stock 1/2 ton brakes with the small rear caliper disc kit so I found out the big bore masters was to much. I had to stand on it with both feet to do any hard braking. I went from one exstreme to another. Just trying to find something in the middle for those of us with these 1/2 ton trucks .

Cadillac, The master from those cadillacs may work but I thing I may have to change boosters to the smaller bore. I have not had anyone confirm if you can run the smaller bore in a bigger bore booster. ( pictures above )My quest is to find a master to work with the stock booster for this conversion.


Greg, Sounds like you definitely needed the bigger bore. As I am learning I could see that you needed the bigger bore for the 3/4 ton calipers. I am trying to keep the stock vacuum booster as well. I do not want to covert to hydroboost.

I do have a master cylinder on order for the 2001 silverado and I will post the results for those who are looking for a better peddle. I think most who do this conversion just settle with the stock master and some what soft peddle on the disc brake conversion.

Love the here other options and opinions.

[cadillac_al]

I thought the booster bore size was pretty much the same in the 70's and early 80's, and half ton trucks shared a lot of parts with big GM cars. If I was betting money I think I would bet on it fitting and working and I'm a very conservative gambler. It sounds like you will get it sooner or later though.

[homemade87]

Originally Posted by cadillac_al

I thought the booster bore size was pretty much the same in the 70's and early 80's, and half ton trucks shared a lot of parts with big GM cars. If I was betting money I think I would bet on it fitting and working and I'm a very conservative gambler. It sounds like you will get it sooner or later though.

This is the size difference I was talking about. Where it fits into the booster.The cadillac master is the same size as the one on the left .The one on the right is what came on the truck. Have you used the smaller bore size in the bigger booster bore. Not talking about the bore of the master cylinder itself just where it fits the booster. I was concerned about the rubber seal in the booster doing its job with the smaller fitted into it.

[cadillac_al]

My mistake. Everything I own is from the 70's. I didn't realize they were using those updated master cylinders in 82. I think the late 80's Iroc Camaros had rear discs. Maybe a master from that would work.

[homemade87]

Originally Posted by cadillac_al

My mistake. Everything I own is from the 70's. I didn't realize they were using those updated master cylinders in 82. I think the late 80's Iroc Camaros had rear discs. Maybe a master from that would work.

I will take a look at the iroc camaro master cylinders and see what they had on them. If the 2002 master from the silverado does not work out the camaro would be another option to try. Thanks for the info. I will let everyone know how it works out.

[craig113]

Autozone has a NM1641, Military use these on the Hummers which are GM built.

[homemade87]

Originally Posted by craig113

Autozone has a NM1641, Military use these on the Hummers which are GM built.

It looks like the bore size on the nm1641 is the smaller one like in the picture in post #17. I am trying to find one so I dont have to change the booster.

I did pick up the master for the new body 2001 silverado yesterday afternoon. Looking at it the reservoir stands pretty tall. Wondering about hood clearance with this one. On my way home I stopped by the local salvage to see if there was another reservoir from something that would be shorter. I found one from a 2000 s10 that would fit on the silverado master that is shorter. Plan on putting it on today and giving a update.

[Just call me Sean]

Yes Camaros and Trans Ams had rear discs. I considered that swap on my S10.

[craig113]

NM1641 is a 40mm / 1.5 inch fits the hydro on my 84 k30

[homemade87]

Originally Posted by craig113

NM1641 is a 40mm / 1.5 inch fits the hydro on my 84 k30

Apparently the hydro has a different size than the vacuum booster where it bolts to it. I am not familiar with the hydro-boost. I did try a hydro master with the 40mm bore and it was to much for the vacuum booster. I had to stand on it with two feet.

[craig113]

check with this company,
http://www.mpbrakes.com/