is the factory brake proportioning valve tunable?

[rpcraft]

Probably the same or similar. Might be able to find a part number on it to compare. I'll be getting one in about a month or so and when I do I'll look and post back. I just never looked many other places at the time and had found that on another thread (maybe from pirate 4x4 or somewhere).

 

[yevgenievich]

where did you source the spring?

I am using 1NCR5 from Grainger. Actually have 3 extras on the shelf because they come in a pack of 5. I am not sure on what strenth spring is in the truck prop valve if it is set up the same.

 

[Frankenchevy]

I think I'm going to roll with the summit one. my main concern after reading some threads, is that the factory prop valve for disc/drum keeps pressure on the rear circuit to overcome the springs in the shoe/drum assembly. sounds like what is causing some people to cook their pads and calipers prematurely.

 

[Craig 85]

I think I'm going to roll with the summit one. my main concern after reading some threads, is that the factory prop valve for disc/drum keeps pressure on the rear circuit to overcome the springs in the shoe/drum assembly. sounds like what is causing some people to cook their pads and calipers prematurely.

Your secondary proportioning valve at the axle would help prevent this as it limits pressure until the truck is loaded with weight.

 

[Frankenchevy]

Your secondary proportioning valve at the axle would help prevent this as it limits pressure until the truck is loaded with weight.

Quite possibly. I was leaning toward the route you went as it is looking haggard. I may get an adjustable prop valve to turn up the rear if a load necessitates it.

My rear pv:

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[Craig 85]

FYI the is enough play in the brake line that leads to this to be able to connect directly to the rubber that connects to the axle. I can't remember if I had to change out the fitting. I remember renting a fair kit from Napa, but I don't remember if it was for this union. You may have to move the clip that holds the brake line to the frame forward a little.

 

[Frankenchevy]

FYI the is enough play in the brake line that leads to this to be able to connect directly to the rubber that connects to the axle. I can't remember if I had to change out the fitting. I remember renting a fair kit from Napa, but I don't remember if it was for this union. You may have to move the clip that holds the brake line to the frame forward a little.

I got a few rolls of nicopp to redo all the hardlines on the truck. Hopefully it will look as good as factory.

 

[77 K20]

Which year vette calipers? Did you swap master cylinders too?

Sorry- I was half asleep when posting. It made sense in my head...

My rear calipers match the front. Stock '77 K20 calipers.

The master cylinder was replaced because my stock one was old and leaking. I went thru 2 different styles. The first one was too big and hit the vacuum fitting on the vacuum booster. The second one was from an older corvette with front and rear disc brakes. Feels a bit "squishy".

 

[rpcraft]

FYI I was digging through the most recent version of the LMC blazer book and they have a proportioning valve for 4 wheel disc conversion on page 151 for about 100 bucks.

 

[shiftpro]

Depending on what brackets you bought for the rear calipers you might need to keep an eye on the inner pad wear. My brackets like to jam up the caliper causing it not to free float. So all the braking is done only with the inner pad. It typically lasts only 7,000 miles.

Seems to be a theme with aftermarket calipers...
Or if they are original and old as the hills do they warp a bit from countless heat cycles? I have this issue with all my squares over the years.
I take extra time to clean up the slide points of the calipers and use brake grease always. By the time the pads get just over 50% wear they seem to begin sticking.

 

[Frankenchevy]

FYI I was digging through the most recent version of the LMC blazer book and they have a proportioning valve for 4 wheel disc conversion on page 151 for about 100 bucks.

I got the one in background of this picture for $49 from summit. it's a 4 wheel disc prop valve.

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[Frankenchevy]

Seems to be a theme with aftermarket calipers...
Or if they are original and old as the hills do they warp a bit from countless heat cycles? I have this issue with all my squares over the years.
I take extra time to clean up the slide points of the calipers and use brake grease always. By the time the pads get just over 50% wear they seem to begin sticking.

the disc/drum prop valve has a residual pressure valve that keeps 10psi on the rear drums for proper function. when you switch to disc in the rear without getting a 4 wheel disc prop valve, it keeps pressure on the caliper piston causing excessive wear on the piston side pad and overheating of the rotor that may lead to warpage.

 

[Frankenchevy]

I've spent the last few weeks researching the hell out of the disc brake conversion and it seems for the best outcome, you need to change your prop valve, make sure your master cylinder is adequate for the disc setup and hydro boost seems to be the way to go. I came across tons of stories of people having issues and soft pedal with vacuum booster and master cylinder setups for disc/drum, but people with the one ton brake master cylinder and hydro boost setups do not. i have a one ton and can verify that the performance of the hydro boost is awesome with 79 caddy Eldorado calipers out back. I also took the time to adjust the e brake just right and it holds on one of my steeper access roads on my property. I also have a factory load sensing secondary prop valve out back which may or may not help the issue.

I was concerned with the heat issue and excessive wear, which is what prompted my research. I pulled the calipers and didn't notice anything extreme, but my truck has had only a few thousand miles put on it in the last 6 years. I'm switching to the above mentioned prop valve as a preventative measure. only time will tell. my truck when used, almost always has some sort of load in the bed from something as light as a couple of dirt bikes to a 1200lb side by side or a cubic yard of gravel. so the rear brakes definitely come into play.

 

[shiftpro]

I've spent the last few weeks researching the hell out of the disc brake conversion and it seems for the best outcome, you need to change your prop valve, make sure your master cylinder is adequate for the disc setup and hydro boost seems to be the way to go. I came across tons of stories of people having issues and soft pedal with vacuum booster and master cylinder setups for disc/drum, but people with the one ton brake master cylinder and hydro boost setups do not. i have a one ton and can verify that the performance of the hydro boost is awesome with 79 caddy Eldorado calipers out back. I also took the time to adjust the e brake just right and it holds on one of my steeper access roads on my property. I also have a factory load sensing secondary prop valve out back which may or may not help the issue.

I was concerned with the heat issue and excessive wear, which is what prompted my research. I pulled the calipers and didn't notice anything extreme, but my truck has had only a few thousand miles put on it in the last 6 years. I'm switching to the above mentioned prop valve as a preventative measure. only time will tell. my truck when used, almost always has some sort of load in the bed from something as light as a couple of dirt bikes to a 1200lb side by side or a cubic yard of gravel. so the rear brakes definitely come into play.

Nice to hear of someone having good luck with Eldorado calipers. I bought a set also for my one ton build. I understand the biggest challenge is getting the e-brake adjusted... does this ring true to you? And do you use the e-brake often?

 

[77 K20]

I believe the issue with my inner rear brake pad wear is the DIY4x brake brackets themselves. I had to return one of them because it was twisted and couldn't even bolt the caliper on. The ones I have now are also slightly twisted. The mounting bolts have wear marks on them where the caliper is supposed to nicely glide along them. I've cleaned them, polished them, greased them, doesn't make any difference.

Perhaps they just had a bad batch- as I know of others that have used them. To me having the bracket have bends at the mounting tabs then welding there is a sure way for them to warp and be out of spec a bit.

Someday I'll get off my ass when I have nothing better to do and order the ones from ORD where there isn't any bending. Just a flat plate. Should be easier to make sure the caliper mounting bolts are pointed straight and correct.

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vs:

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EDIT: I drove around for months carrying my IR thermometer and would measure the rear brake disc temperature anytime I stopped and got out. Never saw them get hot. They were just a few degrees warmer than the front brakes.