Sorry- another rear disc brake question

[77 K20]

can you post a link to the stuff? I wanna check it out

I had read tons of stuff online that always made reference to the fact they used a master cylinder off of something that has 4 wheel disc brakes, but never any real part numbers. I heard references to late 60's corvettes, and often a 99 C3500 truck. As far as the late model truck it seems that only squares in the mid to late 80's could bolt this on. 70's trucks couldn't unless you modified a bunch of stuff. This was finally the first post I saw with a part number (not quite sure why the guy was making a huge spacer in it) He has a nice picture of the master cylinder with the lid off.

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http://www.pirate4x4.com/forum/chevy/533375-my-14-bolt-corporate-full-floater-disc-brake-conversion.html

The link to NAPA didn't work, but found this page with cross reference numbers:
http://www.yoyopart.com/oem/12271791/acdelco-18m161.html#interchange

Rock Auto showed alternate part numbers to the AC Delco one (I've heard bad things about cardone and dorman stuff. Probably works fine, but I wanted to stay away from them)
http://www.rockauto.com/catalog/moreinfo.php?pk=1151732&cc=1059599

This page said fits 4 wheel disc, 77-95. Has the same AC delco part number.
https://www.millsupply.com/gm-workhorse-master-cylinder-10586.php?p=54699&cs=1+2672+2677

And so I ordered it thru Amazon since I"m an Amazon prime member.
http://www.amazon.com/gp/product/B000TN8SHU/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

[77 K20]

And as far as the proportioning valve. If I wanted a perfectly balanced system I would have went with the adjustable one.... but reading on that it wouldn't be perfect unless I kept the weight of the truck the same at all times. Once you start loading up a truck then it should be re-adjusted.
So I just went with a fixed one. Hopefully I'll like the way it feels. Fits 1964-2000 GMs:
http://www.jegs.com/i/Right-Stuff/965/PV72/10002/-1?parentProductId=1502558

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[77 K20]

I also read this page a bunch. Guy built a lot of his own disc conversion for some sort of buggy, but explains a lot in it.

http://www.billavista.com/Tech/Articles/14-Bolt_Disc_Brake_Conversion/index.html

And lastly a very long article about pretty much everything there is to know about brakes:

http://www.billavista.com/Tech/Articles/Brake_Bible/index.html

 

[77 K20]

Well- got the new master cylinder today. It is big. Big and square. Picture doesn't do it justice. Think they said it weighs 15 lbs. And it is probably 1.5" wider than the stock one. It will definitely have enough fluid capacity in it.

 

[Green79Scottsdale]

Putting disc brakes on the back does not add more pressure. They are simply more efficient at doing their job, so that causes them to lock up quicker. You can't push more fluid through the lines by going from drum cylinders to calipers. A simple adjustable prop valve is really all that is needed IMO. I don't really see why a new master cylinder is needed. Those none adjustable ones need to be proportioned for your set-up for them to work properly. I hope the one you ordered is.

What disc/caliper combo are you going with? What are you doing about an E-brake?

The problem you have with your right rear is most likely a leaking axle seal. Mine did that too until I finally got it replaced and sealed correctly. No more grabby rear brakes in the morning.

 

[77 K20]

Putting disc brakes on the back does not add more pressure. They are simply more efficient at doing their job, so that causes them to lock up quicker. You can't push more fluid through the lines by going from drum cylinders to calipers. A simple adjustable prop valve is really all that is needed IMO. I don't really see why a new master cylinder is needed. Those none adjustable ones need to be proportioned for your set-up for them to work properly. I hope the one you ordered is.

What disc/caliper combo are you going with? What are you doing about an E-brake?

The problem you have with your right rear is most likely a leaking axle seal. Mine did that too until I finally got it replaced and sealed correctly. No more grabby rear brakes in the morning.

Everything I have read shows that drum brakes use 400-500 psi, and disc brakes need 800-900. The drum brakes have a much larger surface are of the brake pads, so they get by just fine with that pressure.

The disc brake piston is very large compared to a drum cylinder. True- many just make sure it is filled up after bleeding it and are fine. But when the brake pads start wearing out and both rear brake pistons are extended out 1/4" or so there won't be much fluid left in the reservoir. That is why GM then made reservoirs with more capacity.

And basically I've been going thru the truck replacing everything anyway. I do not like the brakes on the truck and think this should really help. I might be wrong. I'll find out when everything is installed.

I just ordered the same rotors and calipers from the front end of the truck for the rear. No parking brake. I've never used it on the truck to begin with, and using a parking brake in the winter can cause it to freeze in place anyway. There have been times when off road or out in the woods I needed to park on a hill, but I just drive over to a rock/stump/fallen tree and use that for a wheel chock.

I did also buy new axle seals, so when I do the brakes I'll be replacing them also.

I have spent a ton of time researching this and there seems to be so much misinformation out there on a disc brake conversion. It is so hard to filter thru all of it. I spent 3 hours last night reading about the proportional valves alone. Some claim when doing the conversion all you need to do on your stock one is to remove a rubber piston from the isolation valve that is inside of it. Others then say the spring needs to be replaced on the metering valve.

Once I get it done I will be doing some testing on it on gravel roads, and then again when the snow falls to see how it acts. I might need an adjustable proportion valve. I might need to increase the line size back to the rear brakes. I'm simply documenting here what parts I have ordered and then if it turns out. I'm trying to save others the same time I have spent looking up parts and trying to see what has worked for others- when there seems to be no clear cut answer.


Basically I'm doing this because disc brakes cool down much quicker, and if the truck sits in a big mud hole or when I'm launching a boat disc brakes clean themselves quickly. And when it is time to re-do the rear brakes when they wear out it will be much cheaper.

 

[Ryan321]

Everything I have read shows that drum brakes use 400-500 psi, and disc brakes need 800-900. The drum brakes have a much larger surface are of the brake pads, so they get by just fine with that pressure.

The disc brake piston is very large compared to a drum cylinder. True- many just make sure it is filled up after bleeding it and are fine. But when the brake pads start wearing out and both rear brake pistons are extended out 1/4" or so there won't be much fluid left in the reservoir. That is why GM then made reservoirs with more capacity.

And basically I've been going thru the truck replacing everything anyway. I do not like the brakes on the truck and think this should really help. I might be wrong. I'll find out when everything is installed.

I just ordered the same rotors and calipers from the front end of the truck for the rear. No parking brake. I've never used it on the truck to begin with, and using a parking brake in the winter can cause it to freeze in place anyway. There have been times when off road or out in the woods I needed to park on a hill, but I just drive over to a rock/stump/fallen tree and use that for a wheel chock.

I did also buy new axle seals, so when I do the brakes I'll be replacing them also.

I have spent a ton of time researching this and there seems to be so much misinformation out there on a disc brake conversion. It is so hard to filter thru all of it. I spent 3 hours last night reading about the proportional valves alone. Some claim when doing the conversion all you need to do on your stock one is to remove a rubber piston from the isolation valve that is inside of it. Others then say the spring needs to be replaced on the metering valve.

Once I get it done I will be doing some testing on it on gravel roads, and then again when the snow falls to see how it acts. I might need an adjustable proportion valve. I might need to increase the line size back to the rear brakes. I'm simply documenting here what parts I have ordered and then if it turns out. I'm trying to save others the same time I have spent looking up parts and trying to see what has worked for others- when there seems to be no clear cut answer.


Basically I'm doing this because disc brakes cool down much quicker, and if the truck sits in a big mud hole or when I'm launching a boat disc brakes clean themselves quickly. And when it is time to re-do the rear brakes when they wear out it will be much cheaper.

Im looking forward to your conclusion. I am looking at doing disk brakes and fell in the same boat you did with miss information. Please, if you can, include part numbers and where you got them. Thanks

 

[77 K20]

My project on this was delayed as I have spent a full week so far prepping and rolling on a bedliner on the whole outside of the truck, the cab floor, and the bed of the truck. Hopefully I'll be done with it tomorrow. Had to get it done before winter and the temps at night have been dipping almost too low. Then I need to wait for it to dry...

My parts list and where I bought them. I bought a lot from Amazon instead of local stores as I did not have to pay core charges. I didn't think they would accept drum brakes back as a core return.

Amazon:

Raybestos RC4072 Professional Grade Remanufactured, Loaded Disc Brake Caliper
http://www.amazon.com/gp/product/B000C73Z9O/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

Raybestos 5014R Professional Grade Disc Brake Rotor
http://www.amazon.com/gp/product/B001OBMOZ8/ref=oh_aui_detailpage_o02_s01?ie=UTF8&psc=1

ACDelco 18M1887 Professional Durastop Brake Master Cylinder Assembly
http://www.amazon.com/gp/product/B000TN8SHU/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

Right Stuff Detailing PV72 Disc Brake Proportioning Valve
http://www.amazon.com/gp/product/B009NRBBB8/ref=oh_aui_detailpage_o03_s01?ie=UTF8&psc=1

ORD rear brake lines, GU30172
http://offroaddesign.com/catalog/discbrakelinekits.htm

DIY4X disc brake conversion brackets
http://diy4x.com/cart/index.php?route=product/product&path=37&product_id=35

 

[77 K20]

Well- tried to put them on today. Had a bad start to the day, so that delayed me a bit. Got all the old drum brakes off, and put together the driver's the side. That was ok. Then started on the passenger side. When I put the bolts thru the disc brake bracket made by DIY4X, it doesn't line up with the holes in the brake caliper. To get it to start threading I had to use a screwdriver to pry the caliper bolt over so it lined up with the threads in the caliper. And of course it doesn't work right. The brake on that side is dragging and getting hot. I ran out of time to look into it tonight. I'm guessing the holes in the bracket were drilled/machined out wrong. I'll take measurements comparing it to the other side, and measurements vs the holes on the caliper itself.
Not sure how I can go about fixing that. Might just try and drill out the holes in the bracket slightly bigger to get some "slop" in there.

That was pretty much my whole day. Didn't have time to put in the prop valve or the master cylinder. Maybe tomorrow if I can figure out the caliper.

By the way... the Raybestos brake calipers I bought say that they were re-manufactured in the USA. That's rare.

 

[77 K20]

In doing some searching for brake caliper issues with disc conversion brackets and it seems that quite a few had to do some grinding on the brake calipers themselves. Guess depending on who casts them they might be a different size. Installing the loaded caliper on was very tough- thought the piston might have been slightly out- but probably wasn't.

So to prevent drag seems some grind down the caliper a bit, others sand down the new brake pads.

 

[marks86]

they must be the wrong caliper then, because diy4x Has been building those brackets for years and they don't just go around putting the holes in the wrong spots, o and I run them and had no issues

ps. I bought calipers off of a k20 with the high GVW

 

[77 K20]

they must be the wrong caliper then, because diy4x Has been building those brackets for years and they don't just go around putting the holes in the wrong spots, o and I run them and had no issues

ps. I bought calipers off of a k20 with the high GVW

According to Raybestos they are the right caliper. They look just like the front ones. Raybestos has been around since 1902...

So decided to ignore that for now and replace the master cylinder. The reservoir is much larger, and it does hit the vacuum booster plug where it goes into the brake booster. Also the brake lines had to be reversed? Bled the brakes and took it for a drive. Seemed to stop just fine- in fact I liked it better. The old brakes pedal would sink way down, the new master cylinder was more firm, and would only sink about 1/2 way. Went for a drive. Stomped on the brake pedal, things felt fine.

Then replaced the brake proportional valve. Had to remove the ORD steering brace (blocks access). The wire for the warning light had to have the big rubber boot cut off and the connector smashed down a bit as the new proportional valve had a different size electrical post (smaller). Got everything bled again and went for a drive. Rear brakes lock up easily in pavement.

What the hell? Master cylinder is from a disc/disc setup. Proportional valve is for disc/disc.

My first question is why is the new master cylinder have the front and rear brake lines swapped? Wouldn't that mean when the piston moves inside of it, the rear brakes would get fluid first?

Tempted to just put in the 32 year old original proportional valve and try that again.

Amazing how you try to do the right thing sometimes and it ends up biting you in the butt.

 

[77 K20]

I sent an email to the Right Stuff company that made the proportional/combo valve. Hopefully they reply back sometime next week.

I went to the local autoparts to buy more brake fluid and talked to the guy there. In talking everything over with him we thought it was best to order some adapters so I can move the brake lines back to where they were on the original master cylinder. Think by swapping them it screwed with the brake balance.

IF that doesn't work then I'll order a manual dial proportional valve and choke down the rear brakes off of the master cylinder.

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[77 K20]

Today's update. I ordered the Baer brake proportional valve today. Didn't hear anything back from Right Stuff. Between the adjustable proportion valve and swapping the brake lines back this should take care of it.

Took off the rear tire and looked at the brake that is dragging. The outside pad is firmly pressed against the rotor. After MANY hours of searching I did find some others that had that same issue. They "just bent" the bracket over a bit to make some clearance. I bent my 6' spud bar trying to bend the bracket. What a stupid idea.

So my plan is to loosen the 4 bolts that hold the bracket on and order some shim washers to put under the bracket so I can center the rotor. Hopefully I can do this without removing the axleshaft and hub again.

 

[Green79Scottsdale]