Who has done the disc brake conversion on their 14 bolt

[JoshHefnerX]

I just looked at @JoshHefnerX thread last week and will probably be following it. Not sure yet because of my hood clearance. He has an '80 and I don't know how the hood on the '81 and up slope is comparatively.

Cant remember right offhand, but I had to use several washers to space down that M/C. There wasn't enough thread left that I'd have felt safe going any lower, if needed. But it did work... I still have a damn leak in the line that I haven't been able to rectify though...

 

[JoshHefnerX]

Just remember that a brake system is just that, a hydraulic system. So you need to treat it as such. If you make changes to 1 part of the system, you will probably need to make changes to compensate for that or it wont be a good balanced system.

 

[shady]

I was always under the belief that you HAD to swap to a Disc/disc MC when you did the rear disc swap.
I've been wanting to do this swap, so have been slowly collecting info. Here's the adjustable prop valve that I think sweetk30 linked
https://www.summitracing.com/parts/sum-g3906

Also. When I changed a few things on my kids blazer I had a hard time getting much pedal on the brakes. Super long throw and little braking. Turned out the rod the goes from the booster to master, or pedal to booster can't remember which, was too short. Had free play before it made contact. Spaced that out and Instant brakes...

 

[diesel4me]

I believe there are two different push rod depths on GM master cylinders,I ran into that when a few rebuilts I sold ended up having the "deeper hole" in the master cylinder piston ,than the original,which had the "shallow" hole..and the customers had the excess free play and pedal travel issues..they were either assembled with the wrong piston,or boxed wrong or something..

 

[imiceman44]

Yes, I almost forgot, I also switched to a p-30 step van master cylinder after swapping to rear disks.

That's the biggest thing.
Everyone complains about the pedal travel it's because the mc is small and the brakes are bigger you need more volume so more travel.
A bigger mc solves that problem.

 

[imiceman44]

@elyon I agree that you should eliminate the extra valve above the rear axle. Then investigate your combination/porportioning valve. Depending on the size of your rear calipers, you will need to get the master cylinder which supplies the proper volume AND pressure to the whole system. I converted a '90 to rear disc and kept the original master cylinder. I believe that it had the 1/2 ton calipers, but not sure. Lots of years ago.
Josh has a great idea of using what GM did. I have a company truck with 4 wheel discs and hydroboost which is very good. GM did their research on that system.

The only reason to stick with drums brakes is that they are cheap. Not good, just cheap. Semi trucks are moving to air disc brakes as liability risks have gone sky high from accidents. Disc has more stopping power. We have a truck at work with 6 axles, all air disc. It spends all day doing round trips, 7 miles each way, weighing 100,000 lbs when loaded. It has great stopping power compared to the older trucks and better durability.

I know that you can get your truck dialed in, it may just need some research. Sorry that I don't have much personal experience to share yet on this swap. I am planning to do my rear axle this spring. I just looked at @JoshHefnerX thread last week and will probably be following it. Not sure yet because of my hood clearance. He has an '80 and I don't know how the hood on the '81 and up slope is comparatively.

I can't agree completely with this.
Drum brakes do the same or better braking, it's the self adjusting system of disc brakes and the cooling that's finally making the bug rigs switch to disc.

 

[K85 Octane]

I went through 5 different MC. Disc/Disc, larger bore, smaller bore, residual valves in the lines, hydroboost MC on vacuum, etc etc. I'm running the smaller 1/2ton calipers. Outside of going to hydroboost, I've tried it all and even spent the money to have a couple different "specialty shops" try their luck as well. I'm not diving into hydroboost unless I get part numbers and can return everything if it doesn't work.
Until I hear from the retail stores themselves, which pieces to use, I can't see why anyone would by into this.
There are stories of them working and there are equal stories of them not.
Either way, you have no support from those you buy the kits from.

Best set up I ran, currently installed, is an '85 K30 MC with matched booster. Straight hardlines, no valves.

Always bled the system with the old pedal pump method. The shops used both vacuum and pressure machines to bleed.

 

[imiceman44]

I went through 5 different MC. Disc/Disc, larger bore, smaller bore, residual valves in the lines, hydroboost MC on vacuum, etc etc. I'm running the smaller 1/2ton calipers. Outside of going to hydroboost, I've tried it all and even spent the money to have a couple different "specialty shops" try their luck as well. I'm not diving into hydroboost unless I get part numbers and can return everything if it doesn't work.
Until I hear from the retail stores themselves, which pieces to use, I can't see why anyone would by into this.
There are stories of them working and there are equal stories of them not.
Either way, you have no support from those you buy the kits from.

Best set up I ran, currently installed, is an '85 K30 MC with matched booster. Straight hardlines, no valves.

Always bled the system with the old pedal pump method. The shops used both vacuum and pressure machines to bleed.

That should be the best setup.

 

[6872xtc]

I can't agree completely with this.
Drum brakes do the same or better braking, it's the self adjusting system of disc brakes and the cooling that's finally making the bug rigs switch to disc.

Better braking from drums? No way!
Drive one. And then see how long the pads and rotors last. Insurance companies sometimes even offer discounts for air disc equipped trucks.
Automatic slack adjusters for drum brakes have been standard for 25 years, so that isn't a difference.
Why did car manufacturers switch to disc brakes up front, then now 4 wheel disc?

Sorry for the derailment.

 

[6.2Blazer]

Better braking from drums? No way!
Drive one. And then see how long the pads and rotors last. Insurance companies sometimes even offer discounts for air disc equipped trucks.
Automatic slack adjusters for drum brakes have been standard for 25 years, so that isn't a difference.
Why did car manufacturers switch to disc brakes up front, then now 4 wheel disc?

Sorry for the derailment.

I will state that a properly working drum brake setup offers a lot of stopping power. All other things equivalent a disc setup does not offer better braking power. I was a automotive test engineer that performed federal government brake compliance testing on cars, light trucks, and heavy trucks. Part of the test was defeating the anti-lock controls to insure the vehicle maintained controlled and still stopped within a required distance even at a heavy load. Never saw a loaded heavy truck that wouldn't lock up all of the tires during a full apply brake stop (you would trash a set of tires during the test because of this).

I'm not saying that drum brakes are better than disc, nor implying that all cars should go back to drums. Disc brakes do have some advantages in some situations and why they are used, but solely based on braking power drums have plenty. Cost is a big factor in the decision also. For a car or light truck you have to consider the increased cost of the rear disc brakes plus you still need to do a parking brake. Regarding the comment about manufacturers using disc brakes on all four corners on cars that is not always the case. Chevy has gone back and forth on using drum rear brakes on the 1500 series trucks at least once or twice over the years. I know they went rear disc for a few years and then went back to rear drums for awhile.

 

[Blue85]

Drums offer a lot of braking power for a small amount of input pressure due to the gain inherent in the design. They also need way less fluid, which results in a higher brake pedal. Plus parking brake is easy. They also have gobs of thermal mass for a quick stop. But they really do suck when they're wet, which is a real consideration for off-road. Being so big, the cost to replace drums is also significant, sometimes costing almost as much as the rotors and calipers you need for the conversion. And who enjoys trying to remove rusted up drum brakes with the shoes worn into grooves?

 

[Truckman4life]

Check out my K5 thread in my sig below. I am running hydroboost and 3/4 ton 10 bolt front and 14 bff rear with discs and 1/2 ton calipers. My brakes work awesome and pedal is firm. Only complaint is rear locks up too good in wet and snowy/icy conditions. I run a 1983 Chevy P30 step van, diesel, hydroboost, disc/disc, master cylinder and a Summit brand disc/disc combo valve and a Jeg's manual prop valve in my rear circuit. The Jeg's valve is all the way closed at 10 turns out and I run it at 8 turns out in the winter and if I remember I got to like 6 turns out in the summer for a little more rear braking. I don't regret doing the rear discs at all. I do have an auto trans though so I haven't worried about a parking brake yet. I also run ceramic pads front and rear cuz I hate brake dust. Could probably add some more aggressive front pads like EBC and go to not as good rears to help even it out too. The fronts should ideally lock just before the rear to maintain straight line braking control. Mine will spin in circles if I just stab the brakes in a panic stop and it's slick at all.
The combo valve came with a little plastic tool also that you install in place of the warning light switch so that you get the rear circuit to bleed properly.

 

[Truckman4life]

Oh and people always say that there factory drum rear MC works fine for rear discs but I don't see how since they are designed to move a way smaller amount of fluid compared to what disc calipers need.

 

[sweetk30]

2 trucks now with this combo for me and firm pedal and high pedal .

k30 master / hydroboost / brake pedal all as a matched system / dana 60 front stock parts and half junky rotors with new pads / rear 14ff with 3/4 ton rotors and 1/2 ton calipers with new pads / stock prop valve gone and replaced with aftermarket unit with built in adjustable rear valve knob . few test drives and all good . hell my 1st truck with this i could lock up all 4 38x12.50x16.5 tsl swampers on a 6,000lb or so truck .

the only thing i might try different is a master from a 3500hd 5lug/10lug truck late 90's to early 2000 . they were dana 60 size calipers front AND rear and the master has a bigger bore size from 32-34mm to a massive 40mm bore if i recall .

 

[Truckman4life]

I think I tried a 2000 Chevy MC and the pilot that fits into the hydro boost was too big for mine but don't quote me cuz I cant remember exactly. The P30 MC has an aluminum bolt on res too and is cheaper than the newer ones. $70 vs $99 on Napa Online for my quick search.

 

[MTBLAZER89]

What year P30 MC are guys using. I am doing the swap..again on my new axles. It was Meh at best before. Offroad only so it was good enough, but now with a doubler and 5.13s I want to make sure my brakes are a little bit better.

 

[K85 Octane]

Keep putting up part numbers or links if you have them.
I tried the P30 also, actually its the first MC I put on when I did the conversion. I don't remember if it was that MC or another one, but along the way I had to clearance the hood bracing some just to close the hood.
Also tried the vacuum early 2000s tahoe MC too. Even kept the prop valve since it made sense to. Didn't work, but can't remember why. Too far back.

now with the change from 37s to 40s, my 4wdb set up sucks more

 

[sweetk30]

these are just part#'s and vehicle listing aplications i got from napa . i am sure there much cheeper for us budget minded try this guys on rockauto .

this is a bigger disc / disc master option i would like to try

napa nmc-m3305 = new master not reman - only problem i might for see is the reservoir is taller and might be close to the hood or hit . but looks the same as a half ton k5/k10/c10 master reservoir thats shorter so possible swap out if need be .
9/16"-18 & 1/2"-20 line size
bore of the master 40mm or 1.574 inch
Buyers Guide
Make Model Engine Year(s)
Chevrolet C3500 1 Ton - Pickup
2001 - 2004
Chevrolet C3500HD 1 Ton Truck
1992 - 2003
Chevrolet P30 1 Ton - Step Van
1995 - 1999
GMC C3500 1 Ton - Pickup
2001 - 2002
GMC C3500HD 1 Ton Truck
1994 - 2002
GMC P3500 1 Ton - Step Van
1996 - 1999

then the stock k30 say 1985 disc / drum with 13x3.5 drum size
napa nmc-m2533 = new master not reman
1/2"-20 & 9/16"-18 line size
bore of the master 33.337mm or 1.312 inch
Buyers Guide
Make Model Engine Year(s)
Chevrolet C30 1 Ton - Pickup
1983 - 1986
Chevrolet K30 1 Ton 4WD - Pickup
1983 - 1986
Chevrolet P30 1 Ton - Step Van
1983 - 1996
Chevrolet R30 1 Ton - Pickup
1987 - 1987
Chevrolet R3500 1 Ton - Pickup
1988 - 1991
Chevrolet V30 1 Ton 4WD - Pickup
1987 - 1988
Chevrolet V3500 1 Ton 4WD - Pickup
1989 - 1991
GMC C3500 1 Ton - Pickup
1983 - 1986
GMC K3500 1 Ton 4WD - Pickup
1983 - 1986
GMC P3500 1 Ton - Step Van
1983 - 1995
GMC R3500 1 Ton - Pickup
1987 - 1991
GMC V3500 1 Ton 4WD - Pickup
1987 - 1991
Workhorse P31
2000 - 2001
Workhorse P32
2000 - 2003
Workhorse W20
2002 - 2003
Workhorse W22
2002 - 2003

last is a stock vac brake 1/2 ton k5 blazer say 1985 disc / drum unit
napa - nmc-m2424 = new master
1/2"-20 & 9/16"-18 line size
bore size of master 28.6mm or 1.125"
lets just say it fits a LOT of 1/2 ton stuff ! ! !

bonus 1985 k5 blazer 6.2 diesel hydroboost unit
napa nmc-m2414 = new master
9/16"-18 & 1/2"-20 line size
bore size of master 30mm or 1.181 inch

NOTE : the vac booster master register bore is bigger than a hydroboost bore so you cant just swap 1 for the other correctly .

please do your own home work and pic this item of your own free will and choosing . i am just providing info on this item and have no say in your parts picking or workmanship ability's .

 

[nutt7]

13-1668 is the master cylinder I used. It is the p30 one for the trucks equipped with a dana 80 rear. I also did the disc-disc valve too. Just do all hydroboost stuff, or all vacuum stuff, including the pedal. Hydro/vac have different strokes on the pushrod from the pedal so this can cause underutilizing or bottoming out of the master cylinder. Mine work well, the feel is better than vacuum and slightly less travel. Its not perfect, but it stops well...and most importantly, better than before. Oh one more note: some master cylinders swap front rear outputs. Even if the threads line up, the rear may be the front. Just double check.

Here is a link to my build where I did the swap. Rebuild on the hydroboost is on the previous page.

 

[LNielson]

I have disc/disc in my crew cab D60 front 14B rear, running 3/4 ton calipers/rotors on my 14b with Diy4x brackets. My rear brakes do lock before my fronts. I swapped in this disc/disc proportioning valve: It doesn’t have the residual pressure valve like the stock ones do for the rear drum circuit, bolts right into the stock location.


I’m running the stock master cyl right now, it will easily lock up all 4 of my 37’s. My hydoboost booster just started leaking power steering fluid so I am replacing it along with a brand new P30 disc/disc hydro boost master (the same one @Truckman4life posted) and I have an adjustable proportioning valve to put in when I swap it over.

My brakes work great, I miss the parking brake all the time. My truck is a manual trans and I haven’t gotten around to figuring that out yet. I keep a couple of short 4x4 post sections in the bed for the times I have to park it on an incline.