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Which 1-ton master cylinder for K5?

nvrenuf said:
Square body 1 tons will have hydro boost so the m/c is different.

If you have rear disc brakes - I'm using a vacuum m/c from a '99 C3500 (4 wheel disc application) on my K5.

(Edit: made my posted more understandable :doah: )
Click to expand...

Are the lines swapped from square body stuff?
 
i got lucky, when i bought my k30 it was missing a ton of parts. i put in a master cylinder out of a k5 blazer and the brakes were fine. when i eventually put disc brakes in the back is when they sucked.

with 3/4 ton calipers in the back, if you go that route, get a master out of a 1999 c3500 truck. truck stops better then anything new on the road
 
I talked to a guy locally here who dropped the Raybestos one in from the top of this post and had good results. I looked at some ebay pics of that and the K5 MC from all angles (parts shop didn't have them on hand), and the interface looks the same. So, I'm going for that and I'll report back.
 
1984 K5 Diesel Silverado
Ok. Here's what I did. It works. More brakes than a coal train. Using the stock equalizer block.
My k5 was a Diesel Silverado from Detroit. So obviously it has hydro-boost.
I've swapped in ton axles (60/14). The rear brakes are disc's and rotors (kit) from Off Road Design. Now the good part.

1/2 ton Chevys with hydro-boost have a smaller Master Cylinder than 1 ton's with hydro-boost. By smaller I mean Bore/piston size. Half ton K5's w H-boost
have a MC bore of 1.181".
A 1 ton (K30) MC w H-boost has a bore size of 1.312".

The part number for the 1 ton Master Cylinder to upgrade your 1/2 ton K5
w H-boost to a 1 ton Master Cylinder is Car-Quest BPR 20-1584. The nuts (fittings) on the brake lines are the same size as yore old MC. Both take a 9/16" wrench. So no problem there. When you remove your old 1/2 ton MC they're will be a white plastic bushing in the bore of your H-Booster. That's gotta come out so the bigger bore MC can fit into the H-Booster.
Bust it out/Dig it out, throw it away.
NOW, mount your bigger bore MC and bleed to taste.
My K5 stops really good now. This MC upgrade corrected the brake pedal travel problem I was having. My pedal only moves 2" max now. If you have a
Hydro-boost K5 and upgrade to 1 ton axles with rear disc's, this will work for you.

Car-Quest BPR 20-1584

I hope this helps.
GB
 
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Post some pics when you do the swap. I really need to upgrade mine as well.
 
Got the MC today. Looks good so far, the studs line up exactly and the depth and style of piston seems to match. I need to get parts to do the bench bleeding now. Anyone know the fitting sizes of the two MC outputs? The hex part is 14mm, so must be metric, but not sure what to ask for.

Before pic:
20140107_203750.jpg


20140107_204335.jpg


20140107_204419.jpg
 
Got it installed. Still need to bleed it all again, but the MC is fully functional.

Fittings are 9/16"x18 and 1/2"x20. O'Reilly had a bleeder kit in the help section.

20140108_201532.jpg


Installed:

20140108_203657.jpg
 
Nice! Thanks for all the pictures! Can you feel a huge improvement with braking power?
 
I think it's finally bled properly. I can't say I'm real impressed, but it's probably as good as it was with my 1/2 ton setup. There's a fair bit of pedal travel, but I always had that. Almost like I'd want to adjust the pedal or something, but I don't see a way to do that.

The brakes on my CUCV with hydroboost have always been great. Pedal has almost no take up and feels hard right away. Some day I guess that's the way to go, though it's that many more hoses to route and fittings to leak.
 
I don't think vac/hydro matters to the MC.

Hopefully your setup works. When I did my ton swap (eldorado rear calipers), I put the 99c3500 MC on with a stock replacement vac booster. It was too tall and hit the hood so I shimmed it down with washers between the booster and the firewall. Had to switch the brake lines front/rear on the MC and re-used the stock prop valve.

So far, it works well. The pedal is high and hard. The brakes are slightly soft just because everything is new and not broke in and I've only driven it in/out of the garage and up the street while finishing my build, but it feels good.

2013-09-22 12.39.55.jpg
 
just throwing this out there

my cousin started with a 3/4 ton with semi-floater in the rear

went to 1 ton axles, kept the master cylinder, but switched the prop valve with a 1 ton. Says it works perfect, but he still runs disc/drum.
 
Interesting, I wouldn't expect there to be much difference in the prop valve since they are both disc/drums setups, but I really don't know. There may still be "slack" in the system too. I adjusted the shoes until they were barely touching the drum. I don't yet fully understand the D60 caliper setup though, the way the whole caliper seems like it can slide in the slot. Do those have to adjust themselves as well, or actually be manually set up? So far I've just gone up and down the driveway.

EDIT: By the way, are OEM style prop valve unobtanium? Nothing listed at Rockauto or Oreilly.
 
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The Dana 60 calipers work just like the half and three quarter ton calipers. They just slide on the mount instead of on pins. They are self adjusting.

Martin
 
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