Rear disc brake swap, no rear brakes now

336wheeler

Well-Known Member
Joined
Sep 9, 2006
Location
Boone
I did a rear disc swap on my K5 when I put a 60/14b under it. I would say that 95% of my braking now comes from the front. It's the stock MC, but I would've guessed that the big MC's that the K5 has would do the job. I thought that those MC's were 60/40% proportioned, so I'm kinda bumfuzzled. Any thoughts from people who've done this swap? It stops hard on the front, but nothing from the back. When I bled the brakes I wasn't getting any air from the rear calipers (or so the man that was helping me said), but I still have a spongy pedal.
 
You need to use an adjustable proportoning valve to equal out the pressure front/rear.I done that very swap on a buddies K5 and he never had good brakes because he was too cheap to buy the valve.
I used one of the $40 valves from Summit on mine and have good brakes.
 
It is often the other way around......

Because the drums needed so much more fluid to operate but a proportioning valve should be enough. However, if you run into a 1ton unit it dosen't hurt either:rolleyes:
 
How's the pedal feel otherwise? Do you know what the MC diameter is for the K5/K10 stuff vs K30?
 
I didnt have to change the MC on mine but it had the Hydraboost system on it and might have had a bigger MC to start with,but it had 10 bolt axles.
 
1-ton, when you did the summit prop valve change, did it have all the necessary inlets and outlets for the K5? There's 2 inlets and 3 outlets on the K5.
 
I have a '94 Dodge truck that I just did this swap on my D60. I got rid of the factory prop valve (ABS) and replced with hard line at the same time. My rear brakes work fine with a stock 1 ton master cylinder (barely bigger than the 1500)- why would it be any different on this application?
 
Proportioning valves only help when the brakes are already working, they reduce the line pressure going to the rear brakes (since a higher line pressure is required for drum brakes to operate). Typically what happens is that the rears lock up very easily after this swap. Either that problem or the issue of a drum-brake residual pressure valve keeping the rears dragging after getting off the brake pedal.

Either your MC still has air in it, the MC needs a rebuild, or you have air in the lines somewhere. Or it might just not push enough fluid, but I doubt that.
 
Only suggesting it because i did it and had the same problem of no brakes, are the bleeder valves above the brake lines on the caliper...i got mine backwards and after i put them on the right sides they worked fine..
 
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