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Old 05-14-2020, 05:41 PM   #1
Edahall
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Very stiff brakes

The brakee have gotten very stiff and I only get about 10% braking capability. I checked the brake fluid and the reservoir for the rear brakes was empty. I added fluid but it made no difference. Do I have a bad master cylinder or a bad booster?
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Old 05-14-2020, 06:06 PM   #2
jayoldschool
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Re: Very stiff brakes

If you have removed the rear drums and confirmed that the rear wheel cylinders are not leaking, then I suspect a collapsed rear flex hose.

That fluid went somewhere... did you find the leak? Also, did you bleed the brakes after adding more fluid?
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Old 05-14-2020, 07:15 PM   #3
Dead Parrot
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Re: Very stiff brakes

The stiff brakes sounds like a bad booster or leak in the connecting vacuum hose.
The missing fluid also needs to be tracked down. 2nd on pull the rear drums and inspect. Might remove the front tires and inspect the rotors and calipers for good measure.

Did the brake warning light come on? If not, yet another thing to troubleshoot. It should have came on from the empty MC half.
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Old 05-14-2020, 08:01 PM   #4
Edahall
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Re: Very stiff brakes

Thanks for the replies. I bought a new brake booster and master cylinder. The brake booster is original and master cylinder has about 150k miles on it. I've had master cylinders leak fluid before so maybe this will fix it.

I did check for vacuum but have not confirmed if wheel cylinders are leaking.
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Old 05-15-2020, 03:11 PM   #5
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Re: Very stiff brakes

Update:

Still the same issue after replacing the brake booster. However, rear brake fluid is coming out of the left rear brake. I ordered a new rear brake cylinder. Does air in the rear brakes lines prevent the front brakes from working?
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Old 05-15-2020, 03:32 PM   #6
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Re: Very stiff brakes

On older vehicles getting everything new, they appear to appreciate the following:
  1. Bench bleed master is a must.
  2. Install master into vehicle (put rags down under where it goes to minimize the damage to the engine compartment finish).
  3. Fill master as full as you can, leave cap loose so it doesn't seal.
  4. Open all bleeders.
  5. Go have dinner.
  6. Come back and wonder where fluid is. Wait longer.
  7. Tap on calipers and wheel cylinders with wrench. Fluid finally flows from fronts.
  8. Close each bleeder once decent amount of fluid comes out from gravity (usually works on calipers, not so well on drums).
  9. Top off master. Install lid tight.
  10. Bleed Rear Brakes
  11. Pump brakes 10 times.
  12. Hold pedal firm.
  13. Open bleeder on rear wheel furthest from master. AND contrary to popular belief, the wheel furthest from the master is the driver rear.
  14. Pedal drops to floor.
  15. Tighten bleeder.
  16. Don't forget to top off fluid.
  17. Repeat by alternating rear wheels until all air is gone and fluid flows and drips off differential all over the place.
  18. Move to the front wheels.
  19. Open bleeder on passenger front, push pedal slowly to the floor and hold, close bleeder, release pedal.
  20. Repeat for each side and alternate until all air is gone and fluid flows.
  21. Give up on a clean driveway.
  22. Don't forget to top off fluid.
  23. Do the rears again a couple more times till the pedal gets solid.
  24. Don't forget to top off fluid.
  25. Oops, didn't adjust parking brake.
  26. Test drive (noting brake fluid all over driveway when backing out).
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Old 05-15-2020, 03:38 PM   #7
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Re: Very stiff brakes

The front brakes on my 84 k30 CUCV worked fine even when the rear MC reservoir was empty. One of the T shaped push rods had escaped a rear wheel cylinder and resulted in a leak. The brake warning light coming on was my first clue I had a problem as braking was near normal.
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Old 05-15-2020, 05:58 PM   #8
Edahall
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Re: Very stiff brakes

Quote:
Originally Posted by Dead Parrot View Post
The front brakes on my 84 k30 CUCV worked fine even when the rear MC reservoir was empty. One of the T shaped push rods had escaped a rear wheel cylinder and resulted in a leak. The brake warning light coming on was my first clue I had a problem as braking was near normal.
Thanks for that information. My brakes operate on a vacuum pump and I suspect it's the culprit. I checked it and it seems to be putting out less vacuum than normal.
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Old 05-15-2020, 06:48 PM   #9
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Re: Very stiff brakes

Quote:
Originally Posted by Edahall View Post
Update:

Still the same issue after replacing the brake booster. However, rear brake fluid is coming out of the left rear brake. I ordered a new rear brake cylinder. Does air in the rear brakes lines prevent the front brakes from working?
Your proportioning valve will shift over its internal spool and isolate the rear or front brakes if fluid is lost, like in your case. The same valve can also give you fits during bleeding if you dont have the lockout tool that screws in where the sensor wire goes or if you jam on the pedal too much when bleeding.
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Old 05-22-2020, 06:36 PM   #10
Edahall
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Re: Very stiff brakes

Is there a way to know whether or not the rear brakes are actually working as they should? I used a brake bleeder (vacuum type) to bleed the rear brakes.
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Old 05-22-2020, 10:33 PM   #11
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Re: Very stiff brakes

Quote:
Originally Posted by Edahall View Post
Is there a way to know whether or not the rear brakes are actually working as they should? I used a brake bleeder (vacuum type) to bleed the rear brakes.
If you are not getting fluid to your rear lines (both sides) it would likely be a proportioning valve or master cylinder issue. If you are getting fluid then the problem may lie in your rubber hoses or brake assemblies.

Or, you still have a ton of air.
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Old 05-23-2020, 07:24 AM   #12
Dead Parrot
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Re: Very stiff brakes

I didn't notice much difference on my K30. The brake light stayed off after the repairs and the MC stays full so I assume that something is working. The rears don't normally add much braking power anyway.

Did you do the trick of backing up several times and quickly stopping? That is how to get the auto-adjust to work on rear drums.
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