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Discussion Starter #1 (Edited)
Hi,

I have a 1986 Toyota SR5 Carb 22r. Over the course of the last month the brakes would every once in awhile go to the floor or have excessive pedal travel. This got progressively worse until I had little to no power brakes. I than replaced the master break cylinder, power brake booster, and bleed all four tires and the two lines on the master break cylinder. However, I still have no power brakes. I can stop but not as fast as with power brakes. I made sure the power brake booster pin was between .024-.026" clearance.

What could be wrong? There are NO signs of leaks anywhere in the hydraulic system. Symptoms right now are that I can build up pressure in the brake pedal by pumping it two to three times, however, if I wait 30 or so seconds the pedal goes back to almost reaching the floor. There is a vacuum line running from the power brake booster to the intake manifold. However, this line looks good with no visible wear and tear.

Any help and/or suggestions would be greatly appreciated.

Thank you.
 

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Did you bench bleed the master cylinder before putting it in? Also, is it a rebuilt or brand new? I have seen more than one bad rebuilt from Advanced Auto parts. You also didn't mention rear wheel cylinders. Take a look and see if they are leaky.
 

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Discussion Starter #3
Hi,

Yes, the master cylinder is completely bleed. As I said, I bleed all four tires and there are no signs of leaks anywhere in the hydraulic system. Infact, the hydraulic system is quiet strong as when bleeding it shoots out pretty fast and does infact hold the tires strong.

The master cylinder is supposedly new and I bought it from here.

http://www.jtoutfitters.com/product/4720135470

Now, does anyone know about the vacuum line running from the booster to the intake? There is also a diaphragm about midway. Could any of this really be bad and how could I test for this? Also, where could I get a diaphragm such as this one?

Thank you.
 

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I would suspect that there is still air in the system. The fact that "when bleeding it shoots out pretty fast..." means nothing as far as air entrapped in the lines. You state that you can build up pressure by pumping. That could happen as you compress the air trapped in the lines. Also check the brake hoses for defects as they can deteriorate as well. I would suggest taking your truck to a facility that can pressure bleed the system. These systems can sometimes be a bear to get rid of 100% of the air. RE. the "diaphragm about midway" you mention, I think you are refering to the vacuum check valve. This can fail just like any other part but, I think your problem is basically entrapped air. Good luck.
 

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Toyota Fixer
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Did you ever figure out what was the problem with your brakes? I am experiencing a similar problem right now. Thanks in advance.
 

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You did not mention the check valve in the vacuum line to the booster. It must be functioning properly or you will not get the power assist from the booster diaphragm. Did you "bench bleed" the M.C. before installing? You still may have air in the system as well. It can be a real bear to get all of the air out sometimes. The flex lines should be replaced too if they are original. Good luck.
 

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knowltondata said:
Well there's your problem. You should have bled all four brakes.

:D
I like someone with a sense of humor.:bump:
 

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Toyota Fixer
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Well guys I had the same problem. I rebuilt both calipers, both wheel cylinders adjusted the booster and replaced the master cylinder. I bench bled the master cylinder and I even went as far as replacing the intake manifold gasket just in case there was not enough vaccum. After all that I still had a spongy pedal that still sunk to the floor. I checked, rechecked and checked and bled everything again. After doing all that and about 20 bottles of 12oz brake fluid I finally decided to replace the 20 year old rubber brake lines. I bled the system again and bled the wight proportioning valve next to the rear diferential and amazingly the brakes finally worked. Everybody kept saying booster but I have yet to see a defective booster on one of these trucks. If you ask why 12oz bottles of brake fluid its because they are on sale at Auto Zone right now for .69 cents each. This truck kicked my butt for 4 days straight. I believe that even though the rubber brake lines look OK and there is no bubble on them just simple cracks they can still suck or leak air with no actual liquid coming out. Good luck to anyone experiencing this problem.
 
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