Soft brake pedal after YJ booster upgrade - FIXED - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 03-07-2005, 11:46 AM Thread Starter
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Soft brake pedal after YJ booster upgrade - FIXED

FIXED - UPDATED:
Well after reading the posts numerous times VANCOPBS was correct (he is in the brake business after all) in that my problem was the rod between the Master cylinder and the brake booster. I was not initially aware that the rod was so easily adjustable. None of the write-ups I used addressed this adjustment at all so I never considered this issue during the inital installation. I also learned just how sensitive a small turn can be.

I removed the master with the lines still attached and was able to adjust the rod by holding the back of the rod with pliers with using a fixed wrench on the end. At first I decided to do about 5 full turns. Oops! way to much, brakes stiff as a board but all locked up. So I started with small increments (1/2 - 3/4 turns) and after about five adjustments I found a pedal action that is smooth and effective but does not cause the brakes to drag nor have to much play.

The result is amazing braking action when compared to the manual brakes of my CJ. I would certainly recommend this upgrade to anyone running manual brakes and thinking of bigger tires or just a more responsive brake system.

Thanks to all the responses on my post and hopefully this will prove valuable to anyone with similar issues in the future.


Original Post Below
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Finally got around to installing the 93 YJ brake booster w bracket (used) with a new MC on my CJ7 which previously had manual brakes. I have done all the research and think I went about the process correctly. The install worked out well in terms of fit. However, now that the system is in place the brake pedal seems excessively soft before it engages. I would estimate that I can push the pedal about 2-3 inches before the brakes start to bite. If I push hard the brakes will lock up but this is near the bottom of the pedal stroke. It clearly takes much less leg pressue to stop than when they were manual.

The brake system was in decent working order before the upgrade in that I had no leaks, good pads/shoes, new wheel cylinders in back, new hoses/lines at each wheel. The upgrade was to accommodate bigger (35") tires.

I thoroughly bench bled the new MC, and once everything was installed in the CJ I completely drained the old brake fluid out for new fluid by gravity bleeding all 4 points. I used a clear hose on each bleed valve to verify no air in lines. I followed the correct procedure relative to furthest to nearest brake during the bleeding process. I know the rule of bleed, bleed, bleed, and when in doubt bleed some more.

Still I feel the brakes should engage earlier. There is good manifold vacuum to the booster and I do not hear any air when depressing the brakes to indicate a leak anywhere. The pedal will NOT pump up as would be the case if air were in the lines. I'm stumped. Could there be an issue with the stroke length adjustment between the booster and MC? I know power brakes do not have the 'hard' feel that manual brakes do but I cannot help feel that there is something not quite right.

Any advice, comments, recommendations eagerly appreciated.
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post #2 of (permalink) Old 03-07-2005, 01:07 PM
 
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Re: Soft brake pedal after YJ booster upgrade in CJ

How much travel is there, and how firm is the pedal when you press before starting the engine ( all vaccuum bled away)? Is there still excessive travel? Does it feel spongy, or like its taking up clearances?

IMO, it should have a small amount of travel, then feel very firm without the boost kicking in. After you start the engine, with your foot on the pedal, you will feel the vacuum pull the pedal down as it adds boost. If it does that, you know the booster is working.
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post #3 of (permalink) Old 03-07-2005, 02:35 PM Thread Starter
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Re: Soft brake pedal after YJ booster upgrade in CJ

The pedal is quite firm before starting the engine. Not too much excessive travel, it does ever so slightly pump up. Starting the engine does exactly as you describe, the pedal sinks down and become slightly firm near the end of the stroke. I do think the booster is working as it does not require much foot to abruptly stop the jeep, albeit very low on the pedal. Perhaps all is working as it should and I am just not familiar with the feel of power brakes on a jeep. I just cannot help but feel that it requires to much downward push to truly grip.
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post #4 of (permalink) Old 03-07-2005, 02:47 PM
 
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Re: Soft brake pedal after YJ booster upgrade in CJ

I've found that tightening up the rear shoes and parking brake cable keeps the pedal high, as I believe it lessens the clearance between the rear shoes and the drums.
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post #5 of (permalink) Old 03-08-2005, 11:57 AM
 
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Re: Soft brake pedal after YJ booster upgrade in CJ

If you can't pump it up it's an adjustment problem. Could be the rod between the master and booster, could be your rear brakes. Adjust the rod till it barely misses the master cylinder. I like to adjust it up 1 turn at a time till it hits the master and then turn it back down the 1 turn.
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post #6 of (permalink) Old 03-08-2005, 12:03 PM Thread Starter
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Re: Soft brake pedal after YJ booster upgrade in CJ

I am not sure what you mean by 'barely misses the master cylinder", I assume that the rod from the booster has some means of being lengthened or shortened by your reference to 1 turn at a time. Since my pedal takes a while to activate do I want to lengthen the rod such that is impacts earlier?

Sorry if this sounds dumb but I have not done this before and am obviously wanting to be cautious with the brakes.

Thanks again.
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post #7 of (permalink) Old 03-08-2005, 01:20 PM
 
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Re: Soft brake pedal after YJ booster upgrade in CJ

Call me, I'll explain it to you.
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post #8 of (permalink) Old 03-10-2005, 04:33 PM Thread Starter
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Re: Soft brake pedal after YJ booster upgrade in CJ

btt after update
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post #9 of (permalink) Old 03-10-2005, 06:21 PM
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Re: Soft brake pedal after YJ booster upgrade in CJ

[ QUOTE ]
Call me, I'll explain it to you.

[/ QUOTE ]

Credit to Van. [img]images/graemlins/applause.gif[/img]

[img]images/graemlins/40BEER.gif[/img]
Dale
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post #10 of (permalink) Old 03-10-2005, 10:36 PM
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Re: Soft brake pedal after YJ booster upgrade in CJ

[ QUOTE ]
[ QUOTE ]
Call me, I'll explain it to you.

[/ QUOTE ]

Credit to Van. [img]images/graemlins/applause.gif[/img]

[img]images/graemlins/40BEER.gif[/img]
Dale

[/ QUOTE ]

Yup! Me too... Thanks Van [img]images/graemlins/bow.gif[/img]. And you too relsner... [img]images/graemlins/applause.gif[/img] for updating w/ a write-up for the rest of us [img]images/graemlins/thumbsup.gif[/img] (not smart enough to ask about the spongy pedal [img]images/graemlins/wall.gif[/img]). (Just figured it was a downside of an otherwise great upgrade... [img]images/graemlins/bag.gif[/img] )
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