What do you know about brake boosters - Defender Source
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  #1  
Old November 29th, 2011, 12:16 PM
Tyler Wirken
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Tyler Wirken
1997 Defender 90 LE
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What do you know about brake boosters

Anyone know how to test if a brake booster is working properly?

I am getting close to then end of my 90-110 conversion project and it is time to start tackling some problems I was having some 5 years ago when it was a 90.

One of which was the brakes. Towards the end of its life as a 90 the brakes became pretty weak. I was not even able to lock them up on gravel. I remember having the front calipers rebuilt a couple of years before I took it apart but they still were not great. It had 35" tires on it and more amour but I still should have been able to stop it better than it did. It had new front rotors and pads. Never did anything with the rear calipers etc.. as they did not seem to need anything.

So I got to thinking I wonder if the brake booster was not working properly as I always had a good pedal but just not much stopping power.

Any thoughts would be great in addition to how to test a brake booster for proper function.

Can they go bad?

Thanks for the help

Tyler
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  #2  
Old November 29th, 2011, 12:25 PM
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Overlander
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mark kellgren
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Can it hold a vacuum? that's pretty much it. pop the bonnet and turn the engine off. listen for a vaccum leak by the check valve going into the booster. if you dont' hear anything, then wiggle the check valve vigerously to cause a vacuum leak in the grommet and see if you can hear it sucking air in. if there is no static leak, and you can force a leak, then I would say it's good.

if you have no vaccum, you may also want to check the vaccum hose line running to your manifold. leaks along that line would also cause poor assisted braking as the vaccum requires no leaks through the system.

you should still have reasonable braking even without the booster if your hydraulic system is up to par; it would just be a very hard pedal. you may want to check the spec play and adjustments on your master cylinder.
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  #3  
Old November 29th, 2011, 12:27 PM
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rijosho
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Joshua
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It sounds like the brake booster. I was looking to check the same thing, actually, so I'm glad you brought it up. For me, it is when I'm wheeling and I need to hit the brakes in a tight situation while getting over a boulder (for example), I hit the brake pedal hard, but it rolls back a few feet first, THEN grabs or if I pump twice it builds greater pressure on the second pump. I've seen that similar performance can be commonly attributed to air in the lines, or w/ just the rolling factor perhaps just a bad bearing, but I have confirmed everything BUT the brake booster to this point is in the condition it is meant to be in (i.e. no air in the lines, bearings have been tested, etc.). Would also love to know the best way to test a properly functioning brake booster.
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Old November 29th, 2011, 12:43 PM
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rijosho
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Joshua
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Sorry, I think I forgot what it actually felt like somehow. When I'm wheeling and most commonly climbing over a boulder and have hit a point where I'd like to stop for a second, I hit the brakes, and it'll depress about 2-3 inches but the pedal is VERY STIFF to where it is very difficult for me to even maintain that pressure with my foot/leg on the pedal, and the truck is still rolling back a little. I usually can't hold it and let it go for a second and re-depress, and then it grabs better.
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Old November 29th, 2011, 12:47 PM
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Ren Ching
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Skinny Pete
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Josh, sounds like it could be loose wheel bearings. When was the last time you checked those.
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Old November 29th, 2011, 01:02 PM
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rijosho
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Joshua
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Pulled them out during the Summer and inspected while repacking them during new rotors and pads, and checked for any play just a few weeks back (again) at Rovers on the Rocks after having the same pedal pressure issue I experienced at MAR when I got on top of a rock, hit the brakes, slid a foot backward and brushed into a tree with the front fender. Still no play in the bearings though.
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