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Breaks suck until it's really warmed up???


 
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Seattle_Chris
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Joined: 15 Sep 2007
Location: Muddy Seattle WA, USA

PostPosted: Mon Sep 24, 2007 3:37 am    Post subject: Breaks suck until it's really warmed up??? Reply with quote

89 XJ auto with the I6.

Ok, my brakes generall suck. I have to start breaking WAY back their and if I brake too hard, the pedal bottoms out. It doesn't feel at all like I have air in the lines, and pumping them doesn't change anything. And I can't lock them.

However I've noticed that after I drive a while, say 15 minutes (like on my commute home) when I get off the freeway, they are working normally. Still doesn't compare to Maxima power breaks, but I think they're working right. They don't hit the bottom anymore, not by a long shot. And I can lock them up if I want. (found that out the hard way)

What could possibly cause this? Might this be a power break booster? Or a bizzare vacuum leak that goes away with heat?!?

I could well be imagining it, but I think the engine runs stronger, and I have more power once it's warm too, but I'm not too sure about that. It's just occured to me that my intermitandt A/C issue could be related to it. I'll have to check that out tomorrow and see if the A/C works when it's warm like this as well.

I'm also not certain if it requires freeway driving, or just in town driving for 15 minutes. I'll have to experiment. I've only had it for going on 2 weeks now, and it's my second car so it's not driven daily so theirs a lot left for me to notice. Smile But I've only noticed the improved breaks after freeway driving. Otherwise I live pretty close to everything.

Thanks much for any insights ya'll might have.
Chris
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TheBrat97
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Joined: 28 Jul 2006
Location: Dallas, TX

PostPosted: Wed Sep 26, 2007 10:30 pm    Post subject: Reply with quote

I've noticed that when my brakes are cold they are alot more effective. I guess it's because when they warm up they get softer and don't work as well. This is a stupid question but have you checked your pads? If you have then my next target would be fluid level and as a last resort the master cylinder. HTH
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2005 TJ 2" Lift 33" TrXuS M/T's
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Tardis
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Joined: 07 Aug 2004
Location: Ohio

PostPosted: Thu Sep 27, 2007 11:03 am    Post subject: Reply with quote

Sounds vacuum related. The brake booster works off of engine vacuum.
Engine warms up, creates more vacuum, brakes work properly.
I'd check the booster...
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98' TJ, 99' XJ
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Seattle_Chris
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Joined: 15 Sep 2007
Location: Muddy Seattle WA, USA

PostPosted: Thu Sep 27, 2007 7:51 pm    Post subject: Reply with quote

Yeah Brat, I was thinking master cylinder too until the tempurature thing. Thats the part that confused me. Tardis (I'm a Dr. fan too, the waiting for next season is killing me) I wasn't aware that the engine made more vacuum as it warmed up, though it makes perfect sense.

Is their a gauge to use to test your vacuum, and where do you connect it? I'm thinking of doing the dual diaphram swap and would like to make sure it IS the booster with an issue, and not a lack of vacuum. 'cause if it's a lack of vacuum I'm thinking that should be dealt with first. Smile

Thanks for the replies guys. Most appreciated.
Chris
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Brad The Best
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Joined: 14 Jan 2007
Location: Kamloops B.C Canada

PostPosted: Thu Sep 27, 2007 8:18 pm    Post subject: Reply with quote

yes there are vacuum gages
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