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SMC4WD

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Brake Question
« on: January 01, 2006, 07:03:51 PM »
I do not have an aftermarket propersioning valve, but I don't think this is a persorsion issue.  

Jeffy, you've talked about better brake pressures and maybe this has somethinbg to do with that.

Brake fluid level is good, and I've pressure bled and even gravity bled them.  But they're still spongy.  Gotta push them all the way to floor, or pump them up.  But here's the kicker...  When I press really hard, the brake light turns on.  It stays on until I pump them again.

So spongy brakes and the light comes on when I hit them really hard...   What should I look at?

On a side note: I mentioned this before and it bares repeating here...  I have a factory air-box that's been opened up on the side and the two reducers have been taken out.  K&N air-filter, 4.0L bored out TB & TB spacer.  
The reason I mention this is that I have read that somewhere here before.
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Offline Jeffy

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Brake Question
« Reply #1 on: January 01, 2006, 07:33:49 PM »
Well, poor manifold vacuum will cause weak brakes.  The first "reducer" is a turn down at the front of the box.  The second one is a Venturi which increases the air speed (Narrow passage moving air faster = larger passage with slower moving air) to generate the manifold vacuum.

I'm not sure why you're brake light is staying on though.  The switch is associated with the pedal I believe.
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SMC4WD

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Brake Question
« Reply #2 on: January 01, 2006, 10:39:53 PM »
ok...  lemme add...

I did something stupid and it started shortly after that.  It hasn't been a huge problem after removing those reducers, but it became a bit more when I messed up.

I want to see if my rear axle was bent.  So I jack standed the rear, took off one of the tires and started it up.  Cus I was a bit scared, I put my foot on the brake before I started it. (I dunno, thought it was going to roll into the car parked in front of it).  Saw that the rear axle seems bent...  but, I dug deeper and pulled off the caliper.  Went to re-start it and stupid me, I put my foot on the brake.  ARRRGGGHHH!!  Of course it went to the floor.  

I pushed the brake piston back in, bled the brakes, but it's never been right since.  

The light thing started about then too.

Now poor manifold pressure..   Check for leaks?  Vacuum hoses cut or disconnected?   What pressure should it be at and how do I check that?

(Thanks Jeffy so much for you advice!)
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Offline Jeffy

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Brake Question
« Reply #3 on: January 02, 2006, 12:32:24 AM »
I'd bleed those brakes again.  Start with the rear passenger side then do the driver and front passenger and finally the front driver.  You're supposed to start with the longest line and work to the shortest. (if you didn't already know.  :wink: )  Make sure the brakes are adjusted properly while you're at it.  The cog on the bottom will need to be adjsuted so the pads jsut drag then you can back them off a bit.  Once they're close, drive backwards and apply the brakes semi-forcefully.  This should adjust them to the propper position if all of the adjuster stuff is in working order.

I don't know what the readings are on the manifold are.   I believe it's recorded in inHg  though.  I do know, I noticed a change when I went back to my airbox and by brakes worked nicely for once.  They still aren't perfect but are a lot better.  You could experiment and put the venturi back in and see if there is a difference.
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"If the motor car were invented today, there is absolutely no way that any government in the world would let normal members of the public drive one."

SMC4WD

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Brake Question
« Reply #4 on: January 02, 2006, 12:04:25 PM »
El Jefe...

Mucho Gracias!  I will play brake guy!  And I'll try to let you know.  

I never figured brakes are all that important, unless I'm stopping.  Then it's the guy in front of me that needs to worry ;)

Silly thing about a massive ARB Bull Bar and two sets of lights and a winch on the front-end.  People are less likely to cut in front of you when your barrelling at them.
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synapse

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Brake Question
« Reply #5 on: January 03, 2006, 05:53:32 PM »
I think Air is getting in where your master brake cylinder connects to the brake booster, the rubber o-ring inside is worn. This will cause the spratic working brakes and tricky pumping when coming to a stop "most" of the time.[/img]
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SMC4WD

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Brake Question
« Reply #6 on: January 08, 2006, 05:42:25 PM »
Well I just finished bleeding the brakes.  I did it as you discribed Jeffy.  Pass. rear, DR, PF, and the DF.   Get better brakes, I used one of those 'one-man' bleeder tools.  So I didn't see any air coming through the lines.  Brakes felt better, so then I checked all the vacuum lines.  The main one into the brake booster, and all the vacuum lines coming from the manifold.  All seemed good, none of them seemed like they were leaking.  At least not enough to hear.

Still I have no brakes.

They're disc's both front and rear, so there's no cog that needs to be adjusted.

I guess next step is to pull the calipers out and bleed those.  Or at least run something through them.  I didn't pull the wheels off (#1-lazy, #2-too heavy).  I'm pretty sure that the pads are all ok, but for me and my luck, it's probably something that stupid.  

This is just going to drive me crazy.
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Offline Jeffy

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Brake Question
« Reply #7 on: January 08, 2006, 06:32:45 PM »
Are you still running the proportioning valve?  Your rear brakes might not be getting enough pressure.
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"If the motor car were invented today, there is absolutely no way that any government in the world would let normal members of the public drive one."

SMC4WD

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Brake Question
« Reply #8 on: January 08, 2006, 08:13:08 PM »
I'm running the stock valve, under the brake fluid reservoir.
I've been doing some more reading and I see that the proportioning valve assists for the braking bias from front to rear (or vise versa).  I just don't think that is the problem.  Now a friend of mine mentioned that too, but my question is 'why all of a sudden?'

Well I guess it couldn't hurt...   So I'll ask around somemore, and shop for the best priced one...  In the meantime...

STAY OUTTA MY WAY!!
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arkypyro

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Brake Question
« Reply #9 on: January 08, 2006, 09:48:36 PM »
Every consider a bad master cylinder?
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SMC4WD

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Brake Question
« Reply #10 on: January 09, 2006, 05:21:09 PM »
I pray it isn't anything too expensive, like the master cylinder...   But if it is, I've been checking on-line at a WJ master cylinder and if it can be done, I'll try it.

One thing that someone mentioned to me, it is sounds so simple and cheap, is the bleeder check valve.  I'm going to NAPA after work and try it.

See, when I bled the brakes, I also looked at all the vacuum tubes.  I pulled out the tube that connects the manifold to the booster.  I blew through it and put it back.  Well while I was shopping for a proportioning valve, my local buddy at the 4 Wheel Drive shop asked me, “when I pulled that power brake check valve off, was there a vacuum?  Did it pop, or suck when I pulled it out?”  Well, it didn’t.  So, for $5-$10 I might as well replace it.  Maybe it’s as simple as that.

I’ll keep you updated…
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