jeepbme
NAXJA Forum User
- Location
- Charlotte NC
Anyone else have this problem or solution. Think its to the left
-
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Pulls left when brakes are applied
- Thread starter jeepbme
- Start date
Churchlady
NAXJA Forum User
- Location
- Bath, Maine
I assume your tires are in good balance and alignment?
Greg Smith
Jeep addict
- Location
- Spotsylvania, Virginia
Make sure tire pressures are the same on both front wheels. If so suspect a problem w. the front right brake not applying enough pressure due to bad pads or a sticking caliper piston or the caliper slide/guide pins are rusty or need lubing or a recent brake install did not get the pads properly aligned on the caliper during the install (happened to me). Just a few possible causes. Good Luck. Greg
- Location
- NJ, U.S.A.
Here's another thought - how clean is the inside of your brake system?
Over the summer I had my '92 in the dealer for a wierd settling sensation when coming to a stop if I was more than conciously gentle on the pedal. They had replaced pretty much the entire rear brakes about a year previously, and I figured I'd have them check to ensure that all was set up properly.
While they were checking the rear brake operation, they noticed that the while adjusted properly, shoes didn't always actuate the first time the pedal was pressed. A little more investigation, and it was discovered that there was some dirt visible in the master cylinder.
They recommended a good flushing, and referred me to their GM unit (who has a brake system flushing machine) across the street. I had the it done for about $100. The difference in the brakes was very noticeable.
Before this was done, I had some pull to one side or the other (never only one side) on moderate-heavy braking, and even the massive brake job (drums, shoes, cylinders, pads, rotors) I had done a year prior to this didn't completely eliminate it.
Since the flush I have noticed very little if any pull on braking - I think in my case the dirt was hanging one or more of the calipers or cylinders slightly and causing uneven braking.
Having your brake system's "pipes" cleaned might be worth trying, if everything looks to be in good order in terms of condition and adjustment.
Rob
Over the summer I had my '92 in the dealer for a wierd settling sensation when coming to a stop if I was more than conciously gentle on the pedal. They had replaced pretty much the entire rear brakes about a year previously, and I figured I'd have them check to ensure that all was set up properly.
While they were checking the rear brake operation, they noticed that the while adjusted properly, shoes didn't always actuate the first time the pedal was pressed. A little more investigation, and it was discovered that there was some dirt visible in the master cylinder.
They recommended a good flushing, and referred me to their GM unit (who has a brake system flushing machine) across the street. I had the it done for about $100. The difference in the brakes was very noticeable.
Before this was done, I had some pull to one side or the other (never only one side) on moderate-heavy braking, and even the massive brake job (drums, shoes, cylinders, pads, rotors) I had done a year prior to this didn't completely eliminate it.
Since the flush I have noticed very little if any pull on braking - I think in my case the dirt was hanging one or more of the calipers or cylinders slightly and causing uneven braking.
Having your brake system's "pipes" cleaned might be worth trying, if everything looks to be in good order in terms of condition and adjustment.
Rob
jeepbme
NAXJA Forum User
- Location
- Charlotte NC
Cool ...thats what i thought. Over the weekend me and my brother replaced the back wheel cylinders and rear brakes with Raybestos and bled them of course in the rear.
Seemed to help out quite a bit but still there. I still believe it has to do with the rear brakes though.
Dont most disk/ drum setups use the rear first or more when slight pressure is used and then the front disk up under more pressure?
I plan on taking off the front pads this weekend and putting some anti seeze on the front tracks.
Seemed to help out quite a bit but still there. I still believe it has to do with the rear brakes though.
Dont most disk/ drum setups use the rear first or more when slight pressure is used and then the front disk up under more pressure?
I plan on taking off the front pads this weekend and putting some anti seeze on the front tracks.
kubtastic
NAXJA Forum User
- Location
- Tacoma, WA
jeepbme said:
I do. Even with no lift it had been doing it some under really hard braking. Mine was getting annoying after lifting, especially for highway driving.
I also had pulling under hard acceleration. I thought it was bump steer and just my front loading/unloading, so you might look at that (under hard braking, the nose dives a little, changing front end geom)
An alignment cured the problem.
- Location
- Terra Firma
No. Just the opposite.jeepbme said:
You may have a sticking caliper.
jeepbme
NAXJA Forum User
- Location
- Charlotte NC
great ... i hope its something that simple. Ill pull them off this weekend and use some antiseeze.
98JeepXJ
NAXJA Forum User
- Location
- Johnstown PA
Eagle said:
I hate to disagree with Eagle, but jeepbme is somewhat correct. Whenever the brakes are applied, the metering valve holds off pressure to the front brakes just until the rear brakes are beginning to apply (when the shoes are actually contacting the drums). IIRC, this is to help to make braking more "predictable". If the front brakes were the first to apply, there would be a noticeable (though very brief) nose-dive everytime the brakes are applied until the rear brakes 'catch up'.
I'm not too sure about 4-wheel disc braking systems though....
Oh yeah, your problem sounds alot like a frozen caliper.
jeepbme
NAXJA Forum User
- Location
- Charlotte NC
Im with you.. I think the back shoes grab first followed by front discs
- Location
- Terra Firma
Sorry guys, I'm sticking to my story and the FSM backs me up.
The combination valve has two functions. One is the pressure-sensing function that warns if the front or rear circuit has failed. We're not discussing that, so put that on the back burner.
The other function is described in my 2000 FSM as "Rear Proportioning Valve." Description of valve operation is as follows:
I don't know where the idea came from that the proportioning valve delays application of the front brakes, but I don't think that's correct. Please cite your source for this theory.
The combination valve has two functions. One is the pressure-sensing function that warns if the front or rear circuit has failed. We're not discussing that, so put that on the back burner.
The other function is described in my 2000 FSM as "Rear Proportioning Valve." Description of valve operation is as follows:
FSM said:
The reason they need to moderate brake fluid flow to the REAR brakes under high deceleration (panic) stops is because the drum brakes are "servo assist" -- meaning the geometry of the shoes makes them pull themselves tighter against the drums as the drums rotate. Disc brakes can't do this. Combine this with the shift in weight from the back wheels to the front in a panic stop, and it should be obvious that unless the hydraulic pressure to the back is reduced, a panic stop will lock the rear wheels and cause a spin-out.FSM said:
I don't know where the idea came from that the proportioning valve delays application of the front brakes, but I don't think that's correct. Please cite your source for this theory.
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98JeepXJ
NAXJA Forum User
- Location
- Johnstown PA
Eagle said:
What you said about the proportioning valve is true. But I never said anything about the brake valve (more commonly/mistakenly referred to as the proportioning valve) as a whole, just the metering valve in it.
(Source: Textbook, WyoTech Automotive Division, Chassis Textbook. Section 106: Automotive Principles of Brake Operation, Hydraulic System Operation. Page 15)
"Metering Valve Operation
-In light application, reduces pressure to front brakes.
-Reduces pressure to front brakes to avoid lock-up."
((What follows is a cut away numbered diagram of a master cylinder, brake valve(proportioning valve), and related fluid lines. The caption indicates LIGHT brake application. Since I don't have any means of displaying this picture, I'll have to explain it as best I can))
[5](Pointing to fluid lines running from the MC to the brake valve) "Pressure is equal in both lines from master cylinder to brake valve" [1](Pointing to the metering valve) "There is low pressure in the system, so the metering valve is closed." [2](Pointing to the brake lines going to the front brakes) "No pressure to front brakes." [3](Pointing to the proportioning valve, just showing it's location) [4](Pointing to brake line going to the rear) "Pressure to rear brakes is low."
I put 5 first because it is actually pointing to the first 'step' in the system, but the way the diagram is numbered, it ends up being #5.
- Location
- Terra Firma
What I (and the FSM) calls the proportioning valve function is what you are calling the metering valve function. What we have here is a generic textbook saying the opposite of the official factory service manual.
I'll take the FSM. Reducing pressure to the brakes that do most of the work makes less than zero sense. I think your text book got it backward.
The FSM specifically says the valve has NO effect during moderate braking, and reduces fluid pressure to the REAR brakes under high deceleration (hard) braking. All of that is exactly the opposite of what your text book says.
I'll take the FSM. Reducing pressure to the brakes that do most of the work makes less than zero sense. I think your text book got it backward.
The FSM specifically says the valve has NO effect during moderate braking, and reduces fluid pressure to the REAR brakes under high deceleration (hard) braking. All of that is exactly the opposite of what your text book says.
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98JeepXJ
NAXJA Forum User
- Location
- Johnstown PA
You do understand that the metering valve and the proportioning valve are two entirely different parts in the brake valve, and perform two entirely different functions?
I pretty much knew what jeepbme was getting at when describing how the brakes are applied, but that he wasn't too sure of what is functioning to make it work that way. I just plugged in the bit about the metering valve to let him know what was going on there.
Back to the main issue... I guess you thought that I was talking about the proportioning valve, and had it's function incorrect. But I wasn't, and I didn't. I know the function of the proportioning valve. I don't know why you continue to drag it into this when I've made it clear that that's NOT what we're talking about. You have its function correct but it's not in play here, just the metering valve, which I'm guessing the FSM doesn't make mention of...
I pretty much knew what jeepbme was getting at when describing how the brakes are applied, but that he wasn't too sure of what is functioning to make it work that way. I just plugged in the bit about the metering valve to let him know what was going on there.
Back to the main issue... I guess you thought that I was talking about the proportioning valve, and had it's function incorrect. But I wasn't, and I didn't. I know the function of the proportioning valve. I don't know why you continue to drag it into this when I've made it clear that that's NOT what we're talking about. You have its function correct but it's not in play here, just the metering valve, which I'm guessing the FSM doesn't make mention of...
- Location
- Terra Firma
No, I thought you were using a different name for the same part.98JeepXJ said:
What and where is this "metering" valve to which you refer? There is no mention of a "metering valve" in the FSM, either under the base brake system or under the ABS system.
Why would they install two valves in the same system, one that reduces pressure to the front and another to reduce pressure to the rear? That sounds like a sure-fire recipe for no brakes as the two valves compete to see which can reduce pressure the most.
98JeepXJ
NAXJA Forum User
- Location
- Johnstown PA
Ok, we're getting somewhere here, lol...
From what I can tell from the few different brake valve diagrams in my text, the metering valve is located near the output lines for the front brakes.
As far as being a recipe for disaster, all 3 of my instructors for Chassis (former techs, with about 80-85 years of combined experience on all different makes) said that for as many prop. valves as they had seen go bad, they never once had a case of a bad metering valve. I guess that means that they either "never" go bad, or they're a failsafe design.
After we learned the function of the proportioning valve and then the metering valve, somebody in my class asked about if there were ever any certain conditions that they would end up competing between each other. It was then pointed out that they each function under vastly different conditions so there would be no real chance of competition between them.
From what I can tell from the few different brake valve diagrams in my text, the metering valve is located near the output lines for the front brakes.
As far as being a recipe for disaster, all 3 of my instructors for Chassis (former techs, with about 80-85 years of combined experience on all different makes) said that for as many prop. valves as they had seen go bad, they never once had a case of a bad metering valve. I guess that means that they either "never" go bad, or they're a failsafe design.
After we learned the function of the proportioning valve and then the metering valve, somebody in my class asked about if there were ever any certain conditions that they would end up competing between each other. It was then pointed out that they each function under vastly different conditions so there would be no real chance of competition between them.
- Location
- Terra Firma
Well, I trust the FSM a lot more than I trust a generic text book. When you find the metering valve on your XJ, be sure to post a picture of it for the rest of us.
98JeepXJ
NAXJA Forum User
- Location
- Johnstown PA
Eagle said:
That would be an interesting experiment, taking/cutting apart one of those to see whats going on in there....
