ABS Brakes

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  #1  
Old 07-13-03, 12:49 PM
hippy553
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Unhappy ABS Brakes

Hi I have a 1995 Dodge Grand Caravan with ABS Brakes. The problem I am having is the brake pedal gets hard somtimes and you can hear a buzzing noise coming from the engine compartment.I have checked all the brake shoes and adjusted the rear brakes .I have checked to make sure there are no leaks at the wheel cylinders or front calipers. When this happens the van still stops fine and it don't do it all the time.It has no ABS codes set in it. This is a 3.3 v6 with automatic trans. Any help would be great. Thanks Harry
 
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  #2  
Old 07-13-03, 01:28 PM
Joe_F
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Sounds like the ABS unit is going haywire. Suggest professional service on this one....brakes are not something to gamble with.
 
  #3  
Old 07-13-03, 04:27 PM
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I agree with Joe.. Many ABS units have an accumulator that hold pressure in the thousands of PSI.. An easy way to get seriously hurt! Doing an actual brake job on a car with ABS is 1 thing..Playing with the ABS unit requires training,experience, and exact information...
 
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Old 07-13-03, 10:29 PM
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how long have you owned this van

it is normal to hear a loud buzzing from under the hood and the pedal to do weird things when the abs does it's thing(actuates)

this can only happen when your foot is on the pedal and you are trying to stop, what you might not know is you can have one tire on anything to compromise traction, a twig, a rock, a sand patch, a pothole, an oil/diesel slick, rain, snow, ice, anything other than dry asphalt.

the computer senses this in an increase in one tire's "rate of deceleration" over what is a known constant of the vehicle---not compared to the other tires, meaning the tire is stopping faster than it ever could based on the design of the vehicle, and we're talking in fractions of a second here.

if someone looked at it and there's no codes, no leaks and the van stops fast, i wouldn't worry, but, you could have rust pitted rotors, glazed pads, new brakes put on without remachining the rotors, $9.99-'lifetime guarantee' pads that are harder than diamonds and don't do much to stop the car---all overloading the rear brakes and causing them to lock-up(or try to) the point here is--the base brake system has to be close to normal, it's what the abs system is designed around, an 'ideal' system



anyone trying to restart the 'abs argument'---DON'T, computer and wires always beats a brain and foot (i won't even reply to it!)
 
  #5  
Old 07-14-03, 05:15 AM
hippy553
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ABS Problem

This reply is for Mike in nj. Mike I bought this van about 8 months ago and it did not do this when I first bought it.I did adjust the rear brakes yesterday and that seem to make it better.It don't do this all the time.When it does the van still stops fine.The noise that I am hearing is coming from the Modulator assembly mounted under the battery tray .Is it possible that this would do this if the rear shoes are worn? I know the front pads are ok.Thanks for the response. Harry
 
  #6  
Old 07-14-03, 05:20 PM
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Hey there is a TSB on this problem and may be repaired for free at the dealer . We had one in the shop and the same problem was happening. Call or check all data for tsbs. Pump deteration I think it was
 
  #7  
Old 07-14-03, 06:52 PM
knuckles
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Alldata only lists 2 TSBs for the Brake System on this van & neither deals with this problem. One is a service manual update & the other deals w/ "ABS light on at all times".
 
  #8  
Old 07-14-03, 09:30 PM
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sdsdogg---the 91-93 caravans had the abs problems, the updated parts we install now fix them permanently(the pump deterioration was the result of other things wearing out and now carry a lifetime warranty---for the master cylinder seals and master cylinder 'bore' only)


harry, i can't see worn out shoes causing a false abs actuation, unless the wheel cylinder or bearing grease seal is leaking directly onto the shoes, making it want to lock up, but you said they were ok.

two things i thought of you can look at,

first--worn/mismatched brands of tires or even different size tires on the same axle. four decent treaded tires of the same size and brand is what you want.

second, look at each sensor and tone wheel, it sounds hard but it isn't.

on the front, turn the steering wheel all the way out, lock the column and e-brake, lay inside the tire area with a good light, if you don't know what a tone wheel is, it's on the outer most part of the axle, just behind the wheel bearing and brakes, directly under the strut, try to push it with a screwdriver, it's shouldn't move at all, if it slides a little or spins freely, it's cracked and is your problem, if you can't budge it (without scratching or bending any of the teeth) look at the sensor next, all that is is a small magnet with two wires coming out, it will probably have a bit of rust and even metal filings on it, you need to clean ALL of that junk from there, it is 'clouding' the signal to the computer and it can be interpreted as a lock-up, don't try to take it out to clean it, i've broken every one i tried, just get a rag or even compressed air if available and do the best you can.

on the rears, have it up on jack stands, tires and drums off. i'm pretty sure(lot of things for me to remember) that the tone wheel is pressed onto the drum on the inside of it, same procedure as the front, no movement whatsoever and the sensor magnet should be clean(when you're done)

i've seen a few of the front tone wheels crack and sometimes they spin, sometimes they don't, but that will definitely cause your problem.

yes the HCU is under the battery, that's where your noises are made, this type of system doesn't 'store' any pressure like previous years, it uses a pump to build pressure when needed(the noise)

for anyone who is still reading this long post, the abs computer totally eliminates the driver's foot during an abs 'panic' stop, first it isolates the driver's input, then it lowers and builds system pressure based on what it sees at the sensor, that's why it needs pressure(the pump) and why you feel the pedal doing weird things and also why you should never 'pump the pedal' on abs systems. have some confidence in the computer, not only is it flying your airplane, but it is also regulating the pilot as they use the abs on almost every landing too!
 
  #9  
Old 07-15-03, 05:10 AM
hippy553
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abs brakes

Thanks to everyone for the information.Mike I will check everything that you said and will let you know if I found anything.Harry
 
  #10  
Old 08-02-03, 04:54 AM
hippy553
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95 Caravan ABS Problem

This is to Mike in nj. Mike just wanted to let you know that your
diagnosis was excellent.I found that the right abs tone wheel was cracked.I installed a new half shaft and that repaired my problem.Thanks again for the information.. Harry Wertz
 
  #11  
Old 08-02-03, 09:44 PM
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awesome

glad to hear it

thanks for letting US know what fixed it
 
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