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Youch! Bitten by the ABS bug


Richard S
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Well, after months of being an interested observer of others' ABS woes, I have been bitten. Last week started getting ABS light for a moment whenever I touched the brake pedal. Still had strong brakes, but I know better. Ran the tests and my results were tragically lower than averages. Twice now, I applied the brakes only to find an extremely hard pedal and little braking. When I applied considerable force, the pedal sort of "gave way" and strong braking ensued. After that, normal braking, but with ABS light on momentarily on nearly every stop. I am not a big fan of piecemeal repair, and am considering either a conversion, or a Prior Reman unit {$400 + shipping], which keeps the car original in case it ever becomes a semi-classic. I have, by the way, changed fluid twice. First when I got the car, and just the other day to replace all brake hoses [a couple had exterior cracks, but no leaks]. Incidentally, in doing that job, I note that the fitting from the metal line to the hose will rust and corrode somewhat. Loosening a couple of turns right around now might not be a bad idea, because unless some thread lube is put there now, a time will come when this fitting won't loosen at all, which will make this job *real* frustrating. A wrench would have stripped the faces; I had to use vice grips.

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Mine was also "marginal" on the six tests (now seven - wait for the thump) but a new accumulator from Flow (www.gmpartsdirect) brought everything back to snuff.<P>If nothing else had been done, I would flush the system at the same time.<P>From your description, I would suspect that you are suffering from loss of pressure - is the EBCM setting any trouble codes ? <P>Since you still have braking and apparently in a straight line, the likely culptit is the boost system and not the ABS per se.

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I didn't think ABS problems set codes on the display. I'll try it anyway. The thing that made me skeptical of the accumulator was the way the hard pedal "gave way" under force and normal braking returned immediately. When I tap the pedal lightly, just enough to take up the free play but not apply brakes, I hear a kind of hollow pinging. Is this sound normal? I remember somebody [Padgett?] raising some questions about the brake rod.

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To check for brake codes you need to pull the cover from the ALDL connection and jumper two pins (B-G ?). Is a full description in the service manual - you need to count the SES ligh flashes, does not display on CRT.<P>Sensor/electrical problems will display, boost/hydraulic problems probably won't.<P>You second post does not ring any bells. Do you feel a "thump" in the pedal shortly after turning the key from OFF to ON ? How long do the lights take to go off in the morning ?

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Guest Brolliar

Your brake problem is interesting especially your statement:<P> "When I applied considerable force, the pedal sort of "gave way" and strong braking ensued. After that, normal braking, but with ABS light on momentarily on nearly every stop.'<P>It would be nice to know just what is causing your problem - even if you later go to a Prior rebuild. It does seem like it is in the basic system and not when the ABS is activated by a hard stop. *******Do be very careful in your driving since your brakes could not kick in sometime even when you apply considerable force. *******<P>I know Padgett was in a hotel away from his manual so I will provide a little help here. (As an aside - I really wonder what Padgett's day job is?) To read your Diognostics on an 89 Reatta you put a jumper between A and H in the ALDL connector or between H and ground. This is from page 5E1-8 in the 89 manual. Do you have a manual? I could describe how you read the codes if you don't have one. The actual diagnosis section is long - about a 100 pages. I would think the ABS light coming on momentarily at almost every stop would set a code.

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Thanks to both Dick and Padgett. I have a 90 and I do have the manual. Will run all tests suggested to see if something turns up. I had planned on getting some "Deoxit" and doing some of the electrical connections just to see what happens. I am wondering if it is coincidental, but just the other day while idling at a stop light, the rpms dropped and fluctuated, engine missed and stumbled, then went to a fast idle [1000 rpm]. Signal changed, I pulled away and all was fine again. Happened a couple of times, but otherwise OK. Can't say the normal idle is perfectly smooth and constant [seems to oscillate between 600 and 680 rpm], but normally behaves pretty well. Yes, I am worried, and have adjusted my usual somewhat "active" driving style. At present this is my daily driver, so . . . .

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Thank you - actually spent almost 8 hours at home last night but in Atlanta now.<P>First a caveat: I have some strong suspicians about what is going on but have not had a unit to take apart or experienced any problems with mine that a new accumulator didn't cure. Notary Sojac, UDA, YMMV.<P>That said I believe there are two different failures that occur, the first is common and recoverable. The second very uncommon but appears to have resulted in at least two different listmember's cars being totaled.<P>Both are commonly described as "hard pedal" but are very different.<P>The first is caused by a failure in the boost system (bad pump, accumulator, wiring relay, switch). Brakes may seem normal but are marginal or fail the "six tests". On application of the brakes, the pedal will sink an inch or two then become very firm.<P>Hard pressure (possibly both feet) will result in some baking (front wheels only). I would expect both brake warning lights to come on possibly accompanied by a "low pressure" display.<P>The second case may seem the same to the unwary driver by is quite different. Again I have nothing to go on but descriptions of the incidents and a hydraulic analysis of the TEVES system from the documentation I have.<P>Again the complaint would be "hard pedal" but with significant differences. First there would be no braking available. Second on brake application the pedal might depress a bit at first but then would be pushed back against foot pressure, probably to the top of the travel. No warning lights would come on.<P>What I suspect would happen is that the main valve in the ABS could jam open, effectively putting the boost system in reverse. Instead of servo-augmenting the foot pressure, the accumulator pressure would push back against the pedal, considerably harder than most people could manage. In this case there will probably not be any warning lights lit or failure codes set (ABS tests are mainly for electrical problems, not hydraulic ones). Further, if the "stuck open" condition was temporary, the brakes might feel completely normal afterwards.<P>It was for this reason that every time I get in the car, I perform "test seven" - before turning the key on or starting press firmly on the brake. When the key is turned on the pedal may drop slightly as pressure comes up but after a few seconds you will feel (and possibly hear) a distinct "thump" in the pedal. This is the ABS self-test cycling the main valve. Once felt you will know that it cycled properly at least once.<P>No real scientific basis yet other than a hunch but worth thinking about.<P>--------------<BR>ps Have been employed by various elements of the same DoD contractor since 1979. Have been averaging less than a week a month at home (suspect car spends more time at airport than home, fortunately the garage is covered).<P>If you are really bored could do a Google search on "padgett peterson". Yes, they are about all the same person.<p>[ 11-01-2001: Message edited by: padgett ]

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Guest Buick Mike

Our man Padgett has more Web Site matches than Michael Jordan, Mick Jagger, and the Beatles put together! (OK, so I've got some free time) Gotta work on the Category and Inside Yahoo! matches, though. They've got you there smile.gif" border="0 <P>Mike

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Oh that:<BR>"I am wondering if it is coincidental, but just the other day while idling at a stop light, the rpms dropped and fluctuated, engine missed and stumbled, then went to a fast idle [1000 rpm]"<P>Sounds like a sticking IAC (Idle Air Control - name says it all) that is not responding to commands quick enough. (ECU sends command, nothing happens. Ecu keeps sending bigger commands as the revs drop until suddenly the IAC responds. A Lot.<P>They get this black gunk on the pintle and in the oriface. If it didn't die completely, your case is minir.<P>Clean real good with carb cleaner (don't get in the contact cavity) on the end, around the spring, and in the manufold recess. Screws (2) are a little tricky to get at so be careful not to drop. Might put a towel underneath to catch if you do drop one.<P>Have done on several cars with same symptoms and always worked.

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Thanks for looking at that part of the post, Padgett. Will study my manual a bit, find the offending unit, and clean it up. Let you know if you were right.<BR>As to the brakes, my symptoms sound more like the first than the second. With incresing frequency, and more often when initial foot pressure is higher [not a panic stop, but yet distinguished from grandual slowdowns], there will be no braking and hard pedal, followed by the pedal "giving way" and the brakes take over, seemingly as they should given that foot pressure. After cleaning electrics, I am wondering whether to try an accumulator [under $80] first, and a complete reman unit if that doesn't work, hoping Prior will give me some credit if I send them the new accumulator.

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Wufibug as a bit of added info I put a accumulator on My first abs unit and it improved the problem for a month or so. It then started to built slow again tilln I put a used abs unit on it it worked excellent when I first put it on. 6 months or so later it started to fail again by failing to built pressure very fast. I had also changed relays twice and this too helped for a while. I do suggest You change both relays if You put on a rebuilt and flush the whole system good and I would do it about once a year from then on.

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I WAS JUST GOING TO LEAVE A MESSAGE FOR ANYONE WHO WAS STILL KEEPING TRACK OF HARD PEDAL AND RAN ACCROSS THIS, SO I'LL LEAVE THE MESSAGE HERE. I EXPERIENCED THE SAME PROBLEM THE OTHER DAY. WHEN MAKING QUICK STOPS, HARD PEDAL WOULD OCCUR BRIEFLY THEN FOLLOWED BY A QUICK PULSATING STRONG STOP. THE PROBLEM WAS CORRECTED BY CHANGING THE ACCUMMULATOR. THIS RESTORED THE BRAKES BUT I STILL DON'T HAVE ABS. (AND DON'T CARE)I NEVER LIKED THE PULSATING PEDAL. THE REPAIR WAS DONE AT BLVD. BUICK IN LONG BEACH, CA. ACCUMMULATOR WAS $175.00 AND LABOR WAS $225.00. I DON'T KNOW IF IT WAS A GOOD OR BAD PRICE, BUT IT MADE ME HAPPY TO HAVE BRAKES AGAIN. IN ADDITION, IT WAS ALSO NICE TO KNOWN THAT THEY WERE FAMILIAR WITH THE BRAKE SYSTEM, WHICH CARS THEY WERE ON AND THE PROBLEMS THAT THEY HAD. HOPE THIS HELPS SOMEONE. cool.gif" border="0

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From Flow, the accumulator was under U$100 with shipping for me and it essentially just spins on and off like a big oil filter (make sure you release all pressure first by pumping the brakes with the key off until hard - 25 pumps min).<P>There is a small structure that extends up into the accumulator in the center so be gentle and lift straight up.<P>New accumulator will come with a new O-ring (make sure it is there) seal. The O-ring seal means you do not need to play godzilla when tightening, just "tight". Think it felt about like a spark plug for me and mine doesn't leak.<P>Took me less than five minutes to R&R with a T-50 socket AFAIR

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Dick Broliar was kind enough to email me off forum, but I thought his point was worthy of covering, since my reply also involved Padgett's very interesting theory.<BR>Dick noted that my hard pedal followed brake bleeding and wondered if I introduced air into the system. Could be. I use my compressor, set to 18lbs, to bleed the system and always keep plenty of fluid in the reservoir to avoid pumping in air. I have a water filter on the compressor to ensure I am not putting water into the brake fluid. Ran two quarts through just to make sure. I too kept thinking that the hard pedal was consistent with air in the system. Is there somewhere you would recommend bleading in addition to the caliper bleed screws?<BR>The more I think about Padgett's theory, the more it describes what happens. If I apply the brake gradually, I don't get the hard pedal syndrome [ABS light does come on momentarily]. Hard brake pedal seems to co-occur with sudden brake pressure, as though the firm pedla causes a rush of brake fluid that somehow "jams" the valve Padgett refers to, in the wrong position. When that happens I am fighting the reverse effects of a high pressure system. If the "jam" is partial, the valve somehow clears itself and proper braking is restored. One might surmise that if the valve or bore is sufficiently damaged, the jam may become total, and hard pedal will not abate until pedal is released. One might, even then, however, regain normal braking in gradual pedal pressure situations where the valve or piston may ease itself into position. This is my dumbed-down surmise on what Padgett is much more systematically and empirically working through.

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Guest wally888

I hope I don't type anything here that someone might find offensive but:<BR> I constantly read posts about the brakes that imply the author has not read Brakes at reatta.net.<BR> I mentioned the Main Valve as the potential culprit of a weird, " Hard Pedal", a couple of years ago. But-<BR> Initially, when the key is 1st. turned on, the Servos and Main Valve, in the Valve Block are cycled and checked by the EBCM. If all is not well, the Yellow Light will stay on. The wheel sensors are also checked at this time.<BR> I doubt if anything actually fails when a momentary failure or hard pedal occurs, just trash holding something either open or closed ( in the wrong position).<BR> Everyone can, I think, expect one or two Accumulator failures over a period of time. A total failure if the system isn't periodically flushed, infrequent relay failures and inconsistant Pressure Sensor signals.<BR> If I had problems after replacing the Accumulator and flushing, I'd give the system the , "Tests", look for codes at the ALDL and check the Relays. If no solution found I would check the Pressure Sensor. The Pressure Sensor can cause a lot of different problems that lead one to think the pressure os O.K. , when in fact, it is low. It can also fool the Yellow and Red lights! Think all of the above is explained at reatta.net.<BR> The Main Valve is normally closed and opens only to relieve excessive pressure created when Anti Lock is engaged and one of the Servos is opened and is letting excessive pressure escape. If the Main Valve got stuck open ( I suspect it has a rather strong spring holding it closed so the open condition would have to be an erronerous electrical signal or trash somehow holding it open but How did it get open?) it would give a hard pedal, no pulsations.<BR> Surely someone, by now, has disassembled the Valve Block and Main Valve and can tell us what the parts look like?

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Wouldn't mind disassembling one but have had no time to "hit the yards" and mine is working properly (if it works, don't fix it).<BR>If someone has a unit fit only for a "core" would appreciate a loan - will buy if cheap but for study purposes only.<P>I suspect that Wally is being gentle. A parenthetical note in the TEVES training manual (no illustration provided) indicates that the main valve also kicks the pedal back (pulsates). If it were to stick open, the boost appears to operate in reverse pushing the pedal back instead of assisting causing not just a "hard pedal" but a "rock hard pedal" and no braking.<P>(Know am repeating myself but is important) - Whenever I start my car, while turning the key I press down on the brake pedal moderately. A few seconds after key-on I feel a "thump" in the pedal - one pulse only - when the self-test in the ABS cycles the main valve. (haven't checked for before or after the red light goes out). Then I have reassurance that it worked at least once.

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Guest Brolliar

I agree with Wally888 that there is alot of good brake information at <A HREF="http://www.reatta.net/brakes.html." TARGET=_blank>http://www.reatta.net/brakes.html.</A> He has stated this very valid point in a number of brake discussions. I have also found the pictures at <A HREF="http://www.reatta.net/brakes/brakes_pictures.html" TARGET=_blank>http://www.reatta.net/brakes/brakes_pictures.html</A> very useful. <P>The picture at <A HREF="http://www.reatta.net/graphics/001209_antilock_increase.jpg" TARGET=_blank>http://www.reatta.net/graphics/001209_antilock_increase.jpg</A> shows a the brake system during a non-antilock stop. Refering to it, I thought if Wufibug had air in the sky blue region of fluid he initially would get a hard pedal and little braking. He said "I applied the brakes only to find an extremely hard pedal and little braking." The accumulator and pump would have to compress this air, when the control valve opened due to the brake being pushed, before he would get the boost system to help apply the brakes. The regulated booster pressure pushes to the left on the right end of the boost piston to increase the pressure applied to the front brakes (green fluid in the picture) and is applied directly to the rear brakes. I thought that the air being compressed and the boost now helping him might be why Wufibug said "When I applied considerable force, the pedal sort of "gave way" and strong braking ensued." <P>A similar problem could occur if the accumulator did not have enough stored high pressure fluid to boost the brakes and Wufibug had to wait a second or two until the pump created the high pressure fluid needed. A bad accumulator is the more likely cause of the problem.<P><BR>Of course this problem could also occur if the pressure switch did not quickly sense the drop in accumulator pressure and tell the EBCM to actuate the pump relay, the pump relay did not actuate right away and turn on the pump, the pump was slow to start, or the ECBM malfunctioned for a second or two - etc. <P>The picture I just refered to at <A HREF="http://www.reatta.net/graphics/001209_antilock_increase.jpg" TARGET=_blank>http://www.reatta.net/graphics/001209_antilock_increase.jpg</A> does not show in detail the control valve or the reaction sleeve which are shown at <A HREF="http://www.reatta.net/graphics/000922_hydsys.jpg" TARGET=_blank>http://www.reatta.net/graphics/000922_hydsys.jpg</A> . Fluid pressure on the left end of the reaction sleeve when the main valve opens during an antilock stop is what causes the brake pedal to rise and pulsate.

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Guest Brolliar

Wufibug, in reply to your most recent post, if you with the ignition off depressurized the accumulator before bleeding the front brakes, and bleed both front and rear brakes per the manual until the fluid coming from the bleed screw hose was clear and bubble free for each or the four calipers then I would think you had all the air out. <P>If the front brakes had air in them you should get a lot of pedal travel or the pedal should feel spongy similar to non-ABS brakes with air in them. Since the brake pedal does not push directly on the fluid for the rear brakes but only applies pressurized fluid to the rear brakes thru a control valve I don't think you can tell to much about any air in the rear brakes by the feel of the pedal. See <A HREF="http://www.reatta.net/graphics/001209_antilock_increase.jpg" TARGET=_blank>http://www.reatta.net/graphics/001209_antilock_increase.jpg</A> . If you had air in the rear brakes I would think the pressure boost helping you to apply both the front and rear brakes would be delayed some especially if you applied the brakes rapidly. This paragraph is an opinion and others should feel free to comment.<P>Have you had time to get the diagnostics using the ALDL connector?

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Padgett I may be able to help in Your quest for knowledge. I have a unit I started tearing down and decided to quit and work on My conversion. The main portion, valving and cylinder have not been torn down. I only dissassembled the pump. I would send it to You to help everyone if You send Me an address and this unit is an acceptable cadavor.

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Guest wally888

I would do most anything to have a throw away unit to tear down!<BR> If I or anyone gets an old unit, digital pictures are in order. Would be nice for all those interested to see these components torn down. Unfortunately , as I suspect will be true w/ the Teves, there will be a lot of ports and hidden passages better understood by looking at a fluid diagram. <BR> But maybe we will be able to piece together a better understanding of the Main Valve, Reaction Sleeve and the linkage from the Pedal to the Metering Valve.

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Guest wally888

And. I , at one time, thought there were repair kits for the Teves. Hope one of you who have parts catalog can determine if this is true? Cleaning and rebuilding the Unit would not be a major undertaking if there were little pitting and parts were available.

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Wally or Padgett the offer of the old unit is for either one of You. I know that any knowledge gained by either one of You will be for all Reatta Owners. You guys get together and decide Who wants to do it and get Me an address and I will send it. The main part of the unit is still together. I did take off the pump and related parts but it is complete just partally dissassembled.

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