I have an intermitant brake problem with my 1993 245. Best guess is that it is ABS related but never has been fixed. The master cylinder, wheel cylinders, abs sensors ahve been replaced and the system disassembled and cleaned repeatedly. After the disassembly/cleaning the problem will disappear for 1 week to 1 month and then reappear.
Symptoms: When easing up to a light, lightly pressing the brake pedal, the pedal will drop and then come back up. It feel light part of the system connected to the pedal is rolling over a bump. At the same time, there will be a grinding noise from the front of the car in the wheel area. The wheel will also pull to one side at the same time. The pedal feels like it is connected to something rough.
At one point, the ABS light would come on. When the light was on, the problem would not occur. The light no longer comes on but the intermittant problem continues.
Several mechanics have tried to fix(including the local dealership), but the old brick is shy and has only displayed the problem in a mechanic's presence once.
Any thoughts? If not any referral to a good Old Volvo mechanics in the South Pinellas County, Florida Area? Thanks for your help.

I agree w. Stoney but will add that if the caliper is seizing, the ABS may be sensing this and pumping the system in an attempt to correct it. When this happens at low speeds, it can sound like a quick series of deep twangs. My advice is to get two new/rebuilt calipers and do both the front wheels at once. Also bleed the system, but remember to clamp the lines going from the caliper to the ABS unit so dirty fluid doesn't get into it.

but remember to clamp the lines going from the caliper to the ABS unit so dirty fluid doesn't get into it.

I'm sorry to differ on this "clamping" brake lines to protect the ABS unit, for 4 reasons:

1) It's not mentioned in the 200 or 700/900 Volvo factory brake manuals.

2) What the manuals do say is to open bleeders at each caliper and depress the pistons to expell the fluid behind them.

3) With fluid forced out the open bleed line, I doubt any fluid will go upstream against the fluid in closed line, even from the closest caliper. Where would it go? It's a closed system.

4) Brake hoses may be different now, but the last one I dissected had a pretty hard, plastic-type inner line, which I expect could crack if pinched off.

IMO, this clamping of ABS brake lines is a myth here on the BrickBoard, maybe originating as a FAQ tip. If you or anyone knows of a credible Volvo source for this practice, I'll eat my words (but I still won't clamp any brake lines).
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

OK, fair enough. What aout this from the FAQ:

http://www.brickboard.com/FAQ/700-900/BrakesABS.htm#BrakeFluidBleedingFlushingProceduresforCarswithABS

I don't have a green book for brakes, so I can't claim to have a Volvo source for this. I have seen many references to clamping off brake lines, especially when using a C-clamp to depress a brake caliper in order to prevent fluid from possibly contaminating the ABS unit. I've also seen references to using a clamp on the line to prevent fluid loss when changing the caliper. So I think your concerns about crushing the brake line are unfounded. In fact I've done this myself with no ill effects. These clamps are widely sold for this purpose, but I wouldn't use any clamp that doesn't have a wide clamping surface. As far as proving old brake fluid (that doesn't typically get changed in a brake bleeding, BTW) can screw up the ABS unit, well I don't really know how you could definitively prove that, since even dissasembly of a ruined ABS wouldn't prove it was caused by old fluid for sure. I guess you roll the dice and you take your chances.

I hope I'm not offending you by opposing what I believe to be a myth. But it upsets me to think how many "newbies" come across it, repeated endlessly here as "Gospel". My concerns about crushing the brake line may be unfounded, but in my opinion so is this brake line clamping tip. And to me it's not worth risking needless hose damage.

Yes, I thought the clamping idea probably came from the FAQ, but I don't consider this magazine tip to be a credible source—especially one with so many vague qualifying terms and a questionable understanding of the "path of least resistance" as applied to brake fluid. Here are my views on it:

"[Tip from Motor Magazine] Add the step of line-clamping the brake hose to the caliper when you retract caliper pistons. If you don't, you may be forcing brake fluid from the caliper bore (where rust and other debris may have collected) and sending this dirty fluid upstream. It's long been standard practice to open the caliper bleeder screws to give brake fluid a place to go while retracting pistons. However, sometimes the bleeders are partially blocked. In these cases, they may not let out all of the fluid that you meant to let escape. Instead, the fluid may take the path of least resistance - upstream. Nowadays, that's likely to send it to sensitive ABS components."
• This doesn't make any sense to me. Even a "partially blocked bleeder", would offer "the path of least resistance", when compared to the totally closed "upstream" path to the ABS modulator. Or does the writer suppose there is empty air space "upstream"?
IMO, this alone discredits the whole "tip", as presented.

"If the vehicle you're servicing has a blocked bleeder, you may get around the problem by cracking open the fitting where the brakeline attaches to the caliper before retracting the piston."
• With a "blocked bleeder", I wouldn't be "retracting the piston" I'd either be fixing the bleeder or replacing the caliper. Advice like this makes me question the writer's experience and credibility—and thus the whole "tip".

"For added assurance, you may also want to line-clamp the hose feeding the caliper with genuine clamps designed for this purpose."
• I've never seen any "genuine" brake hose clamps. Probably because I've never needed any. I doubt many DIY'ers have either. And I think it's wrong to send them looking for something that may not exist (or be worth using) based on a questionable magazine tip.
I do have line clamps that I use on pliable fuel, vacuum, or coolant hoses. But I don't agree with needlessly subjecting brake hoses (with their semi-rigid inner liner) to any crushing forces.

I don't know where you've "seen references" to clamping a brake hose to prevent fluid loss when changing the caliper, but it's just not necessary. Fluid loss from an open line can be easily prevented by blocking the brake pedal depressed (while bleeding off the resulting pressure). The MC piston seals will block off the reservoir ports so no fluid will flow, except for a drop or two when the line is first opened.
This method is in the 700/900 brake service manual, although not explicitly explained. (Maybe it's assumed to be common knowledge?)

If I knew of a convincing reason for brake hose clamping, I might try it (reluctantly). But this FAQ magazine tip doesn't convince me in the least. And I hope you will try the "pedal down" method the next time you have to open a brake line, instead of clamping it.

Bruce




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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

i can't believe what i'm readin! you clamp one of those, say with a pair of vise grips, and it's toast! do people actually do things like this?? again, i don't know much about this car yet, but i do know that stuff like that will just cause even bigger problems very soon thereafter. shortcuts are great, but, not when it comes to stuff like brake-jobs, fuel delivery, or wiring shortcuts,and, this is just my opinion, it ain't worth the time, or money you think you're gonna save. if you don't at least try and take the time to do it right the first time, it could end up costin u big $$$ in the end.another case where,"don't believe everything you read" comes into play. i have only been working on our volvo for three weeks, and, i have learned so much from the members of theses forums in the last few days alone, that it would behoove anyone who attempts any repair(s) to take a few minutes to read thru some of the posts involving whatever it is you are trying to accomplish BEFORE you put a wrench to your work. i am sure glad i did! these guys sure as hell know what they're talkin about, as they answered all my questions in a very timely and polite manner, couldn't ask for better advice if i had had someone from the Volvo factory standin next to me holding my hand! However, gettin back to the subject at hand, i couldn't agree w/ Bruce more, that is a very questionable "shortcut", and i wouldn't attempt that. i'd rather go the long way around if necessary when changin out the pads, or whatever brake maintenance they were doing before i'd resort to actually clamping down on the rubber hose that goes to the caliper.besides, brake fluid is cheap, and it never hurts to bleed it all out, and refill w/clean fluid before replacing pads, etc. by the way, there is a product called PB Nutbuster, seriously, best rust penetrant/metal lubricant in a spray can i've ever used.......(makes WD-40 look really bad), one of my bleeders on my porsche caliper was all but about to break off, i applied that stuff, and, the next morning, it came loose with very little effort, and the rust from around it just fell away, like magic.besides that, when maintaining brakes, you should never involve any shortcuts, or the like! just one reader's opinion! good luck and God speed!PS: what magazine was this article posted in? anyone know?

I'm with Bruce on this - I'm not a fan of pinching the hoses. I've never seen one break from doing it, but the idea of crimping that nylon/teflon inner liner doesn't sit well with me. If you're really worried about not forcing fluid upstream, wouldn't blocking the brake pedal down serve the same purpose, preventing fluid from running upstream to the m/c? Once the seals cross the reservoir ports, there's nowhere else for the fluid to be displaced to is there?
-Chris

Thanks,Chris.

The concern seems to be about the ABS modulator getting corrupted by back-flushed old fluid. But given the small fluid volume behind the piston vs. the upstream distance to the ABS unit, IMO it's not likely. Especially if one follows the greenbook (700/900 any way) procedure and presses the pistons back while draining at the bleeder.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Sounds like one of the calipers is siezing and the disassembly/cleaning frees it up until it jams again-which could mean rust or crud in the lines or other contaminant. Siezed calipers can warp a rotor very quickly.

No, it doesn't sound like an ABS problem; it might be something to do with the brakes (caliper or rotor, including the pads) on one front wheel.
I would take off the front wheels and take a really good luck at everything there -- the condition of the pads (e.g., how it's wearing, whether the it's straight and properly held by the pins and spring clips, whether rubber boots around the pistons are seating properly, and whether there is too much "warpage" of the rotor leaving the pads spaced out a bit. I'd go over the front brakes with a fine-toothed comb.

Gook luck.