In a separate post, I outlined my brake problem and what I have done to fix it, and the responses were "You have warped rotors, replace them." I responded to those posts with this, which I am posting here in case anyone has any ideas about how to proceed:

Let's start over here...rotors, I am told, don't warp without a cause, and that cause is almost always sticking calipers. I replaced warped rotors in April, and within a few weeks or less, the new ones started pulsing, leaving me to suspect that they are getting heated up too much for some reason.

I checked the rotors with a dial indicator, when they were cold, and their runout is less than .002", and Volvo specifies a maximum of .003". I have to measure them hot next, because it is when they heat up that they go out of whack.

Simply replacing warped rotors with new ones without dealing with the cause of the warping is futile. That is what I am trying to figure out now. I replaced the pins and boots of both calipers, greasing them liberally, and hoped that would free the calipers up enough to keep them from sticking. Perhaps it has, but the rotors are still warping when they are hot, after driving for awhile.

So the next line of attack will be replacing the calipers with rebuilt ones (I am told rebuilding them onesself is a waste of time). It may be that I have to replace the rotors as well if they are permanently damaged, and of course, the brake pads, etc.

Honestly, if I knew of a shop I could really trust to take care of this, I would take my car to it, but no one gives the job the kind of attention and scrutiny I do, and I have caught my local Volvo dealer in several misdiagnoses (costly) which show that beyond the basics, doing it yourself often is the only way.


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Darius in Albany NY '86 744 GLE (175K, given to my mother-in-law); '91 745 Turbo (173K-my 'Little Red Wagon')

Thanks, everyone. From the various suggestions I am hearing, my plan is to clean the ABS sensors (though the pulsing I experience is nothing like what happens when ABS kicks in) and have my bushings and suspension thoroughly checked by a capable shop, and then as a last resort, replace my calipers with rebuilt ones, and, of course, the rotors and pads. I also will consider replacing the brake lines with the metal ones IPD sells, but they are pretty pricey, and my wife gets a little worried that "nicety" and "necessity" get kinda confused in my feeble brain.

Thanks again for all the suggestions. I will report back when I have found the solution!
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Darius in Albany NY '86 744 GLE (175K, given to my mother-in-law); '91 745 Turbo (173K-my 'Little Red Wagon')

Well a few things to consider:

Not all rotors are going to be within factory spec, even when new.

Yes, it's usually something overheating the rotors that causes them to warp.

However, I believe that if you've got the strut rod bushings and slide pins replaced and lubed appropriately you've probably solved the cause of your rotors warping in the first place.

The only other things I can think of are: failed soft hoses and unevenly torqued lug nuts.

The thing to keep in mind is that once you've warped your rotors, they're not going to magically unwarp.

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alex

I had continued problems with sticking pins on front brake calipers. Replaced the pins and in a couple of years same problem. Also with worn parts the hole clearances were not what they should be, causing a little bit of binding. When sticking, only one pad contacts the disk and causes it to warp. Also, if the caliper piston is sticky and not retracting (holding pressure on the disk), you also have overheating and warping.

I bit the bullet finally and bought new calipers and greatly improved braking performance. If they are the originals, and you don't have nice free movement at pins and pistons, or if you have slop in the pin guides, I would consider replacment.

In some cases, the brake hoses start to deteriorate inside, which impedes the flow of fluid back out of the calipers when you release the brake pedal. This causes the pads to drag on the rotors for extended periods of time.

My Dodge Dakota had a problem eating rotors, even after the calipers were replaced (by a tire store). I asked the owner of a brake shop if collapsing hoses was a common problem and he replied with "I see it all the time".

Now, you decide what "all the time" means. In the case of my Dakota, I replaced the hoses and it was a whole new truck in terms of brake performance - no more pulling, pads where more evenly. (In terms of the paint flaking off the body it's still the same old truck.)

My experience with 700s is that brake pulsing is related to the strut rod bushings; I've replaced them on both of mine with ipd's urethane ones and cured the problem.
FCP has 'em for a lot less money, but I have no experience with theirs.
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Jim McDonald

In addition to strut rod bushings add worn wheel bearings and tie-rod ends (inner and outer). All can contribte to pulsing during braking.

Mine are new.
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Darius in Albany NY '86 744 GLE (175K, given to my mother-in-law); '91 745 Turbo (173K-my 'Little Red Wagon')

"New" as in stock or "new" as in polyurethane?

Did you replace the pads when you installed the new rotors? Did you properly “seat” or “bed” the rotors (and pads if applicable)?

Here’s a great article that was in IPD’s last catalog: http://www.ipdusa.com/company_whatsnew.aspx

Here’s how I’d trouble-shoot a caliper problem:

Lift the front of the car, and hand-spin each front wheel. If they spin freely, then get in the car, start it, and pump the brakes good and hard. Shut off the car, and hand-spin the front wheels again. Do they still spin freely? If so, then I bet a new set of rotors and pads will do the trick. Make sure you “seat or “bed” them properly. (5-6 cycles of hard braking from about 45mph – 5mph -- don't come to a complete stop)
If the wheels did not spin freely after the test, track down where they’re hanging up. It’s either going to be the slide pins or the caliper piston.

Good luck. Post back with the results.

Jeff Pierce
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'93 945 Turbo ( one kickass family car ! ), '92 Mercedes 190E (my daily driver), '53 Willys-Overland Pickup (my snow-plow truck/conversation piece -- sold to a loving home), '85 Jeep CJ-7 w/ Fisher plow

Yes, new pads when I put the new rotors on (it's required, isn't it?).

Your test sounds good - I found that the wheels spin less freely when I turn on the engine, interestingly enough - may be the ABS waking up or something.
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Darius in Albany NY '86 744 GLE (175K, given to my mother-in-law); '91 745 Turbo (173K-my 'Little Red Wagon')

Why would replacing the calipers help?

Maybe the pads are the problem. Too thick, wrong material, etc.

Maybe the rotors are on the thin side or aftermarket and you just need another brand.

Isn't spending the $ to resurface the rotors a lot cheaper and easier than replacing calipers? My local Autozone charges $8 apiece.

Sticking, dragging calipers are the main cause of warping rotors.

Machining Volvo rotors doesn't help; they warp again in a few weeks. I had that experience and I have read several posts about it here, as well as on the FAQ.

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Darius in Albany NY '86 744 GLE (175K, given to my mother-in-law); '91 745 Turbo (173K-my 'Little Red Wagon')

Did you clean the ABS sensor on the front calipers? When I orignaly got my car, it had pulsating action and fellow brickboard members gave me the above advice. I pull said sensors and it was caked with brake dust and metal shavings. I clean them using electrical parts/contact cleaner. (Don't use brake cleaner.) Put them back on and the pulsing went away. I would try this procedure before getting new calipers. Its cheap, easy to do, and hopefully will solve your problem. Good luck.

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91 Volvo 745 Turbo, 91 Nissan 300ZX TT, and 01 Volvo S60 2.4T

Where are the sensors and how hard are they to "pull?" This sounds like a real possibility because the wheels spin freely when the car is turned off, but when I turn it on, pump the brakes, and then try to spin the wheels again (engine still on), they spin a lot more reluctantly. My ABS kicks in at odd times, too, leading me to think it is a little "off." Perhaps clogged up sensors could be the problem. Anything else I need to know about this?
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Darius in Albany NY '86 744 GLE (175K, given to my mother-in-law); '91 745 Turbo (173K-my 'Little Red Wagon')

Please refer to the 700/900 FAQ. There is a section reserved for Brakes/ABS. Good instruction are in there as well as your Haynes Manual. Good luck and post your findings after cleaning said sensor.
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91 Volvo 745 Turbo, 91 Nissan 300ZX TT, and 01 Volvo S60 2.4T