|
|
|
I've got an interesting situation with poorly bedded front rotors causing pulsation and I'm not sure if there's a worthwhile fix other than new rotors. These are nearly new and barely even worn Bosch Quietcast coated rotors and Quietcast pads in otherwise perfect condition. On inspection just now, there is a thinner area of the rotors, the size and shape of a brake pad, on both sides of the rotors -you can feel the edge with your finger. It's clearly an area where the pad friction material hasn't fully coated.
More specifically, it's an area of the original bedding that was soft under high heat and at a prolonged full stop during the high speed bedding process some of it cooled back onto the pad. I know where this likely happened, a long traffic light I was forced to stop at the bottom of a steep mountain highway where I'd been doing the heavy braking bedding from highway speed and it didn't have a chance to cool and set with the brakes off, but rather cooled at the traffic light with the brakes applied. Now in city braking conditions, I didn't notice any brake pulsation at the time so never realized this had happened.
Over time (say 2000 km of highway driving), it's gotten worse to the point there is now horrid pulsation when the rotors are hot and expanded. What's happened is that as the high area of the rotor (90% of the face) goes under the pad, at high heat it keeps picking up friction material, whereas the low area picks up nothing, accentuating the difference. I just measured it and the difference is now .0007" thickness variation in that pad-sized area. Runout is still well within spec and also thickness variation. Because it's such a small and distinct indented area plus the brake friction is different in that poorly coated area, it's felt as pulsation and as I said it's magnified when the rotor is hot.
So my question is, is it worth trying to resurface the rotors and re-bed them properly? New rotors aren't that expensive, but it seems a shame to waste two barely used rotors that are otherwise in perfect shape. There are a few options and my online research indicates mixed results. Lots of theories and advice on possibly cutting corners, but little in the way of follow-up reporting.
a) Having the rotors turned is a definite option as there's lots of material, but you're soon at half the cost of mid-priced new rotors and turned rotors are never as good as new rotors. Years back I had badly scored rotors turned that their machine didn't do to spec, possibly not centering the mounting hub properly.
b) Try to resurface them manually to remove the friction material and restore uniform width around the rotor then re-bed them. It can't be done chemically, so abrasives are needed. A tufted wire wheel likely isn't good enough for this job, but it would at least be a start. Grinding would be too severe. Sanding would seem the best option. Hand sanding might take forever. I was thinking a pad sander, or better still a belt sander with a 220 grit aluminum oxide belt.
c) Simply try re-bedding it. Some have tried this with limited success. This might take three to ten times the usual number of high speed stops to get the brakes good and hot to fully soften and redistribute the embedded pad friction material. I'm tempted to try this, but it means a bit of travel to get to a suitable stretch of highway and doing it in the middle of the night.
d) Bite the bullet, open the wallet wide and get new rotors, this time going up a step in quality to Zimmermanns with Pagid pads. Now knowing better, I will go out of my way to ensure they are properly bedded by doing it in the middle of the night where I can crawl through a red light if needed in order to ensure a proper cool down. The old pads can be kept as spares when the Zimmermanns get closer to end of life. The good and lightly used rotors either go to metal recycling or take up space in my workshop for the next x years figuring I might someday have them turned.
Thoughts? Anyone have this kind of experience?
As additional discussion, I'll mention that many people (and shops) don't bother to bed in the brakes with the newer technology pads and rotor metals and simply let nature take its course. There's nothing really wrong with that approach as long as you don't make the kind of mistake I did. Over time the friction material will build up on the rotor. With extended city driving and moderate highway braking the build up will be reasonably uniform. The problem is for people like me who might do mountain highway driving before the rotors are fully bedded. If you come to a full stop with the brakes hot and keep your foot on the brake (such as at a very long light), if the brakes get a chance to cool there may be uneven bedding until the pads and rotors have reached a state of equilibrium and no longer transferring significant friction material. Until now, I've been more middle of the road on bedding new rotors, usually only the initial step of bedding doing numerous hard stops from city speeds to low speed to mate the friction surfaces under heat followed by a bit of cool down driving.
|
|
-
|
|
|
I was just getting ready to try dressing the front rotors to remove the high spot friction material and level it when I noticed something very odd. I'm going to work my way up in abrasives until I'm convinced the surface is perfectly the same all the way around.
Oddly, what I just noticed is that these opposite pad sized areas of slightly thinner thickness (.0007") begin precisely at the balance milling notch on the edge of both rotors and extend in the direction of forward driving rotation. These are supposedly decent quality Bosch Quietcast rotors with relatively little mileage on them. The milling on one is fairly significant, about a 3-1/4" long area that's a good 1/16" deep in the middle. It's about half that length on the other rotor, which is more typical of the milling I've seen over the years.
Why would these areas start at the same point on both rotors??? One thought was it has something to do with their milling process that slighlty affects the surface. My only other theory is that when the brakes are hot, the metal expansion in the milled areas is a hair less and may cool a hair different than the rest of the vented rotor. Over time, the build-up of friction material will be greater where the rotor is thickest and hottest. If this was in any way a production issue with the milling, I would expect Bosch would know about this by now.
Any other theories?
I think this is worthy of bringing to Bosch's attention in case it's a problem caused by the way the milling was done. The only contact listed is a toll-free number so we'll see how far I get or whether I even get a response.
Based on this, for the moment I am no longer recommending Bosch rotors or Bosch Quietcast pads unless they can convince me it was somehow my problem and that it was a total coincidence it was the same on both rotors. I now have a pair of Zimmermann's on the shelf waiting to be used if the problem comes back again after dressing the Bosch rotors. At this point, I'm treating the Bosch rotors as an experiment. I've got also got relatively new Quietcast rotors on my other 940 that have a hair of pulsatoion, so I'm going to be checking those out as soon as the garage is clear.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
|
|
-
|
|
|
Hi,
I also had such issue last time. IME its about pad to disc matching (quality and material wise).
I've tried OE pads with Meyle disc. Followed bedding procedures but it warped afterwards with less than 100km travelled. Once warped it can't be repaired unless skimmed. Discarded Meyle disc and installed Bosch. Followed bedding procedures again (re-using same pads) and still got warped after 500km. Finally installed ATE disc, same procedures again and this time ok.
Bedding procedures are important otherwise the brakes won't bite effectively. Won't know what braking situation you'll encounter along the way so don't take the risk. The 900 series is a heavy car.
I also tried not to step on the brake during red light (to avoid the hot pad material marking the disc) by shifting to N, but this also not effective when using Meyle and Bosch disc. They still warp. Repeated same thing later with ATE and all ok.
Always using OE pads. Haven't tried disc brands like Zimmermann or Brembo.
Regards,
Amarin
|
|
-
|
|
|
Hi Amarin,
Do you know if any of those rotors were made in China?
It seems that brake pad compatibility slips under the radar of many.
I noticed at the Zimmermann FAQ that ceramic pads are not compatible
with their Z-coat rotors.
One thing I found is that Zimmermann has a great site with lots of technical
info about rotors and brakes, but they don't respond to e-mail.
ATE however has techs that will talk with you and are very cooperative.
ATE is huge in Europe with dealers everywhere, but in the USA you can
find a few sources for rotors but then you wont find the matching pads.
Perhaps part of some sweetheart deal with EU auto manufacturers?
Cheers, Bill
|
|
-
|
|
|
Bill, I'm not seeing where Zimmermann specifically advises against using ceramic pads with their Z-coated rotors. There is no mention of that in the pamphlet that comes with their rotors. What I see in their FAQ is the following:
1) "Zimmermann brake pads are not suitable for an installation together with ceramic / carbon brake discs. Zimmermann brake pads are developed for cast brake discs and have been tested for this application."
Here, their talking about their composite pads not being suitable for use with high friction composite carbon-ceramic rotors used in motorsport and aerospace applications, such as those made by Brembo.
2) "We recommend a brake pad from Otto Zimmermann (brake pads with a high degree of comfort), but original or approved brake pads from other manufacturers (with ECE R90 approval) may also be used."
ECE-R90 is a European-only rating that brake pads and rotors have been tested and accredited to meet a common European standard for manufacture and braking performance. There is no equivalent in North America. A number of ceramic pads have that certification, including ATE ceramics.
3) "When using other brake pad material, especially sports brake pads with a higher hardness, Otto Zimmermann cannot guarantee an optimal braking function, and the brake disc can thus also be damaged or considerably impaired in its service life expectancy."
I take that as saying, "If you're not happy with your braking or the life of your rotors, we won't necessarily agree it's a problem with our rotors, it might also be your pads. That is of course unless the pads are made by us (ours are of course perfect for our rotors) and especially if they're harder than ours." Hard pads, such as ceramics, will naturally run a rotor hotter and wear it faster compared to softer pads, so it almost goes without saying rotor life may be shortened and high heat might damage them. For everyday driving purposes, your rotors aren't going to get red hot or likely wear out any faster than other rotors of similar quality used with ceramics. IMO, they might as well be saying best not to use ceramic pads on any kind of normal rotor.
Basically, it's always a good idea to make at least some effort to match the pads to the rotors to achieve the braking you need, the noise and dust you're willing to tolerate and the consequent life you expect. One ideal is equal wear of pad and rotor for maximum friction, needing a new rotor for each set of new pads. Having said that, you need to temper that ideal with other considerations, such as noise, dust and brake fade, also the cost savings and convenience of being able to easily change pads compared to rotors.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
|
|
-
|
|
|
Hi Bill,
About the discs, ATE & Meyle - both made in Germany but I suspect Meyle uses different metal composition than ATE. I'm not saying Meyle is bad choice per se. I'm saying Meyle's disc was unsuitable to the OE pads I use.
Bosch have both Germany and China made. The ones imported to Malaysia were made in China
Volvo OE also have Germany and China made. The Germany ones are pre-Geely and China ones are post-Geely. Both still expensive by any means.
I haven't got the time to experiment with other pads brands. Car needed for daily commute to my forensic practice. All parts were obtained from brick & mortar Volvo shop here. Easier for me this way.
Regards,
Amarin
|
|
-
|
|
|
Hi Dave,
I’m no guru but I agree with SPOOK on everything he said.
I would have written the same thing about using the parking brake since you knew the brakes had to be very hot.
My thinking is if you have to use your brakes you are probably driving too fast into the next curve anyway. Find a lower gear and let the engine work for you, especially going up hill! 🙃
I too, never intentionally try to “bed” brake pads as that idea sort of went away with drum brakes shoes.
There is a lot of differences of surface area contact in that the brake shoes had to be arced to individual drums to get any more appreciable braking power from drums.
The pads are just directly mashed to conformity as they are made parallel to begin with.
The size of the pistons change dramatically as the surface areas could be considered decreased from drums somewhat but basically in order to stop the torque it’s a balancing act of engineering.
The vacuum assisted power boosters where also a boon to braking systems as our human leg capabilities differ so more so as to our desire to have such a variety of vehicles in operation.
Along with those changes the newer brakes disc systems literally turned the drums inside out for better cooling. Vented rotors were another addition to dissipate heat.
I’m skeptical of slots and drilled rotors being something a normal driving street consumer would ever need or notice in everyday driving.
The idea of spiraling grooves or drill holes is to remove gases.
As far as your problem it’s mostly surface contamination.
It came from the pads own out gassing of the bonding material.
The term is “impregnation transfer.” The heating of the cast irons “surface structure” opened up pockets. They are now packed full.
The heating and cooling has caused a surface disruption.
The surface Metal undergoes either an annealing or hardening of grain structures that rearranged the lattice microscopically.
On an engine flywheel they are called hard spots. Sometimes blue in color from a really abused clutch disc.
The flywheel should be ground again and not turned as it doesn’t take much.
You’re almost unnoticeable .0007 thickness sounds about right considering there’re two surfaces within that distance you have.
A thousandth or “so” of TIR (Total Indicator Runout) if you check the spin of a rotor is normal.
“Never expect perfection and you won’t get disappointed.”
It truly should not be much of problem from my standpoint.
The sheen of the rotor is affecting the pads performance.
Like a stone skipping across a body of water.
The rest of the exposed areas, around the outside, cooled at a different rate or even lost some of the gases.
You need to remove or scuff away a few shrunken molecules of both the rotor and of brake pad material.
Sanding the pads will bring up fresh material. Like the rotor, the pad materials changed from being burnt. How deep is questionable but the glaze will not wear away on its own at this point.
Use an “open faced” flat sheet of sanding paper on a flat surface and move the pads with even pressure downwards. I like garnet paper as it is a softer grade of abrasive. If any comes off the paper and tries to embed the garnet cannot impregnate the cast iron like other abrasives.
Garnet is just barely tougher than the brake material.
It will take some repetitive motion, i.e. work, with a😀.
Reminds me of a Portuguese mechanic friend that had a phrase he used.
He would invariably say, while stripping a thread of a fitting, “this is like my Maria, she gotta go!” I knew then something was wrong on what he was fixing.
Scrub until all the pads surface changes from a sheen to an evenly shaved color.
On the rotor I suggest using a flap disc of 40or 60 grit abrasive. They fit on held angle grinders. The discs are plenty aggressive enough to remove contaminants.
Use it while spinning the rotor by hand unless you can rig up a belt drive.
You will need to remove the brake caliper to access both sides.
Use the flap wheel randomly across the faces of the rotors and leave it as scuffed as you can. Remove any ridges outside the pads running areas.
Use brake cleaner before and after the sanding.
You want to leave that random spiraling for the new material and room for burnishing.
If you read up on a long time company Flex-Hone for cylinders http://www.brushresearch.com/brushes.php?c1=6 you will find out that they also make a device for putting a finish on brake rotors.
I Never bought one but you get the idea of what’s needed.
As Spook said, the surface of the rotors is the major problem but I’ll add in the brake pads are too.
Phil
|
|
-
|
|
|
Good thoughts, thanks Phil. I'm heading off to the tool store right now for a jumbo wrench for the trans cooler line fitting and will add an angle grinder flap disc to the shopping list. Bill's right, almost all brake manufacturers recommend some kind of bedding procedure, but how many bother doing that is open to doubt. What's really important is getting the new coatings off and letting the pads get to work on venting off and impregenating whatever microscopic pitting is present on the rotor. Modern brake discs and pad options are so much better than those of the long bygone days with my early Volvos. Racing enthusiaists go on and on about high speed bedding until smoke comes out.
|
|
-
|
|
|
My tactic has always been to leave the wheel bearing slightly loose and brake only lightly. Certainly don't get in stop and go traffic or any city. Just go for a leisurely drive in the country. Later on you brake a little harder. Then go home.
The loose wheel bearings will allow some drag evenly on the pads. Then later you adjust the wheel bearings properly (40 lb/ft - 1/4 turn). Obviously this technique only works on the front brakes. The backs aren't even vented, work very little anyway.
Also, use of EBC pads helps immensely due to their self-bedding surface. I have a 1993 240 creampuff up on the lift right now for discs, pads, bearings and Bilsteins all around. Hope to break in the brakes later today. The rears are Bosch pads and old discs never turned. The fronts had been turned so now are all new OE and EBC Red Stuff pads. I don't turn discs anymore.
|
|
-
|
|
|
Unlike 240s, 700/900 front wheel bearings are a different design and are simply torqued to spec. Loosening or tightening the nut doesn't make a difference. They also tend to last longer. At 350K and 400K km, my two 940s are still on the original bearings.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
|
|
-
|
|
|
Hi Dave,
It is interesting that you say that the 700 & 900 have a different design when they are still anti-friction bearings with rolling elements.
I agree with the idea of not tightening up and loosening the bearings for years. I think that heavy torque was to insure seating the back bearing’s shoulders against the spindle shoulders and hub shoulders.
The idea of backing it off a certain number of slots for cotter pin was controversial as long as no play resulted.
The preloading was then left as a vague specification in my book.
I just reinterpreted what they were trying to achieve and have gone to using my final tight down torque to be in inch pounds.
A reading on the torque wrench while having the cotter pin line up was my end goal.
I too go a long time on my bearings even between servicing them.
I check for spin and any play.
The specification appears to 15 to 35 INCH pounds seems to work for me.
No play and the nut stays put.
I think the manuals call out is a bunch tighter.
Sometimes it’s a translation of typo from using foot pounds.
So I have written off those numbers off, as for my 240s as an errors.
I expect it sells a lot of wheel bearings.
In my young-dumb early years, I used those specifications and found the bearing’s rollers turning with a slight yellow tinge. Not a bad or noisy bearing at all, but not a comfortable feeling came from seeing it.
I’m curious what is the final torque specification for those other cars being mentioned?
I would be totally lost with a front wheel drive vehicle.
Phil
|
|
-
|
|
|
Dear machine man,
Hope you're well and stay so. The torque spec for the stub axle nut on 940s:
74 pound/feet + 45° angle-tighten.
(Volvo, pocket data booklet - Cars; 750, 850, 900 [-1995], p. 111.) The years covered are 1991 through 1995.
The hubs are very stoutly made: the bearing balls - about 3/8" in diameter - do not require maintenance.
Hope this helps.
Yours faithfully,
Spook
|
|
-
|
|
|
Yer a brave man, stickin' with 700/900s. Both are imho superior cars but finding parts is daunting and chasing bugs is worse. I can still get 240 parts at NAPA. If only Volvo had put OBD2 on 900s I'd be all over that like white on rice. Never shoulda turned in my leased 944T...
|
|
-
|
|
|
After over 50 years of Volvo-only ownership and over 25 years here on the Brickboard, I've spent plenty of time on both sides of the fence owning both 140s/240s and 700s/900s, hearing about issues and helping others maintain them. I wouldn't at all say finding 900 parts or chasing 900 bugs is more difficult than with 240s, in fact for me it's now the opposite. Each of course has its own idiosynchrasies and a lot of it is what you're used to and have recent experience with. Finding parts for 900s (and 700s) in the aftermarket and as well from Volvo is every bit as easy as for 240s, if not better. To start with, they share a lot of systems, starting with the powertrain. As for used parts, in many yards for the longest time 240s outnumbered 700s and 900s, but in many, if not most areas that's no longer the case. The 940s with dual airbags, seatbelt pre-tensioners and ABS are a far safer car than the early 240s. Red-block B230 engines with OBD-I are in some ways easier for shadetree mechanics to diagnose and maintain than earlier K-Jet and later OBD-II if people want to take advantage of the self-diagnostics.
If a 900 series RWD Volvo with OBD-II would excite you, the 1996-on 960 and the early S90/V90 Volvos were mandated to have OBD-II. Although 940s continued with 4-cyl red-block engines until 1997 in a few markets outside North America, none ever got OBD-II that I'm aware of. Those 1996-on in North America were also mandated to have 2-stage airbags and limited passenger side deployment, which helps cut down on insurance writeoffs.
|
|
-
|
|
|
This post gives me hope. As much as I like 240s, I only fit in a 242, which are rare. Too tall and long legs. My nephew is 6'9" and my legs are as long as his. I keep breaking the 240 door pocket with my huge feet, for example. So I'm building this 244 for one of our daughters. I only test drive it.
But a 900 fits me fine. The last 960 years got rebadged and lower final drive gears, plus more torque from the motor. Then they renamed it. Then finally they made it fwd, which is not my cup of tea anymore.
I can dream of finding the perfect last-year rwd 960 with OBD2
|
|
-
|
|
|
Volvo once had 140/240 seat rail extenders for tall people like you. Especially good with 2-doors with the pillar further back. Odds of finding any now are slim, but if you search hard enough I recall seeing a home made version somewhere. Seat mounts are critical for safety, so good welds and proper fastening to the chassis are important.
240 front door pockets are something Volvo never got right in almost 20 years of production. The tan ones were seemingly made of peanut brittle, so if you ever replace those pick a different color. IPD had a repair kit cover that lasted. I'm not sure if it's still available. I can't remember if the 2-doors had longer pockets. One fix I did that lasted for many years was gluing a metal support rod right across just behind the lip, using something structural like JB Weld after roughing and prepping the surface with acetone or MIBK. Best to do that before or just as it starts to crack, not after pieces break off unless you've got the proper kind of plastic cement to weld the pieces in place. A good ridge of JB Weld inside along the bottom corner may help reinforce that area from steel toed boots, so also give that a thought. I haven't experienced broken 700/900 door pockets, but I'm always afraid it's going to happen when some big lug in boots heaves themselves into the passenger seat.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
|
|
-
|
|
|
Hi Phil,
You can find plenty of faulty brake installation directions by the
major auto parts chains and others that generally omit critical details
such as cleaning hubs and checking run-out and breaking in pads.
Here's some technical excerpts from Zimmermann's terrific website:
https://www.otto-zimmermann.de/en/products/messeinrichtung-fuer-bremsscheiben/
Testing Unit for Brake Discs
Run out can also be generated by incorrect assembly. If the wheel hub is not metallically bright during assembly or if grease paste was used during assembly, steering wheel flutter and / or a pulsating brake pedal may occur after approx. 1,500 - 5,000 km service life.
https://www.otto-zimmermann.de/en/service/faq/
11. Run-in notices
The following run-in notices are recommended to ensure a safe and proper operation of the brake disc / brake pad system:
Perform the run-in processes on road sections that allow for the following maneuvers to be carried out safely and within the provisions of road traffic regulations (StVO).
Violent or shock-braking should be avoided during the first 300 km of travel after the change of the brake discs.
When running-in Coat Z coated brake discs, kindly perform approximately 5-10 short and moderate braking operations for braking off the coating layer.
After that kindly ensure a bedding-in process of brake discs and brake pads. This process causes that the brake disc heats up gradually and serves to adapt the friction surfaces of the brake disc
and brake pad.
If the road conditions permit, perform several short, moderate braking actions (without ABS intervention) within the first 300km.
Failure to observe the recommended running-in procedure may result in impairment of the brake function and worse braking performance.
See the Videos, a wealth of technical details:
https://www.otto-zimmermann.de/en/service/tutorials/
Cheers, Bill
|
|
-
|
|
|
Dear Dave Stevens,
Hope you're well and stay so. I've never "bedded" rotors. I simply drive/brake as usual. If I have to make an abrupt stop at a red light - or any other place where I can't at once resume moving - the instant the car stops I set the parking brake and take my foot from the brake pedal. When the light goes to "green", I release the parking brake and proceed. Airflow quickly cools the rotors.
As to your in-service rotors, I'd use a belt-sander but start with a 100-grit belt and finish with a 220-grit. Even if the surface ends-up a tad rougher than it should be, normal braking should slowly "polish" the surface. This approach will save much time and elbow-grease at the cost of a modest shortening of pad life.
Hope this helps.
Yours faithfully,
Spook
|
|
-
|
|
|
Hi Dave,
I had very bad braking vibration starting over 35-40 mph and worse at high speed
when I first got my 940. After changing some sloppy tie rod ends it was still there.
You can try new pad break-in procedure that finally sorted out the problem.
over some time. I'm guessing the P/O had a panic stop at high speed and
messed up the rotors/pads.
I replaced both hubs and reused the old rotors and pads that looked fine
and the vibration is gone. I haven't put many miles on the new hubs to see
an improvement in MPG. It looks initially like 17.0 mpg which seems low.
Maybe I'll change out the rear wheel bearings and see if that helps.
What's the best MPG you've got, and does Canada pollute your gas with 10% ethanol?
Bill
|
|
|
|
|
