Kitty, are you talking fronts, rears or both rotors? People always have varying opinions on brakes. Just my personal experience and preferences here:

For fronts, which do the most braking and take the most wear, I'm getting fussier in my old age. I've generally used Brembo (uncoated), Bosch Quietcast (coated) and Zimmermann rotors (Z-Coat, unslotted) on the fronts. I'm now a definite Zimmermann Z-coat fan, still made in Germany (almost everything else is now China). I find these are generally machined truer than the others (never needed a shim to minimize the lateral runout spec, while always with the others) and the quality of the casting metals seems more uniform and less susceptible to developing thickness variation leading to brake pulsation (which people often call warped rotors). After being so pleased with my last two sets of Zimmermanns, I'm happy to recommend them and say they're worth a premium price.

For front pads, for years I used softer semi-metallic pads, then switched to harder ceramics like Textar and Akebono, then to Bosch Quietcast for a number of years. Now I much prefer Pagid semi-metallics as a compromise between good braking, rotor wear, dust, cost and noise. RockAuto carries them at a very affordable price.

For rear rotors, I've used Genuine Volvo (uncoated, now NLA), Brembo (uncoated), ATE (uncoated, slotted and unslotted) and Bosch Quietcast (coated). My preference varies depending on what's available and at what price. ATE slotted was probably the overall best on the rears, but I think only unslotted is available now. I'd love to go for Zimmermanns on the rears, but haven't been able to find them.

For rear pads, I always now use Volvo blue box and they're generally quite affordable. Volvo RWD rear brakes have always been prone to squealing, so a softer pad helps with that, but dust soon becomes a problem, especially the hotter fronts where it gets baked on the rims. Volvo experimented for years with the 140 and early 240 brake pad materials as noise and dust were common customer complaints, until finally coming up with a pad compound they liked as a compromise.

For bleeding, I've got a homemade pressure bleeder using a small garden sprayer connected to a 500 ml Nalgene bottle (as a fluid reservoir) that's fitted to a spare reservoir cap using a threaded metal tube that extends down into the brake reservoir so as not to overfill it. Mityvac has a commonly available vacuum bleeder that many prefer. Trick with them is making sure the reservoir never accidentally empties and being sure to only crack the bleeders a little (so as not to suck air and fool you) and to shut the bleeders off under vacuum while fluid is still moving (so as not to let air get sucked back in). Many still happily do a two person pedal bleed. The main caution there is to use short strokes and be able to coordinate shutting the bleeder off under flow and not to push the pedal all the way to the floor. That will put the master cylinder seals into less travelled territory on the cylinder walls where possible scale, rust or scoring might prematurely damage the seals. Bleeding order is generally master cylinder gets done first and closest last. You can do either left or right triangle pistons first if you've got the independent braking system. For ABS brakes with left hand drive, it's right side rear first then left side rear second then right front then left front closest to the brake junction box and master (for right hand drive ABS it's the opposite).

Bleeding the ABS unit (important if you let the system run dry) takes extra effort to either trigger it electrically under fluid pressure (not easily done with our ABS systems), or simpler just to find a vacant road with a gravel shoulder (and no ditch) and slam on the brakes with one set of wheels on the gravel (being absolutely careful not to spin out of control). Do that a couple of times then re-bleed the brakes.

This is all just my two cents.

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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Hi Dave,

What rotor shims? There's no shims.
You can "index rotors" to reduce run-out, checking with a dial indicator.
See Zimmerman's nice tech pages at their website.

Check out the rotor installation How-to's at many popular parts chains
and note that most of them overlook cleaning the old hub and don't mention
the special tools for that. The bulk of them never heard of indexing rotors.

It is odd that ATE and Zimmerman brake parts are sometimes not available in
North America, probably due to corporate efforts to control parts competition,
availability and pricing, mostly to improve the dealer experience.

Zinc coated rotors are a big improvement.

Bill

Ah, rotor sims. After indexing the rotors (which the Zimmermanns impressively didn't need, it made virtually zero difference how I rotated them) I then use strips of aluminum foil as shims between the back side of the rotor and hubs to bring the combined hub and rotor lateral runout to within less than Volvo specs using my dial micrometer on the outside edge of the rotor face. Between my well worn hubs and less than perfectly machined rotors from the factory (other than the Zimmermanns) it's become a standard in my purist brake mentality to use foil shims to get the brakes running true as they can be.

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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Hi Dave,

According to Zimmerman installation instructions and ATE tech support:

"Nothing between the Hub and rotor faces except a coat of light oil which you
apply and wipe off with a rag" (No Grease, No shims, No anything...)

I thought anti seize grease there would be good, but they say "NO!".

You must clean the hub face (and old rotor if you are reinstalling) to a pristine condition. There's hub tools to clean around the wheel studs etc.
There's run in instructions for rotors and pads.

You'll find Zimmermann wont talk to the public, but has a nice website loaded with solid tech support articles.

ATE has super tech support and you can chat with them via email or phone.
They have new offices in North America:
Maybe this means seeing ATE's full parts line available widely?

Continental Automotive Systems, Inc

6755 Snowdrift Road | Allentown, PA 18106 | USA
Tel: (800) 564-5066 | Fax: (610) 289-1766
E-mail: salessupport-us@continental.com

Technical Support
E-mail: techsupport-us@continental.com
Tel: (800) 265-1818
Hours: 8am to 5pm EST, Monday-Friday

Bill

Bill, I'm surprised that a purist like you isn't into shimming rotors. Shimming and lubrication of the hub face are of course not required, but there's nothing to say you can't if it's done half-properly. You of course want nice clean faces on both the hub and rotor. I'll use a wire wheel cup on a drill if needed. For new and uncoated rotors, wiping with a very light coat of oil or high temp brake grease to help avoid future rust isn't at all a bad idea as long as you avoid lubing the braking surfaces and threads (wheel nuts are supposed to be torqued dry). In most cases it will quickly disappear with road spray and dirt, so probably not worth the effort. Regarding shimming, here's from some old brake notes of mine:
-----------------------------------------

What is important is staying within the overall lateral runout spec. With quality rotors and lower mileage hubs, most shops won't even bother checking the runout unless someone is reporting slight brake pulsation on new rotors. With cheaper rotors and/or worn hubs, a decent mechanic should be expected to at least index them, meaning to mount them on the studs in all possible orientations to achieve the least runout. With the 10 mm Volvo wheel pins used as the basic rotor mounting bolts, that may mean only two possible orientations 180 degrees apart for some brands of rotors. If desired and it really made a difference, you could run without the mounting bolt, or you could do like I do and resort to shimming, but only if and when needed.

There's always going to be some rotor lateral runout and purists like me will want to minimize it to help with more even braking and brake wear, and especially to help avoid brake pulsation both initially and down the road. With new brakes you can tell it's there when you turn the rotor by hand and hear/feel the pads scuffing unevenly around the rotor. A small amount won't cause problems and may actually lessen over time, but larger amounts of runout can make for uneven braking and uneven hot metal expansion that can lead to noticeable pulsation and ultimately make the runout worse, which we call warped rotors. What many call warped rotors usually aren't actually bent. It's mostly that they're unevenly worn for thickness, which makes them measure as warped. If you measure thickness around the rotor looking for the thickest and thinnest spots (as I do), these spots normally correspond side-to-side with the high and low runout spots to say they're not actually bent.

There are two sources of lateral runout: runout of the hub and runout of the rotor. Hub runout is a combination of slightly bent hubs (which can happen with an older car with rough roads and potholes) plus the runout in the original hub machining. Rotor runout is two-fold as the runout of the machined hub mating surface and runout in the machined braking surface. Combined, this all makes for the lateral runout measured near the outer edge of the rotor face in reference to the axle hub mounting with a dial micrometer. Runout is supposed to be measured a nominal 0.15 mm or 1/16" from the outer edge, but 1/8" is generally acceptable for rotors, and for used rotors you may need to measure in a bit further to get past the ridge. The dial micrometer base needs to be fixed in relation to the axle hub mounting, not the body, suspension or ground. I use the front strut and the rear axle housing.

The Volvo spec for hub runout (both fronts and rears) is 0.03mm (0.0012"). For worn wheel bearings, you need to measure this keeping the hub uniformly pushed in. Technically, a hub that exceeds this should be replaced along with the bearings, but if it's just a little bit over then rotor indexing may be all that's needed, in fact that's what the Volvo manual suggests.

The Volvo spec for lateral runout depends on the model and brakes used. Specs can be found in Chilton's Volvo 1990-1993 Repair Manual (p 9-31) and others, but I've found they're not as tight as the numbers I've found elsewhere, such as in the Volvo green manuals, the various Pocket Data Books (as used below) and the Volvo TSBs that may have tighter tolerances.

o When starting with old rotors, the first thing to measure is thickness (generally requiring caliper removal). Measure just inside and safely away from any outer ridge and avoid score lines. If less than the minimum thickness then it needs to be replaced (it varies by type of rotor, sometimes stamped inside or on the rotor, sometimes not, too many to list here, see the charts).

o Next with old rotors is to note the thickness variation between minimum and maximum thickness around the rotor. This is actually the easiest and best indication of whether your rotors are "warped" to confirm they're causing brake pulsation, but does require careful measurement and interpolation between micrometer marks. I use a felt pen to mark the rotor.
... For the fronts, it's 0.008 mm (0.0003") for all later 700/900 single piston Girling brakes. For 240s, it's 0.01 mm (0.0004") for the '79-on ventilated rotors and 0.02 mm (0.0008") for earlier ventilated rotors, with 0.015 mm (0.0006") for the very early solid front rotors.
... For the rear rotors, the max thickness variation for the later 240/700/900 RWD is 0.012 mm (0.0005") for solid axle and 0.008 mm (.00032") for multi-link rear axle suspension (760/960).
... Basic rule of thumb is the thickness variation should be less than one half a micrometer division (0.0005") otherwise you need to measure more carefully or just go for new rotors.

Now for checking and indexing the rotors, here's the maximum lateral runouts you're looking for (and hoping to do better):
... For the fronts, it's 0.035 mm (0.0014") for both ventilated Jumbo Type I (287 mm dia) and Jumbo Type II (280 mm dia) used in the 700/900s. For 240s, it's 0.04 mm (0.0016") for the '79-on ventilated rotors and 0.05 mm (0.002") for the earlier ventilated, with 0.04 mm (0.0016") for the early solid front rotors.
... For the rear rotors, it's 0.05 mm (0.002") for solid live axle in the 240/740/940s and 0.04 mm (0.0016") for multi-link rear suspension (760/960)

If indexing isn't enough then shimming can be used to get them running even truer. I've made cardboard crescent templates with holes for the studs (one two hole, on three hole) that I use to cut shims from aluminum foil. They must be kept flat, not wrinkled. Sometimes 2-3 layers are needed, and for a really bad rotor I've gone as high as 5 layers. To make sure they're fully compressed, I'll often over-torque the wheel nuts a bit, then back off and re-torque to spec. When measuring runout, I've made 1" spacer collars out of metal tubing to place over the studs and be able to tighten the nuts close to spec.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Hi Dave,

We're on totally different pages with shimming rotors to hubs.

If you can't index the run-out out then you probably didn't do a good job cleaning the hub. Use a tool like this that will do a good job around the wheel lugs: (and probably fill your nostrils with PFAS)

https://www.ebay.com/itm/266689700559

I struggled with using antiseize on the hub to rotor face with the ATE rep in Germany, who finally convinced me. No grease, no nothing except light oil
on the hub to rotor faces that you wipe off.
Use only zinc coated rotors so they come apart later without having to use
a sledge hammer to remove.

I looked again at ATE's USA parts catalog for the 940 and was disappointed.
They have rotors and maybe rear brake shoes, but no brake pads in the USA catalog.
I know that ATE has a chain of garages that do brakes in EU and probably has the
OEM quality or better pads there. It looks more and more like a dealer /manufacturer sweetheart deal for parts.
I'll call ATE USA to find out tomorrow.
Maybe ATE sells 940 brake pads in Mexico?

Perhaps it's the same story with Zimmermann where you can't find the rear rotors.

When I first got my 940 I had nasty high speed brake judder, and replaced
sloppy inner and outer tie rods. The judder was still there with no apparent slop and very low rotor runout. I got the Zimmermann coated rotors and Volvo
pads new brake hoses, etc but stalled the job as I did brake-in routine
slow steady gentile stops from speed when possible. Now the judder is gone
with the same parts. My guess is that a hard panic stop can mess up the rotors.

Keep smiling, Bill

Hiya B.B. and Mr. Stevens,

My own advice is usually new rotors with new brake pads.

'Cause toilet-rado, the hyperpriced property scam state (the state statutes drive up property values massively as well as TX and CA folks coming here by the wheelbarrow) makes a rental garage with power and light be like $500 to, in stupid Boulder, $3000 a month, for a regular garage or a double-wide garage with roll-up doors.

I have a collection of the front and rear brake shims and re-use these if not provided. Always blue box Volvo. I used PBR metal master pads and these thing rusted in the caliper. Braking was awful with these.

I got a set of regular Zimmermans once (not sure of the brand, yet appeared made in Duetchland, made in China versions, and the things warped rather quickly with new pads, and all new hardware, like each time. I forget what pads I used. Maybe the terrible PBR metal masters?

I have no means to fabricate a thing in my 30-month escape from the un-flushed toilet named St. Louis, MO. (Walk around in Central West End or Soulard or Dogtown and Downtown on hot Summer days and you get the fragrance, and the trash collection is failing again, adding more aroma.) I could not ever get a job for any city trash collection in the 1980s in St. Louis city or county as I did not want to move to Kalifarnia with a drunk relative. Unions?

Not resourceful like the Snake Bliskin character. That film was filmed in the 1979 toilet St. Louis. MO version, and East St. Louis, not New York.

So merely brake pads and do so in some vacant car park. The rear calipers need it also. And I need to flush in new DOT4. Way overdue.

Or motor to a more utilitarian and useful state, yet much corruption in WY and MT.

Merely to find a safe place to reside and be able to work the three 240s. yet brakes and a transmission mount (not yet broken) before the motor mounts get distressed.

The 1992 GL and the 1990 DL li'l red wagon rot in a an outdoor storage facility well west of St. Louis, since OCT 2021. They each have COVID masks on. Ha.
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