I can't comment on what the play should be. I will comment that this a primary symptom to the vibrations these cars develop.

The center hole should be a snug fit, this is what the wheel centers on as well.

 

there is typically a lot of play until you tighten the rotor screw, but after you tighten the rotor screw they shouldn't move. The brakes never touch the hub though and with have a few mm of clearance

 

I think the rotor centres itself on the outer shoulder of the hub, and not the inner hub that's used to centre the wheels.

The screw does hold down the rotor, but it could still pivot around the screw. And that would make the rotor out-of-round with respect to the axle.

I don't know how much the rotor can be off-axis and not contribute to vibration, but I do know that my initial install, when I wasn't thinking about this or checking, the rotor was out enough to bounce the entire wheel and tire assembly around when spun off the ground.

 

Did you clean th rust off the hub face of the wheel bearing completely ? VIP. AND assemble with anti seize. Lloyds moly anti seize is the best, a company out of Peterborough.

 

Funny enough, almost all the rust was on the old (Zimmermann) rotors. The hub was pretty clean. I used Permatex anti-seize that I had on hand.

If I had the official specs for the various hub ODs and rotor IDs, I could check whether the NAPA rotors are simply machined to the wrong dimensions. But short of springing for Saab OEM rotors, that seems pretty hard. Although I guess I could pull the rotors off and measure the dimensions I have.

 

The WIS lists the following measurements:

Front Rotor:
OD: 284mm
Thickness new: 24mm
Thickness Min: 21mm
Max thickness after treatment: 22.5mm
Runout: .08mm
Max Variation of thickness: .014mm

Rear Rotor:
OD: 260mm
Thickness new: 10mm
Thickness Min: 8mm
Max thickness after treatment: 8.5mm
Runout: .08mm
Max Variation of thickness: .015mm

There are no measurements for ID of the rotors... Ron

 

Iirc the hub diameter should be either 65 or 69 mm in diameter

 

The runout and variation in thickness specs are for movement in and out, and I am pretty sure I'm good on that. There's nothing in WIS for out-of-round.

As far as I can tell, both my rotors are out of concentric by ± 0.01", or ten thousanths. So one side is twenty thousanths further in/our than the other side. I have no idea whether this is significant or not. I suppose I could work out the total difference in weight. I just don't feel like it at the moment.

When I get a chance, I'll check if my old rotors were hubcentric. If not, they must have rested on the outside shoulder of the hub, but the old rotors are so rusted there that I won't be able to tell anything.

 

I just did brakes on a 9-3 yesterday Ed using cheap Wearever rotors from Advance, there was barely any movement around the hub once I had them fully seated (maybe fractions of a mm) if you have significant movement then I would say it is the rotors.

 

Yeah, to be clear, the 0.020" wobble is the best I can do, fiddling with the rotors and locking them down (as much as possible) with the set screw. I wonder if I simply need to go cheap, or get Saab OEM? As long as I can find the receipt from NAPA I should be able to return these as defective.

 

Have you tried putting a piece of aluminum foil behind the low spot on the rotor? One piece is about .010", if I remember right. I used a piece on my wife's 9-5 on one of the front rotors, and it brought it right into spec. If you shape it to fit around the bolt hole, once everything's clamped down, it shouldn't move.

 

Have you tried putting a piece of aluminum foil behind the low spot on the rotor.

I have some hubs/rears and a bunch of rotors. Is there anything you want me to check or measure?..If you are checking for side to side/wobble run out, the 1 set screw will not keep the rotor flat against the hub when you run your dial indicator.

I don't know what the correct phrasing is. The runout isn't in/out against the brake pads. The runout is orbital. The rotors aren't really hubcentric. They can be shifted about in various directions while sitting on the hub. The hold-down screw will kind of keep them in place, but there are two obvious problems:

1. My adjustment is by hand and eye, and then I try to tighten the screw.
2. The screw doesn't really hold the rotors perfectly; they can shift.

When I first put on these rotors, I thought nothing of it, just tightened the hold-down screws. Boy was there vibration!


All this being said, if I can find the NAPA receipt, I can return them for a refund. I'm sitting in a Saab dealer getting an alignment at this moment, and they have Saab rotors in stock. I think I will just buy them instead of struggling. And look for that receipt.

 

I have some hubs/rears and a bunch of rotors. Is there anything you want me to check or measure?..If you are checking for side to side/wobble run out, the 1 set screw will not keep the rotor flat against the hub when you run your dial indicator. What i do is, using 2 or 3 lug bolts, i bought some large nuts that fit over the threads of lugbolts(to use as spacers) and hold down the rotor that way, for measuring/testing purposes

 

If you have an accurate caliper, measure the ID of the rotor hole on the Saab rotors when you buy and compare to the NAPA. Then post here so we all know what to measure for.

If you don't have a caliper and there is a Harbor Freight near you, you can get one of these for $20 with $5 off using their coupon sale. Invaluable when working on a saab! http://www.harborfreight.com/6-in-digital-caliper-61585.html

FWIW- instead of aluminum foil, you can buy aluminum duct tape in the heating section at Home Depot, Lowes, etc. Great for shimming and it stays in place.

 

If you have an accurate caliper, measure the ID of the rotor hole on the Saab rotors when you buy and compare to the NAPA. Then post here so we all know what to measure for.

Will do very soon-like. Just don't feel like pulling front wheels again at this moment.

The center bore of rotor is 2.582 or about .024 larger than the Saab hub that it is slipping over.That leaves .012 on each side if it is centered.Im not sure if that can cause vibes or not. Ive never d one anything special when i install rear rotors in those regards.

My problem is with the front rotors. After I installed these new ones, I still had shaking. Put the front end of the car up on blocks, started engine, put in gear. One of the front wheels was bouncing up and down an inch! I thought it was (inexplicably) the wheel. It was only when I tried the same experiment with the wheels off that I saw the rotor(s) were doing this eccentric orbital motion.

It's not clear to me how you measured the runout. I got a dial gauge and magnetic mount. I set it up so the dial gauge was sitting at 12 o'clock, square to the rotor's outer edge, and turned the wheel. This verified run-out even when I had hand-adjusted the rotor as concentric as possible.

Given the nature of folks trying to be wise with their money Ed may have puchases cheap rotors. I would use first line brands from known reputable vendors.

Ah, I know better than that! :nono; These are NAPA Premium rotors. Middle of their line, eighty bucks apiece. I expected better from NAPA. I would be willing to try the cheaper ATE rotors from Crappy Tire/PartSource (my brother installed a pair on his Fusion), but they don't carry them for my car.

If they'll take them back, return is the best option.

Yep, that's my plan. NAPA verified that I will get my money back.....and that I got the 'right' part. Next stop, Saab dealer for OEM front rotors. Hopefully it will all be done like dinner and I won't have to fudge around with this any more.

 

Okay, here are some facts...

Saab OEM hubs measure 2.558.I measured 2 OEM hubs. I once bought an aftermarket hub(rear) and the OD of hub was much smaller. I immediately returned it. Im sure running that hub could have caused some vibes running a stock Saab wheel or a wheel with a Saab OEM hub bore/size.

I also measured just a cheapo/standard rear rotor, like an autozone or advance auto parts piece.Its mint with no rust...

The center bore of rotor is 2.582 or about .024 larger than the Saab hub that it is slipping over.That leaves .012 on each side if it is centered.Im not sure if that can cause vibes or not. Ive never d one anything special when i install rear rotors in those regards.

Looking at the front of rotor, and measuring from the center bore to outside of hat(e-brake section), my rotor was concentric to within .002, so very close.

If we flip the rotor over and look at the back side, measuring from the machined e-brake surface to extreme OD of rotor, my numbers came up just about perfect; .001 at most...Id say thats a pretty nice rotor in terms of those numbers...

So, thats what we know..

 

So a few posts ago I said 65 or 69 mm. It's 65. Ed says he cleaned the rust off or the hub was not rusty.

Given the nature of folks trying to be wise with their money Ed may have puchases cheap rotors. I would use first line brands from known reputable vendors.

Halten rotors I reported elsewhere fully zinc coated and very inexpensive have proven to me to be junk.

I just spent 115 each for first line vented rear rotors for my car, scrapping three month old Halten rotors (69.00 each) because they are warped

I would stop screwing around take the rotors back get a refund and buy ac delco on first line/ Zimmerman / centric/OEM.

And stop the shimming idea with metal tape etc. Come on people.

Brakes and steering do it by the book and spend money for quality first. My take

 

If they'll take them back, return is the best option. If not, I'd shim. Mostly because I'm frugal, but also because I don't think it's an issue. Brake performance wont' be affected by a thin shim to center the rotor. Lots of engineered parts get shimmed to adjust...this is just a little custom shimming.

I'm guessing the rotors are machined too big... more Chinese quality engineering.

Hap: .024 seems like a lot. That's about .6mm... although distributed it's .3mm per side, which isn't quite as bad. Still seems like a lot though.

 

The set screw is only there to help with assembly, it is the lug bolt that center and hold the rotor in place (not how tight the fit is on the hub). I don't think this is an issue of the rotor sitting to loose on the hub, as the lug bolts will hold it once all assembled. However if the lug bolt holes are not centered correctly, it could cause this run out. or if the lug bolt holes were too large it could also allow the rotor to not be installed centered.

Put another way when all assembled it is the lug bolt going thru the lug bolt hole that hold the rotor centered and keep it from moving. Rotor could have way to much space betweeen the hub and the rotor should be centered because it is the lug bolts that take the stress.

When you tested with the tire off did you have the lug bolts installed? If not your test was flawed.

 

The set screw is only there to help with assembly, it is the lug bolt that center and hold the rotor in place (not how tight the fit is on the hub). I don't think this is an issue of the rotor sitting to loose on the hub, as the lug bolts will hold it once all assembled. However if the lug bolt holes are not centered correctly, it could cause this run out. or if the lug bolt holes were too large it could also allow the rotor to not be installed centered.

Put another way when all assembled it is the lug bolt going thru the lug bolt hole that hold the rotor centered and keep it from moving. Rotor could have way to much space betweeen the hub and the rotor should be centered because it is the lug bolts that take the stress.

When you tested with the tire off did you have the lug bolts installed? If not your test was flawed.

I agree that it's the force from the lug bolts pressing the wheel, rotor, and hub assemblies together that keeps the rotor in place. I have to disagree that the lug bolts centre the rotor. They don't. Neither do studs if that's how the car is set up. The only thing that really holds the rotor in its proper position is the hub. Then tightened lug bolts (nuts) are what keep it from rotating or otherwise moving around.

That being said, yes if you are checking for side-to-side wobble (or inconsistent rotor thickens or warping) then you do need to have some bolts in to keep the rotor pressed hard against the hub. I did not have that. However, I can't actually get the rotors to sit properly, and they're relatively free to move around even with the rotor screw tight, so it's a matter of luck as to where the rotors wind up, once the wheel is installed and the bolts tightened down.

 

If it was me, i would leave the set screw out or loose. Carefully assemble and torque tire on. and check rotor lateral run out of the rotor with the car jacked up and from underneath and inside the rim. Then check runout of the rim and tire all assembled.

 

Ed, this thread is becoming a nightmare. It's simple. Clean hub of rust. Especially around the studs. I have a tool to help with that. Quality rotor. Anti seize flanges. Install. Done.

IF the calipers pistons are seized or the calipers guides are seized you will end up with brake pulsation.

I think you are over thinking the whole deal, follow SOP WIS instructions and it will be fine.

I believe that using shim stock to shim the rotor to the hub flange is redonkulous

 

The problem with those theories is it assumes that the holes in the rotors for both the lug bolts and the hub are made to a somewhat decent tolerance, they don't need to be an exact press fit but if they are over machine by several mm you will have excess play no matter how you tighten things.
Seems like Ed got a set of poorly machined rotors and they are allowing for too much play. Not sure why it is so hard to understand his issue.

 

While it is very possible he has a bad set of rotors, that is NOT clear. You can't test the radial run out without something taking the place of the lugs, and if you are over tightening the set screw you can force an otherwise good rotor to be off center. Tolerances of the lug holes needs to be pretty exact! Tolerances of the hub opening in rotor just has to be big enough to fit on.

Agree 100%, to follow the WIS, clean all surfaces, install rotor, tighten set screw to 3 lbf ft ( 36 inch lbf), which you will think is too loose, fit pads, and caliper, install tire and proper torque sequence of lug bolts.

If you do that, and have radial runout of the rotor, then you have another problem, like bad rotor, or bearing issue in the hub.

 

I think that was the purpose of his thread to ask for comparison to confirm he had bad rotors, or at least that is how I understand it.

I don't believe he has any issue with run out of the rotors, just the rotors being properly centered (now be due to the poor machining of the holes for the hubs, lug bolts or combination of), exact same issue you would have with aftermarket rims with a larger hub bore and without hub centric rings or incorrect bolt spacing and wobble bolts.

 

My point is that you can't test if rotor are centered without lugs installed, and if you over tighten the set screw you can essentially lock the rotors in a non-centric position. Both of these things will cause the rotors to not be centered, are a easily tested/fixed. The radial run-out I am taking about would be due to the rotor not being centered around the axis of rotation.

 

Of the 50 Saabs (og9-3 and ng900) I have owned of which I have done 30+ brake jobs all of my rotors have fit snuggly enough to the hub that there is no noticeable play between the rotor and hub without the lugs installed, most definitely not the multiple mm of play that Ed mentioned he had. This is with everything from the cheapest Chinese rotors to high performance high cost brand name rotors and everything in between.
In fact the fit of the rotors to the hub have been of the same tolerance of the rotor to the lug bolts.

 

Agreed,done equally as many brake jobs but not all on Saabs. But, he then put a dial indicator on it to measure the radial runout caused by rotor being not centered with only the set screw holding the rotor down and determined it to be a problem. That inside rotor to outside hub is a close but non contact surface once all assembled. There is some slop in it before lugs center everything up, which is what his test showed.

I have also seen lots of botched brake jobs by people messing up little details like over tightening the set screw, never once seen a rotor with non-centric lug holes... Possible sure, but which is more likely?

 

I have also seen lots of botched brake jobs by people messing up little details like over tightening the set screw, never once seen a rotor with non-centric lug holes... Possible sure, but which is more likely?

Well... I never saw an axle with a shaft made too small in the bearing area before Chinese parts; I think now, with companies trying to do everything as cheaply as possible, all bets are off .

 

Ok, well since my whole front suspension is off and waiting for parts figure I would take some pictures....

This is what I believe the OP is seeing, and it is 100% normal. These rotors properly fit on the hub, the set screw is in and tightened down to proper torque spec.. But you can pivot the rotor on this set screw, and you can see the effect this as on the lug bolts holes in rotor as compared to the hub.

Now I didn't buy these rotors, they came on car, but they appear to be nicer then your cheapest rotors, very well might be Saab spec rotors, but didn't look for part number for them.



Again this is normal, the lugs will fix this once tires is installed. Problems happen when you crank down the set screw to something more then the 3 ft lbf of torque WIS specifies and essestially lock the rotor in a non-centric position. Which is what the OP was doing. Yes there is probably 2-3 mm of movement at that bottom hole from one extreme to the other (I can shift it to be off center equal as much the other way).

Hopefully this picture actually gives the OP what he is looking for.

btw, look at the bevel on the rotor's lug bolt holes. Bet that bevel is 60 degs, and matches up with the lugs bolts, but which would center up rotor perfectly....

 

btw, look at the bevel on the rotor's lug bolt holes. Bet that bevel is 60 degs, and matches up with the lugs bolts, but which would center up rotor perfectly....

If the beveled part of the lug bolts are hitting the rotor and bottoming out there then the wheels aren't being held on correctly. You can see in your picture you don't have 2-3mm of play between the hub center and rotor, where Ed said he had a lot of movement.

 

No offense, but I call BS on you 3mm of play, that picture doesn't show remotely near that amount, and most notably not around the hub center.
Also the play Ed was referring to was between the center opening of the rotor and and the hub, not the lug holes.
The play you are seeing is also caused by the hub being able to rotate within the rotor, not the rotor being shifted off center, you can see in the picture that the gap difference at the top and bottom of the the upper lug hole is very similar it is, it is just off from side to side, you could remove the lock screw and have only half of the hole showing and yet the rotor would still be pretty well centered assuming it fit the hub correctly.

 

So just went out and relooked at everything while reread the post, and think I see where the mis-communication is coming....

I saw OP, also talking about this pivoting on the set screw, which is where I assume he is talking about exactly what I pictured. Which is normal. Others are assuming it is actual 2-3 mm of movement between inner part of the hub vs inner hole of the rotor...

Which is right, depends what exactly the OP is seeing. I read it one way, but see how it could be read the other....

 

I saw OP, also talking about this pivoting on the set screw, which is where I assume he is talking about exactly what I pictured. Which is normal. Others are assuming it is actual 2-3 mm of movement between inner part of the hub vs inner hole of the rotor...

Which is right, depends what exactly the OP is seeing. I read it one way, but see how it could be read the other....

I'm seeing the rotor move around in any direction I may want with respect to the hub. The only way I can try to get the rotor approximately concentric is to use the set screw.

Your own pictures show that the diameter of the lug bolt holes in the rotor are much bigger than the diameter of the threaded part in the hub. Because the conical part of the lug bolts never contacts the rotor, the bolts cannot possibly align the rotor, except in the grossest sense.

And if I don't tighten the set screw with the rotor approximately concentric, then the rotor will immediately fall "down" on the hub, being tight to the hub centre on top, and quite loose on the bottom. This will give lots of runout.

The center bore in a rotor is about .024 larger than the OD of an OEM Saab hub..

Sooo, about .012 on each side if its centered

Ed, i hope your brakes are all fixed up!

I didn't pick up the OEM rotors for reasons that made sense at the time, which means an extra trip this Saturday. I hope to have this all done by Saturday afternoon, complete with measurements.

 

The center bore in a rotor is about .024 larger than the OD of an OEM Saab hub..

Sooo, about .012 on each side if its centered

Ed, i hope your brakes are all fixed up!