[fishzine]

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.

 

[EdT]

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.

 

[qwikredline]

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

 

[fishzine]

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.

If this were true then the hub to rotor would need to be a machined pressed fitting, aka you would need press to install and remove..

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.

Rotors should be free to move around with the rotor screw in!! if they aren't you have it too tight, because it IS the lug bols that center it all up. NO LUCK required. You should not be trying to tighten that set.

BTW, WIS specifics the torque spec on the set screw as 3 lbf ft, with threadlock on it. That isn't even hand tight and loose enough so when you tighten the lugs to 81 lbf ft, it will center everything up.

Over-tightening the set screw locks the rotor into potentially the wrong position, then it is just a matter of luck.. Leaving it loose enough to allow the lugs to do job and it will be right everytime.

 

[jakejm79]

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.

 

[fishzine]

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.

 

[jakejm79]

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.

 

[fishzine]

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.

 

[jakejm79]

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.

 

[fishzine]

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?

 

[BobSaabit]

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 .

 

[fishzine]

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....

 

[jakejm79]

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.

 

[fishzine]

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.

I have 2-3mm of play at the bolt hole opposite from the set screw, actually probably closer to 3-4. Look how far off centered the hole is from the threads underneath, and the will rotor pivot back to center then offset equal distance the other way.

Point being, there is a fair amount of play normally, and the set screw isn't there to get rid of that play (and you can't over tighten that set screw or risk locking the rotor in a non-centric position). The rotor can be off centered with the screw torqued down, and the rotor still moves on the hub. All this is 100% normal.

Hey, it is still very possible his rotors are bad. But, without a correct test with lugs in there is no way to know....

 

[jakejm79]

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.

 

[fishzine]

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....

 

[hapcj7]

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!

 

[EdT]

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.

 

[earthworm]

Hundreds of "brake jobs", over a 55 year period, never, TTBOMK, a problem with mounting the rotor and without rust removal and anti-seize ..Of course, I did improve ( a better fit and anti-seize, a thin layer on all contact surfaces .) ..

IMO, it is "common sense" to have a "perfect" fit( plus or minus 0.001" or so , in all aspects ..But, for me, anyway, simply not a problem ..luck ??

 

[EdT]

Saab OEM rotors fit perfectly. No moving about. Install retainer bolt and replace wheels.

The NAPA "Premium" rotor is going back. It looked okay in the box, but comparing with Saab rotor showed that it was much more crudely cast and machined. No bevel on the outer edges, the vent holes were smaller, and obviously the hub opening machining was defective. The NAPA rotor also gave no evidence of being balanced, while the Saab rotors, as well as the Zimmermann rotors that came off in the first place, have been balanced.

If you're going for more than the least expensive rotor you can find, I'd say go with the Saab one. The price in Canada was only about $20 more than the NAPA for each rotor. Considering the amount of aggravation the NAPA have caused me, $20 would have been a bargain had I gotten the Saab originally. (But I was in a hurry and I did not expect the Saab dealer to have rotors in stock.)