Installed trailing arm on 914-4 that came from member bdstone914 (Bruce).

I called him, just a while ago because the rotors I'm trying to use don't seem to want to fit flush up against the hub.

Using 901-352-401-18 rotors, which are for a 914-6.

Bruce suggested that the hub may have swelled up from the studs being pressed in and said I may need to file the hub down around the edges.

I guess that sounds OK, but upon further inspection... I see that there is a small lip (ridge) inside of the rotor. Hard to explain, but if you flip the rotor over and look inside where the hub should fit flush, there is a ridge on the inside face that seems to be maybe 1/16 th of an inch all around.

Is that ridge supposed to be there to act as sort of a centering ring?

Filing down the hub is a bit daunting.

Any thoughts / experience / help?



Thanks,

Len

We need pictures

First picture shows rotor on hub and the gap between the hub and inside of the rotor mounting.

Click to view attachment

This is the hub

Click to view attachment

Finally the ridge that is on the inside of the rotor that should fit flush against the hub...

Click to view attachment

The only problem I experienced was the hub was tight fitting on the studs so I put two steal lug nuts on and tightened them to snug everything up!

Photos would help us to understand your problem!

Edit: OK the photos show the same problem I had!

Just put a couple of steal lug bolts on and use an impact to snug everything evenly down! Don't forget that if the rotors are 6 rotors you will need to mill off a few MM from the diamiter to allow your calipers to fit!

Oh and removing the rotors after you snug them down can be difficult! I found a bolt that fit the threads of the screw holes in the rotor, then I tightened the bolt to push the rotor off the hub!

The wheels studs are designed for a thick collar that they fit into on a 911/914-6 rear hub. Drilled hubs do not have this UNLESS a spacer collar has been welded on. See -6 rear conversion threads in classics

It is a precision fit. If the hub is out of round from pressing in studs this can happen.

Try what Jeff mentions. Use some lug nuts to tighten everything down and see if it will snap into the groove inside the rotor. If not, you should file the hub in the areas adjacent to the (4 new) studs as that is probably where your problem is.

When spot facing hubs and pressing in studs like this the hub itself becomes very thin; about 3mm. At that point, the stud being pressed in can and will bulge the side of the hub ever so slightly making it not fit in the rotor.

When I did mine it was obvious that the base of the studs have grooves and are wider than the threaded portion. When pressed into the Hubs there is about 3/8" that needs to fit into the rotor holes. The first few times you put them on and take them off they are a tight fit! I think this would go away, making the studs shorter, if they had the the backing colars that eric mentions!

You can see what I am talking about in your photo!

Interesting. He could test your theory by putting the rotors on backwards and see if they sit flush on the hub.

Thats how I figured it out!!

I did put them on backwards for fit - no problem with the studs at all.

I had the same problem with my new carrera rotors. I ended up having a machine shop machine down that inner lip on the rotors to get a good fit ...

OK so you were able to get them all the way on flush then I would listen to Andy!

This seems to be the hub-centric thing rearing it's head. Andy, which stub axles/calipers are you using? If I knew I forgot! I'm using SC rotors and stub axles with Carrera calipers for the moment. But I was using the 914-6 rotors until last years with the same setup (I know the problem there by the way so don't start). I'm ignorant about fours so...

1. There was no difference when I changed over to 914-6 stub axles and rotors... of course.
2. There was no problem when I changed t SC stub axles (no spacer required) while running 914-6 rotors.
3. The SC calipers were fine and bolted right up with the proper spacers to center the rotor in the caliper.
Edit:
4. I'm not sure which hubs I have. I'll have to look next time they're off. They worked with 914-6, SC, and 108mm stub axles.

does this mean there is a difference in the 4 and 6 stub axles in their diameter at the rotor? I don't have any around here to compare.

I forget what year hubs i have, but they are 911, not redrilled /4.

And no, it's not a hub-centric issue as it is the outer edge of the hub that hits the lip inside the rotors.

The lip on my carrera rotors looked like some leftover from the initial machining process and was easily removed by the machine shop.

Next time i have them off, i can snap some pictures but it looked exactly like in the pic above.

To clarify, in the pic below, the *outside* edge of the flat hub surface hits the little edge you can see in the corner at the transition from the flat rotor mating surface to the conical rotor material.

That's a -4 hub an a -4 rotor. That groove inside the rotor is there for a reason. It a precise fit. I just checked it and verified it on 22 rear rotors.

911 hubs with 911 Carrera rotors, same issue as the OP described.
The Carrera rotors had to have that small lip removed in order to fit the 911 hubs.



Hub:




Hub with rotor:

Well... something was wrong then. Just like the OP. Carry on.

It is a 4 hub (redrilled w/studs), but that is a 914-6 rotor from what I can tell.

The rotor part number is 901-352-401-18

I think that's a 914-6 rotor.

Double check the rotor is not bottoming on the stud splines sticking out past the hub mating surface. If the studs are not fully seated flat may have one or two studs slightly canted causing a minute misalignment and bind. Turning the rotor backwards to fit test will help but may just not fit the way its supposed to. Get the nuts on and snug them down around the clock, see if the rotors will seat. The threads at 9 and 4 oclock look like something is tight. Throw a wheel on lose to eyeball if the studs are properly spaced.

So it is... too bad.

The rotor mounting holes won't line up (914-6 rotors are made to mount to 914-6 hubs which are actually 911 hubs) and, you should probably turn about 2mm off the edge for an overall reduction of 4mm in the diameter if you plan to use the 914-4 calipers. The 914-6 rotor can and will rub on a -4 caliper.

So what rotors (other than 914/6) can be used then?

Why would 914/6 rotors not line up on a redrilled /4 hub?

If done correctly, the studs should be in the exact same location. And he already said the rotor fits fine backwards.

I didn't say the studs won't line up.

With redrilled -4 hubs it's best to use redrilled -4 rotors. Here's why:

1. The mounting holes line up.
2. You have to machine "either" set of rotors so, why not machine the less expensive pair?

914-6 rotors will cost you $60.00 more than their -4 brethren. They will both require roughly the same amount dollar wi$e to have them machined to work properly.

I took my 6 rotors to a local small brake shop and they just turned the tool so they could cut a few MM off the ends instead of the surface of the disk! They charged me $10 per rotor!

Well... there ya go. See if you can have someone do that.

Aha, i see what you did there ...


I wouldn't really call them "mounting holes", more like "locator holes".

I've been trying to tell you guys for years Eric doesn't know what he's doing

Eric is new and improved. He is cool because his tag line says he is. I checked Snopes!!!

I had the same problem, when I got my re-drilled hubs back. But I did something different, I took the excess MM off the hubs. Before I pressed in the hubs into the new bearing, I had the brake guy put the hubs on the milling machine and cut enough off so the 914/6 rotors seated flat on the hubs. That way when I needed new rotors, I didn't need to do any more cutting on rotors. Good Luck John

Will pick up the rotors tomorrow, had 2mm taken off the diameter so they don't hit the calipers.

As far as fitting flush, I'm going to do a bit of filing on the hub as well as using some lug nuts to snug them up to the hub.

Should turn out OK.

Thanks all.