Disc rubbing on caliper

[Steve_Lindford]

Standard twincam - I have replaced front bearings, stub axles and discs. When I came to put the driver side caliper back on - the disk was rubbing on the casting. Gap on the other side of disk to casting was around 2.5mm - so 1.25mm incorrect. Typically my first thought was that the new discs were machined differently from my original and possibly incorrect. When I put the caliper on the other side of the car it was OK - not spot on but probably within acceptable tolerances.

Someone suggested the bearing race might not be seated correctly - so I took them off to check - and on the problem side I could get a 4thou feeler gauge behind the race on part of its diameter - so it was not seated or straight. I havent got access to the car til next week - do you think this would be enough to cause the hub to sit 1.25 mm forward??

I thought I had been so careful when I put the races in - but only checked with strong magnifying glass and mirror. Presumably this was not accurate enough... I also noticed that the outer bearing was a tighter fit on one stub axle than the other - so it seems one stub axle has a larger diameter by a miniscule amount I tried both outer bearings on both axles...

Steve

[4129R]

Have you put the bracket the caliper attaches to, around the wrong way?

I did, easily done.

Alex in Norfolk.

[Steve_Lindford]

Thanks - I didn,t remove that from the upright - so it is as it has always been. . .

[EuropaTC]

possibly a daft question Steve, but did it rub before you took it all apart ?  (just trying to eliminate a bent axle,etc)

If the hub bearing race isn't in square then possibly yes, it could make the difference because it would be magnified at the edges of the disc. But if I understand you correctly and this clearance is only at one point, then this would be an intermittent contact as the hub rotated.

If your contact is constant then something else is wrong, the hub is either too far in or out. Is it the inner or outer disc surface that's rubbing ? That will give a clue which way the hub is misaligned.

Brian

[4129R]

I would take it all apart, clean it all thoroughly, and put it back together again cleaning everything as it goes together.

If it still rubs, compare the left and right to see what is not aligning properly. If the bolts are going through the caliper into the bracket properly, it must line up correctly. Check to see if there is a washer in the wrong place, i.e. between the caliper and the bracket.

Also, rotate the disc to see if the disc is square on the stub axle. If it is not, the gap might change as the disc turns.

Make sure the felt washer at the back which acts as the grease seal, is seated correctly.

Alex in Norfolk.

[BDA]

I wonder if there is any perceptible runout in the disc. If so, the cause of that might be the problem. It wouldn't be out of the realm of possibility that the parts guy gave you one disc with the wrong hat height. Less likely (if possible at all) is that maybe you got two different sets of bearings - one that moves the hub out further than the other.

With that last point, you know I've come to the end of my ideas!

[4129R]

Another thought, has the disc seated properly onto the hub when you did the 4 x 9/16" bolts up very tight?

[jbcollier]

The replacement felt seals are almost always too thick.  You need to cut them down, or, as I always do, simply reuse the old felt seal (after re-impregnating it with grease).  So check the seal first by removing the the new seal and reassembling the hub.  Nut in a different position?  The felt seal is the issue.

[Steve_Lindford]

I'm pretty sure the disc didn't rub before I took it apart It might have been helpful if I had kept the old discs so I could do a comparison with thickness - although I doubt if the problem is that. The hub appears to be too far away from the upright by approx 1.25mm. It is the outer part of the disc rubbing on the caliper.

I don't want to remove the stub axles as it is possible to damage them - but I can check how far they extend and compare both sides. I am daring to assume they have both been machined correctly for now.

There is no point adding washers between caliper and bracket as this would make the problem worse as it would move the caliper in the wrong direction. The disc runs true - that is to say it doesn't appear to sway from side to side. When I removed both hubs the felt seal became unseated - so I can't check how it was when in position.

The felt seal does seem quite thick - and difficult to compress off the car onto a flat surface - so that could be the problem - one I would not have thought of - although - I put a wheel on the hub before I dismantled and there was no unusual movement and I would have thought there would have been if the seal was supporting the rear of the hub.

I will check the bearing sizes and a few other things. It is annoying that the car is kept 25 miles away. Will probably look at it Monday or Tuesday...

Thanks - Steve

[4129R]

When tightening up the castleated nut, I tighten it until the wheel won't turn because the tapered bearing is too tight, and then undo it 1 flat or 1/6th of a turn. This normally frees the bearing up enough for free turning. This would compress the felt grease seal enough for a good tight normal fit.

Alex in Norfolk.

[EuropaTC]

I'm pretty sure the disc didn't rub before I took it apart It might have been helpful if I had kept the old discs so I could do a comparison with thickness - although I doubt if the problem is that. The hub appears to be too far away from the upright by approx 1.25mm. It is the outer part of the disc rubbing on the caliper.

Hi Steve,

The disc should be 10mm thick and it's a relatively tight fit in the caliper body even when aligned properly so I can see the problem now. I doubt the felt seal is the issue, they are normally oversize but when you adjust the bearing they crush easily. There's a metal shield part to the seal assembly which if not fitted fully home could cause the hub to be displaced outwards.

Question - when you replaced bearings I'm just wondering if the larger, inner bearing seat isn't fully home in it's housing ? That would allow you to adjust the bearings for no play but push the hub outwards.  Is the metal cover/seal support for the inner bearing flush or slightly inset with the hub body ? I've just put my front hubs back together this week and the metal cover was flush with the top of the hub.

It's got to be something simple that we're missing !

Brian

[Steve_Lindford]

Thanks for the info about tightening up the castle nut - there is a chance I didn't tighten it up enough as it felt 'wrong' somehow. Presumably if the hub didn't free itself after undoing one flat - it soon would when driving loads are put on it.

There appears to be a microscopic difference in the diameter of the stub axle for the outer bearing - as I can slide the bearing on and off by hand on one side (nice snug fit) - but it could not be done on the problem side - it will go on and off - but not by hand. I tried to measure the difference with digi vernier gauge but kept on getting different results as it was difficult to know if the angle was exactly correct when using the tool.

The disks are 10mm thick. I have checked the inner bearing seat (which would have been the best place to find an error) - but was ok on both sides. There seems to have been an error on the seat for the outer bearing - as outlined in my original post - which I have corrected.

It would be so much easier to solve all this if the car was in MY garage - but when I purchased the car - I hadn't quite purchased my house - so until I get an MOT certificate it is kept 25 miles away...

Will report back when I get a chance... - it probably IS something simple...

Steve

[4129R]

I used coarse grade green emery cloth from Halfords on my old stub axles to get the surface rust off to allow the loose bearings to fit by hand.

If the bearing does not free up after 1 flat, 1 more should do it. But tighten it again to make sure the felt is compressed and the bearings are seated properly. The hub will be hard to turn, even with the wheel fitted, until you free it off a flat or two. Fit new split pins, and pack the bearings with grease until you can fit no more in both bearings, and fill around the castelated nut before putting the grease cap back on.

I have plenty of spare bearings, hubs, uprights, and stub axles if you want to compare, I received loads from Louisiana when I bought a 40ft container of 2 cars in bits,  + loads of spare bits.

Alex (in Norfolk weekends, and London weekdays).

[Steve_Lindford]

The stub axles are new and shiney. Because the outer bearing seems tight on the axle - Im thinking that when I free off the nut - the bearing will stay in the same place on the axle. I will find out tomorrow. It could be that I have solved the problem as I have checked the seats on all of them. One of them was a little suspect...

Sounds like you have a fantastic collection of spares!

Steve

[Steve_Lindford]

Don't think the problem is with the bearings now - having checked the inner bearing seats, tried swapping hubs and using the original old bearings - the discs rub on outer edge just the same (one side only) - so it seems likely something is not straight or true - upright or caliper bracket (that bolts onto the upright) - or both. They are difficult to assess and measure without a perfect one to compare with. This doesn't explain how there didn't seem to be a problem before it was dismantled but a previous owner may have had the disks skimmed - or whatever.

I can solve the situation by using a bit of a bodge - putting 1mm spacer between disc and hub on one side. I may have to do this as I am now under pressure to move the car quickly as my storage area has been sold. I can then look into the problem without a time pressure.

I wonder how many other people's caliper run exactly true...

Changing the subject - the short top rubber thermostat hose - which has a different diameter each end - Can I buy a universal hose - cut it to size and stretch to the larger diameter - or do I have to purchase a Lotus part??

Steve