brake disc wobbles... what gives?

[andylawcc]

was rotating my wheels the other day, and found out my left front brake disc wobbles, i notice there is no screw/bolt that holds it to the "whole assembly thing", so i thought the missing screws is the issue. But when i look at the right front brake disc, there are no screw/bolts neither, and that one does not wobbles. what gives?

the car is a Nissan Sentra 1999.

 

[jlee]

The rotor is seated to the hub by the wheel. If there's no wheel bolted to the car, the rotor will (well, should..haha) move unless there's a screw to hold it there.

 

[phucheneh]

A few makes, iirc all Japanese, use a phillips screw to secure the rotor to the hub.

As far as I know, it serves no purpose other than to hold the rotor in place during assembly. You can also say that it 'indexes' the rotor, in case you need to remove it during some brake or suspension work, but in practical use this does nothing. Some manufacturers only recommend machining rotors with on-car lathes for a similar purpose- the misguided thought that a rotor removed and machined competently on an old-school lathe may still cause brake pulsation or other issues on a sealed hub that isn't garbage. I've not once observed this to be the case...a good hub simply shouldn't have any runout.

Some American cars/trucks will come with a little disposable washer pushed over a couple of the lug studs for the same purpose- don't want brake parts rolling across the factory floor before the wheels can be put on. Remove these by grabbing the little tabs with a pair of dikes (side-cutters) and giving it a good jerk (there's a 'that's what she said' in there somewhere). It will either pull off or break (...again).

Once the car has been driven a bit, corrosion around the protruding hub ring will usually affix the rotor a little more securely. Or a LOT more securely. Hammer the face of the rotor (the center, not where the pads contact) to knock it loose, being careful not to whack the lug studs. If it's really stuck, spray around the ring with some penetrating oil and let it sit for a while before trying again.

[insert 'the more you know' graphic]

 

[slugg]

Yea, I was wondering the same thing when I first started to learn about working on cars. My Miata is the same way. The brake disks just kinda "float" on there until the wheel sandwiches it tight. That's normal!

 

[FuzzyDunlop]

wait... clarification: it wobbles with or without the wheel bolted on??

If it wobbles without the wheel on, that is completely normal. The other ones would also come loose with a light tap of a rubber mallet.

If it wobbles with the wheel on (i dont see how this would be possible) then there is something MAJORLY wrong.

 

[andylawcc]

wait... clarification: it wobbles with or without the wheel bolted on??

If it wobbles without the wheel on, that is completely normal. The other ones would also come loose with a light tap of a rubber mallet.

If it wobbles with the wheel on (i dont see how this would be possible) then there is something MAJORLY wrong.

it wobbles without

but, the left side WITH the wheel on has a slight wobble, the guy who did my wheel alignment said the tie-end rod is having a little play, so, will get that replaced later...

 

[andylawcc]

okay, thanks guy for all the info.

 

[phucheneh]

If you need a tie rod and you had an alignment done, you wasted money.

All the guy did was set front toe...and that's moot if a part that controls toe has play in it.

 

[rifken2]

At my dad's shop, even the cars that needed on the car turning for rotors we found a way around leaving the assembly on the car, we unbolted the entire assembly and would mount it to the lathe being careful to reinstall exactly as it came off. It typically took three extra bolts to remove the entire assembly.

Turned out much better than an on car lathe. Of all the jobs we did this way, not one required a realignment.

Also, the guy that did the alignment should have found the play before he aligned the car and let you know that needed to be replaced... money grab...

 

[phucheneh]

At my dad's shop, even the cars that needed on the car turning for rotors we found a way around leaving the assembly on the car, we unbolted the entire assembly and would mount it to the lathe being careful to reinstall exactly as it came off. It typically took three extra bolts to remove the entire assembly.

Turned out much better than an on car lathe. Of all the jobs we did this way, not one required a realignment.

Also, the guy that did the alignment should have found the play before he aligned the car and let you know that needed to be replaced... money grab...

You talking about vehicles with the hub built into rotor (with taper bearings)? You just take the bearings out and use those little doodads that look like steel barrels in the 'box/shelf o' lathe parts.' They sit against the bearing race. When done, you just have to do a good job of making sure you get any metal shavings out and pack everything with new grease (might need a new rear grease seal, too).

 

[andylawcc]

well, the play on the tie-end rod was small, and he did tell me the alignment need to be done again if the TER was replaced. In retrospect i should have the TER replaced before the alignment, but my shocks were also shot too, so I rather drive the car a little long, then contemplate whether to do the whole shocks+TER all together then the re-align all over again.

 

[andylawcc]

i just picked up this car, 1999 Nissan Sentra, 178k miles already. I figure it has 70k more miles left before major engine and/or tranny work, then at that point i just junk it, skipping the shocks and TER all together.

 

[phucheneh]

Outer or inner tie rod? Inners, which or more or less part of the steering rack (they're literally attached directly to the 'rack gear' inside those rubber boots you see, often develop play as a pair, and can wear very slowly.

Outer tie rod ends, which are easier to replace, can often develop severe play on one side of the car with none in the other. I could offer some possible reasons as to why this happens, but in reality, I'd just call it 'chance.' If, with the car in the air, you can see the wheel visibly move from side to side, you've got a problem that needs addressing.

Moreover, front toe, that alignment angle that was set? That can vary by more than he probably even adjusted (you get a before/after printout?) with just a small amount of play in a tie rod end.