Hey everyone - just finished a 4 wheel disc brake conversion - I think I should have done the front and the rears at different times, but hey, what's done is done.

Anyhow - everything is working good, I just have a slight 'wobble' at low speeds when I'm braking. It brakes excellent all the way down to about 15 mph I'd say, and then it kinda wobbles, like the brakes are having a hard time grabbing or something, or like the rotors need to be ground. But, they're brand new rotors, so I don't think that's the case.

Any suggestions?

The wobble is usually warped rotors. But everything is new right?

So, either you don't have the rotor(s) seated properly, the calipers aren't true to the rotor, or the new rotors aren't flat (it happens), heck it could even be wheel bearings.

You might want to try greasing the caliper sliders, maybe you have a caliper not moving easily.

How about more info, what is new and what is not?

Everything is new. And I mean, everything.

I'm starting to believe it's a problem with low vacuum. If it really were warped rotors like I kind of suspected, wouldn't the problem be more noticeable at higher speeds? It only seems to happen now when the car is finishing downshifting, and the manifold vacuum is low.

I think I'll try to pick up a cheapo vacuum pump or a vacuum can, and see if the steady vacuum will help take care of my problem.

If it's not that, then it could definitely be warped rotors. You never know with the "new" parts being manufactured these days - the quality just isn't there most of the time.

When my rotors have warped, van, truck, or car you only feel it at lower speeds. At high speeds the caliper gets spread out and it's not grabbing the rotor.

And new rotors can be off, some guys always "face" (barely score) a new rotor. I myself never have., Also depends how the race was pressed in to the rotor. It may be slightly off, throwing off the rotor.

Originally posted by DG:
When my rotors have warped, van, truck, or car you only feel it at lower speeds. At high speeds the caliper gets spread out and it's not grabbing the rotor.

I've had the opposite happen with my experience. My daily driver has some warped rotors on her now. I checked the runout with a magnetic based dial indicator. I've got about .007" runnout on the passenger side and .005" on the driver's side. The vibration is really bad at highway speeds.

Max allowable runout for our cars is about .003" (that's not a lot!) according to my parts books.

I'm wondering if your pads are glazed over :confused:

Joe

Hey - anything could be possible with this thing - I'm definitely happy with the input you guys have given. I'll take my rotors off and head them down to the local brake shop and see what they say about them. How would I tell if my pads are glazed over?

Originally posted by SNFU Mobile:
How would I tell if my pads are glazed over? They'll look almost like a glazing on a glazed donut (that's the best I can come up with right now graemlins/clonk.gif )

If they look like that, take some 120 or 80 grit sandpaper and scuff them up and reseat the brakes.

Joe

Check the runout on the rotors, as mentioned even new rotors can be warped. Torque everything to specs.

Originally posted by 72SSAbody:
I've had the opposite happen with my experience. My daily driver has some warped rotors on her now. I checked the runout with a magnetic based dial indicator. I've got about .007" runnout on the passenger side and .005" on the driver's side. The vibration is really bad at highway speeds.

Max allowable runout for our cars is about .003" (that's not a lot!) according to my parts books.


Joe Ditto. Have rotors on my Monte that need resurfacing and you cannot feel it at low speed, soft stops. However, on the highway when braking from 60+ or harder stops you can really feel it in the wheel. This has always been the case on all my cars that needed a rotor resurface from new to old.