Chasing Down Braking Vibration

[Gorpon73]

Hello,

I'm chasing down a vibration I've observed after a recent brake service.

The vibration occurs at about 10-20 mph from the front when stopping all the way down from speed ~50 - 60 mph. I've recently refurbished (stripped, cleaned, reassembled) my hubs, wheel assembly and calipers and added new discs, lines and pads.

I've checked the run-out with a gauge at the outside of the wheel rim, on the brake disc and on the wheel assembly and can measure virtually nothing. I've also thoroughly cleaned mating surfaces and had the wheels balanced twice.

Any recommendations for what I could be missing greatly appreciated!

Cheers

[h20hamelan]

do you feel it in the steering wheel
or body of car
wheel is front brakes

[StressCraxx]

I went through this as well. I finally discovered I had almost 0.006" lateral runout from one of my brand new rear rotors.

[Andy8421]

I went through this as well. I finally discovered I had almost 0.006" lateral runout from one of my brand new rear rotors.

I had a similar issue with a new disc, it had no runout on one face, but significant runout on the other - the two faces of the disc had not been machined parallel.

Question for the OP, when you checked the disc runout, did you check both sides?

[Gorpon73]

Thanks for the feedback.

Interesting note on the non-parallel faces. I measured the run-out on the outside of the disc. I actually did consider taking the measurement on the inside of the disc as well. However, I was taking the measurements with the discs still mounted and with the brake shield installed on the back of the disc, did not see a spot large enough where I could get the gauge in to the disc on the back side.

Did you take the measurement with the disc still mounted up?

There may be enough room to measure at different spots around the edge of the disc using my micrometer gauge which would tell me if the faces were not parallel....

[sprintsoft]

Hi,

I think it very unlikely disc runout is the culprit I.e. causing vibration at 20 mph and not at higher speeds, normally the faster you go the stronger the vibration if the disc is warped.

Can you describe the vibration in more detail?

Have the tyres been sat in one position for long?
Old tyres can look perfectly good but get stiff with age….

Cheers
Iain

[Gorpon73]

Yes, agreed, the vibration is slightly odd.

The vibration primarily occurs when braking to decelerate from speed. Say 55 mph down in a consistent and reasonable fashion. Vibration starts to occur when nearly stopped, say 20-10 mph. Continues to stop but is less noticeable due to slower speed. Definitely coming from the front end.

I'm certain its not the tires themselves. They are brand new. The vibration also was present with previous set of tires which were brand new (I changed them after only about 1 year).

The rims seem round and straight. However, I only checked for run-out on the outside face and along the circumference, so I should possibly check that from the inside as well.....

The brakes are EBC, so presumably good quality....

[joe7]

Just a thought, wheel bearings set to spec?

[Gorpon73]

Hey, Yup, wheel bearings are new and lubed. Set to the service manual recommendation. Although I feel like its surprisingly un-tight set to the factory spec. Don't recall exactly what the rating is off the top of my head.

[RichardHawkins]

Gordon,

Have you tried swopping the wheels front to back in order to see if the vibration stays at the front, or moves to the back? This might help determine if the problem is with the wheel/tyre assembly or the brake/hub assembly. Even better if you have a lotus owning friend whose car does not have this problem, you could try his wheels.

Hope this helps,

Richard Hawkins

[Bigbaldybloke]

Do you have a servo fitted? Could it be the cause, if you are nearly stopped you will presumably be fully off the throttle and I guess pulling a higher vacuum than you would be at part or full throttle.
Just a thought as you seem to have replaced or checked most other things.

[rgh0]

What is the surface of the pads and disks like? it sounds like it could be low speed stick / slip friction between them causing the vibration

Generally I don't like EBC pads and I personally would try new and different pads and also maybe clean up the surface of the disks. First I would try 10 or 20 very hard stops from 100 km/h down to around 30 km/h to see if that cleans up the pads and disks surface

cheers
Rohan

[Gorpon73]

Thanks for the feedback.

Yes, I have swapped the wheels front to back. Did not seem to change anything.

I have always been extremely happy with EBC brake pads, but its only been on modern cars. I was fairly careful with the break in of the new pads and discs and followed a procedure fairly strictly. They are fairly new still and I had suspected it may have been because they are not fully worn in yet, but have not ever observed this from pads/discs that were not yet broken in fully. They are vented, so perhaps this is overkill?

The old discs are shot, so I can't switch those back to check. Perhaps will need to purchase a new set of discs and see what happens.....