Brake pedal judder / vibration

[Asiangunner]

Hi guys,

A few months ago i put new front discs on my 944 LUX 83 and i started getting a slight vibration on heavy braking, my local mech asked if i'd wire bushed the hubs and brackets properly and i thought that must be the issue so planned to clean them up. I also told him my backing plates were totally rusted so he said just get rid of them.
(he tracks 924s) so trusted his comments on the plate.

Today i took the discs off and i gave the brackets a proper clean up with a wire bush drill bit, they cleaned up really well.

I also took the rusted backing plates off to bin them.

I took the car out for a test drive and I've still got vibrations when pressing the brake, I didn't got too far so i can only confirm i'm getting feedback via the pedal.

Any suggestions what i should try next? replace seals/rings on the calipers..... the seals did look fine.

 

[Asiangunner]

http://i2.photobucket.com/albums/y16/Asiangunner/FBF02D5F-CA69-47A9-965B-7DBBE81EBE61-110-000000036C512770.jpg

 

[edh]

Did you clean up the hubs?

Do you just feel the vibrations through the pedal, not through the body of the car?

Any other knocking sounds anywhere?

 

[944Scott]

At high speed or low speed?

 

[eddieedmo]

could be discs warped , pistons sticking , pads not seated properly.
Nick

 

[Asiangunner]

ORIGINAL: edh

Did you clean up the hubs?

Do you just feel the vibrations through the pedal, not through the body of the car?

Any other knocking sounds anywhere?

Cleaned the hubs up with wire brush bit on my drill

Just getting vibration through the brake pedal and not through the car

No unusual noises from else where mate


Scott - Just at medium to high speed mate, totally fine at low speed

Nick - Hoping the discs aren;t warped as they are nearly new, Pisotn sticking is an possibilty... I need to recheck seating of the pads too.

 

[eddieedmo]

do you know the make of discs ? some are prone to warping ,when I got my car the discs had only done 1k miles , new for mot , but because of sticking piston and uneven pressure being applied they warped and had same problem as yours.Check disc run out first.

Nick

 

[Asiangunner]

Cheers mate, forgive my lack of knowledge, but what is "disc run out"?

When i turn the disc's in situ with the caliper and brake pads in they do NOT spin freely and there is a sticking point(s) about 2 on each disc.

 

[zcacogp]

My S2 suffers from the same problem, although to a tiny degree. I've checked the run-out on the disks and it's within spec. The disks themselves aren't in the best shape so replacing them could be an option, but I will check the calipers for sticking pistons and make sure the pads are seated properly as well.

AG - if you have a DTI gauge then check the disks for run-out. If this is within spec then check the pads are in place. What of the calipers? (it's a Lux, so I presume they are not Brembos.) Are they in decent nick? Is the sliding bit of the assembly sliding as it should?


Oli.

 

[Asiangunner]

ORIGINAL: zcacogp

My S2 suffers from the same problem, although to a tiny degree. I've checked the run-out on the disks and it's within spec. The disks themselves aren't in the best shape so replacing them could be an option, but I will check the calipers for sticking pistons and make sure the pads are seated properly as well.

AG - if you have a DTI gauge then check the disks for run-out. If this is within spec then check the pads are in place. What of the calipers? (it's a Lux, so I presume they are not Brembos.) Are they in decent nick? Is the sliding bit of the assembly sliding as it should?


Oli.

Hi Oli, Its got standard LUX single piston calipers mate and looks wise they look old and rusty lol, I'm planning to take them off and machine wire brush them down like i did with my hubs.
When you say the sliding bit, do you mean the single piston?

I'm planning a caliper rebuild/powder cost colour change on my 996 so as thats off the road i need to keep the 944 on the road so caliper refurb might have to wait.

 

[peanut]

did you clean the new disks thoroughly with spirit before you fitted them ? any traces of preservative grease or oil etc will create glazed areas that will 'grab'

Don't just assume that it is associated with the brakes . the judder could be caused by wear anywhere in the steering and suspension which can set up a reoccurring movement under the stress of braking like a occillation

 

[Asiangunner]

ORIGINAL: peanut

did you clean the new disks thoroughly with spirit before you fitted them ? any traces of preservative grease or oil etc will create glazed areas that will 'grab'

Don't just assume that it is associated with the brakes . the judder could be caused by wear anywhere in the steering and suspension which can set up a reoccurring movement under the stress of braking like a occillation

Hi peanut,

I did clean to discs when they were new, I'm re-tackling the problem now and the discs have about 1000 miles on them.

the front suspension does need looking at in the future, I did do the bushes on the front ARB a little while ago but other than that that front suspension has got some age to it.

The feeling i'm getting from the brakes does feel like a pulsating feeling as the brakes are on.

 

[geoffbateman]

Check the condition of the wish bone ball joints (HUB END) Play in the joint can result in judder under braking. Also check the condition of the UJ's on the steering shaft at both the rack end and by the bulk head.

 

[zcacogp]

ORIGINAL: Asiangunner

Cheers mate, forgive my lack of knowledge, but what is "disc run out"?

When i turn the disc's in situ with the caliper and brake pads in they do NOT spin freely and there is a sticking point(s) about 2 on each disc.

'Run-Out' is best explained here:

http://www.youtube.com/watch?v=Pmb9MlWvCD8

The gauge that appears about half-way through is measuring how much the disk itself 'wobbles' when it rotates. The gauge is called a 'Dial Test Indicator' (DTI) and the run-out on that disk was quite bad (Porsche specs are <=1mm for a rotation.

The sticking points when you turn the disk yourself may be relevant but it's not always as simple as that. Testing with a DTI is a better way.

Yes, you need to make sure that the sliding part of your calipers slides freely. You will have one piston which pushes the pad on one side of the disk. This piston is mounted on a frame which slides slightly, and will hence exert force on the pad on the other side of the disk, forcing that in the opposite direction (so the two pads 'squeeze' the disk.) As Peanut says, everything needs to be in good working order as anything in the suspension, steering or braking system can cause this sort of symptom. (Which is why it can be a bit of a pain to trouble-shoot.)


Oli.

 

[Asiangunner]

Thanks for the link Oli, I think i'll take the car down to a garage to have the run out checked as it'll be cheaper than buying the gauge plus the missus is busting my balls for the constant flow of new tools that keep coming in the post...haha.

I can get a caliper seal kit for £20 so i'll get the calipers off anyway and clean them up plus might give them a lick of black paint to tidy them up aswell.

 

[zcacogp]

Bet you can buy a gauge for less than the cost of the garage doing the work:

http://www.ebay.co.uk/itm/Dial-test-indicator-DTI-gauge-magnetic-base-stand-clock-gauge-TDC-TE107TE108-/120985547302

This is the one that I have, although I paid £25 for it a few years ago. It's good quality and excellent for occasional use. And if you own the tool, you can use it next time as well, PLUS you get to learn how to do something new PLUS it will be useful for other jobs too (setting up the cams correctly, for instance)!

(PLUS you know you want more tools in your man-cave. Particularly nice complicated ones with dials and needles and all that. [])


Oli.

 

[Asiangunner]

Ah man you've convinced me....lol

If my missus moans i will show her your post and tell her the magic voices on the world wide web told me to do it.....