Vibration Under Braking- Check My Homework?

[Tyrell Corp]

StreetDragster said:

As far as known, no accidents.

A lot of cars have a secret history, and previous accident repairs not always recorded.

Sometimes the difficult to fix problems can be unseen damage from a previous knock -as with my 'warped disc' .

Replacement front numberplate and paint repairs on the front would be a to a previous knock clue here.

good luck tell us what you find

[StreetDragster]

Afternoon all

So I'm heading towards a potential fiery death with the clamping. Brake pipe idea. But......

... the car showing this problem at sub 1mph has got me thinking.
If it was only at higher speeds I'd be fully on board with getting the wheels balanced and checked for trueness, tyres for bulges etc.
Then from there id move onto bushes, tie rod ends etc.

But if this problem shows itself at less than 1mph, creeping forward in traffic just holding the car back on the brakes. You get a definite feeling of none linear breaking, whoom-whoom-whoom if you will.
Surely, there isn't enough momentum for anything wheels related, bushes, balljoints etc.
If it was a bulge in the tyre, it would be like driving over a bumpy road if it was big enough to be noticed, and wouldn't be effected by brakes on/off.
Given that the pads in all four calipers have been checked intact, free to move, no binding etc, and all 20 pistons have been checked to be free and easy to move and also not binding. Also, brake effort at this speed has got to be majority front biased.
Then it's got to be the discs not being been at 90 degrees to the pads right, i.e, one of the wheel bearings?
Both rear discs are true when DTIed, so it's likely to be on the front end?

[Maxdecel]

StreetDragster said:

Afternoon all .......Both rear discs are true when DTIed, so it's likely to be on the front end?

However

StreetDragster said:

Diagnosis So Far- Front discs and pads were checked. Found a warped passenger side disc. Front discs and pads replaced, no change in symptoms.

The fact changing the discs & pads had no effect suggests the problem isn't the front.
I take it the warped disc was diagnosed by measuring the run-out ? What was the run-out on the replacement discs ?

Also

StreetDragster said:

Evening all, Rear end - Due to the drilling/grooves, i couldn't get a DTI to read properly on the friction surface of the discs, but running it on the flat part where the wheel butts up against, both sides appear to be running true.

If I understand the above you measured run-out on the Top-Hat as it's sometimes referred to, the mating surface of the wheel/Disc ?
Run-out is not measured there so you cannot be certain the rear is to spec.
Pt 6 https://mintex.com/wp-content/uploads/2015/12/Disc...

[StreetDragster]

Maxdecel said:

If I understand the above you measured run-out on the Top-Hat as it's sometimes referred to, the mating surface of the wheel/Disc ?
Run-out is not measured there so you cannot be certain the rear is to spec.
Pt 6 https://mintex.com/wp-content/uploads/2015/12/Disc...

Correct, front discs had run out, measured at the disc edge. 360mm odd solid steel discs i think, 1.2mm runout, i think, it was a while ago.
New discs were fitted, no run out, now have run out but not much, 0.1mm i think.
However, the originals are solid steels, replacements are fully floating 380mm ones.
Front hubs have been dtid, true.

I completely agree with what you are saying about the rear discs, and correct that it was measured at the top hat, you can't get a dti to read due to the drillings and grooves on the friction surface.
But my point is at 1mph, they are not likely to be putting any force in, and it's all from the front, right? I'm only breathing on the brake pedal to hold the car at that speed in traffic.

I imagine alot of people are wondering why i don't just replace them to rule them out, they are ~£800 a pair. Wheel bearings at the front are ~£900, the front discs and pads OEM would have been £1600. Everything's big money to be fault finding by replacing parts.
Hence, why i took it to a specialist, who half heartedly looked it over and then just quoted the entire diff needs replacing, at 15% the cars value, just for the part, plus labour.

I don't mind spending money, but it's got to be on the right bits.

[sam.rog]

Go for a drive and see if one wheel is hotter than the others. Could be sticking calliper.
Get it on a ramp and pry on all the arms to check the bushes. A torn bush can give similar issues.
Finally check the topmounts.

[StreetDragster]

sam.rog said:

Go for a drive and see if one wheel is hotter than the others. Could be sticking calliper.
Get it on a ramp and pry on all the arms to check the bushes. A torn bush can give similar issues.
Finally check the topmounts.

No obvious wheel hotter than the others, even after extended periods of heavy braking.
All pistons in all calipers have been confirmed free and moving smoothly.
All arms and bushes have been levered/pryed and no movement.

[archie456]

I had an issue with a motorbike disc that had the symptoms you are describing.

It turned out that the disc wasn't sitting true due to some residual powder-coating being left on the mating surface. Disclaimer: It was like this when I bought it.

The brake was fine initially, but it developed the pulsing that you describe. Because it wasn't true the disc had been rubbing lightly on alternate pads every half revolution with no brakes applied. After a while this wore down the disc unevenly, and was thinner at 2 points 180 degrees apart.

I'm not saying this is the case for you, but it may well be worth checking.

[Maxdecel]

Totally agree re. throwing parts at it whether they're £1000's or tenners, doing that would only succeed by replacing the hub, flange etc AND the run-out still needs checking !
Your comment re. slow speed detection:-
There will be very light pressure going to all brakes, it may be proportioned by a valve but without knowing the system ..?
If it's equipped with ABS then I can assume equal system pressure will be distributed to all four brakes.

New fronts from installation did not rectify it, indicating to me it is the rears; however just throwing on a pair of discs may not cure it as the hub may be the cause of the run-out ! If you can't establish the run-out is within tolerance then your doing the equivalent of using the parts cannon again.
I had to set the R.O on AP slotted discs, there was only one DTi rubbing path of possible use at the extreme perimeter where the slots ceased and the edge of the disc. It was fiddly but necessary.
How could the R.O. be checked on initial fitting ? Or were they thrown on with fingers X'sd.

Isolation of the axles is the only satisfactory method, that will confirm which end of the car is giving trouble.

Edit - Archie above just reminded me, have the wheels been refurbished around the time this began ?

Edited by Maxdecel on Friday 2nd February 20:36

[StreetDragster]

The discs have been changed on the front. The front I've been able check on the disc surface no problem, with the old and new brakes. And I've been able to check the hubs.

The rears, have not been replaced, and can't be checked with a dti for run out on the friction surface. Hence why i had to do it on the hubs

This problem has been building, used to do it a tiny bit, now it's more obvious.
One wheel has been refurbished in the middle of this, no change before/after. That was the front passenger wheel

Edited by StreetDragster on Friday 2nd February 20:40

[Maxdecel]

I asked about the wheels as I was reminded about a situation once where the wheel flange was coated with a very uneven, if not lumpy paint finish.
When tightened up it was distorting the disc, just a thought.

[mercedeslimos]

Whenever I have discs off, I clean the hub flange very well with an angle grinder wire brush and brake cleaner. Anything at all under there is magnified when between the disc and the hub. Symptoms like this are the most annoying of all, and you'll go to the ends of the earth to make it perfect.

[Maxdecel]

mercedeslimos said:

Whenever I have discs off, I clean the hub flange very well with an angle grinder wire brush and brake cleaner. Anything at all under there is magnified when between the disc and the hub. Symptoms like this are the most annoying of all, and you'll go to the ends of the earth to make it perfect.

There are bespoke kits for that very job. - https://www.ate-info.de/en/details/produkte/felgen... Also available for hubs with studs.

[mercedeslimos]

Maxdecel said:

mercedeslimos said:

Whenever I have discs off, I clean the hub flange very well with an angle grinder wire brush and brake cleaner. Anything at all under there is magnified when between the disc and the hub. Symptoms like this are the most annoying of all, and you'll go to the ends of the earth to make it perfect.

There are bespoke kits for that very job. - https://www.ate-info.de/en/details/produkte/felgen... Also available for hubs with studs.

Been meaning to get one of those, I tend to get around the edges and go a bit overboard. I also find that even brand-new discs need a good clean inside and out, the crap that is on new parts!

[wild rover]

I agree with your diagnosis to date. I ahead a similar problem which was eliminated by stripping and replacing all the bushes on the ante roll bar. Once stripped you could see sufficient wear on the bushes not detectable under pressure. Best of luck.

[StreetDragster]

Hi All, thought i'd update this thread.

So a few months on now, and a few more thousand miles on the car, nothing is better, nothing is worse.

So what i definitely haven't done officer, is clamped off the rear brakes and took it for a drive.
And whilst i wasn't doing that, i didn't discover that the problem completely goes, then returns a bit with one side unclamped, and as per with both sides unclamped.

So, given that-
1) I wasn't able to DTI the rear discs for tru due to the grooves running all the way across the friction surface
2) The problem is present at both high speed, and also just creeping on the brakes, less that walking pace, you can feel the none linear brake effort
3) Heavy engine braking with no foot brake doesn't show any vibration, and clamping off the rear brakes would make no difference if it was in the drive train
4) The front discs and pads have been replaced

My next step is to measure the thickness of the rear discs. If thiccccc then i'll have then skimmed, if not, i'll replace and see what happens

One of its rear parking sensors has failed now, it never ends

Thanks all

[Pica-Pica]

I had this. After lockdown, little use, and assault by gritters, my discs were scored. Result: vibration on moderate braking. I don’t use the brakes much, but it was annoying. I tried heavy braking to clean the discs. As the fronts were low, I replaced discs and pads. Better, but still there. Come MOT, they passed as effective, but noted as ‘pitted and scored’. Replaced rear pads and discs. Issue gone completely. Skimming discs may have worked, but I believed it was money down the drain. Mileage was 46k, first change of any discs or pads.

[donkmeister]

So what actually is this mystery car? Both the cars in your current profile are FWD but you say this is RWD. Just pays to be specific in case this is a latent defect or an issue related to how it's used that others have experienced.

[donkmeister]

mercedeslimos said:

Maxdecel said:

mercedeslimos said:

Whenever I have discs off, I clean the hub flange very well with an angle grinder wire brush and brake cleaner. Anything at all under there is magnified when between the disc and the hub. Symptoms like this are the most annoying of all, and you'll go to the ends of the earth to make it perfect.

There are bespoke kits for that very job. - https://www.ate-info.de/en/details/produkte/felgen... Also available for hubs with studs.

Been meaning to get one of those, I tend to get around the edges and go a bit overboard. I also find that even brand-new discs need a good clean inside and out, the crap that is on new parts!

Search for "roloc discs". I use the purple ones to clean up hubs and have one with a wire brush and ring shaped discs for doing around studs. Just the generic is fine. Whilst it looks like scotchbrite in pictures, it's quite different in reality. My process is:

Remove disc
Use brake cleaner to remove any anti seize from the hub flange
Douse the area with water for keeping down dust
Do all the studs for a few seconds each
Do all the in-between bits for a few seconds each
Go round the outside a few times
Douse with water and use blue roll to clean it up
Repeat if necessary
Use a brass brush for any nooks and crannies not yet scrubbed
Use brake cleaner for a final wipe down.

I also do the mating faces of the wheels:

Use brake cleaner to remove the copper slip that some well meaning person smeared into the interface relying on friction between the wheel and disc instead of torquing the fasteners correctly
Douse with water for keeping down dust
Use a disc to clean up for a few seconds
Rinse
Inspect
Dry
Brake cleaner.

I also use a flux brush for applying any pastes and greases now - much easier to get a nice thin coating.

[richhead]

StreetDragster said:

Hi All, thought i'd update this thread.

So a few months on now, and a few more thousand miles on the car, nothing is better, nothing is worse.

So what i definitely haven't done officer, is clamped off the rear brakes and took it for a drive.
And whilst i wasn't doing that, i didn't discover that the problem completely goes, then returns a bit with one side unclamped, and as per with both sides unclamped.

So, given that-
1) I wasn't able to DTI the rear discs for tru due to the grooves running all the way across the friction surface
2) The problem is present at both high speed, and also just creeping on the brakes, less that walking pace, you can feel the none linear brake effort
3) Heavy engine braking with no foot brake doesn't show any vibration, and clamping off the rear brakes would make no difference if it was in the drive train
4) The front discs and pads have been replaced

My next step is to measure the thickness of the rear discs. If thiccccc then i'll have then skimmed, if not, i'll replace and see what happens

One of its rear parking sensors has failed now, it never ends

Thanks all

i did kinda point you this way, general rule of thumb is, feel it through the steering wheel its front, feel it through the seat its rear.