Vibration/judder on braking - any ideas?

[andy-rogers]

As some of you may know I've had a persistent problem with a very severe vibration when I brake. Only at 50mph - no problems at lower speeds or above 60. The thought of keeping my speed below 50mph does not appeal, so I have to cure this.
I changed the front disks last year and that seemed to cure it for a while. The front RH disk was a little out of true, although not much. Then during the Spain trip it recurred on the LH side, so changed disk and again cured the problem. Now it's back again. On the RH side I think. The disk is true. I've checked the suspension strut and joints - all fine. I dismantled the caliper, which seems fine, all 4 pistons move. Everything seems tight, including wheel bearings. Am running out of ideas. Help!
My sportster has Cortina uprights & hubs, Capri ventilated disks and Princess calipers. All have seen little service, the car having done 7000 miles on new equipment.

[djj_engineer]

Re: Vibration/judder on braking - any ideas?

How are your discs held on?
FMB had small spring washers taht meant the wheels may not sit flat on the disc.

[stevejgreen]

Re: Vibration/judder on braking - any ideas?

Very strange that the problem changes sides.
Presumably your wheels are balanced OK.
Its not unusual for odd vibrations under braking to be caused by a stuck caliper piston, but you say you have checked them. Are all four pistons moving easily and both hydraulic connections are Ok and bled on both sides.
It may be that a piston is being pushed further into its bore on assy, esp if new pads are fitted, and the slight corrosion on the exposed piston area making it stick slightly and not retract when you take your foot off the brake pedal.
Usually easily spotted if one hub gets unusually hot, even though bearings are in good condition, as a brake pad is constantly skimming the disk.
Good luck tracking it down.

[h_m_cumming]

Re: Vibration/judder on braking - any ideas?

Can you try swapping front and rear wheels and see if it makes any difference? It may be something to do with your tyres as the weight comes on the front under braking.

[b_caswell]

Re: Vibration/judder on braking - any ideas?

Try dressing the leading edge of the pads so that they dont grab.Another tweak although to stop squeeling really is to cut a groove across the middle of the pad at right angles to rotation. This allows gas escape from the pad face.

[andy-rogers]

Re: Vibration/judder on braking - any ideas?

Thanks for the replies. Yes I've tried swapping front and rear wheels. My disks bolt directly to the hubs, so no washers, I don't think it's that. In any case, the disk hasn't been off hubs for 6 months and the vibration only started recently.
I think Steve is more on the mark, although I haven't noticed the hub getting hot. When I press the brake pedal with no pads in, all 4 pistons do move, but not at the same rate. Not sure if this signifies anything. I guess I could look at the LH side and see if that is any different. Shame the calipers are handed, otherwise I could swap them over. Also a shame they're so damned expensive - am reluctant to shell out £200 on speculation.
I did take the caliper apart, but couldn't get the pistons out - probably need to pump them out before taking them off. Anyway, not sure what I'd be looking for, other than obvious signs of corrosion or sticking. I do need to take it apart again as I now have a slight fluid leak, probably due to re-using the old seal, so may see if I can get the pistons out for a good inspection.

[dogoncrazy]

Re: Vibration/judder on braking - any ideas?

Andy
If the pistons are Not moving at the same rate there will surely be a tendancy for the pads to be pushed 'out of square' with the disc causing vibration. the pistons can be pushed out using air pressure [I've even managed to do this with a foot pump] and providing the corrosion hasn't caused deep pitting can be dressed with 1200 grit or finer wet and dry. You do need to renew the seals, do not be tempted into putting the old ones back.New pistons used to be available from motor factors and presumably still are obtainable otherwise the reconditioners would I assume be out of business. Most seal kits come with small sachets of a red coloured grease which is applied to the outer surface of the pistons and helps prevent the corrosion forming amongst other things

[Mike]

Re: Vibration/judder on braking - any ideas?

I would be surprised if the pistons DO move out equally when not under load. Under hydraulic (or air)pressure the easiest piston to move will move first, however slight that difference is.
I used to run Sierra company cars, and they suffered a lot from brake shudder - the answer was new discs each time.
These days they are designed as a service replacement item.
Have you checked the thickness of the discs if you think they are not warped?
Mike

[andy-rogers]

Re: Vibration/judder on braking - any ideas?

Yes Mike, the disk thickness is fine - it's only done 100 miles or so, and is true. Will dismantle the caliper over the weekend, and have ordered a replacement seal kit from EBay. Fingers crossed!

[Tnick]

Re: Vibration/judder on braking - any ideas?

Andy

Many years ago I had a Triumph Acclaim with the same problem . The problem occured some 3 or 4 months after fitting new discs and pads and was particuarly noticable at high speeds. Checked every thing but nothing obvious - eventually in desperation I fitted a new set of new pads - no more vibration! I don't have an explanation and I was anoyed at having to dispose of some 3 month old pads which looked identical to the new ones. However the problem was solved - perhaps the fit of the pads in thee calipers was not quite right? But if all else fails it might be worth a try.

Regards

Nick

[andy-rogers]

Re: Vibration/judder on braking - any ideas?

I removed the front RH caliper today and drove the car. Obvuously pulling to the left, but the judder is still there, so not the RH caliper after all. Changed the pads on the LH side to the original ones (took out the Greenstuff ones, which didnlt really make any difference anyway), judder still there. Will put re-fit RH caliper and remove LH side, to check if it's that. Then at least I'll be able to rule out the brakes themselves and will look for something else, such as wheels (donlt think so) or something loose. Again, I donlt think it's that, but need to eliminate things one by one. What a saga!

[neiltechspec]

Re: Vibration/judder on braking - any ideas?

Just my opinion of course :-

I've had similar problems over the years. Usually the problem is down to disc runout when new discs are fitted. Over a very short period (only a few hundred miles) you end up with a disc thickness variation.

The solution is fit new discs and check the runout before driving anywhere. It there is any runout then this must be eliminated first or the you will end up with the same problem again.

The fault is probably down to the hubs / bearings. Use a dial indicator and check if the indicator moves more than 0.005 inches or 0.1mm. If it does then try rotating the disc on the hub one bolt hole at a time and see if you eliminate the runout. You might even need to get the hubs 'refaced'.

[b_caswell]

Re: Vibration/judder on braking - any ideas?

It could be a suspension bush or track rod end with play allowing the upright to vibrate as the brakes are applied.
Your a brave man driving the car with only one front brake!

[b_caswell]

Re: Vibration/judder on braking - any ideas?

Meant to say ebc has a good info on its page.

[pearwood]

Re: Vibration/judder on braking - any ideas?

i had the same problem it turned out to be the tie rod bushes changed for power flex bushes and the judder stopped.
bob