Pulsating brake pedal and vibrations when braking.

Hello LEONIDAS,

Your predicament is a bit difficult to solve. Pulsating brake pedals are usually due to warped brake discs; you have, had yours, renewed.  I suppose with that, the dealer renewed the brake pads as well.  Your dealer having renewed the brake discs, whilst, working in the vicinity of the brakes would or should have picked up on any other possibly concerns of this complaint.

The wheel bearings for insistence, but you are not complaining of any drumming noises whilst driving, a usual indication of dry or excessively worn bearings.  The other give-a-way is play at the bearings, but the dealer has not reported this to you.

Flat spots on the tyres generally do not cause pedal pulsations, the vibrations are translated into the steering wheel and tyre rumbling noise and body shake.  I would also say, that if flat spots are rebervarting 
through the tyres, any steering shake would inherently multiply its force through gearing system that if the steering damper were weak, the steering wheel would violently shake, so as there is no complaint of this either, the steering damper can not be at fault. 

You have mentioned that the pulsations have  dampened down, this suggests to me the rear drum brakes, these can become oval, if these are, then this could be test out whilst driving and gently applying the handbrake lever on, keeping the release button depressed so the handbrake does not lock on.  If you feel the lever pulsating, the drums are oval and the cause of your problem.

Should you still have an issue, try swapping the tyres from front to rear, this may change the results but then may not as, flat spots would be impressed on all the four tyres.

If these measures have not worked, the only other consideration apparent to me is an ABS problem.  The ABS prematurely activating, this as I am aware happens at low speeds of, and around 5 MPH. You have said that the higher the speeds, the more pronounced the vibration, indicates to me there is a problem at the bearings or somewhere on the axle, control arm bushes?  Fronts, predominately.  Or the new set of disc are warpped too.  Get the discs checked out with a micro-meter and take readings of run out to see if these come up to Mercedes specifications.

Good Luck,

Just a little addition from experience many years ago with a G that was left standing for a bit longer than 6 months...we had vibration issues that weren't cured until we changed the tyres - apparently some flat spots might go away with some use but others permanently deform the tyre, so replacing is the only solution.

Before you go the replacement route, try over-inflating them a bit (but not exceeding the tyre manufacturer's max allowed pressure printed on the sidewall) and see if that cures it.

Reply to thread No: 2,

Rear brakes consist of Drums, shoes and wheel cylinders as the main components.

You say there is a binding like feel to the brakes, this could mean a slightly leaking wheel cylinder. or simply a collection of brake dust.

The brake dust has to be cleaned out, should there be excessive wheel cylinder weep, this has to be replaced, a slight weep is tolerable but the cylinder will need more regular checks to gauge the situation does not worsen, in which case the cylinder would need to be replaced as necessary.

The shoe lining need only be replaced if excessively worn.  To check for for shoe wear examine the height of the shoe material at the rivet if riveted, otherwise gauge this from the side of the shoe, if the lining is bonded on.  If, I were to check the shoe for thickness, I can tell you if the shoes were excessively worn, but I find it difficult to translate this to you for your checking.  I will need to refer back to you latter with specifications.
 
The drum has minimum thickness too, when reached requires new drums or the other reason is if the drum has become oval. The thickness is measured with a micro-meter and the ovalness will need an engineering shop to measure with a run out gauge, or very carefully with a set of verniers.

When re-assembling rear shoes be careful to get the rods that go to the auto-adjusters back in the correct way round! I had real problems with shoes sticking last year after idiot mechanic made this mistake. (see previous posts)

And new shoes from Merc ridiculously expensive - get them re-lined.

Chris 

I see some one has beat me to giving you some data.  I have the shoe thickness for you, New shoe thickness is 55mm; the minimum thickness is 3.50mm.  If you are going to have the drums off, any way.

Check that you have between 1mm to 2mm of thickness left before the rivet head at it lowest point, i.e. check at the rivet that the point the shoe is most worn.

Cheers,

Pistonhead - I had a good teacher ;-)

Leonidas - I used to hear of cars with stuck brake caliper pistons, but they used to drag constantly, causing the truck to pull to one side. Piston seals can be replaced (there is a gasket kit on the EPC) but I recall reading from an old WIS document that 460 calipers should not be split, not sure if this applies to the 463.

Hang up.. you say there are bright and non bright parts on the inside of the discs.. that will cause a pulsation feel under light braking as the brake pad passes over the the different areas (presuming that you are talking about the swept area of the disc) .. this is because bright shiny metal has a higher coefficent of friction than rusty bits.

I would jack up each axle, put the transfer box into neutral (to limit drag) and then turn wheel while someone just lightly pressed brakes until you felt resistance.. then continue to turn. If you get a change in resistance as you are turning then that is your wheel of trouble.. repeated for more than a full turn for each wheel  (it will be hard work) .. then attach those with varying resistance. MOT tests will be passed with brakes in less 100% condition so do not expect the MOT to pick everything up. I suspect you have rusty patches where the pads have been sitting on the calipers (or shoes on the brake drums) and that a good long hard brake from 70mph about 5 times would sort it moslty all out.. brakes like to work and hate to sit... and after a few thousand miles you will have nicer brakes! Alternatively you may have sticking pistons on front (prise off inner dust boots and lubricate with special "rubber" grease which is brake fluid compatible) or maybe contaminated drums or similar.. anyway I always make sure the brakes are exercised by fully retracting the pistons on each caliper and pumping forward about 3-5 times every year .. then fully clean swept disc/drum area and it all works nice.