Brake drum issues with pulsing brake pedal

[Marmalade67]

Didnt have time to sort out my brake shoes on the back so took it it to my garage that have been using for years. The drums were also replaced as I had let them go so long. Got the van back and noticed the brake pulsing especially if heavy braking. Took it back and they replaced the drums like for like, also welded something, not sure what. Took it away again and still pulsing, Back again and they have now put some quality drums on changed the brake hoses but still pulsing. They say there is a slight pulse coming from the front also. Prior to the first visit the brakes were smooth.
Any ideas that I can take to them?

[MGP]

What sort of garage doesn't have a dti gauge? It's not hard to measure which corner is out of round or not running true.

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[MGP]

Just another thought if the rears were that bad and the drums were really seized, if they have gone at it like animals there is a possibility that they could have bent the hub

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[Mr Bean]

When you say pulsing do you mean that the pedal is applying a pulsing reaction to your foot on the pedal or do you find the deceleration is pulsing as for instance with ABS? Of course an eccentric drum or high spot/area in a disk could cause both but his mention of slight pulsing on the front seems to indicate that this is indicated on a rolling brake tester. In my view the same problem is unlikely to occur simultaneously on say both rears or both fronts or especially on front and rear wheels out of the blue. Depending on any dual circuit system I guess it is possible for pulsing back pressure in one wheel to give a false indication in one or more wheels. Similar symptoms to this can be caused by Slack in bearings or geometrical changes under braking due to loose or worn track control arms, wish bones etc. Brake hoses unless say kinked or trapped will either work or balloon/burst under pressure. I think you need to get someone on board who has a broader Knowledge base. That is if I have understood you correctly.
CS

[Marmalade67]

If heavy braking the foot is pushed back repeatedly. If braking at slow speed it it is much slower and less aggressive. They worked it back to the rear brakes on the rolling road and also isolated one front disc. Had an advisory for a rear bearing on last MOT. When I bought the van 4 years ago the previous owner had done a major overhaul of the rear suspension so I think every bush etc was replaced then. He never got as far as the front end but did leave me with the rubber goods to do it as and when required.

[AlandAnn]

Just another thought if the rears were that bad and the drums were really seized, if they have gone at it like animals there is a possibility that they could have bent the hub

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For what it's worth this would be my initial thought as well, sometimes garages get over confident and think that they just need to use even bigger scaffold poles

[Marmalade67]

Plot thickens. Rear now has new drums, cylinders, shoes, hoses and fluid. I couldnt feel it on way home but mechanic said it is but he can not understand as it seems to be intermittent.
May try new front discs next month if it is still bad.

[jimrat]

Got the exact same symptoms on my van: pulsing pedal on hard braking.

I changed rear drums, cylinders etc as they were knackered/leaking, which improved braking efficiency but made no difference to the pedal. I just assumed it was a partially warped front disc(s). My discs/pads have plenty of life in them, so I left them alone as it doesn't bother me and hasn't failed the last 3 MOTs.

If you decide to change the discs, I think the wheel bearings have to be changed at the same time

Cheers
Jim

[Oldiebut goodie]

Vacuum leak?

[kevtherev]

Vacuum leak?

On the servo?

[petethefeet]

Jim, can I ask where you got your drums from? I have a similar issue that has appeared since I replaced the rear drums and shoes with some from VW heritage . The drums have been off and on loads of times, cleaned and adjusted but still have the issue, never there before. Just a thought it might be a duff batch of drums
.

[jimrat]

Hi

I got the drums from Schofields in sept 2013. I'm fairly sure the pedal was pulsing when I bought the van, so I don't think the problem with my van is related to new drums

Cheers
Jim

[jimrat]

Yeah, hadn't thought of vacuum leak . So presumably there's a long vac hose running from the engine in the back to the servo upfront - plenty of scope for leaks there.

[Mr Bean]

I kind of eliminated the servo as try as I might I couldn't dream up a way of a servo or associated components causing pulsing. I think it would require some kind of feedback mechanism would need to be involved. I have had a situation with a juddering clutch caused by a busted engine mount. Here the feedback loop is quite easy to envisage i.e. clutch engages, engine/bell housing/gearbox assembly twists/lifts changing geometry, clutch disengages slightly, engine plops back etc. etc.

I am struggling to envisage an feedback loop including the engine vacuum which would have the right frequency/beat/resonance to match the pulsing at the pedal. It would take something like a bulkhead doing a wobble board trick or similar which just doesn't seem possible. I believe the vacuum in the servo to intake manifold to be fairly constant and smooth as would be any leak in the system.
PS anyone remember vacuum windscreen wipers embarrassingly slowing up and stopping when climbing a hill?

[tobydog]

I've had discs with corroded patches matching the pads caused by being parked in damp weather. It doesn't take much to corrode a pocket in the disc which can be felt through the brake pedal.

1958 Prefect, first car, foot off the accelerator up hills to generate vacuum to keep the wipers going.