Lackluster brake performance on my 4-ton motorhome

[roadwarrior]

i have got a 4 ton mercedes sprinter based winchcombe, it has got new disks and pads all round but i have to stand on them if there is a sudden stopping situation, they are bedded in as i have just returned from the pyranees, but they are still lackluster and dont inspire confidence - your thoughts ? they take a couple of seconds to bite and are fine in normal circumstances but.. as they are all round new discs im surprised they are not better.

 

[David and Sally]

Sounds like wrong pad compound or a failing turbo?

 

[Otter Spotter]

Have they been bled properly ?

 

[Spriddler]

they take a couple of seconds to bite

I had a similar fault that was due to a faulty non-return valve in the brake servo vacuum pipe, but yours may be a different braking system. (With a turbo?)

 

[herald_400rl]

Sounds like wrong pad compound or a failing turbo?

Is turbo meant to be booster/servo?

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[David and Sally]

Is turbo meant to be booster/servo?

Yes. But unlikely. Might be wrong pads or maybe the callipers were not properly freed to adjust themselves?

 

[Guigsy]

Is it still the case that new pads and discs can be bedded in incorrectly and get glazed? It used to be the contamination or incorrect first use would mean poor performance.

 

[herald_400rl]

I'd say incorrectly bled or mechanical failure of something. Incorrectly attached vacuum line, one way valve gone, servo nackered. Or... contaminated pads if the installer had greasy fingers and slipped some copper grease on the pad inadvertently. Heck, could be anything

I'd still hope for incorrectly bled, is it one of those vehicles where the clutch shares the reservoir, does that also need bleeding?

 

[David and Sally]

But why would a change of disc and pads involve bleeding?

 

[herald_400rl]

But why would a change of disc and pads involve bleeding?

You have to push the pistons back to get the thicker material in, with all the will in the world this will introduce air even if just in the last foot of pipe you've pinches off.

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[Guigsy]

You have to push the pistons back to get the thicker material in, with all the will in the world this will introduce air even if just in the last foot of pipe you've pinches off.

Where does the air get in? I thought when you squeezed the calipers back, the fluid it just went back to the reservoir?

 

[Derbyshire wanderer]

i have got a 4 ton mercedes sprinter based winchcombe, it has got new disks and pads all round but i have to stand on them if there is a sudden stopping situation, they are bedded in as i have just returned from the pyranees, but they are still lackluster and dont inspire confidence - your thoughts ? they take a couple of seconds to bite and are fine in normal circumstances but.. as they are all round new discs im surprised they are not better.

I have the same van and think the brakes are also poor.
They are not able to bite hard as I found out on the M5 when someone swooped into my lane just before some roadworks and stood on his brakes . I had to swerve to avoid running into him and have been thinking of replacing the pads with something of known quality.
Bedding in properly is crucial for getting the best from new pads.

 

[David and Sally]

I have changed many sets of motorcycle pads. Never had to bleed anything. Push the pistons back in after a clean and the fluid just goes back into the master cylinder.

 

[herald_400rl]

I might be massively mistaken here I'm a mechanic by necessity not trade but I've never wanted that fluid pushed back and this is likely some form of urban myth but I was under the impression its not ideal to do so and instead the rubber flex should be pinched off and the bleed valve opened to allow fluid to come out.

 

[Derbyshire wanderer]

I might be massively mistaken here I'm a mechanic by necessity not trade but I've never wanted that fluid pushed back and this is likely some form of urban myth but I was under the impression its not ideal to do so and instead the rubber flex should be pinched off and the bleed valve opened to allow fluid to come out.

Pinching the flexible hoses is more likely to cause damage than letting the fluid be pushed back. Bleeding through fresh fluid after replacing the pads is a better option if you are doing the full Monty overhaul

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[roadwarrior]

i have not had the fluid replaced but i will say there is no air in the system and contact is solid from the get go and feels fine, its possible it needs replacing i will put that on the shopping list for next year, I do wonder though what pads everyone uses, i did not specify on the rears and the fronts were fitted when it had corroded disks which the dealer i bought it from rectified at the time of sale., so pads and discs unknown - we can assume cheapest available. hence - what do you use, this is my 4th van and by some measure the worst which does surprise me as the disc sizes are very good ( BIGGER IS BETTER)
Just to annoy me i have also had the disk fault pop up, my feeling is the garage did not replace the wear sensor when replacing the rear disks and pads. Am i right in thinking there is one on the front and one on the rear ?

 

[herald_400rl]

Always Pagid for me or OE from manufacturer if I'm feeling flush.

 

[Guigsy]

Wear sensors are integrated into the pad. I think it's just a filament within the pad material that forms a circuit that gets broken when the pad gets too worn?

 

[our poppy llll]

Personally I would take it back and say, Hoy, you trying to kill me, sort out these brakes..

 

[Figaro]

and the fronts were fitted when it had corroded disks which the dealer i bought it from rectified

So have the front pads been previously fitted to old corroded disks ?
That could be your problem if I read it correctly ?
New quality front pads needed

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[gus-lopez]

I thought when you squeezed the calipers back,

most need a rewind tool these days unless you know how to do it with water pump pliers & a G clamp.

 

[Kybod]

A seized brake caliper or the pads weren't renewed as you expected.
The brake wear sensors are normally built into the pad and break a circuit when the pads get too low.

 

[donkey]

To rule out the brake servo and/or the vacuum supply, there is a simple test.
First with engine off, pump the brake repeatedly until the pedal is rock hard.
Then while pressing down on the brake pedal, start the engine. The pedal should immediately dip, as much as 60mm or so. If it creeps down then suspect the vacuum system. Most likely a collapsed hose or blockage.
If it does indeed dip correctly, you can rule out a servo/vacuum fault.

You have said the brakes take a couple of seconds to bite. This could indeed suggest the wrong compound pads. Racing pads are useless when cold.

Geoff

 

[poppycamper]

I might be massively mistaken here I'm a mechanic by necessity not trade but I've never wanted that fluid pushed back and this is likely some form of urban myth but I was under the impression its not ideal to do so and instead the rubber flex should be pinched off and the bleed valve opened to allow fluid to come out.

Yep Massively mistaken and therefore at some point in past misinformed.
Absolutely no need to pinch hose and then bleed brakes when changing pads, all you doing is pushing fluid back into resoviour with no danger of air being drawn in., and also possibly damaging hose.
Removing calipers however differant story.. pinch (gently) hose to stop fluid leaking, remove caliper, replace and then release clamp and bleed caliper.

 

[herald_400rl]

Yep Massively mistaken and therefore at some point in past misinformed.
Absolutely no need to pinch hose and then bleed brakes when changing pads, all you doing is pushing fluid back into resoviour with no danger of air being drawn in., and also possibly damaging hose.
Removing calipers however differant story.. pinch (gently) hose to stop fluid leaking, remove caliper, replace and then release clamp and bleed caliper.

Always happy to have incorrect information updated.
Plus saves a job

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[Silver-Fox]

You have to push the pistons back to get the thicker material in, with all the will in the world this will introduce air even if just in the last foot of pipe you've pinches off.

Please share how air gets into the system winding the calliper pistons back.

I’m intrigued.

 

[poppycamper]

Please share how air gets into the system winding the calliper pistons back.

I’m intrigued.

Check post before yours.. # 25..
OP admits he may have been misinformed.
Edit to add....
Sorry not OP but herald_400rl ..
Apologies roadwarrior

 

[Raul]

If is a significant decrease in breaking performance I would look for calliper sliders, they can get mucky and corrode. A pad will bite no mater of compound. The solid wood feel pad it’s a classic slider or calliper piston seizing.

 

[VXman]

Where does the air get in? I thought when you squeezed the calipers back, the fluid it just went back to the reservoir?

Yep. I've changed dozens of pads on my cars over the years. Never needed to bleed the system. It's sealed. If you get air in it from replacing pads there is something seriously wrong.

 

[poppycamper]

If is a significant decrease in breaking performance I would look for calliper sliders, they can get mucky and corrode. A pad will bite no mater of compound. The solid wood feel pad it’s a classic slider or calliper piston seizing.

OP Said new discs and pads fitted which would mean the removal of calipers..
Now any mechanic who did not clean calipers and sliders and associated area IMHO is a cowboy.
Question to OP... do you think the mechanic? Was competent enough to carry out this procedure???