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.

 

[roadwarrior]

thanks for the quick preach, i tend to do 3000 miles stints and as brakes are bedded in after 200 miles i think we can say they were. I posted my adventures as many have spoken of poor sprinter brakes and i thought it might be helpful or at least thought provolking to some, I did not invite negative comments but as you seem to like a quick preach i hope it made you feel useful.
I note you have a little van, so none of your extensive experiance would be relevent to a 3.5t chassis with 3,5 t brakes that was extended by autosleeper to 3.8t and futher extended by me via professionals to 4.250 t - brakes still to 3.5 t please note - what would a desk bound transport operator such as yourself advise an ex trunker long distance lorry driver such as me to do if he felt his brakes were a little lacking. Im not sure if i had worked for you, your advice of "drive it around a bit more " would have been appreciated.
I am of course well aware rust sets in during winter and non use but driving it during winter is not my idea of fun any more, been there, sold the t shirt, and my personal life does not allow for it.

I think we have to accept we are not all alike and have differant lives and problems.

So while i am aware they rust and i like things right i am very happy to replace disks and pads in order to have good brakes when i need them, and for good measure its obvious you were not paying attention in physics class as they woukld have explained that weight when asked to stop moving is transferred to the front and is why front brakes perform about 70-75% of the work load when braking, and for that reason is why discs are always larger at the front than the rear.

We all know brakes work by converting kinetic energy to friction which produces a lot of heat which needs to be dispersed
into the disks and pads. As we cant make the discs bigger or indeed the pads we need to get the heat away better.

The size of the discs is critical as light commercial vehicles always have small wheels - ie 15/16" as opposed to cars with big wheels like 18- 22" wheels which allow for much bigger disks - its a joke to think that my passat has bigger disks than my 4 ton motorhome dont you think ?

 

[L' Hobo]

thanks for the quick preach, i tend to do 3000 miles stints and as brakes are bedded in after 200 miles i think we can say they were. I posted my adventures as many have spoken of poor sprinter brakes and i thought it might be helpful or at least thought provolking to some, I did not invite negative comments but as you seem to like a quick preach i hope it made you feel useful.
I note you have a little van, so none of your extensive experiance would be relevent to a 3.5t chassis with 3,5 t brakes that was extended by autosleeper to 3.8t and futher extended by me via professionals to 4.250 t - brakes still to 3.5 t please note - what would a desk bound transport operator such as yourself advise an ex trunker long distance lorry driver such as me to do if he felt his brakes were a little lacking. Im not sure if i had worked for you, your advice of "drive it around a bit more " would have been appreciated.
I am of course well aware rust sets in during winter and non use but driving it during winter is not my idea of fun any more, been there, sold the t shirt, and my personal life does not allow for it.

I think we have to accept we are not all alike and have differant lives and problems.

So while i am aware they rust and i like things right i am very happy to replace disks and pads in order to have good brakes when i need them, and for good measure its obvious you were not paying attention in physics class as they woukld have explained that weight when asked to stop moving is transferred to the front and is why front brakes perform about 70-75% of the work load when braking, and for that reason is why discs are always larger at the front than the rear.

We all know brakes work by converting kinetic energy to friction which produces a lot of heat which needs to be dispersed
into the disks and pads. As we cant make the discs bigger or indeed the pads we need to get the heat away better.

The size of the discs is critical as light commercial vehicles always have small wheels - ie 15/16" as opposed to cars with big wheels like 18- 22" wheels which allow for much bigger disks - its a joke to think that my passat has bigger disks than my 4 ton motorhome dont you think ?

I love the bit about 'desk bound transport operator '.
After leaving the service and, as the holder of ALL the UK Governments drivers licences. I worked , both here in the UK and also in Sweden as a agency truck test /demonstration driver for a number of National companies including Ford, S&D & Scania in Sweden.

For many years before I expanded my business I was an owner driver/mechanic with, first a transit then, Ford D series, Leyland ?, DAF 2600 and finally a Volvo F88 until Maggie's recession.

During this time, as a holder of an International Operators Licence, I tramped all over Europe, but mainly France, Belgium and Holland as much as the restricted permits at the time would allow, doing much of my own work in partnership with a Belgium National & and a forwarding agent in Zeebrugge and also contract work for Supermarket Delhaize and Transport company VimVos.

During Maggie's recession, I got the opportunity to transfer into Buses & Coaches.
This was not my first choice or what I wanted but it was more financially secure in a troubled time as most Bus work was subsidised by County Councils and Coach work generated a 50% prepayment deposit.

I think that answers you question about my experience and, by the way, I have TWO leisure vehicles, the one I think you are referring to, is a VW T25 Westfalia California and the OTHER is a 3.500kg Ducato Murvi Morello so, as a long standing qualified heavy diesel mechanic, I know a little bit about 3.500 also!

As I have always said about most things, IF it doesn't harm others, especially me, you do what you like.

PS. Read the last post of yours I replied to, you DID invite others opinion!

 

[Guigsy]

The size of the discs is critical as light commercial vehicles always have small wheels - ie 15/16" as opposed to cars with big wheels like 18- 22" wheels which allow for much bigger disks - its a joke to think that my passat has bigger disks than my 4 ton motorhome dont you think ?

It's partly fashion. But there are scientific reasons. A Passat doing 130mph on the Autobahn has more energy than a 4 ton motorhome going 70mph. And it's much more likely to hit a series of tight bends on a country lane in quick succession, leaving less time to disipate the heat. It's only big descents that a motorhome could do with bigger discs.

 

[TheMobileWanderer]

Interesting that some people just make stuff up.

Picking up on a few comments raised in this thread;

1. If any component on a vehicle comes with the 'E' value, denoting it can be sold in the EU (B***it irrelevant),and used on motor vehicles, it can be used without notifying insurers because it complies with the legal requirements.
2. Any vehicle regardless of size, when braking, transfers weight to the front. Simple physics.
3. The old adage; if you don't use it you lose it, is quite apt for a vehicle. None likes to sit around for long periods and the location (garage or seafront, for example) just affects the speed of decay.
4. Rust is not necessarily a bad thing on brakes. Obviously if it affects the performance of moving parts, it's a bad thing. Rust on the non-moving parts, such as the caliper body, is a good thing because rust is much better at dissipating heat than is paint (painted calipers) or bare non-rusted steel as when they're new.
5. Whether air may ingress when adjusting the position of caliper pistons is kind of irrelevant. When brakes are adjusted, they should be bled. That will give information about the condition of the fluid. Brake fluid is more likely to be dangerous (or is it just that the driver is more likely to be caught out for penny-pinching), if it has darkened/dis-coloured than if air in it.

You know that air in the fluid will make the pedal spongey but just because the pedal may feel spongey, that doesn't mean there's air in it. It could be a dodgy servo for example.

Dirty fluid is another ball game completely. Much more potential for danger. Dirty fluid shows no such symptoms straight away or when starting off, for example. However, when it gets hot, and because dirty fluid has a lowered boiling point, it can vapourise. In that situation the pedal will go to the floor with no braking effect at all. Known as vapour lock. Not nice when coming down a hill, needing to stop and there being no braking effect. imo.

Were it mine with a spongey brake pedal, I would take it to a mechanic with a rolling road, or similar, who can do a brake test with computer analysis and a written (computer-generated) report. It can show percentage braking effect per wheel and per 'axle'. If it's outside tolerances, work may need to be done. I like a good bite because it is reassuring but, in reality, the overall braking effect is what matters. There can be good bite immediately before vapour lock takes over.

Unfortunately, it's not possible in a forum, to say what that issue might be, given that if wrong information is given and, if it were followed by a reader, the brakes may fail with unpleasant consequences.

hth.

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[Diabalo]

thanks for the quick preach, i tend to do 3000 miles stints and as brakes are bedded in after 200 miles i think we can say they were. I posted my adventures as many have spoken of poor sprinter brakes and i thought it might be helpful or at least thought provolking to some, I did not invite negative comments but as you seem to like a quick preach i hope it made you feel useful.
I note you have a little van, so none of your extensive experiance would be relevent to a 3.5t chassis with 3,5 t brakes that was extended by autosleeper to 3.8t and futher extended by me via professionals to 4.250 t - brakes still to 3.5 t please note - what would a desk bound transport operator such as yourself advise an ex trunker long distance lorry driver such as me to do if he felt his brakes were a little lacking. Im not sure if i had worked for you, your advice of "drive it around a bit more " would have been appreciated.
I am of course well aware rust sets in during winter and non use but driving it during winter is not my idea of fun any more, been there, sold the t shirt, and my personal life does not allow for it.

I think we have to accept we are not all alike and have differant lives and problems.

So while i am aware they rust and i like things right i am very happy to replace disks and pads in order to have good brakes when i need them, and for good measure its obvious you were not paying attention in physics class as they woukld have explained that weight when asked to stop moving is transferred to the front and is why front brakes perform about 70-75% of the work load when braking, and for that reason is why discs are always larger at the front than the rear.

We all know brakes work by converting kinetic energy to friction which produces a lot of heat which needs to be dispersed
into the disks and pads. As we cant make the discs bigger or indeed the pads we need to get the heat away better.

The size of the discs is critical as light commercial vehicles always have small wheels - ie 15/16" as opposed to cars with big wheels like 18- 22" wheels which allow for much bigger disks - its a joke to think that my passat has bigger disks than my 4 ton motorhome dont you think ?

A bit harsh matey.

 

[Barriesimpson]

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.

No it won't.

 

[Daffy64]

Interesting that some people just make stuff up.

Picking up on a few comments raised in this thread;

1. If any component on a vehicle comes with the 'E' value, denoting it can be sold in the EU (B***it irrelevant),and used on motor vehicles, it can be used without notifying insurers because it complies with the legal requirements.
2. Any vehicle regardless of size, when braking, transfers weight to the front. Simple physics.
3. The old adage; if you don't use it you lose it, is quite apt for a vehicle. None likes to sit around for long periods and the location (garage or seafront, for example) just affects the speed of decay.
4. Rust is not necessarily a bad thing on brakes. Obviously if it affects the performance of moving parts, it's a bad thing. Rust on the non-moving parts, such as the caliper body, is a good thing because rust is much better at dissipating heat than is paint (painted calipers) or bare non-rusted steel as when they're new.
5. Whether air may ingress when adjusting the position of caliper pistons is kind of irrelevant. When brakes are adjusted, they should be bled. That will give information about the condition of the fluid. Brake fluid is more likely to be dangerous (or is it just that the driver is more likely to be caught out for penny-pinching), if it has darkened/dis-coloured than if air in it.

You know that air in the fluid will make the pedal spongey but just because the pedal may feel spongey, that doesn't mean there's air in it. It could be a dodgy servo for example.

Dirty fluid is another ball game completely. Much more potential for danger. Dirty fluid shows no such symptoms straight away or when starting off, for example. However, when it gets hot, and because dirty fluid has a lowered boiling point, it can vapourise. In that situation the pedal will go to the floor with no braking effect at all. Known as vapour lock. Not nice when coming down a hill, needing to stop and there being no braking effect. imo.

Were it mine with a spongey brake pedal, I would take it to a mechanic with a rolling road, or similar, who can do a brake test with computer analysis and a written (computer-generated) report. It can show percentage braking effect per wheel and per 'axle'. If it's outside tolerances, work may need to be done. I like a good bite because it is reassuring but, in reality, the overall braking effect is what matters. There can be good bite immediately before vapour lock takes over.

Unfortunately, it's not possible in a forum, to say what that issue might be, given that if wrong information is given and, if it were followed by a reader, the brakes may fail with unpleasant consequences.

hth.

I disagree with quite a bit of this,

1, if you modify the brakes on your vehicle even with an E marked part, you are getting into a very risky situation, also it is not permissible in most of Europe.

2, it does but commercial vehicles are biased to the rear, this much reduces load transfer to the front.

3, agreed.

4. It depends on the amount of rust, a coating of surface rust is fine and they are designed to cope with it, deep pits caused by serious risk are another thing.

5, air won’t get in when pushing caliper pistons back if the piston is clean, if it isn’t then air is the least of your worries

Disk brakes are self adjusting anyway but regardless Brakes don’t need bleeding every time they’re adjusted providing service recommendations are followed, the same with dirty fluid, change it when required and it’s not going to be a problem.

I have some experience with MB product albeit a while ago and my moneys still on a failing hose to the vacuum pump (assuming they really aren’t performing how they should be)

 

[TheMobileWanderer]

I disagree with quite a bit of this,

1, if you modify the brakes on your vehicle even with an E marked part, you are getting into a very risky situation, also it is not permissible in most of Europe.

2, it does but commercial vehicles are biased to the rear, this much reduces load transfer to the front.

3, agreed.

4. It depends on the amount of rust, a coating of surface rust is fine and they are designed to cope with it, deep pits caused by serious risk are another thing.

5, air won’t get in when pushing caliper pistons back if the piston is clean, if it isn’t then air is the least of your worries

Disk brakes are self adjusting anyway but regardless Brakes don’t need bleeding every time they’re adjusted providing service recommendations are followed, the same with dirty fluid, change it when required and it’s not going to be a problem.

I have some experience with MB product albeit a while ago and my moneys still on a failing hose to the vacuum pump (assuming they really aren’t performing how they should be)

1. In the context of this thread and the issue around using Brembo (for example) instead of Ferodo (or which ever company made the factory-installed pads), that is not modification but simple replacement of the pads. Likewise if done with a caliper as well. So long as it complies with the manufacturers specification and it is permitted to be sold in the UK for use on motor vehicles, all should be well. The 'E' symbol denotes such permission.

2. moot

4. Not sure how deep pits are caused by serious risk. They can lead to increased risk, such as fluid leaking out but the driver will feel that with a pedal that goes easily to the floor when stationary if they haven't noticed their very gradual deterioration over months and years beforehand.

5. Disc brakes are self adjusting as they are used however, when replacing the pads or disc, that is not so. The piston needs to be manually pushed back into the caliper to allow for the extra thickness of new pads - extra thickness compared to that of the old, worn down ones. Changing discs should always involve replacement of pads.

Regarding 'bleeding'; For all the time it takes, a simple bleed should be done. Drain off enough from each front wheel to be able to see what condition it is in. It's pretty difficult to see through flexi-hoses. I suppose it depends on whether the person wants to comply with the minimum for safety or to be as safe as possible.

I don't rely on an MOT test to say whether my vehicle is safe and roadworthy. I maintain it.

Back to the OP and there could be several issues causing the spongey pedal, which is why I recommend the computerised brake test.

 

[Daffy64]

1. In the context of this thread and the issue around using Brembo (for example) instead of Ferodo (or which ever company made the factory-installed pads), that is not modification but simple replacement of the pads. Likewise if done with a caliper as well. So long as it complies with the manufacturers specification and it is permitted to be sold in the UK for use on motor vehicles, all should be well. The 'E' symbol denotes such permission.

2. moot

4. Not sure how deep pits are caused by serious risk. They can lead to increased risk, such as fluid leaking out but the driver will feel that with a pedal that goes easily to the floor when stationary if they haven't noticed their very gradual deterioration over months and years beforehand.

5. Disc brakes are self adjusting as they are used however, when replacing the pads or disc, that is not so. The piston needs to be manually pushed back into the caliper to allow for the extra thickness of new pads - extra thickness compared to that of the old, worn down ones. Changing discs should always involve replacement of pads.

Regarding 'bleeding'; For all the time it takes, a simple bleed should be done. Drain off enough from each front wheel to be able to see what condition it is in. It's pretty difficult to see through flexi-hoses. I suppose it depends on whether the person wants to comply with the minimum for safety or to be as safe as possible.

I don't rely on an MOT test to say whether my vehicle is safe and roadworthy. I maintain it.

Back to the OP and there could be several issues causing the spongey pedal, which is why I recommend the computerised brake test.

1, you were talking about any component that was e marked and not about fitting an approved alternative.
4, a typo, should have said deep pits can be a serious risk rather than cause them. On a Modern (in the last 40 years) linked system the pedal would not go to the floor.

There’s no such thing as a simple bleed on a modern vehicle with ABS.

You clearly think a modern braking system is a simple hydraulic system, trust me it’s not, as for a computerised brake test, it’ll really only tell you that a minimum std has been achieved in terms of drag, bias and performance as there’ll be no info relating to the relationship between performance and pedal pressure and that’s a the issue here as the OP’s vehicle has passed its MOT iirc…

My moneys still on a failing vacuum pump pipe.

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[TheMobileWanderer]

1, you were talking about any component that was e marked and not about fitting an approved alternative.

I thought what I wrote was clear. I hadn't thought that someone might try a set of pads for a mini, on a van. If the parts are designed for a vehicle, whether a pattern part or OEM, then, provided its got an eu number it's a suitable part. If 'pattern', it may not be as functional but it's not illegal or dodgy to use it.

4, On a Modern (in the last 40 years) linked system the pedal would not go to the floor.

ok, so I must have dreamed that event that happened about 3 yrs ago in a four year old car. Dealer and manufacturer were held jointly and severally liable.

There’s no such thing as a simple bleed on a modern vehicle with ABS.

It's not difficult to do but what I actually meant by 'simple bleed' was just that; a drain off of enough to (a) know any air is removed and (b) to have enough fluid removed to see its condition. All that, as opposed to a full bleed/drain down along with replacement.

You clearly think a modern braking system is a simple hydraulic system, trust me it’s not.

If you were actually to day that, you'd be putting words in my mouth.

My moneys still on a failing vacuum pump pipe.

You may be correct but I'd rather not put money on it thank you. I'd rather steer the OP to finding a competent mechanic who'll find the root cause of the issue and fix and reassure him.