Brake lagging in operation

ht
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Brake lagging in operation Nov 13, 2020 16:08:29 GMT 1 spinky likes this

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Post by ht on Nov 13, 2020 16:08:29 GMT 1

A problem I’m seeing a lot of lately seems to stem from stuck brake pads or seized slides as a result of poor maintenance and/or infrequent use causing the brake components to become restricted in their movement.
restriction is a major cause of lag and can be awkward to judge in many or most cases where this is assessed from visual appraisal alone although clues may be there.
At what point during a roller brake test would an assessment of brake lagging in operation result in a fail on a front axle where this problem can be seen from the readings produced.
I use over 25% across the front axle as a benchmark to call this a fail if lag is measured to this degree
does anyone use different criteria to assess lag during brake increase or decrease and if so what in your experience would that be and where would you find information in the manual about this assessment of lag.

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mike617 AE/Manager/Owner owner ae tester Posts: 1,006 Class tested: 4 Last Online: Apr 18, 2024 17:17:24 GMT 1 Likes: 498	Brake lagging in operation Nov 13, 2020 18:19:25 GMT 1 Dynamo likes this Back to Top Quote Select Post Deselect Post Link to Post Back to Top Post by mike617 on Nov 13, 2020 18:19:25 GMT 1 If it is lagging in operation would you not fail it on imbalance

rocket AE/Manager/Owner Posts: 3,429 Class tested: 4 Last Online: Apr 18, 2024 21:43:05 GMT 1 Likes: 1,043	Brake lagging in operation Nov 13, 2020 19:57:38 GMT 1 Back to Top Quote Select Post Deselect Post Link to Post Back to Top Post by rocket on Nov 13, 2020 19:57:38 GMT 1 I've had a couple this week binding on one wheel through lack of use I only fail if it shows on the RBT

ht
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Brake lagging in operation Nov 13, 2020 20:11:54 GMT 1

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Post by ht on Nov 13, 2020 20:11:54 GMT 1

Nov 13, 2020 18:19:25 GMT 1 mike617 said:

If it is lagging in operation would you not fail it on imbalance

Imbalance is measured at maximum braking effort, brake lagging is the rate of increase/decrease between each steered wheel in this instance for which I seek opinions . I fully expected your answer to factor in replies to this question and I doubt you will be the only one to mention this. Thank you for taking the time to reply, can you tell me how do you measure lag if it is seen to exist during increase and decrease and decide if it’s excessive ?

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ht
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Brake lagging in operation Nov 13, 2020 20:20:06 GMT 1

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Post by ht on Nov 13, 2020 20:20:06 GMT 1

Nov 13, 2020 19:57:38 GMT 1 rocket said:

I've had a couple this week binding on one wheel through lack of use I only fail if it shows on the RBT

A road test is permitted , sometimes it can be used to form an opinion also, although a RBT is the best way to determine a reliable measured calculation for brake lag. Bind does not form part of the question though in this instance.

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Brake lagging in operation Nov 13, 2020 20:50:03 GMT 1

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Post by Dynamo on Nov 13, 2020 20:50:03 GMT 1

I'd be inclined to work with the following information...

The braking effort from any wheel is less than 70% of the maximum effort recorded from the other wheel on the same axle. or,

The braking effort from any wheel is less than 50% of the maximum effort recorded from the other wheel on a steered axle, and

The Brakes imbalance across an axle is such that it is greater than 30%
, although this figure does not seem to be mentioned in the regulations as I can find at the moment, but using the above percentages creating a mathematical model 30% is the maximum specification before a Major is issued.

You can't "unbreak" the broken,you can only break the unbroken to break the break of the unbroken, for me, you cannot unbreak me, for I am already broken,so you have no need to break the break because I am not unbroken.

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Brake lagging in operation Nov 13, 2020 21:12:38 GMT 1

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Post by rocket on Nov 13, 2020 21:12:38 GMT 1

Nov 13, 2020 20:20:06 GMT 1 ht said:

Nov 13, 2020 19:57:38 GMT 1 rocket said:

I've had a couple this week binding on one wheel through lack of use I only fail if it shows on the RBT

A road test is permitted , sometimes it can be used to form an opinion also, although a RBT is the best way to determine a reliable measured calculation for brake lag. Bind does not form part of the question though in this instance.

Transmission drag on a 4×4 is a different matter

ht
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Brake lagging in operation Nov 13, 2020 21:20:34 GMT 1

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Post by ht on Nov 13, 2020 21:20:34 GMT 1

Nov 13, 2020 20:50:03 GMT 1 Dynamo said:

I'd be inclined to work with the following information...

The braking effort from any wheel is less than 70% of the maximum effort recorded from the other wheel on the same axle. or,

The braking effort from any wheel is less than 50% of the maximum effort recorded from the other wheel on a steered axle, and

The Brakes imbalance across an axle is such that it is greater than 30%
, although this figure does not seem to be mentioned in the regulations as I can find at the moment, but using the above percentages creating a mathematical model 30% is the maximum specification before a Major is issued.

Your examples only refer to the readings obtained at maximum effort and would be correct if I was asking that question,

I am asking about lag which is a different fault that can cause a vehicle to veer to one side before reaching maximum braking effort and which is also classed as a major defect.

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Brake lagging in operation Nov 13, 2020 21:25:38 GMT 1

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Post by ht on Nov 13, 2020 21:25:38 GMT 1

Nov 13, 2020 21:12:38 GMT 1 rocket said:

Nov 13, 2020 20:20:06 GMT 1 ht said:

A road test is permitted , sometimes it can be used to form an opinion also, although a RBT is the best way to determine a reliable measured calculation for brake lag. Bind does not form part of the question though in this instance.

Transmission drag on a 4×4 is a different matter

Entirely. 🤔

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Brake lagging in operation Nov 13, 2020 21:31:22 GMT 1 mike617 likes this

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Post by Dynamo on Nov 13, 2020 21:31:22 GMT 1

Nov 13, 2020 21:20:34 GMT 1 ht said:

Nov 13, 2020 20:50:03 GMT 1 Dynamo said:

I'd be inclined to work with the following information...

The braking effort from any wheel is less than 70% of the maximum effort recorded from the other wheel on the same axle. or,

The braking effort from any wheel is less than 50% of the maximum effort recorded from the other wheel on a steered axle, and

The Brakes imbalance across an axle is such that it is greater than 30%
, although this figure does not seem to be mentioned in the regulations as I can find at the moment, but using the above percentages creating a mathematical model 30% is the maximum specification before a Major is issued.

Your examples only refer to the readings obtained at maximum effort and would be correct if I was asking that question,

I am asking about lag which is a different fault that can cause a vehicle to veer to one side before reaching maximum braking effort and which is also classed as a major defect.

I don't think the example is wrong, I think it is down to the individual to understand correctly what the wording in each sentence is actually pointing out, i.e.

The braking effort from any wheel is less than 70% of the maximum effort recorded from the other wheel on the same axle

That reads to me as saying that if I have a brake recording a maximum effort and the remaining brake on the same axle is 70% less in effort, then that brake which is recording 70% less in effort is lagging in operation.

To me it's common sense knowing that each wheel brake on an axle must perform through the same working stroke and and achieve the same efforts within the guidelines above to ensure that the vehicle is safe to drive, and will slow down and stop without veering off to one side.

You can't "unbreak" the broken,you can only break the unbroken to break the break of the unbroken, for me, you cannot unbreak me, for I am already broken,so you have no need to break the break because I am not unbroken.

conker AE/Manager/Owner Posts: 394 Class tested: 4 Last Online: Apr 18, 2024 23:02:38 GMT 1 Likes: 154	Brake lagging in operation Nov 13, 2020 22:34:21 GMT 1 Back to Top Quote Select Post Deselect Post Link to Post Back to Top Post by conker on Nov 13, 2020 22:34:21 GMT 1 The way I look at it is if the difference is greater than 40 kg then it is lagging excessively.

Dynamo MOT tester He who is without oil shall throw the first Rod. See the book of Compression's 8.7.1 Posts: 4,298 Class tested: 4 Last Online: Apr 29, 2017 15:36:01 GMT 1 Likes: 1,309	Brake lagging in operation Nov 13, 2020 23:56:22 GMT 1 Back to Top Quote Select Post Deselect Post Link to Post Back to Top Post by Dynamo on Nov 13, 2020 23:56:22 GMT 1 But what makes 40 kg significant?
	You can't "unbreak" the broken,you can only break the unbroken to break the break of the unbroken, for me, you cannot unbreak me, for I am already broken,so you have no need to break the break because I am not unbroken.

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Brake lagging in operation Nov 14, 2020 1:55:29 GMT 1 ht likes this

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Post by baldrick on Nov 14, 2020 1:55:29 GMT 1

Use your judgement as an experienced 'vehicle technician' .... If the readings don't look right do they have the 'wow factor' ? Irf the readings suggest to you that is is likely to be unsafe should you need to do a road test than fail it .

Ever had a Corsa with a shagged out ABS pump in the rollers ? Try driving it up the road and keep it in a straight line as you apply the anchors .
In the rollers they work ok individually but the pedal is hard to press despite the servo working test ok . Roll them together then the nsf and osr are usually slow to get the reading up to the opposing side .
First one I encountered nearly threw me though a fence on the way up to the carpark . Customer hadn't even noticed there was anything wrong with it .

Last Edit: Nov 14, 2020 2:02:50 GMT 1 by baldrick -

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Brake lagging in operation Nov 14, 2020 8:05:01 GMT 1

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Post by ht on Nov 14, 2020 8:05:01 GMT 1

Nov 14, 2020 1:55:29 GMT 1 baldrick said:

Use your judgement as an experienced 'vehicle technician' .... If the readings don't look right do they have the 'wow factor' ? Irf the readings suggest to you that is is likely to be unsafe should you need to do a road test than fail it .

Ever had a Corsa with a shagged out ABS pump in the rollers ? Try driving it up the road and keep it in a straight line as you apply the anchors .
In the rollers they work ok individually but the pedal is hard to press despite the servo working test ok . Roll them together then the nsf and osr are usually slow to get the reading up to the opposing side .
First one I encountered nearly threw me though a fence on the way up to the carpark . Customer hadn't even noticed there was anything wrong with it .

The issue with the Corsa results in no effort at all to the affected brake, there would be nothing worse as the lag in operation would be 100% with the difference at maximum effort also 100%. Certainly Wow factor but greater than the >25% that I use as a benchmark to call a major fault.

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Brake lagging in operation Nov 14, 2020 8:36:48 GMT 1

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Post by rocket on Nov 14, 2020 8:36:48 GMT 1

Nov 14, 2020 8:05:01 GMT 1 ht said:

Nov 14, 2020 1:55:29 GMT 1 baldrick said:

Use your judgement as an experienced 'vehicle technician' .... If the readings don't look right do they have the 'wow factor' ? Irf the readings suggest to you that is is likely to be unsafe should you need to do a road test than fail it .

Ever had a Corsa with a shagged out ABS pump in the rollers ? Try driving it up the road and keep it in a straight line as you apply the anchors .
In the rollers they work ok individually but the pedal is hard to press despite the servo working test ok . Roll them together then the nsf and osr are usually slow to get the reading up to the opposing side .
First one I encountered nearly threw me though a fence on the way up to the carpark . Customer hadn't even noticed there was anything wrong with it .

The issue with the Corsa results in no effort at all to the affected brake, there would be nothing worse as the lag in operation would be 100% with the difference at maximum effort also 100%. Certainly Wow factor but greater than the >25% that I use as a benchmark to call a major fault.

Ive had a corsa d with 3 lock outs on every wheel bar no effort on the NSF wheel I was un aware of this problem until I posted a query

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Brake lagging in operation Nov 14, 2020 9:20:17 GMT 1

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Post by castrolrob on Nov 14, 2020 9:20:17 GMT 1

Nov 14, 2020 1:55:29 GMT 1 baldrick said:

Use your judgement as an experienced 'vehicle technician' .... If the readings don't look right do they have the 'wow factor' ? Irf the readings suggest to you that is is likely to be unsafe should you need to do a road test than fail it .

Ever had a Corsa with a shagged out ABS pump in the rollers ? Try driving it up the road and keep it in a straight line as you apply the anchors .
In the rollers they work ok individually but the pedal is hard to press despite the servo working test ok . Roll them together then the nsf and osr are usually slow to get the reading up to the opposing side .
First one I encountered nearly threw me though a fence on the way up to the carpark . Customer hadn't even noticed there was anything wrong with it .

yeah particularly in the wet,summa them the working brake is locking out just as the other side starts to come up,drive down road,brake,fooks off to one side and the abs throws in cos one front is all thats stopping it,the other side now comes up and fooks you off the other way,both fronts now locked/abs at which point the rears are all thats left and almost immediately do the same-lock/abs on-utterly lethal and eerily similar to losing it on black ice.still cant work out how theyve never been recalled.imbalance/lag?when one side hits 200 and the others on 100(or worse) in the rollers i consider that a significant lag and am perfectly capable of judging it as such.one side doubling its buddys efforts is pretty clear for me.other opinions are available....

mike617 AE/Manager/Owner owner ae tester Posts: 1,006 Class tested: 4 Last Online: Apr 18, 2024 17:17:24 GMT 1 Likes: 498	Brake lagging in operation Nov 14, 2020 9:46:16 GMT 1 Back to Top Quote Select Post Deselect Post Link to Post Back to Top Post by mike617 on Nov 14, 2020 9:46:16 GMT 1 Lag is the time the brake pedal is applied and the system operates on air brake systems

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Brake lagging in operation Nov 14, 2020 10:49:25 GMT 1

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Post by castrolrob on Nov 14, 2020 10:49:25 GMT 1

Nov 14, 2020 9:46:16 GMT 1 mike617 said:

Lag is the time the brake pedal is applied and the system operates on air brake systems

stand to be corrected but i dont recall the guide/rfr whatever being restricted to air,its just an rfr,also seem to recall us getting told via matters of testing /sn or summat that it was the rfr to use for major lag/imbalance.like i said cud be wrong.make the system work for you remember.....

mike617 AE/Manager/Owner owner ae tester Posts: 1,006 Class tested: 4 Last Online: Apr 18, 2024 17:17:24 GMT 1 Likes: 498	Brake lagging in operation Nov 14, 2020 12:53:04 GMT 1 Back to Top Quote Select Post Deselect Post Link to Post Back to Top Post by mike617 on Nov 14, 2020 12:53:04 GMT 1 My interpretation is hydraulic fluid cant compress air systems can compress and lag is the time for the air brakes to start operating maybe stealth would like to educate us on this one.

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Brake lagging in operation Nov 14, 2020 13:53:34 GMT 1 via mobile

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Post by aylesburyjock on Nov 14, 2020 13:53:34 GMT 1

Nov 14, 2020 12:53:04 GMT 1 mike617 said:

My interpretation is hydraulic fluid cant compress air systems can compress and lag is the time for the air brakes to start operating maybe stealth would like to educate us on this one.

Correct, but the lag hit is talking about is not from the compression of the fluid, but a sticking pad causing requiring more effort to move it than the other side. Difficult to distinguish a difference between lag and imbalance for this scenario. Another idea to throw into the mix - a spongy pedal meaning alag between the time you depress the pedal and when the braking effort starts. No imbalance.

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