Lotus Elan

MOT fail, handbrake imbalance

PostPost by: paddy » Thu Mar 03, 2011 9:58 am

I went for the MOT yesterday and got a fail with a significant imbalance in handbrake efficiency. I've been to the same place several times before, and the complaint isn't about the overall inefficiency, but the imbalance side-to-side which is new.

My first thought was oil contamination on one disc but the service brake balance is fine.

I haven't investigated in detail yet, but you can't turn either wheel by hand after putting the handbrake on by a few clicks, although one does come on sooner than the other. I can't see anything impeding the movement of the tree so I don't have any idea what's up at the moment. Maybe the mechanism on one caliper is partly stuck and it needs lubricating.

Any prior experience of a similar issue?

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PostPost by: bcmc33 » Thu Mar 03, 2011 10:22 am

paddy wrote:I went for the MOT yesterday and got a fail with a significant imbalance in handbrake efficiency. I've been to the same place several times before, and the complaint isn't about the overall inefficiency, but the imbalance side-to-side which is new.

My first thought was oil contamination on one disc but the service brake balance is fine.

I haven't investigated in detail yet, but you can't turn either wheel by hand after putting the handbrake on by a few clicks, although one does come on sooner than the other. I can't see anything impeding the movement of the tree so I don't have any idea what's up at the moment. Maybe the mechanism on one caliper is partly stuck and it needs lubricating.

Any prior experience of a similar issue?

Paddy

I guess that's what the adjuster nut is for.
Give the side that appears loose a couple of cliks on the nut.
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PostPost by: GrUmPyBoDgEr » Thu Mar 03, 2011 10:24 am

paddy wrote:I went for the MOT yesterday and got a fail with a significant imbalance in handbrake efficiency. I've been to the same place several times before, and the complaint isn't about the overall inefficiency, but the imbalance side-to-side which is new.

My first thought was oil contamination on one disc but the service brake balance is fine.

I haven't investigated in detail yet, but you can't turn either wheel by hand after putting the handbrake on by a few clicks, although one does come on sooner than the other. I can't see anything impeding the movement of the tree so I don't have any idea what's up at the moment. Maybe the mechanism on one caliper is partly stuck and it needs lubricating.

Any prior experience of a similar issue?

Paddy


Will closing up the pads of the less efficient brake balance it out maybe?
My last MOT showed up a slight problem like that & that's what I intend to try, as like your car everything else is fine.
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PostPost by: gerrym » Thu Mar 03, 2011 12:26 pm

Paddy, are you sure you are not falling victim to over zealous interpretation.

I thought the MOT handbrake rules only covered efficiency and not side to side balance. The rear service brakes for example are tested for side to side balance but will only fail on lack of efficiency.

Last year, in getting rid of my elderly daily driver, I completely rebuild all the rear brakes and had some small issues with this. The MOT man explained all the details at the time.

Tip one, if efficiency is an issue because of tyre slip on the roller, place some heavy weights are in the boot. This does help. Tip 2, install a tandem master cylinder and the required handbrake efficiency pass mark almost halves i.e drops from 25% to 16%

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Last edited by gerrym on Thu Mar 03, 2011 12:40 pm, edited 1 time in total.
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PostPost by: paddy » Thu Mar 03, 2011 12:37 pm

Gerry,

He is a sensible tester who has done the MOTs for a few years and he's definitely not the jobsworth type. I did discuss it with him and commented that the handbrake isn't that good that the best of times, but he reassured he that he did think there was a genuine issue on one side.

Brian,

I had assumed that the tree would compensate to some degree and balance the force across the two sides even if they are not perfectly adjusted - but if the tree doesn't do that it sounds like that's probably the issue.

Thanks all.

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PostPost by: gerrym » Thu Mar 03, 2011 1:00 pm

Paddy, yes the tree will balance the force across the tree on to the rods (it has to because the tree on its own has no bending strength) but what happens to the force thereafter is a different matter, ie will it produce a balanced bracing force on the disk.

Basically you are up against a number of things:- A/ Friction/Wear in the handbrake mechanism due to lack of lubrication and /or wear in the pivots. B/ difference in mechanical advantage caused by the pads being closer or further from the disks and length of the handbrake rods C/ Friction surface differences (pads and disk surface).

If you want to get this right, pull the rear calipers off the car and clean/lubricate the pivot mechanism. You may need to remove the pins and disassemble as well (all the pins should be center drilled and tapped to enable them to be pulled). If you are really scrupulous, change the handbrake pads for new (also degrease and clean the disks)

Once you get the handbrake to a state that you are personally happy with because you have had them apart and know all the components are in a good state of repair, I would be more prepared to argue the "rules". Ie there is no brake balance fail criteria as such for a handbrake. Check out the online Tester's manual.

Good luck
Gerry
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PostPost by: UAB807F » Thu Mar 03, 2011 5:11 pm

Handbrake imbalance, well that was a new one on me as well. So I had a look at the official website (http://www.motinfo.gov.uk/htdocs/m4s03000704.htm) and sure enough, a reason for failure of the handbrake is if one side works and the other doesn't. The reference actually says "little or no effort on a wheel" so if yours does lock both wheels a failure seems a harsh interpretation. After all it's referred to as a "parking brake" these days in the regulations and as has been pointed out, a dual circuit system only needs a 16% efficiency.

But you need a ticket, so it needs adjusting to the tester's acceptance. In this case I'd guess that the pads on one side are significantly "looser" than the other. Thus as the h/brake is applied the tighter side locks up, then the force moved through the h/brake tree swivel joint on the chassis and any further pulling on the lever brings the other side into play. If everything is freely moving I wouldn't have thought that the difference in reaction times was enough to cause a real-world problem providing both sides locked up once it was fully applied, but the first thing to try is to adjust both sides so that the pads are in equally light contact with the disks.

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PostPost by: paddy » Thu Mar 03, 2011 5:39 pm

Thanks for the feedback.

On 2 or so clicks it is definitely the case that one wheel is clearly binding when you turn it by hand, and the other is more or less completely free. So I guess that points to something in the mechanism binding somewhere, or simply being too far out of adjustment.

Thanks again, I'll keep you posted.

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PostPost by: JJDraper » Thu Mar 03, 2011 5:57 pm

I put my +2 to the tester a couple of weeks ago. Their rollers were out of action so he used a mysterious wooden box held on his lap to test the brakes.. Main brakes nearly sent him through the screen. The handbrake had to be tested by pulling it full on from around 20mph - scary thought, but even he was surprised when it passed (he has experience of these handbrakes). With regard to imbalance, add a few clicks adjustment to the side that is down. If you have a reasonable tester, he may allow this to be done there and then, with just enough adjustment to get it to pass.

My tester was more interested in the clearance of the wheels in the wheel arch, with my 14" Minilights, especially at the front where the leading edge of the tyre protrudes slightly on straight ahead.

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PostPost by: Galwaylotus » Thu Mar 03, 2011 8:52 pm

JJDraper wrote:I put my +2 to the tester a couple of weeks ago. Their rollers were out of action so he used a mysterious wooden box ...

It's called a decelerometer and is used when a vehicle can't be tested on the roller brake tester. :wink:
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PostPost by: robertverhey » Thu Mar 03, 2011 10:05 pm

Here in NSW a decelerometer is the only way that brakes (service and parking) are tested. To quote from RTA bulletin: "The test of brake deceleration capability is taken from a nominal 30 km/hr for the service braking system and 15 km/hr for the emergency (parking) brake system". In other words they hit the brakes at 30km/hr and the decelerometer prints out a reading.
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PostPost by: john.p.clegg » Thu Mar 03, 2011 10:13 pm

Paddy

I just recently passed my MOT,it'a a long story and I'm not into that but to cut it short the MOT centre was passing on its business to other MOT centres,the Plus2 passed,but when I got it back,gave it a wash and ten minutes later I found it in the middle of the road....it seems that the travel between the MOT centres was done by some dipstick who didn't know how to release the handbrake....anyway,a few clicks later and it was as good as new...better really as I had replace the tree for a home-made copy of the later tree...but back to your problem,any inbalance needs the tree and onward stripping and lubricating.

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PostPost by: types26/36 » Thu Mar 03, 2011 10:45 pm

Galwaylotus wrote:It's called a decelerometer and is used when a vehicle can't be tested on the roller brake tester. :wink:


The Decelerometer ....Oh yes, back in the late 60's I used to do MOT's and we had this heavy wooden box that contained this round device, if I remember correctly we would set it to level, set to zero, and at a given speed slam on the brakes, take the reading then repeat on the handbrake.
Well it read in % but it was not unusual for it to go past 100% so I suppose theoretically we had stopped and started going backwards...........well that never happened :lol:
Seriously though it was a very crude device and you could make it read what you wanted....surely times have moved on and I havent seen one in years.
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PostPost by: cal44 » Thu Mar 03, 2011 11:00 pm

Enemy bombers killing people on buses and trains and the government is focusing on hand brakes? WTH! Sounds like things are upside down...................
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PostPost by: robertverhey » Fri Mar 04, 2011 6:16 am

Well.....statistically I'm probably more likely to get wiped out by some fool whose brakes fail due to lack of maintenance than I am by terrorist attack, so mot and pink slip. (as we call it) are just fine with me!
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