MOT failure

[Knucklehead]

Just had my cruiser knocked back for the first time at the MOT. Gutted.

Have no idea how I am going to fix this one.
It failed on Service Brake Efficiency 44% needs >50%.

Never had any issues before so can only think it is all the extra weight that came with the new 35" MT tyres.
Tester reckons could be down to the weight.

Going to swap back the lighter BFG AT/remove the spare for the retest and see how it goes.

Anybody else with larger/heavier tyres on had any issues?

 

[Shayne]

How about changing the fluid .

 

[stumog]

Fluid and pad change. Clean the discs and ask to brake test before you book your retest.

Check for a sticky caliper as well

 

[Knucklehead]

Yeah, new pads in a month ago and all seemed ok with the calipers when fitting them.
Was looking at last years printout and had 68% efficiency.

Only difference this year is the 35" MT which I am thinking might be too much rolling resistance weight for standard calipers and disks on their rolling test.
Think they calculate the efficiency against the weight of the standard vehicle.

I am going to fit the old AT back on and stick in again and see how it looks.
Fails again then could be looking at some expensive replacement calipers & disks. Hope not.

Dave.

 

[StarCruiser]

With the extra radius of the bigger tyres, there is more leverage against the brake disk and pads so easier to turn against the braking force. A bit like not being able to loosen the bolt with a socket wrench where a longer 'breaker bar' undoes it easily.

It should pass with the smaller wheels, but do you really want to be running on the edge of your braking force with the bigger tyres fitted? Not sure how it would be viewed if God forbid you were involved in an accident.

Just a thought that might be worth thinking.

Richard

 

[clivehorridge]

Sorry for the failure KH, disappointing I'm sure.

However, I can't understand the logic of bigger tyres compromising the braking.

Yes Rich, I'm ok with your theory, but brakes would have to be mighty poor to be that badly affected surely?

I run 305/70/16 on aftermarket steels, ok they're not 35s, but they're heavy, yet with a bit of heavy pedal, I can just lock them up.

For sure I wouldn't want to drive any vehicle that you couldn't lock the wheels up on braking. I'm inclined to think there's something wrong with the brakes, a bit of glazing maybe. JMO.

 

[Dave2000]

During the test was it you at the wheel? If so when braking hard did the pedal feel spongy or hard? Even with the bigger wheel you should have been able to lock them. Also look at the balance between the wheels, was one side more powerful than the other? It could be glazed pads but that is more likely on the rear than the front so again look for individual wheel efficiency. Possibly air in the system, sticky pistons in the calliper,

regards

Dave

 

[Knucklehead]

Just had closer look at their printout and brake readings are all over the place compared to previous years:

Brake Effort Service Brake:-
Axle1 Nearside 3.59kN Offside 2.61Kn Imbalance 27%
Axle2 Nearside 3.77Kn Offside 2.69Kn Imbalance 29%
I find it odd they have imbalance on same side. Can't see there could be piston sticky issues front and rear on the same side.

Even the Parking Brake is off which surprises me as a cable/brake shoes nothing to do with pads/disks:
Nearside 3.28kN Offside 2.11Kn

We unfortunately do not have 'MOT Garages' like the mainland.
They are government run centres that you need to pay up front before doing test.
The tester does the brake test but I know using the brakes they do not feel spongy so bit at a loss what needs looked at.

That was why I started thinking the heavy MT tyres could be causing the problem as would take a lot more effort to stop but that wouldn't explain imbalance between sides.

 

[StarCruiser]

With fairly consistent readings I would almost say the brake tester had some sort of fault as the difference on the rear axle is 1.17 on both foot and hand brake but it is slightly less on the front so may not be.

I wondered what it would read with the truck on the tester backwards? Don't even know if possible.

 

[Knucklehead]

Really don't know what has gone on.
Looking at last years print out my imbalance on both axis <5% with 68% efficiency.

The MOT centres basically take the car off you and put through their machines with pass/fail at end.
You have little interaction with the testers and as they do not carry out any garage work there is no feedback to possible causes.

I would have thought with such a large imbalance the car would pull to one side under heavy breaking.
No issues even when I give it the heavy boot from 60mph. Baffled and slightly ****** off.

Dave.

 

[frank rabbets]

If you do not have ABS you could do your own brake test by trying to lock the wheels on tarmac.

Bit hit and miss in UK as the tester has no way of knowing how hard he is pushing the pedal.

Could be your brakes have not been up to temperature for sometime or the pads are not bedded in. If I have not driven mine for some months I blast it in 3rd gear with my left foot on the brake pedal for a few hundred yards and repeat this for a few miles. This really cleans the discs and pads and gets the callipers hot to help free stuck pistons. I'd strongly recommend you bleed the system also. Plenty of drake dust appears . You WILL solve it. It's a basic system.

 

[Sag]

Don't know much about calipers on the 80 but on the 95 mine have been known for the outer lower piston to stick on both sides,with them been 4 pot calipers don't feel them sticking under normal driving,worth a quick strip down for how long it takes and a bit of sand paper to take any shine off the pads.hope you get it sorted.

 

[Dave2000]

As expected mate, the imbalance is the issue. Start by pulling the callipers, put a clamp around one pair of opposing pistons and have someone SLOWLY push the brake pedal, ideally you need to get the pistons out about half way, then push them back in, do this a number of times, then swap the clamp and repeat, be careful not to push the pistons out too far. Do not short cut by levering against the disc with you best screwdriver, you may do more harm than good. Next check the pads are free to move in the holder, manufacturing cut backs, means the guy who used to grind the casting flashing of the pad backing has been sacked, you may need to give them a tidy up with a file to make them move easily also the holes where the pins go through. Now bleed all the brakes, the actual cause of the piston sticking is normally corrosion in the calliper caused by water absorbed by the fluid, water being heavier than the fluid collects in the lowest part of the brake system i.e. the callipers. Do ALL the callipers, it is unusual to see the rear axle effort higher than the front.

Repeat at the rear but also check the hand brake linkage for free movement. Re the brake rollers being out of sync is a real possibility, I was given a warning about my Land Rover Discovery hand brake being out of balance, and asked if perhaps there was some wheel slip/skid, he said no as the machine would detect that, so I took him under the car and showed him the transmission brake, then asked him to explain the differences, he shrugged his shoulders and gave me the pass ticket, I go there two or three times a week with customers cars so thought it better not to push my luck.

regards

Dave

 

[stumog]

I would say there is a problem with the brake tester to be getting readings like that.

How does the cruiser drive do you worry about running in the back of people when driving as I think you would with that set poor results.

Can you take it to another tester?

 

[Dave2000]

I would say there is a problem with the brake tester to be getting readings like that.

Whilst I would concede that imbalance can occur and the rollers have to be within something like a tenth of Kn of each other, those figures indicate the imbalance is out by around....sod my maths.......lots!

regards

Dave

 

[Knucklehead]

Thanks for all the replies fellas. Much appreciated as usual. Greet forum as always.

I am now the proud owner of a new MOT certificate.
And what did I do to achieve such an award??? Bugger all.
I pulled the calipers to check no sticky pistons but all looked good, so put it back together and went for retest - big tyres and all.

Different tester who put me on their HGV machine.
Imbalances back to below 5% with 79% efficiency.

As rightly indicated in a few of your posts, there was obviously a stuff up with their machine last night or maybe the young fella selected the wrong mode.
Not amused so will be putting in official complaint first thing Monday to get my fees back.

Lesson - don't always believe the MOT print outs and if seem ridiculous then argue them there and then.

Dave.

 

[Sag]

Glad to know it's all sorted buddy.

 

[clivehorridge]

Result!

Good luck with your refund!

 

[chadr]

Glad you got it sorted without too much hassle or wallet pain.

On a slight tangent, my Collie (AFAIK) never gets put on the brake test machine at Mot time. Is the 80 in a different category when it comes to the test?

 

[Beau]

Glad you got it sorted without too much hassle or wallet pain.

On a slight tangent, my Collie (AFAIK) never gets put on the brake test machine at Mot time. Is the 80 in a different category when it comes to the test?

I was just going to mention this too. I thought with 4WD or LSD diffs you can't use them on a rolling road. My MOT tester has always taken my cruiser for a short drive with a in car device to measure the breaks.