MOT parking brake performance

My Rover 220 has failed its mot on poor handbrake performance (7%) what is the minimum for a parking brake ? I have had the car from new in 93 and the handbrake as always been crap, it will lock the wheels when parked and will nearly stall if you try to drive away, but whilst moving it seems to have never had any effect at all. I replaced the pads today , cleaned and greased everything where necessary, adjusted the cable to take up any slack in the cables and its still the same, are rear disks always crap, what can I do to get it through its mot retest ?

Reply to
orbiter
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It must be 16% to pass. I assume from your description, that it has the handbrake built into the calliper. Make sure that the handbrake cables are adjusted such that the lever is able to return fully to the off position, adjusting the cables up to take slack out sometimes prevents this lever fully returning, which in turn stops the self adjusting mechanism inside the calliper working properly. It may be an idea to slacken the cables right off, then go for a drive making lots of fairly sharp footbrake applications, to allow the calliper to adjust itself up, then adjust the cables up so that they just remove the slack in the cables, without pulling them away from their rest position.

Reply to
SimonJ

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Reply to
Chris Whelan

From memory I think it's 14or15%, for a vehicle with a split braking system.

Common for the rear calipers to seize on these. If what you've done hasn't helped it any, then sometimes pumping the caliper pistons out, and winding them back in a couple times helps. Also working the handbrake lever with the pads out can help (make sure the lever also returns against it's stop on the caliper)

If none of that helps, then only solution is new calipers.

Reply to
Moray Cuthill

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Hello Chris,

Interestingly, the particular webpage you have indicated, gives incomplete information: ** % of what? The information on the page in itself, this does not mean anything to the reader.

John

Reply to
John

% braking effiency. All done by dividing the brake readings, by the gross vehicle weight and multiplying by 100. However if the wheels lock, you can disregard having to calculate anything.

Although there is an error in the page layout.

Reply to
Moray Cuthill

There's a note at the bottom of the page explaining it. If the brake manages 16%, it can just hold the car stationary on a 16% hill.

Cheers,

Colin.

Reply to
Colin Stamp
[...]

Yes,, I thought that might have been a "Firefox" thing but I've just checked and it's the same in IE.

Chris

Reply to
Chris Whelan

Thankyou for that I had overdone it with the cable adjustment, the levers on the calllipers are now against the pins and the cable adjusted up as far as possible without moving them away, the wheels lock by hand turning at 6 clicks on the lever. On the road handbrake movement seems excessive with little braking effort at the rear, it is difficult to pull away when stationary with the park brake applied. I can only take it back see what it reads, if the car is unladen will it make any difference because it has alot of stuff in the boot ?

Peter

Reply to
orbiter

No - my ol' P6 Rover with handbrake working on the same pads as the main brakes managed 50%. It would actually lock the rear wheels on the move. So it can be done.

Reply to
Dave Plowman (News)

Now the cables are right, have you tried giving it a few sharp stabs on the footbrake, to try and persuade the calliper to adjust itself up?

The stuff in the boot should make no difference to the handbrake test.

Reply to
SimonJ

They're notorious for the self adjusters failing.

Firstly, try removing the pads and winding the pistons back in, refitting the pads and pumping back up.

Secondly, on the back of the caliper near the handbrake cable is a dust cap. Take that off and there's a small adjuster inside.

Reply to
Conor

I have been out and given the brakes a work out the rear wheels where hot so they are working with the new pads, I jacked up the rear and they rotate free so not sticking on and I cant turn them when the handbrake is on at a reasonanable level with plenty in reserve. So I will take it back for its retest see what it reads now.

Reply to
orbiter

Ihave done this and fitted new pads

The pistons have pumped up and the footbrake is not a problem, what is the purpose of the adjuster is it for the handbrake ?

Reply to
orbiter
16%, 25%, 50%, etc of what.. ?

...of the vehicle's weight. (weight used is unladen weight plus weight of driver, vehicle toolkit & half a tank of fuel)

For vehicles with dual circuit footbrake, a vehicle weighing 1000kg would need a parking brake capable of holding a minimum of 160kg (80kg per wheel).

With single line hydraulics,

1000kg vehicle would require 250kg (125kg per wheel).

Visit the MOT Forum:

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Reply to
NT

Now you mention it, for cars and light commercials you refer to the braking weight chart (or at least you used to before computerisation). I'm not an mot tester so haven't ever needed to bother about calculating brake effiency for cars. For anything over 3500kg, you always use the GVW (which i have to do on a regular basis)

It's kg-f, not kg. Think of it as if the wheel was lifted up of the ground, and a sprung scale pulling vertically down from the circumference of the tyre.

Reply to
Moray Cuthill

Yes. They had to adjust this on mine for the MOT - failed the same as yours.

Reply to
Conor

The footbrake effort.

Reply to
Conor

The DGW (Design Gross Weight) is used for Class VII vehicles, too. Class VII are goods vehicles 3000 - 3500kg DGW.

Reply to
NT

That's still not a percentage of anything though.

Assuming the brake force meter (not to Septics - that's what the word 'meter', spelt like that, should be used for) readings are in Newtons, and the GVW is in kilos, then that is in Newtons per kilogram (N/kg), which if you bugger about with physics enough*, is exactly the same figure as the deceleration that maximum braking force will cause on that mass, in m/s^2.

  • - I can't be arsed to work it out now, but basically gravitional force on earth is 9.81N/kg (i.e. a 1kg mass weight 9.81N), and acceleration due to gravity is 9.81m/s^2, and it's not just coincidence.
Reply to
AstraVanMan

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