letting gravity bleed the brakes

[xpress]

hi there. i have a situation where i have bled the brakes, i am very close to the figures for passing the rolling road test. the service brake efficiency pass mark is on or over 50% (pre jan 1968 it was 40% even if the car is the same! so after this date they moved the pass mark to 50%). i have new fresh fluid in there, and have bled already, but there might be a bit of sponginess in there and it could be the difference between a few percent. i was thinking about what bmc has said "time immemorial" about opening up the bleed screws and

letting gravity do the rest and
instead of fully bleeding again with ezibleed!

to try this out,

1. how many half turns should i open up all the bleed screws so that gravity will push any residual air out?
2. how long should i leave the bleed screws open? could i go in the garage, couple of half turns on the bleed screw, leave it overnight and then nip them up, check the master cylinder and top up and hey presto, air out of the brake lines or should i leave for a couple of days?

[bmcecosse]

I just do one at a time - half a turn - and tube into jar of fluid. But your brakes should be FAR ahead of 50% efficiency. They should be able to lock the wheels which is surely 100%!! There is something very wrong. Not heard of 40% pass for pre 1968 - where are you getting that ??

[xpress]

link here:

http://www.motinfo.gov.uk/htdocs/m4s03001001.htm

Vehicles with 3 wheels with a service brake operating on ALL wheels and a parking brake operating on at least one wheel which were first used:
i) before 1 January 1968 ** 40% 25% 16%
ii) on or after 1 January 1968 ** 50% 25% 16%
** First figure is SERVICE BRAKE, then: Vehicle with a single line braking system, and: Vehicle with a split (dual) braking system.

bmc, i think the efficiency is more than the wheels locking but i am not sure what it is yet, but i am trying to find out, if anyone else can let us know then please reply to thread!

[PSL184]

My MOT man won't pass my car unless he can take the car out and lock the fronts with the foot brake and the rears with the hand brake. Even then it has to pull up straight.....

[xpress]

http://www.ukmot.com/3-8.asp

8.1 Brake Efficiency
Total up the braking effort recorded from all the wheels of the vehicle when the service brake is applied. Total up the braking effort recorded from the appropriate wheels when the parking brake is applied. Calculate the service brake and the parking brake percentage efficiencies by following the procedure detailed below according to the class of vehicle tested

Class III and IV Vehicles
Determine the weight of the vehicle from the current Brake Data Chart (the data includes an element of 140kg or 300lbs for the weight of the driver, fuel, tools, etc) Calculate the service brake percentage efficiency by dividing the total brake effort achieved when the service brake is applied by the vehicle weight and then multiplying the result by 100,ie Total brake effort x 100 = % Efficiency Vehicle Weight Calculate the parking brake percentage efficiency by dividing the total brake effort achieved when the parking brake is applied by the vehicle weight and then multiplying the result by 100, as above.

[xpress]

PSL, I don't know what it is but out of 3 or 4 testers I have spoken to, they all want to just put it on the rolling road, (might try and find out what weight they used on the computer when they did the test).

my fronts lock and it pulls up nice and straight. but they aren't keen on testing them any other way than rolling stones. (erm, rolling road!) remember, efficiency depends on kerbside weight, can they weigh the car, or do they have to put in the weight, and also, do they have a setting for morris minors?! highly unlikely! it might be worth thinking about taking the car unladen with spare radiators, gearboxes, clutch plates in the back! lol. what's the unladen kerbside weight of the morris two door saloon? remember weight is important due to stopping forces.

[xpress]

dual line braking system - refers to the morris parking brake
service brake - main braking system.

[bmcecosse]

The critical thing is the weight - they need to enter the correct figure. Express - you say above '3 wheels' - but a Minor has 4 ?? It can't do better than lock the wheels - and of course the rollers are ribbed and designed to grip well. They do have the option to use a Tapley Meter on the road - especially if they don't have a weight figure ?
The fact remains - they should lock the wheels at 20 mph on a dry road - do they ?
Single!

[xpress]

bmc, this is why i am dubious as to the test. i will find out tomorrow what weight has been put in that computer for the last mot. at 20mph the front wheels skid and not to one side either! i agree, that should be 100% efficient but i guess it takes into account all four wheels summed up and then multiplied. the quote about the three wheels, came from an mot testers forum. nobody around here seems to know or care about a tapley meter!

[xpress]

they can probably get the kerb weight off the v5 at test time, is that right?

[bmcecosse]

The Workshop Manual tells us the 2 door is 1662 lbs, the 4 door 1748 lbs, the convertible 1656 lbs and the traveller 1776 lbs. All 'kerbside' weight.

[xpress]

thanks for that, will check the weight on the computer tomorrow and see if it's right!

[PSL184]

I think from memory the chart at my MOT station lists the traveeler at around 840kgs which is the weight that should be entered if using the rollers. The guy who does mine is more sympathetic and does it on the road with the tapley but is only really happy if he can lock the wheels as I said above. If you can find an old country garage that's been around a few years you usually find more knowledgeable ? testers.....

[rayofleamington]

mine usesa Tapley meter - they are not obliged to use the rollers for efficiency test as the Minor's weight isn't listed in VOSA system (therefore looking it up on a chart may be sensible but it's not "official").

If you can lock the fronts up, then you won't get a significant improvement by bleeding. The Minor system is well known for not being able to remove much air by gravity bleeding as the reservoir is too low and therefore you can't get enough flow to move the air from high points. People get the best results by using pressure fill systems, however even these can struggle to bleed the rear cylinders if they are full of air - the rear cyclinder does not have a bleed, as the bleed is on the pipe. To get the air out they can be stroked (piston moved in and out) to dislogde the air back to the pipe.

[xpress]

i just spoke to my tester, he said they take the weight off the v5 so that's cleared up.

the park brake at 15%, with some new cables or washers to take up some slack, will sort that out to 25%+ for a pass.

he said that they can adjust the footbrake and it should pass, to get efficiency up from 45% to 50%+

i am pretty sure if the tester jams on the brakes a bit harder, (he might not be used to doing this since everything is servo assisted/abs nowadays), i would think it will pass.

however, can anyone concur with adjusting the footbrake? i thought you can only adjust at the wheels, and back off one notch? is there any way to adjust the footbrake?

[MarkyB]

He probably needs to push harder as you say.

If the shoes are new they need a little time and miles to bed in.

[les]

The 'footbrake' has an adjustment, but once set correctly should not be touched again, I think you are getting too bogged down with all this data. As long as you present the car with a firm pedal and the car stops evenly you will be ok. I'm sure most folk haven't the faintest Idea of the ins and outs of the brake percentages etc, me included, but still manage to get an mot cert!

[bmcecosse]

If the parking brake is only 15% - it''s going to need a bit more than some 'washers' - the levers must be seized and/or the shoes are worn or contaminated with oil. Again - it should lock both the rear wheels on a dry road at 20 mph. I think when he says he will 'adjust' the brakes - he means he will 'massage' it through ! No doubt they will charge you something for the 'adjustment'......

[xpress]

bmc, shoes are good, not contaminated, they're dry and i have seen the levers move with the cables, they move fine. it's just that you have to lift the handbrake up quite a bit, i expect that he wasn't interested in lifting the handbrake about six clicks and pressing a bit harder on the footbrake at the time lol.

[charlie_morris_minor]

bmc, shoes are good, not contaminated, they're dry and i have seen the levers move with the cables, they move fine. it's just that you have to lift the handbrake up quite a bit, i expect that he wasn't interested in lifting the handbrake about six clicks and pressing a bit harder on the footbrake at the time lol.

have you readjusted the shoes having driven the car? (sorry if that has been covered before)

have you turned the nuts a few turns on the handbrake cable? if you can not turn them any more it is time for a new set of cables or fit a few small washers between the nut and the handbrake levers?