I received an advisory on my MOT that the brake efficiency (service brake) was low (58%). Looking at how this is tested 58% seems slightly worrying...
The brakes have never been the greatest (standard fiesta behaviour) but recently I have been noticing that the braking is a little variable: sometimes when I press the pedal it feels a little soft and the braking is not as good as it should be (but adequate for normal stopping), releasing the pedal and reapplying normally gives a better result. There's also a bit of juddering when braking hard (although this could just be a bit of run-out on the discs as they're not vented and have a tendency to warp).
Searching through the back-room posts I'm coming to the conclusion that the master cylinder could be at fault, especially as I didn't see the advice not to fully depress the pedal whilst bleeding the brakes (which I did when I replaced the flexible hoses) so I may have damaged the seals.
The discs and pads were changed just over a year ago and the rear brakes (drums, shoes and cylinders) were all changed about 2.5 years ago. The minimum pad and thicknesses specified for the MOT are very similar to those specified for normal service in the haynes manual so I"m guessing it's not just an issue of changing the pads. The fluid was changed and the entire system bled when the flexible hoses were changed (less than a year ago).
What's the best way of diagnosing the cause of low braking efficiency and/or any potential fault in the master cylinder?
Cheers,
G
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It's a thousand times more likely that the calipers or wheel cylinders depending upon whether it's front or rear that's at issue are beginning to seize up.
Check and if necessary replace them - using good quality pads and shoes is also worthwhile.
I expect that the spongy pedal is because when the system was last worked on, all the air wasn't bled out properly. Is the system fluid tight?, or do you need to keep topping it up? If you need to keep topping it up, there's an underlying problem that needs sorting ASAP.
If you aren't experienced or confident with working on brakes, it might be better left to a garage to sort out.
Number_Cruncher
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STANDARD FIESTA BEHAVIOUR!!! I've owned numerous Fiestas(and Ka's-same brakes) and have never had the slghtest concern on any of them.Never had an MoT advisory either.
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ditto jc2, my mk3 can stop on a sixpence (2 1/2 new pence)
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Check the silly plastic pipe that goes into the inlet manifold is tight, it goes to the servo.
As said check for sticky pistons in calipots and rear cylinders
Try a branded make of new front pads as these go off either due to unuse or overuse
de-glaze the rear shoes and drums with some 80 grit.
If the brakes are set up correctly and everything is tickety boo the pedal and handbrake can be up with the best on a mk-us 3 so no need to stand for second best
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The system is fluid tight, I've had the car nearly 4 years and never had to top up the brake fluid. I've checked the servo pipe connections and they're all fine.
I'd discounted the servo as a potential source of error as the issue is not that the pedal needs excessive force to brake but that a given level of pedal depression doesn't seem to give the equivalent level of deceleration.
I spoke to the garage again today and they gave me a breakdown of the braking forces on all of the wheels. Both the fronts are around 250 which the guy said was fairly standard, the rears however, both came in at around 60ish which he said was low. He reckoned a new set of shoes would probably fix the problem.
What brand of pads and shoes would you guys recommend? (I'd been thinking about putting a better set of pads on the front as I'm sure this will help the braking performance anyway and its not an area worth skimping on)
I can check the pistons in the front calipers when I change the pads.
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if you've had it four years and never touched the brake fluid this might be a good opportunity to replace it at the same time. Go for a good name, I put pads from BrakeWorld on once and while they stopped the car I reckon they're a bit hard.
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hi
have you ajusted the rear brakes in 2.5 years it sounds like rear brakes req ajusting
my self i would have the rear brakes down
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maybe a change of brake fluid might help as it is hygroscopic , thus reducing its efficiency because any water in the system reduces its hydraulic potential
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As mentioned in the first post, the fluid was changed less than a year ago. The rear brakes are self-adjusting on the mk3 fiesta but it might be worth me checking that the self-adjusters are correctly functioning.
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The rear brakes are self-adjusting on the mk3 fiesta
>>>>>>>>>>
>>>>>>>>>>> ha ha ha an old ford where the adjusters work as designed..........i wish
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I have the exact same problem with spongy brakes on a 1.1 HCS engine Mk3 Fiesta, the last of the Mk3s - 1995/96. They changed the master cylinders in 94 so later cars (94/5/6) use a different one to 91 to 94.
Very spongy brake pedal, rear brakes just had new shoes and cylinders are ok. Perfectly OK on MoT but the pedal goes down a long way and bleeding does not help. Cannot get a repair kit for this cylinder so it may have to be a new one. reluctantly (£117).
Can someone advise what exactly was the advice not to push pedal to floor when bleeding?? Why not? I've looked after this car for years and always used pressure bleeding as far as I can remember. The sponginess seems to be getting worse. New pads and shoes make no difference - needed them anyway. Calipers OK, MoT brake pressures 100% ok. Just spongy brakes and a LONG way down before anything happens..
Edited by paula on 20/12/2007 at 22:02
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take back wheels off ,drop the jack to the floor so the rear axle is as low as you can get it then gravity bleed the rear cylinders one at a time
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