odd brake problem

Mk4 Fiesta, 1998. 1.25l Petrol 5dr Ghia model. No ABS.

Failed MOT on "little or no braking effort" on both rear brakes. Handbrake only working at 58% efficiency.

Tester thought rear wheel cylinders had seized so replaced them. No change. There appears to be no fluid pressure reaching the rear wheels. That garage says this is beyond their skills now.

Any ideas? Or a recommendation for a garage near Oxford that could do further investigation? I can't really drive the car other than carefully to garages now I know that the rear brakes are defective.

Front brakes are both working perfectly and the brake fluid was changed (along with the rear cylinders) in March 2008; 10,000 miles ago.

All suggestions greatly appreciated as we're a bit stumped here!

Thanks,

Tony

Reply to
Tony Brett
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I am sure that any competent garage will be able to fix it, my guess is that air got into the system when the cylinders were changed before and the rear brakes have not worked properly since. Under normal driving most drivers would not know whether the rears work or not, they would miss the fronts but not the rear.

If it came into me the first thing I would do would be to blow some fresh fluid through the system and get any air out. If there is then no action from the rear brakes (very unlikely) then the master cylinder will be the next suspect. Fiestas usually have brake limiting valves on the master cylinder (little cylinder like a sparklets CO2 cartridge) it is possible but highly unlikely for those to fail.

I think the fault is something very silly.

Reply to
Mrcheerful

Well ATS certainly did change the brake fluid when they changed the brake cylinders. I hope I haven't just done the last 10,000 miles with no rear brakes. I am never heavy on the brakes so you're right in saying that I probably wouldn't have missed them.

Wouldn't the garage that just changed the cylinders again and done a proper bleed of the brakes?

Tony

Reply to
Tony Brett

If they can't diagnose the fault then no, they are probably not capable of an effective brake bleed. We are talking about a simple vehicle here, not a Veyron or a Citroen.

Reply to
Mrcheerful

Indeed! That's what worries me.

Tony

Reply to
Tony Brett

Is there a balance valve feeding the rear brakes? Quite common with a disc drum setup - to prevent the rears locking first. That could have failed in some way. I assume a visual inspection of the pipes doesn't show one crushed flat? ;-)

Reply to
Dave Plowman (News)

If they're testing the pressure with the back on axle stands then it's working & doing it's job.

Reply to
Duncan Wood

you sure you have that right as you say handbrake only working at 58% efficency ? it only needs to meet 16% ! & the service brake (footbrake) 50%. shame you hav'nt got all 4 brake readings,they only get written down on the vt 40 & then inputed into the computer which then works out the fail/pass criteria, before the computer we had to work it out by hand (calculator).

brake efficiency table

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Fiestas do tend to struggle when it comes to rear footbrake readings, what tends to happen they just scrape through thus becoming a pass/advise.

carrying on from Mr C's post about the fiestas usually having brake limiting valves if they arnt located on the master cyl end, you should find them at the rear where the brake pipes meet the flexi hose.

id also be worried that they cant diagnose a fault on something so simple as this !!

Reply to
reg

but this is an mot station, they must have rollers or the equivalent

Reply to
Mrcheerful

I dunno this vehicle - but one I owned used a system similar to a seatbelt lock - worked on deceleration.

Reply to
Dave Plowman (News)

I had a similar problem man years ago on an old Mk1 Fiesta. After many flushes, bleeds, cylinder changes, adjuster checks and frustration I suddenly realized that a previous owner had connected the brake pipes incorrectly: From master cylinder to top of wheel cylinder, then from bottom of that wheel cylinder to bottom of opposite cylinder. Of course the first cylinder could not be bled properly. After swapping over the in an out brake pipes problem solved; brakes bled well and adjuster functioned correctly.

Just thought you mentioned cylinder change, could the same have happened? Lenny

Reply to
LennyK

late fiestas have a pipe to each side and of course a bleed nipple each side

Reply to
Mrcheerful

In which case how do they know there's no pressure? & if the valves stuck shut you can't bleed them. Thereagain if they can't work it out with the car there then I'd be suspicious of anything they told you.

Reply to
Duncan Wood

that was what I said! AFAIK late fiestas only have limiting valves on the master cylinder outlets with no load compensation. A fiesta will generally get about a 100kg brake force on the footbrake and up to locking on the handbrake. but the mot requirements are even less than that.

Reply to
Mrcheerful

Right - could those fail closed as it were?

Reply to
Dave Plowman (News)

Not that I have ever seen, anything is possible, but I would definitely look for the simple solution first.

Reply to
Mrcheerful

If they had, how would the garage have bled the rear brakes after replacing the wheel cylinders?

Chris

Reply to
Chris Whelan

OK - We're still fighting with this and now have new shoes and new adjusters but it's still very poor. The brakes have been bled and there was no air to be found.

If there was air surely the pedal would have been soft? It's not, in fact the opposite if anything, and the front brakes are working extremely well.

Tony

Reply to
Tony Brett

What's the master cylinder look like? If the piston for the

Reply to
Duncan Wood

when you say very poor, can you define it? What effect is there in a measurable sense? As a guide a rear brake on a small car can still be turned by a strong bloke gripping the wheel while someone is standing on the pedal (due to the pressure limiting valve) What figure does it produce on the rollers? Do you have the brake shoes the correct way round?

Reply to
Mrcheerful

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