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I have to say shken or not your wife is one cool cookie and a skilled driver to boot !
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I have to say shken or not your wife is one cool cookie and a skilled driver to boot !
Yup agree my wife would have wrapped it around the tree & blamed me!
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I reckon M/cyl failure as well seen this several times on cars in the past year or so. Both had old brake fluid so that may excerbate the problem, but both were knackered. One OK after a seal change & the other was replaced completely.
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Glad to hear wife is well, and car also.
But I dont go for master cylinder flipping both seals at same time.
More likely 1 circuit had already failed? and 2 nd one failed causing the problem.
Be good idea to get brake test done at mot centre after repairs to ensure all is correct.
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Changed the master cylinder this morning and went to bleed system to discover the O/S brake disc is slight blue. Inspection showed a tight pot in the caliper. Removed dust cover cleaned and lubed with lots of exercising the piston and put it back together and bled system Brakes are OK but I still have air somewhere but will do that tomorrow when I'm goint to strip the other side. Thanks for your comments. I got the wife to push pedals for me to exercise the caliliper and she accused me of forcing her 'to get back on the horse' I woun't be letting her drive it until I am totally happy, wait though I have just had an idea, no best not. Regards Peter
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Almost certainly, one seal has failed in the master cylinder leading to a failure of that circuit. The chances of both failing together are remote.
On any dual circuit system, the pedal travel required to activate the remaining (good) circuit is dangerously long and in a panic situation will feel like a complete brake failure. In fact, the second circuit will pressurise just before the pedal hits the floor, but this is of little use in an emergency.
There is no substitute for good preventative maintenance - master cylinders do not last for ever and I would suggest 10 years as a reasonable life. Next time you change your brake fluid (as I'm sure you do at the prescribed intervals), leave one nipple open and see how long the pedal travel is.
659.
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Remote but reasonably common, out of the 2 m/cyl that have failed in the last few years both were dual circuit & both failed completely pedal to the floor & no braking! One was a TR7 & the other was my Scimitar SS1 so 1980 & 88 cars. The scimmy had grotty brake fluid but the 7 was fairly clean.
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I have fitted a new Master Cylinder and stripped cleaned and checked all calipers and bleed just over 1.5 litres of fliud through the system. The fluid was changed less than 2 years ago but hey it's cheap and all pads are recent less than 10% worn. Without the servo the pedal is very firm and near the top of the travel however with the engine running there appears to be about3cm of travel that does not do anything then very firm resistance.. She stops well and under a controlled lock up the fronts locked sortly followed by the rear n/s then o/s. I can tell by looking at the dry peice of road and the rubber marks. I will run it for a while and she how she behaves as I might just be over sensitive to the pedal travel. Regards Peter
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sortly followed by the rear n/s then o/s
This shouldn't happen, is the load sensing valve sticking?
Number_Cruncher
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It's probably just the weight on one side of the car. I swoped side on the road which does hav a camber and the rear both locked together. Regards Peter
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Sorry Peter, I didn't make myself clear. It wasn't the aysymmetry that I was concerned about, it was the fact that the rear brakes locked at all. The load sensing valve should reduce the brake pressure to the rear brakes to make rear lockups exremely unlikely. It's possible that the valve is sticking in the high load position, so that more brake pressure is applied to the rear brakes than there ought to be.
Typically, either the valves stick, or the spring that connects the axle to the body becomes weak, which both can cause too much pressure to get to the rear drums. Either way, the rear brakes shouldn't lock.
Does the Volvo have a load sensing valve? I would expect one, but it is possible that a so-called G valve is specified.
It is worth looking into, because having the rear brakes lock during an emergency braking application is potentially a trouser soiling moment if not worse!
It happened to me once, happily without the smelly biohazard!, with a modified car, where we had fitted a rear axle with a different ratio and bigger brake drums, but had forgotten to change the pressure reduction system. As I rounded a corner, a broken down car made me brake hard (OK, I was going too fast), but, as the back end of the car came round, I had to let off the brakes to straighten the car up, and then re-apply with the car in a straight line. We stopped in time, but it isn't something I want to experience again!
Cheers,
Number_Cruncher
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There are pressure-limiting valves in the pipe runs to the rear brakes, but I don't know whether these actually adjust for different loads . Do they feed say 30% of whatever braking effort is applied, or is it an absolute limitation regardless of the pressure at the front? I'd have thought with no load in the back the rear brakes are bound to lock at some point if enough weight is transferred to the front?
I've had master cylinders fail internally in a less dramatic way - usually to the point where it takes several pumps to build up pressure. In each case I wasn't aware of any difference between the circuits, so assumed they had both failed. Certainly the warning lamp for different circuit pressures never came on.
These master cylinders seem very suscepible to unused sections of the bores becoming corroded, so when rarely the pedal travel is longer, eg during bleeding, the seals are instantly scored on the unfamiliar bores and then start leaking. There are enumerable reports of master cylinders failing immediately after some other brake work, eg replacing calipers, or flushing fluid.
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Without ABS, there is no positive means to stop the rears locking, but good design should prevent that happening.
Catastrophic failure of the brakes in a Volvo 240 must be unlikely, dual circuit and four pots per front caliper IIRC, years ahead of any comparable car when it first appeared (144 in the late 1960s?) Loss of one circuit might go unnoticed though. If one caliper seizes (usually a rear), there is a venting device on the 244 which bleeds off fluid onto the road, so it's possible to drain the master cylinder, but the warning light should indicate a problem.
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Volvo 240 have one in each cct, pressure regulator for the rears they are not load sensitive and with a light load in the car you can lock the rears. The later 240's 1992 to 1993 had no cct balance switch or a warning light just a block of metal to connect the pipes. Micky what do you mean a venting device. The only waf fluid can get out of a 240 is via a worn seal of out of the back of the MC towards the Servo. On close inspection of the old MC it is clear that air has been entering via the rear seal ( badly scored ) into the large bore cct and the tight piston on the front caliper that got hot was on the other cct so that appears to be why she lost the brakes. All is well know, good braking just this free travel issue. Regards Peter
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>>pressure regulator for the rears they are not load sensitive ...
I haven't worked on one of these cars for years, and I imagined (incorrectly!) that they would have load sensing valves, because one would expect the load on the rear of an estate car to be subject to much wider variation than the rear of a saloon car.
As a comparison, most Vauxhall estates do have load sensing rear brakes, where the equivalent saloons and hatches do not.
Purely for the sake of curiosity, are the valves just fitted in line, in the brake cicuits, or are the valves also tilted by a set angle from the horizontal, pointing up towards the front of the car? (i.e., are they purely pressure reducing valves, or are they G valves, which sense the deceleration of the car?)
Number_Cruncher
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They are steel cylinders looking very like clutch slave cylinders, mounted horizontally and pointing at right angles to the fore and aft line. So presumably they are merely pressure reducing valves?
They are incidentally virtually at the highest point on the brake line, and can cause troublesome air locks when bleeding from scratch.
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">Micky what do you mean a venting device. The only waf fluid can get out of a 240 is via a worn seal of out of the back of the MC towards the Servo<"
I had a 244 many years ago, it dripped brake fluid from a six way union
Brake details for 144:
www.gcp.se/CD4/140 73-74/bromsar.pdf
Page 17, either part no 17 or the unmarked union immediately after the master cylinder (can't remember which, too many years ago now)
Lots of head scratching, the car braked in a straight line so it couldn't possibly be a sticking caliper. Ha! All other possibilities checked, so it was one of the rear calipers sticking, freed it off and the leakage stopped.
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Coincidence the device you are refering to on a 240 is the brake pressure inbalance switch and was prone to leaking, it is not a venting device I assure you. Regards Peter
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take the car to an mot place tomorrow and ask them to do a brake test for you this will determine whether the whole system has any faults,any good tester can tell you straight away with all the figures and if you are right with them they will sometimes do it for nowt---------
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