Hi Guys,
Just got the Xsara back from a service. Rear brake pads were replaced. There now appear to be two problems:
1) The car is slow as a dog, it has lost all of its throttle response.
2) There is a high pitched resonance between 2800rpm and 3200rpm. It occurs whether under load or not.
Any thoughts on where to start for either of these?
I pulled the rear wheel and it looks as though the brake pads are touching or at least *very* close to touching the disc, but then again so were the fronts. So I'm stuck.
Any help would be greatly appreciated.
Xsara Problems - performance and resonance
Moderator: RichardW
Langers -
The brakes can NOT be the reason for the slow dog in your engine bay.
If the brakes binds to such an extent - the engine would rather quickly overheat.
The pads have to be close to discs - but must of course not drag.
My bet is that the garage missed the cambelt timing - a VERY common problem these days.
Gives exactly the indication of a tired engine & low MPG value.
The brakes can NOT be the reason for the slow dog in your engine bay.
If the brakes binds to such an extent - the engine would rather quickly overheat.
The pads have to be close to discs - but must of course not drag.
My bet is that the garage missed the cambelt timing - a VERY common problem these days.
Gives exactly the indication of a tired engine & low MPG value.
-
Dave Burns
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It is the nature of the disc brake that the pads should remain in "light" contact with the disc, if they had to move even a short distance to contact the disc the brake pedal travel would be unacceptable.
This is due to the large diameter of the caliper pistons and the relatively small diameter of the master cylinder piston, the reason caliper pistons are so much bigger is that the disc brake relies on shear brute force to operate effectively as it has some inefficiencies over the drum brake, and the shear brute force overcomes these inefficiencies.
Check the rear pads have been installed correctly with the pin on the back of the pad correctly engaged with the notch in the piston, if the piston bears down on the pin it will bind in its bore and cause serious brake drag.
Dave
This is due to the large diameter of the caliper pistons and the relatively small diameter of the master cylinder piston, the reason caliper pistons are so much bigger is that the disc brake relies on shear brute force to operate effectively as it has some inefficiencies over the drum brake, and the shear brute force overcomes these inefficiencies.
Check the rear pads have been installed correctly with the pin on the back of the pad correctly engaged with the notch in the piston, if the piston bears down on the pin it will bind in its bore and cause serious brake drag.
Dave
Anders - I don't think the mechanic messed around with the camshaft timing, it was just meant to be a minor service. Any other ideas?
As for the engine overheating, the car does behave strangely in this way: if I turn off the air conditioning (i.e. disconnect/declutch the compressor) the temperature will soar almost straight to the warning light. What on earth would cause this?
As for the engine overheating, the car does behave strangely in this way: if I turn off the air conditioning (i.e. disconnect/declutch the compressor) the temperature will soar almost straight to the warning light. What on earth would cause this?
The teperature problem I would say would have to be the thermal fan switch (the one operating off the radiator temperature) is stuffed, as the fans are on when the air/con is engaged & cut out when they aren't. I'd suggest removing the plug & bridging the contacts to see if the fan spins sometime when the engine is hot.
Not a big job to replace but messy if you have recently changed the coolant & want to save it.
Alan S
Not a big job to replace but messy if you have recently changed the coolant & want to save it.
Alan S
Then you definately have an engine overheating problem Langers.
When the A/C is on - the A/C control overrides the coolant fans circuit to force-run the fans. This will also force cool an engine possibly under abnormal load.
From cold - start engine & let it idle (A/C off !!). In a couple of minutes the fans should cut in at low speed when engine hits the normal operating temperature. If fans only cut in at high speed - you have a problem in the fans radiator thermoswitch circuit.
If they behave - better have a look again on the brakes as pr DaveBurns advice. With wheels off ground - wheels MUST turn w/o ANY noticeable drag from the brakes.
Since the car is a slow dog AFTER a garage service - they MUST have missed something - you definately have a problem.
Mechanics are humans - and humans makes mistakes - all the time (if NOT - we were all robots [:)]).
Besides the brake & fans test above - check the obvious :
Engine oil level -
Coolant level -
Tyre inflation -
Try look over the engine for any strange things.
Any electrical connectors - or hoses - mysteriously dangling around on, near or under engine ?
All connectors & hoses secured properly ?
Try a drop of the engine oil (from dipstick) between fingers -
Does it look/behave like black ink on your fingers ?
- or is it a normal greasy feeling from fresh oil ?
Contact your garage for a list of work actually done - then tell them patiently & politely (why) you're not satisfied with the result - plus any strange observations.
When the A/C is on - the A/C control overrides the coolant fans circuit to force-run the fans. This will also force cool an engine possibly under abnormal load.
From cold - start engine & let it idle (A/C off !!). In a couple of minutes the fans should cut in at low speed when engine hits the normal operating temperature. If fans only cut in at high speed - you have a problem in the fans radiator thermoswitch circuit.
If they behave - better have a look again on the brakes as pr DaveBurns advice. With wheels off ground - wheels MUST turn w/o ANY noticeable drag from the brakes.
Since the car is a slow dog AFTER a garage service - they MUST have missed something - you definately have a problem.
Mechanics are humans - and humans makes mistakes - all the time (if NOT - we were all robots [:)]).
Besides the brake & fans test above - check the obvious :
Engine oil level -
Coolant level -
Tyre inflation -
Try look over the engine for any strange things.
Any electrical connectors - or hoses - mysteriously dangling around on, near or under engine ?
All connectors & hoses secured properly ?
Try a drop of the engine oil (from dipstick) between fingers -
Does it look/behave like black ink on your fingers ?
- or is it a normal greasy feeling from fresh oil ?
Contact your garage for a list of work actually done - then tell them patiently & politely (why) you're not satisfied with the result - plus any strange observations.
Thanks for the help guys. I've already had a good look around the engine bay when I was trying to find out what's causing the resonance. And the first thing I checked was if it had had the oil changed and a new oil filter; got screwed by the last mechanic as well.
I thought the engine temps/air con thing might have been designed for the European market; I.e. in winter when you don't run the air con, the engine heats up much more quickly and saves from excessive cold start-up wear.
Any ideas what could be causing the resonance? I pulled off the spark plug cover and resealed it, all the O-Rings were present there. Also disassembled the air box and resealed that. I was just going over everything the mechanic might have done, but I'm out of ideas now.
I may have made the performance sound worse than it is, but it is DEFINATELY missing the kick it used to get around 4000rpm (torque peak), esp. under full throttle in 1st gear. The steering wheel now no longer shakes violently left and right trying to cope with the torque.
Oh yea forgot to mention... before I took the car in for service I put some Techron (injector/combustion chamber cleaner) in the fuel tank and proceeded to flog the c@!p out of the car. What could I possibly have damaged doing this?
I have a day off tomorrow so I'll go over the car again with a fine tooth comb.
I thought the engine temps/air con thing might have been designed for the European market; I.e. in winter when you don't run the air con, the engine heats up much more quickly and saves from excessive cold start-up wear.
Any ideas what could be causing the resonance? I pulled off the spark plug cover and resealed it, all the O-Rings were present there. Also disassembled the air box and resealed that. I was just going over everything the mechanic might have done, but I'm out of ideas now.
I may have made the performance sound worse than it is, but it is DEFINATELY missing the kick it used to get around 4000rpm (torque peak), esp. under full throttle in 1st gear. The steering wheel now no longer shakes violently left and right trying to cope with the torque.
Oh yea forgot to mention... before I took the car in for service I put some Techron (injector/combustion chamber cleaner) in the fuel tank and proceeded to flog the c@!p out of the car. What could I possibly have damaged doing this?
I have a day off tomorrow so I'll go over the car again with a fine tooth comb.
Another thought: I'll have to check, but in the few days before I took the car in for service, Sydney was experiencing a cold spell, I.e. very low air temperatures. This changed back to normal about the same time I got the car back, and has remained that way since. Perhaps the extra air density was giving me more power then than now?
Are you sure it isn't an engine mount that's collapsed giving the feeling of this resonance?
If you're in Sydney, give Tom Dolan a call at Citromet. He's well thought of by most Cit owners in Sydney, knows his Cits, good tradesman & prices are right.
There's a couple down there that I have either had experience with or know those who have who could screw up pumping up a bike tyre and it sounds like one of them may have had a go at your car.
Alan S
If you're in Sydney, give Tom Dolan a call at Citromet. He's well thought of by most Cit owners in Sydney, knows his Cits, good tradesman & prices are right.
There's a couple down there that I have either had experience with or know those who have who could screw up pumping up a bike tyre and it sounds like one of them may have had a go at your car.
Alan S
