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Discussion Starter #1
I picked up my 155 at 1 Sunday morning & took it on the 640 mile drive home. Everything worked on it, all the electrics, it is clean inside & out & no issues apart from a wing mirror housing which I can take my time with but more importantly the brake pedal is soft. Giving it a few pumps & it works fine but as soon as you run & try to brake again you have to push the pedal near to the floor.

Could this be a 155 issue or just a general brake problem? I'm not keen on driving around in such a swift car with no way of stopping quickly.
 

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This sounds like either air in the brake lines (bleed brakes to fix) or less likely (but still possible) old brake fluid (replace fluid). Pump the brake pedal and hold, if the pedal slowly goes to the floor you may have a leak.
 

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Discussion Starter #3
Thanks. Since I just got the car I'm going to put it in for a proper service anyway, new pads & discs, new timing belt & tensioner, bla bla all the usual so I will have the brake fluid changed at the same time. Better safe than sorry :)
 

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Get them to check that there are no leaks on the calipers.
also get them to check if the brake hoses are ok.
It does sound like air in the system if you pump and all is ok, once they have changed the fluid and bled through you'll find a big difference.

You may also want to check the rear brake compensator at some time, cos a little bit of adjustment makes a difference.
Check if the rear brakes look like they are being used, ie the discs are shiny, not rusty, it helps to stop the car when you have 4 brakes instead of 2 !
 

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No... if air is in the system, then pumping the brakes would not make any difference.. you would have a consistently spongey pedal as the air that causes the sponginess isn't going anywhere. Sponginess gets worse with hot brakes (as the volume of air increases) but pumping the pedal won't change anything caused by air in the system.

If the pedal sags the more you press it, then the master cylinder is letting fluid past the internal O-rings. You need a rebuild or a new master cylinder to sort it.

You can bleed it first before you rush out to buy a new m/c.. just to prove it to yourself... but if you have worn o-rings or a worn inner bore, then when you press the pedal the fluid in front of the piston that is acting on the brake circuit escapes back into the reservoir with the pressure, so the pedal drops. Pumping it helps because you effectively reload the fluid volume ahead of the piston... but if you hold the pedal under pressure, it'll start to sag again.

Ralf S.
 

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No... if air is in the system, then pumping the brakes would not make any difference.. you would have a consistently spongey pedal as the air that causes the sponginess isn't going anywhere. Sponginess gets worse with hot brakes (as the volume of air increases) but pumping the pedal won't change anything caused by air in the system.
If there's air in the system pumping the brakes compresses it, so the pedal goes firm but it will be spongy next time you brake as releasing the pressure allows the air to expand again.
 

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Discussion Starter #7
I topped up the fluid today, it was a bit low & gave it a test, seems fine now, have done the checks that you said & there seems to be no leaks & the pedal is firm all the time. Havent had a chance to give it a proper run to see if the heat will do anything but when I get a chance I will take it out for a blast & see what happens.
 

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Keep an eye on the fluid level.
The reservoir is also used for the clutch, and feeds the clutch slave cylinder on top of the gearbox.

If the fluid level keeps dropping check that the clutch slave isn't leaking, you'll see the escaped fluid on top of the gearbox (underneath the battery tray).

And of course, if you have any questions, don't hesitate to ask on here.
You may also want to frequent a dedicated 155 forum for additional help
 

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How lond did it stand before you collected it? Brakes might just have needed to re adjust for pad wear if the pedal ha come right.

If the fluid was low and no signs of leaks then you will either need new panda and discs or you have a leak on the master cylinder leaking into the servo.
 

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Discussion Starter #10
It was being driven daily until I picked it up. I took it on a 640 mile drive home & the brakes went when I was almost home. I did hit a rabbit on the way up so maybe its mangled carcass broke one of the brake pipes? I will have to have a good check of it when I get time off of work.
 

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Just topping up the fluid reservoir can't make any difference if you have air in the system or if the m/cylinder is FUBAR'd...

If the pedal gradually goes down when you press on it and you have no external leaks, it's the master cylinder.


Ralf S,
 
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