Brake pedal goes to floor but no fluid loss?

[lockwood77]

I\'ll quickly describe my setup and what\'s happening with my brakes:

New Mintex Xtreme pads all round a month ago
Unknown brand slotted/drilled discs (on car when purchased)
Braided hoses
Fluid changed and bled a couple of months ago (Motul RBF600)

I can very easily press the pedal to the floor and braking retardation is not what I would expect (although it never has been since I bought the car - I put this down to the Red Stuff pads that were on until I changed to Xtremes). The pedal hasn\'t always been like that - only since my first trackday (before fluid and pad change).

When the fluid was changed, I was told there was a leak on the clutch master cylinder, although I can\'t really see much of a leak myself. What really puzzles me though, is that the fluid level has remained rock solid. Is this likely if there\'s a leaking cylinder in the system?

A possibly related thing occurred last night too - I dropped from fifth to fourth for a bit of extra grunt as I joined a derestricted road, with a blip of the throttle to smooth things out. It was just as if the clutch was slipping (4-5k RPM) so I changed back up and it still sounded like slippage was occurring. However, I couldn\'t replicate it again, despite doing exactly the same manoeuvre, or high gear uphill, or full boot first/second/third etc. Could this be a symptom of a failing clutch cylinder? I would have thought the spring would be enough to push the plate back without hydraulics, but I\'m no expert. Going out again this afternoon to see if it\'ll do it again.

Anyone had a similar experience? I\'m not really sure where to start, short of changing the clutch master, slave and brake master cylinders!? :confused:

[shaunwil]

Most likely the clutch slave cylinder is leaking. Its just passing the seal when the peddle is pressed. Best bet is to change both master and slave because usually the state of the seals are similar in both.

Shaun

[m4drx]

seals mate as shaun said meaning no fluid loss but fluid is passing the seals.

[Wombat-007]

I agree with the guys above.
 
I\'ve experienced this a few times in older cars after changing pads etc. Sometimes it seems to knacker the seals. I can only put it down to the bleading procedure.
During regular driving only a small part of the master cylinder is used as the preasure raises the pedal stops moving.
When bleeding the brakes, usually you are pushing the pedal far further than it normally travels, running down the rougher part of the master cylinder with sediment as this is normally never used. This in turn wears away the sealsand hey presto, you have an extra job to get on with. I suppose the same can happen to hydraulic clutches if you never need to completely floor the pedal each gear change (hopefully not)
For this reason, I hate bleeding brakes this way and am always grateful if all is ok after.
 
I know there is a vacum system about that prevents this issue as no pedal pumping is required, just not sure where to get them from.

[buckman67]

For this reason, I hate bleeding brakes this way and am always grateful if all is ok after.
I know there is a vacum system about that prevents this issue as no pedal pumping is required, just not sure where to get them from.

Gunson\'s eezi bleed is the one man bleeding kit. No pumping , just uses low air pressure from a tyre etc. Sets you back about £14, halfords, ebay etc etc.   I bought a replacement for my 94 as mine was " well used " and it has all the caps you need in the kit, and as the clutch is fed off the brake resevoir you can do that while your there. Works well !


Bob

[clive]

Always real difficult diagnosing these type of things down the internet but lets have a go.

Reading the above you would seem to have two totally separate things going on,

First of all I would suggest that unfortunately you never ever got all the air out of the brake system when the brake lines were changed, so a proper bleed should sort this part of your problems.

As for the clutch side of things to check the leak you will need to look for wetness where the rod goes into the cylinder at the pedal end under the dash.

Various things can stop the pedal retuning how you suggest,

Seized cylinders, very unlikely unless the car has stood enough for proper serious rust to form.

Fluid getting the wrong side of the rubber seals but normally this would show as fluid loss, also you can check the master cylinders integrate by starting the car with the clutch down in first gear then just sit there like this and see if the car starts to drive off after a few minutes by itself without lifting the pedal  .

Another is a partially collapsed rubber hose between the master and slave that acts as like a one way valve.

Oil on the clutch plate is another possibility that then burnt off, but you would normally smell that and see an accompanying leak under the car.  

BTW air in the clutch system will not cause slippage just lack of full pedal.



As you said you could not replicate the fault again could it possibly be that without realising that at that particular time you mistakenly rode the clutch and it did not fully let the pressure off just at that particular time?  

Years ago we had a driver of a lorry that we were always changing clutches for, turned out he used to lightly rest his foot on the pedal all the time and without knowing was slightly disengaging the clutch leading to rapid clutch wear, as soon as he became aware of this as being a problem he stopped riding the pedal and never killed another clutch!

If are on a stock clutch and standard twin turbos you can check your clutch by charging into third gear and at quite low speed then flooring the throttle then listen and watch the rev counter for when the turbos change over, normally this shows the first signs of clutch wear.

Even if you have monster clutch and a single turbo monster engine another way is try and pull away in 4th as this will also show slippage if the cluch is worn.    

Sorry if you already know lots of the above but as I said, "real difficult diagnosing these type of things down the internet"!  


Hope something above helps.

[lockwood77]

Cheers guys, all useful advice. The bleed was done at a garage (who also pointed out the apparently leaking cylinder), but that\'s not to say they did a perfect job (although you\'d hope so!) Would a leaking clutch cylinder introduce air into the system?

Still haven\'t replicated that clutch slip again, so I\'ll try the third gear-low revs into second turbo test.

Having been told about the leaking cylinder previously and now understanding that it could do so without losing fluid, I guess I will be changing them both.

Trackdays aren\'t gonna be much fun until I get this sorted!

[clive]

You will only introduce air into either system via the master cylinders if the level goes low enough to suck in air .

If it were me I would check the cylinders for leaks before just throwing money at it, the clutch is as described above and the brake master if leaking will normally leave a "snail" mark where fluid runs down the servo unit under the cylinder flange.

[lockwood77]

Cheers Clive, will do.

If the brake cylinder isn\'t leaking and we assume the bleed did remove any air (it better have done, having paid for it! ), what would the next most likely cause of rubbish brakes be? Servo failure? Would\'ve thought that would make for a very hard pedal though?

[clive]

Still think you have air in the brakes personally.

Trust me you would know if the servo membrane had split, hard pedal is an understatement, ever towed a car on a rope with no engine running and tried to stop with out the servo assistance!.

[lockwood77]

OK, I\'m starting to think it\'s me and not the brake system at all...

Checked all cylinders (clutch and brake), no fluid loss at all. Checked servo (pedal down at ignition), operates fine.

I think what I consider to be "to the floor" is based on what I\'m used to in Integras (awesome brakes, loads of initial bite) - my old man doesn\'t think the pedal goes to the floor at all, it just has more travel than I\'m used to. So basically, I think I need to get used to pressing considerably further down on the pedal to get a strong bite from the brakes - I did get the ABS to kick in going round Donington in the wet recently, so I guess they must be gripping pretty well!?

If anyone has any mods to make the brakes behave more like an Integra (loads of initial bite at the top of the pedal, but still progressive), that would be useful! I\'d also like to do a few hundred yards in another FD to see what the brakes are like as a comparison, so if there\'s anyone around Nottingham with an FD willing to let me try the brakes (not in an emergency stop way!), that would be awesome.

As for the clutch slipping, I haven\'t managed to get it to do it again so I\'m going to have to assume that despite being sure my foot was off the pedal, it wasn\'t and I was slipping it myself.

[pdtaylor18]

Ian, brake disks came from USA along with the braided hoses, got these as I too thought the brakes were not that good.  The set up did improve a hell of a lot but as you thought they should be better.  I mean they did stop you fairly sharpish but then sometimes its like .......god stop !!! but then mosty of the time i forgot what speed i was doing and realised i was trying to stop from 100 down to nothing in a few yards.  The cars are just so smooth and you never realise what speeds you are doing.  As for your problem then as far as bleeding I must have bled this dozens of times to get it better and it did most of the time. Perhaps as Clive has stated it needs bleeding again especially after you have had fluid change.  I had ceramic pads in there once but they were eating the disk away so got the red stuff in there. Ceramics were very good but not good from cold !!!
So I have not helped you much but there may be something lurking there to have the both of us wanting more from the brakes.  Maybe its air within the ABS unit itself. Is there a way of bleeding that unit on its own,some do but not sure on the Rx7\'s.  Anyway hope car is otherwise going well for you and hope its good on the trackdays.

[lockwood77]

Thanks for the help Pete, I think the best thing is for me to get a drive of another FD and see how well their brakes work. As I say, I can get the ABS kicking in (in the wet at least), so they can\'t be that bad!

Otherwise, car is going well, trackdays are great fun (although in the wet, it\'s a slightly nervy experience!) Only mods have been gauges (missing a water temp gauge as I couldn\'t get the sensor to seal properly in the hose! Doesn\'t matter as there\'s the Commander for that), the downpipe I bought off you (remapped at WGT), new DAB stereo and Mintex pads. I also had it fully undersealed a few weeks ago. I promise you it\'s being well looked after!

Would be interested to know if anyone has an answer on the ABS bleeding question?