variable brake pedal travel

23e Heure · Post by **23e Heure** » Tue Jun 21, 2005 12:33 pm

Fresh back from Le Mans, I've got a whole list of questions to run by you all.
It was the first long trip I've done in my car, and boy did I learn a lot about her on the way there and back!

First up, the brake pedal travel. Mine varies. A lot.
I know the travel can be adjusted with the rod behind, but what of the travel varying willy nilly?
And I mean by whole inch and a half, often between two succesive applications.
I'd thought of an air lock in the brake lines, but wouldn't this be a bit more constant, dependent upon (eg) temperature?

It doesn't seem to alter the effectiveness of the brakes themselves though...

Your thoughts?

Lightweight_911 · Post by **Lightweight_911** » Tue Jun 21, 2005 1:18 pm

I would start by changing the brake fluid - glycol-based hydraulic fluid is hygroscopic (ie will absorb water from the atmosphere). It could be that moisture in the brake fluid is being converted to steam due to the heat generated by the brakes causing a change in the 'compressibility' of the fluid & hence an alteration of the pedal travel.

However, it could be due to a whole host of other factors - binding pedal bushing, defective seal in the master cylinder, internally swollen flexible brake hoses, etc.

Barry · Post by **Barry** » Tue Jun 21, 2005 8:40 pm

My old BMW 323i suddenly started doing this (no iffy period at all), turned out to be master cylinder. One minute fine, next time you braked, pedal nearly to the floor (as the dual circuit cut in I suppose). With air in the brakes you would expect a spongy pedal, very spongy for that amount of movement in fact, plus the ability to 'pump' them up.

BTW the master cylinder problem was internal, with no external leaking. It is possible that the master is randomly just using one of the circuits (if you've got dual: two output pipes from the master??), which would give you at least normal braking on that circuit, nothing on the other (don't forget though that all of your braking leg effort is focused one circuit, not split across two).

23e Heure · Post by **23e Heure** » Mon Jul 11, 2005 4:49 pm

Thanks for the suggestions, but I think I got red herring-ed on this one.
I've realised that it's not variable pedal travel in the way I thought...

What's happening, in fact, is that the pedal does not always release all the way once i take my foot off it.
It's just a matter of the final half inch of pedal travel,
But that's just enough to (sometimes) leave the brake lights illuminated.
But not enough to keep the brakes applied at all. (Or I would've noticed earlier, i hope!).

Now, good ol' Haynes seems lacking once again in the info to help me out...
Presumably there's a pedal bar I need to access, first up?
And is the 'release travel' spring driven?
Clutch and accelerator don't suffer the same symptoms.
Am I making sense!?

Gilbert '71 T · Post by **Gilbert '71 T** » Mon Jul 11, 2005 9:22 pm

Hi 23e Heure

Sounds like you need a pedal cluster rebuild, mine suffered the very same symptoms, you can buy the bushes from roger bray (item 25):

http://www.rogerbrayrestoration.com/cab ... luck[/img]

Gilbert '71 T · Post by **Gilbert '71 T** » Mon Jul 11, 2005 9:31 pm

ps you need to remove the pedal cluster to replace the bushes, it's straightforward enough, haynes has info on the procedure

cheers, and again good luck