Long Brake Pedal

[AlanJH]

I’ve been doing some serious lurking since joining the community in March with my first Lotus Elan, every time I have a question I find an answer already posted. But I’m really struggling with a long brake pedal, the previous owner, who did a lot of work in a short time, had replaced the front calipers, brake lines and rebuilt the master cylinder. I’ve installed the pads that the previous owner had, but never installed, which improved the feel, but several bleeding of the brakes later I still can’t get the pedal off the floor.
I’m totally out of ideas and have no confidence in the brakes because of never experiencing a pedal that doesn’t respond until almost to the floor. It is an SS so has the dual master cylinder but hopefully someone has some ideas on how I can get confidence in the pedal?

[richardcox_lotus]

I recently had this on a single master cylinder, after my local garage screwed up.

I found that placing a weight against the brake pedal overnight would help to bleed any tiny air particles trapped within the master cylinder.

It helped firm up the pedal a lot.

Regards
Richard

[HCA]

previous owner, who did a lot of work in a short time, had replaced the front calipers, brake lines and rebuilt the master cylinder. I’ve installed the pads that the previous owner had, but never installed, which improved the feel, but several bleeding of the brakes later I still can’t get the pedal off the floor.

My concern would be what was actually done by the previous owner - did he know what he was doing when he attempted the m/c rebuild...?

I am wondering if it not a good idea to start again?

[AlanJH]

Weighting the pedal seems like an easy thing to try, but, and this might be a rookie question, where does the air go? It has to go somewhere, is it followed by bleeding the system?
The previous owner had a mechanic that did all the work for him, but I was thinking along the same lines that maybe I should have the MC rebuilt again?

[Craven]

Common problem with dual circuit brakes is air in the master cylinder, see
https://www.youtube.com/watch?v=vOuDEiwiozQ

[richardcox_lotus]

Weighting the pedal seems like an easy thing to try, but, and this might be a rookie question, where does the air go? It has to go somewhere, is it followed by bleeding the system?
The previous owner had a mechanic that did all the work for him, but I was thinking along the same lines that maybe I should have the MC rebuilt again?

As I understand it, the air that’s trapped in the MC, when under constant pedal pressure is essentially broken down into bubbles that are so so so tiny, they are able to pass through the gap in the seal and into the main reservoir, where they will rise and disperse.

[baileyman]

I tried this a number of times and I think it worked a little. What finally did it was Gary Anderson's advice to crack open the line at the master cylinder and then advance the piston until the bubble showed up. And it did!

John

[AlanJH]

I tried wedging the pedal down but sadly no change. I’ve ordered a rebuild kit so I can take the MC apart and check it all out. Hoping the bore is good and no sleeve is needed. Wish me luck.

[nmauduit]

I would investigate under 2 directions, in that order :

- make sure there is no air left in the circuit (can be more tedious than it seems, esp.with DOT5 fluid prone to small bubbles, and may involve bench bleeding the master cylinder and calipers)

- then if this consistently fails (and I understand the symptom is constant, not intermittent) check whether the pistons may pull back, leading to a need for more travel which can translate in a long pedal (esp. with a small bore MS and Girling 16 at the front, which is what I have) : then fitting springs (anti knockback) would solve that issue.

good luck !

[AlanJH]

I have to admit that I love the suggestions offered on this forum and I’m embarrassed to say I had to look up knockback springs. There is just so much knowledge and experience to tap into.
I’m running DOT 4 so I don’t have the DOT 5 issues, as was the previous owner. And I hope that one day I have the confidence to run the car hard enough to need knockback springs now that I know what they are.

[AlanJH]

I now have brakes I have faith in for the first time since buying my Elan in March. I rebuilt the MC and the only obvious issue was the circlip holding the pushrod was floating around inside the rubber boot! I feel very fortunate the boot held the pushrod in place as that could have been a disaster.
Anyway, bench bleed, reinstall, bleed and everything seems good.