brake pedal travel

[Europatc]

Morning all, after having another servo play up on me I decided to look at alternative methods of having a sufficient braking system without the servo. I've fitted +2 calipers to the front of my sprint but I can not achieve an acceptable pedal, there is to much travel. Has anyone had a similar experience and what was there remedy. Thank you in anticipation
Stuart

[661]

I've changed to +2 calipers too and de-servoed. The pedal is rock hard with very little travel. Given the new piston size I guess it must be more than before but it doesn't feel it in practise. Forgive me, but yours doesn't sound quite as it should be.

[wotsisname]

Are you comparing like-for-like ? Do you both have the same (type of) master cylinder ? I don't know how different they are, but the Lotus part number for a +2 is different to the Elan... [just throwing my thoughts into the pot]

[Europatc]

same master cylinder, +2 mounting brackets, calipers and discs, I've bled the system several times, on the second pump of the pedal the foot pedal has the amount of travel that is acceptable, its like there is air in the system but if there is then I don't know how

[john.p.clegg]

You'll have to do the math ( as they say in the U.S.) and work out the ratio of master to slave cylinders , sounds like mis-match,one way is lots of travel adequate force,the other short travel low force...

John

[wotsisname]

does it feel a lot like the previous servo issue ? in other words is there something else wrong ?
old flexible hoses, which are ballooning under pressure ? leaky seal (master cylinder), leaky union.
are you using silicon fluid ? Eezy bleed or jamjar & tube ?
Are there any solid pipes which have a bit of a loop... The front brakes on an Elise can be a pig to bleed properly if they are empty because of the way the two halves of the caliper are connected.

[Europatc]

Hi wotsitname, new hoses nothing like the servo issues , the pedal travels about half the distance the second pomp brings it to where it should be, there are no loops in any of the pipes and the bleed nipple on the caliper is the highest point. I just wondered if anyone else has had this problem and if they had a remedy. I shall have another attempt tomorrow
thanks
Stuart

[rgh0]

It sounds like the system is bled OK and there is some other problem. That problem does not appear to be in the brake lines as new ones are fitted and I presume you are not loosing fluid which rules out leaks

I would do the following checks around the master cylinder and calipers

1. Check for piston retraction and observe how the pads move as you depress the pedal the first time and then pump it to get an acceptable pedal. If the Pads have not been bedded or the pistons are retracting to far when the pressure is released you can get this problem due to excessive pad movement on application of the brakes.

2. If the problem only occurs when driving and not when the car is stationary then check for bearing play and or pad knock off due to disk run out

3. Have a look at the reservoir fluid when the pedal is first depressed. If you have a leaking reservoir valve you will see a slight disturbance in the reservoir fluid as fluid leaks back from the master cylinder until cylinder pressure seals it.

If none of the above checks show anything I would rebuild the master cylinder and try bleeding again.

cheers
Rohan

[SF69Elan]

Hi Stuart,

My brake pedal has a similar feel to what you describe and I'm following this thread to learn about options for addressing the problem. I have a 69 S4 Federal with a dual master and the brake pedal is spongy. The system has been bled properly, but no change in feel. The pedal feels the same whether the car is running or not. I have braided stainless steel brake lines.

Per the feedback from Rohan on your thread, I plan to check the items that he's identified after I get my car back from the shop next week (for a separate fix). The workshop manual indicates that worn seals can potentially let air into the caliper cylinders causing a spongy feel. I have no idea the last time the calipers or master cylinder were rebuilt, so those are on my list to try. There's also a comment that weak master brake cylinder mounting can cause similar symptoms, I plan to take a look at that as well.

Don't mean to highjack your thread, just responding to your original query as to whether others are experiencing a similar problem.

Rich

[Andy8421]

I have had exactly this problem - but only when the car was moving. First pump lots of travel, second pump just fine. Eventually traced it to run-out on a rear disk that was knocking the pads back.

It was a swine to find as it was due to a failing rear wheel bearing. I had rotoflex at the time, and the loading on the bearing from the distorted rotoflex when the car was jacked up was sufficient to mask the bearing play. It was only when I removed the driveshaft that the problem became apparent.

[UAB807F]

Hi Stuart,

It sounds like we have similar set-ups, I have 16b front calipers and a 0.7" m/cylinder with no servo. I find brake travel one of those funny things where a small amount of "extra" travel preys on my mind, so I understand what you're on about.

Can you measure the amount of travel you have so we can compare numbers ? Sadly, it involves the lotus position in the footwell but you can get an idea by grovelling round with a ruler alongside the pedal to get the rest position. Then hold the pedal down as hard as you can, either by hand or press with your foot and use a length of wood between the wheel & pedal whilst you measure again.

I don't have my notes to hand but seem to think mine was just over 4 cms against a calculation of 3.7cm.

Brian

[Europatc]

Thank you one and all. It had a new master cylinder last march, I will check out the travel distance and get back to you Brian, Rich feel free to Hijack the posting, Andy the rear discs where replaced last year but thanks for the possible cause, Rohan Im humbled by your knowledge on the matter. Watch this space

[UAB807F]

Hello again Stuart,

I've been in the workshop this afternoon and decided to measure the pedal travel on both cars. The Europa won't be of interest but the Elan one might be. The marks are top & bottom of travel with the direction arrow pointing to the bottom of the footwell.

Elan is 4.1cm, a bit longer than calculations but there's some play in the linkage to the m/cyl pushrod. I find this ok but of course we all have our own perceptions of what's acceptable. For instance the Europa initially had exactly the same travel and yet I didn't like it. The current figure is down to a different pedal ratio, higher pressure but crazily enough, now I like it !

Brian

[PBK]

Hi All I put +2 fronts on my S4, initially with a 0.7 M/C and had no confidence in the brakes. Oddly, a 0.75 M/C did little to improve it. I thought about it and decided that my real issue when driving was pedal height rather than travel. I was most uncomfortable with the lack of confidence in braking and heel and toeing that a brake pedal going below the accelerator gave me especially when going quickly.

We modified the pedal to raise it 1.5" at the pad and my confidence is returned with strong retardation at a confidence inspiring working pedal height. It took about 5 minutes before the "issue" of the new initial pedal height disappeared.

Just another perspective.

Peter

[SF69Elan]

Brian, Peter - thanks for posting these updates with the additional information.

Peter it sounds like you raised the brake pedal up 1.5 inches so that the brakes would then engage higher up when pressing on the pedal, and that the additional height meant that even thought the pedal retained its sponginess you didn't feel like the pedal was getting too low by the time it felt fully engaged. Is that correct? So you essentially had more leverage on the pad because the pedal was fully engaged higher up? Did you notice any change in stopping power or effectiveness?

Do you recall how you modified the pedal?

Thanks!
Rich