excessive brake pedal travel

[YellowS4DHC]

I recently converted my 72 Federal TC over to a tandem brake MC based on the very fine tech article by Brian.  Everything that needed to be considered was addressed by Brian and I made the conversion from a single stage MC quite easily using a Spitfire MC and 4 new hard brake lines (no servo).  My LHD configuration coupled with the adapter at the front of the frame made it all very easy.

I've had the car up and running now for a couple of months. The new pads and linings are fully seated.  There is no air in the lines and the MC push rod doesn't have excessive free play.  That said, I'm disappointed with the amount of pedal travel I have.  I estimate that with the rears fully adjusted up, the pedal travel is about 1.5 inches.  I assume this is typical for a Europa with this mod given the design of the rear wheel cylinders [sliding, single piston]

I'd gladly trade some increased pedal pressure for reduced pedal travel.  I'd like to get a MC with a larger bore but I don't know what MC with, say, a .8 " dia bore would fit in the available space.

Comments and suggestions invited.  If I'm missing something here I'll gladly use the red-face icon and cop to it.

Rick

[EuropaTC]

Hi Rick,

Well, if it's any consolation, that's almost exactly what I calculated the pedal travel would be with a 0.7" bore master cylinder, and I measured mine at 1.5" as well.

You can easily fit a 0.75" bore m/cylinder in there, or probably even larger as it's the same casting with just a bigger internal bore on the ones I looked at. I made up a spreadsheet when deciding which one to use and will enclose it on this post in case it is of interest.

A couple of caveats; firstly I'm far from being an automotive designer, just a hammer wielding injuneer. Secondly, I struggled to find detailed information in terms of pad & brake lining movements, and so made some assumptions based upon the allowable disc run-out in the manual and a pure guess on the rear lining movement, which is the greatest inaccuracy in the calcs I think.

If you want the exact pedal travel these numbers are obviously important, but if all you want to do is compare a 0.7" bore with a 1.0" bore then it's not so critical because the ratios of movement will be comparative. 

I compared 0.625" (OEM S2 ?) with 0.7" (OEM TC) and 0.75" m/cyls. Pedal movement came in at 1.87", 1.49" & 1.3".  I think that's a lot compared with modern cars (my wife's TT brakes are almost like a light switch - on or off) and so I do understand your concern, but the only way to reduce travel is for a larger m/cyl. I had a 0.75 single circuit previously and it was notably sharper although I also had a servo installed so I don't know how much effect the bore of that had on the overall movement.

Brian

edit to add - I can't post a spreadsheet. I shall try and convert it to a pdf and add it later.

[EuropaTC]

Second post. I enclose 2 PDF files, the first shows the numbers used on the Europa and the second, spread over 2 pages, shows the data I collated on the Triumph range of cars which I used as background for converting my Elan & Europa. The logic was that these cars use essentially the same brake components as the Lotus, I don't know their pedal pivot dimensions but the amount of fluid they're moving should be comparable even if exact pedal travel isn't.

I shall try to get a single page conversion of the Triumph data as I think it's useful for anyone doing these things. I also include a link to one of many of the on-line brake calculators should you decide to get deeper into the design. I found it quite interesting, so please post any conclusions you make.

http://www.jakelatham.com/radical/info/brake_calculators.shtml

Brian

[cal44]

Rick,
our Elan is without the vacuum canisters and the travel is around the same distance you are referring to.
Did you change out all of your soft brake lines? Old brake lines are the worst for a well functioning  system. 

Also when it comes to bleeding brakes, I push the fluid in from each wheel up through the MC.  Works every time and is a one man operation.

mike

[EuropaTC]

Also when it comes to bleeding brakes, I push the fluid in from each wheel up through the MC.  Works every time and is a one man operation.

mike

Not wishing to hijack the thread, but how do you do that Mike ?

[YellowS4DHC]

Brian,
thanks for the response, you've validated my observations.  I admire you for attempting to calculate pedal travel based on MC bore dia.  I'm retired and just too lazy to do that sort of thing anymore.      

I thought of having my existing .7" bore opened up to, say, 0.8 or 0.825.  intuitively, I knew going to 0.75 wouldn't do much good (and you have the calc to prove it).  My servo-less S4 MC is .875 and the pedal pressure is a bit on the high side but is acceptable with EBC pads (has only about 0.5" of travel)  But, assuming the casting wall thickness would permit a rebore, where then would l get a replacement piston? This is not normally a component of a MC rebuild kit.  I suppose I could have that machined too, but now machine shop costs start becoming a problem.

So that's where I am now, considering options and looking for something off the shelf that I could bolt in.  It shouldn't be too hard to make up a different mounting adapter to accommodate a MC with a different flange than the MC I already have.   However, I would like left side metric ports so I wouldn't have to junk my nice new hard brake lines from Dave Bean.

Later tonight I'll peruse you pdf file and maybe consult the Dave Bean catalogue.  Gotta do something, the car deserves better.


Mike,
All flexible brake lines are SS braided in near new condition on both cars.  No air in the lines, I use a power bleeder and it works fine for me, don't have to pester the wife or anybody else.  Never had a problem bleeding brakes, it's really a pretty simple thing to do.

BTW, I would think pushing the hydraulic fluid backwards past the seals in the MC would require a fair amount of pressure, is that correct? 

Rick

[EuropaTC]

(part quote)
I'm retired and just too lazy to do that sort of thing anymore.      
Rick

  

the only reason I have time to do such things is because I'm also retired.     A few years ago I'd never even considered it, I'd just have bought the parts, fitted them and then gone for a drive !

If you can make an adapter/spacer place then you'll have lots of options. I only picked the Triumph range because the parts are quite common here and the flanges are the same spacing.

When I was looking around I found lots of dual circuit m/cyls from European & Japanese cars which would do the job but the bolt holes didn't align. Lots of choice in bore sizes, I think the Land Rover range was very cheap and went up to a 1" bore for example. Anything sold in the UK from late 70s onwards, or Europe before, is going to have metric fittings because we became legally "metrified" around that date.  (although a lot of companies went over to metric beforehand for the European market)

I haven't looked how practical it is as regards angles, etc, but the other way to reduce travel is to alter the point at which the push rod is attached to the brake pedal. Moving it towards the actual pedal should reduce leverage but should also make it feel as if your foot isn't moving so far ?

Brian

[cal44]

Well, since you both asked here goes.

Three years ago when I had some P cars and a  Boss 302 I needed to do brakes.  So I started investigating the process other than the typical person in the car pushing down the brake pedal.

I came across a discussion on pushing from each corner of the brake system to get the air out of the line.  The biggest issue that stuck with me was in a liquid where does air want to go?........up.

So I bought the Phoenix Brake Bleeding system.  A bunch of money for some plastic bits so I was just a little concerned I may have screwed myself.   Once I figured out the best way for me to use it....(all thumbs) this has become a piece o' cake to bleed a system. 

I have done at least ten hobby cars and the results are always the same.  When I sold my 356, the buyer asked me what I did to make the brakes work so well (drums are not supposed to be that good...right?).  Of course my all thumbs had rebuilt the brakes as well.

I suspect my average time to bleed a brake system is now at 30 minutes and always working my way from the furthest to the closet.  They call it a reversible brake bleeder but it seems to me pushing air down would be reversible bleeding. 

No, I don't work for them nor am I an investor.  Their website is not the best but you do get the point.  Since I am far from a professional I purchased the V12 Professional bleeder to make myself feel like one.

mike

http://www.brakebleeder.com/

[EuropaTC]

That's interesting Mike, I'd not heard of that method or the kit before.

The logic (bubbles rise) is not something you can argue with, and after reading the blurb and thinking about it, I'm now wondering why this idea hasn't taken off more. Or maybe it has and I've just missed it ?

I'm interested though, anything that provides more confidence when you press the stop pedal is a good thing, and worth having a shot at.

Brian

[cal44]

Brian,
it works each time without fail.  The first use was a real learning.  I made sure the MC bowls were empty then I started the process.  What I failed to do was cover the MC with a paper towel.  I pushed the little plastic gun handle with great zeal.......aaaa, that wasn't a good thing nor was it necessary.

Value added learning, surround and cover the MC with paper towels, squeeze slowly the handle on the gun, check the MC bowls for fluid about to over flow.  Do these measures and you won't have brake fluid all over your Sunbeam Tigers engine compartment.  Luckily nothing was damaged.......well, maybe what is left of some ego...........

There.

mike