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Brake pedal travel

PostPosted: Mon Jun 03, 2019 9:31 pm
by Mick6186
I have a 1973 +2 130/5. I have rebuilt the brake master cylinder and servo. The calipers have new pistons & seals. The brake pipes are new copper or ss aeroquip.
My problem is excess travel of the brake pedal.
I have bled the system a number of times and no air comes out during bleeding.
The pedal goes down about halfway then is solid and if depressed again is solid after about one quarter travel. The pedal isn't 'spongy'
The pedal pumps fluid immediately with no free play in the push rod.
If left for a while there is an audible 'click' from the rear when the pedal is depressed, but I have checked the rear calipers and all seems OK.
Any suggestions as to a cure gratefully received,
Mick

Re: Brake pedal travel

PostPosted: Mon Jun 03, 2019 10:42 pm
by Pastapesto
Hi Mick

I had a similar problem on my +2S130 I had a few years back. No matter how many times I bled the system, it always had a long pedal travel at first "pump", followed by a shorter travel the second or third pump. It turned out to be calliper seal "pull back" whereby the seals being new & tight on the Pistons would pull the Pistons back a couple of mil or two after releasing the pedal ( gradually over a few seconds of so). It was enough, although slight, to give exactly the same symptoms you suggest. To rectify this I had to remove the pads and "carefully" one calliper at a time, push the Pistons out using the pedal (you need a helper for this) until they were just past the position where the pad would normally sit & then very slightly ease the calliper piston back to allow re-fitment of each pad. You need to do this at each corner. What happens is that where in normal use the piston automatically self adjusts as the pad wears, when you put new pads in and then pump up the pedal to take up any of the "slack", the last millimetre or so is held back by the piston rubber which is too tight to allow the piston to move forward and so ever so slightly moves or "flexes" but then pulls the piston back again. I was told or "taught" this by Miles Wilkins and since then, I have never had this problem to date. i hope that is helpful, please let us/me know if it is.

All the best

Adam

Re: Brake pedal travel

PostPosted: Mon Jun 03, 2019 10:50 pm
by Pastapesto
P.s......when pumping out the Pistons with your friend, be careful not to push them out too far or you will lose brake fluid & have to bleed the system again from scratch.....also, when putting the pads back in, you only want enough room so that the pad "only just" fits back in its space. It needs to go in a little "tight". Then when you do need to apply the brakes under normal useage, the slightest possible pressure/movement of fluid should move the pad and allow the brakes to do their job as intended....... Good luck....

A

Re: Brake pedal travel

PostPosted: Tue Jun 04, 2019 12:54 am
by snowyelan
I found the residual valves below while looking for other brake bits. Untested but may be an option.
I have a Datsun dual circuit master to be installed. It has these valves built in but I have been told that they are too strong at 10psi and need to be modified.
At first thought it seems like the brakes would be dragging but if you figure in the opposing 'spring' from the seals it seems to make sense.

Scroll down to the bottom
http://www.russellperformance.com/mc/br ... ries.shtml

Re: Brake pedal travel

PostPosted: Tue Jun 04, 2019 5:46 pm
by Gordon Sauer
I hope you’ll get back with information about whether this worked as I have a similar problem on my same car but it was after about six months of putting the rebuilt servos in that it went to the long pedal travel, having been high at first, and I have been thinking it’s just failed servos which I have not re-done yet so let us know thanks Gordon Sauer

Re: Brake pedal travel

PostPosted: Thu Jun 06, 2019 9:09 pm
by dougal9887
Interesting topic and info about setting up the pistons/pads. I have same problem, same car, its also done this since the rebuild.
I'll try the suggested remedy and report back
Dougal.

Re: Brake pedal travel

PostPosted: Fri Jun 07, 2019 6:46 am
by jono
..has anyone fitted pad 'knock back' springs to resolve this issue?

Re: Brake pedal travel

PostPosted: Fri Jun 07, 2019 8:18 am
by john.p.clegg
..another cause could be "out of true" discs , especially on the rear as the drive-shaft ears may not be true , causing the pads to be pushed back more...

John :wink:

Re: Brake pedal travel

PostPosted: Fri Jun 07, 2019 12:41 pm
by nmauduit
jono wrote:..has anyone fitted pad 'knock back' springs to resolve this issue?


I have, quite happy to have that behind me now... :D

Re: Brake pedal travel

PostPosted: Fri Jun 07, 2019 1:48 pm
by snowyelan
Any info available on the springs? There's not much space behind the pistons. Are the springs conical?

Re: Brake pedal travel

PostPosted: Fri Jun 07, 2019 4:26 pm
by nmauduit
snowyelan wrote:Any info available on the springs? There's not much space behind the pistons. Are the springs conical?


iirc I got about the smallest and weakest I could get (esp. for the rear), and they were slightly conical. I think I got them from AP Racing (no affiliations). http://www.apracing.com/Info.aspx?InfoI ... roductID=7

ps: I may have shortened some when fitting... the idea is to have calipers in good conditions in any case, so that the effort to get the pads back should not be huge.

Re: Brake pedal travel

PostPosted: Fri Jun 07, 2019 6:07 pm
by disquek
I found this was an issue too after my complete brake rebuild. You actually see it visually after we bled the brakes and went to pump the pistons out to the pads. It took WAY longer than I've seen any car take.

I figured that with some use, it would abate, and it did. The first few stops were OMG pump pump pump!!!!!

In 50 miles its far far better than it was and now almost as good as it's going to get.

Knockback springs are for floating rotor cars to keep the pistons and floaters aligned. They dont overcome the sticktion of the square seal (the issue here), they just keep everything pushed to the rotor side. We have used them in some of the tube cars for years. Good stuff, but not the solution to this issue.

FWIW: I used Casterol red grease on assembly, and wondered if that contributed to this.

Residual valves are for drums. You DONT want to use them on discs. It's like lightly dragging the brakes all the time. We found this out by accident when a TIlton master rebuild kit had one built into the replacement parts. Makes for very "interesting" brake bias when one end has been dragging slightly all race.

Drive it carefully for a bit and it'll go away. You're dealing with the natural tendency of a square seal to stretch and then retact the piston when you apply and release the brakes. Over time vibration and pressure will move the seals on the piston to where they need to be.

-Kyle

Re: Brake pedal travel

PostPosted: Mon Jun 10, 2019 8:46 am
by Mick6186
Hi again,
I followed the advice given and pushed the pistons out slightly one at a time and refitted the pads tightly. This only took a couple of hours. I adjusted the front wheel bearings to make sure I had no pad knock off. The brake pedal is now much firmer so thanks very much for the help,
Mick.

Re: Brake pedal travel

PostPosted: Thu Jun 20, 2019 9:00 pm
by dougal9887
Great tip, thanks pastapesto!
Finally got round to adjusting the pads tonight. Instant result after putting up with the problem for 4 years.
Dougal.

Re: Brake pedal travel

PostPosted: Thu Jun 20, 2019 10:57 pm
by Pastapesto
Glad to help guys!

A