Lotus Elan

Brake pedal travel

PostPost by: Mick6186 » Mon Jun 03, 2019 9:31 pm

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
Mick6186
Second Gear
Second Gear
 
Posts: 205
Joined: 11 Mar 2014
Location: Gravesend

PostPost by: Pastapesto » Mon Jun 03, 2019 10:42 pm

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
Pastapesto
Third Gear
Third Gear
 
Posts: 260
Joined: 12 Nov 2006
Location: Tunbridge Wells, Kent. UK

PostPost by: Pastapesto » Mon Jun 03, 2019 10:50 pm

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
Pastapesto
Third Gear
Third Gear
 
Posts: 260
Joined: 12 Nov 2006
Location: Tunbridge Wells, Kent. UK

PostPost by: snowyelan » Tue Jun 04, 2019 12:54 am

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
Scott
45/9011
Hawkestone, On, Ca
snowyelan
Second Gear
Second Gear
 
Posts: 158
Joined: 14 Sep 2003
Location: Hawkestone, Ontario, Canada

PostPost by: Gordon Sauer » Tue Jun 04, 2019 5:46 pm

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
Gordon Sauer
Fourth Gear
Fourth Gear
 
Posts: 535
Joined: 20 Aug 2004
Location: Irving, Texas

PostPost by: dougal9887 » Thu Jun 06, 2019 9:09 pm

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.
dougal9887
Third Gear
Third Gear
 
Posts: 246
Joined: 23 Aug 2013
Location: United Kingdom

PostPost by: jono » Fri Jun 07, 2019 6:46 am

..has anyone fitted pad 'knock back' springs to resolve this issue?
jono
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1572
Joined: 17 May 2007
Location: The wet bit in the top corner of England

PostPost by: john.p.clegg » Fri Jun 07, 2019 8:18 am

..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:
User avatar
john.p.clegg
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 5553
Joined: 21 Sep 2003
Location: Manchester

PostPost by: nmauduit » Fri Jun 07, 2019 12:41 pm

jono wrote:..has anyone fitted pad 'knock back' springs to resolve this issue?


I have, quite happy to have that behind me now... :D
S4SE 36/8198
User avatar
nmauduit
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1158
Joined: 02 Sep 2013
Location: France

PostPost by: snowyelan » Fri Jun 07, 2019 1:48 pm

Any info available on the springs? There's not much space behind the pistons. Are the springs conical?
Scott
45/9011
Hawkestone, On, Ca
snowyelan
Second Gear
Second Gear
 
Posts: 158
Joined: 14 Sep 2003
Location: Hawkestone, Ontario, Canada

PostPost by: nmauduit » Fri Jun 07, 2019 4:26 pm

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.
S4SE 36/8198
User avatar
nmauduit
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1158
Joined: 02 Sep 2013
Location: France

PostPost by: disquek » Fri Jun 07, 2019 6:07 pm

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
'70 S4 Elan - Cosworth BDP & Spyder Chassis
'62 S2 Super Seven Cosworth
disquek
Second Gear
Second Gear
 
Posts: 78
Joined: 25 Oct 2018
Location: USA - Philadelphia

PostPost by: Mick6186 » Mon Jun 10, 2019 8:46 am

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.
Mick6186
Second Gear
Second Gear
 
Posts: 205
Joined: 11 Mar 2014
Location: Gravesend

PostPost by: dougal9887 » Thu Jun 20, 2019 9:00 pm

Great tip, thanks pastapesto!
Finally got round to adjusting the pads tonight. Instant result after putting up with the problem for 4 years.
Dougal.
dougal9887
Third Gear
Third Gear
 
Posts: 246
Joined: 23 Aug 2013
Location: United Kingdom

PostPost by: Pastapesto » Thu Jun 20, 2019 10:57 pm

Glad to help guys!

A
Pastapesto
Third Gear
Third Gear
 
Posts: 260
Joined: 12 Nov 2006
Location: Tunbridge Wells, Kent. UK

Total Online:

Users browsing this forum: No registered users and 3 guests