Lotus Elan

double pump to get good brakes??

PostPost by: tedtaylor » Tue Apr 11, 2017 11:04 pm

WOW, all very good helpful hints!
now to get to the bottom of it all... :)
TED
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PostPost by: carrierdave » Wed Apr 12, 2017 9:43 pm

Hi Ted
I put a large weight on the brake pedal that depresses it and applies pressure over night. I use a sledge hammer.
This seems to force air out of the system through the master cylinder. I think the cylinder is slightly inclined and air gets trapped and won't bleed out in the normal way.
I have used this process for a number of years after doing the normal brake bleeding process.
Good luck
Dave
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PostPost by: rgh0 » Thu Apr 13, 2017 9:17 am

carrierdave wrote:Hi Ted
I put a large weight on the brake pedal that depresses it and applies pressure over night. I use a sledge hammer.
This seems to force air out of the system through the master cylinder. I think the cylinder is slightly inclined and air gets trapped and won't bleed out in the normal way.
I have used this process for a number of years after doing the normal brake bleeding process.
Good luck
Dave


This approach certainly appears to help difficult bleeding situations and i have used it successfully on my Elans clutch though never tried it on the brakes. I believe that if you get a significant pressure in the system and hold it for a long enough time then air that is sitting at the top of the master or slave cylinder or calipers will slowly find its way past or through the seal rubber while the fluid will not due to its larger molecular size.

cheers
Rohan
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PostPost by: jk952 » Mon Apr 17, 2017 6:43 pm

Looking at an old pair of Elan rear calipers (split open) , I noticed the fluid passage/bleed hole enters the rear cylinder(s) at the Top when held such that the brake mount holes are almost Vertical, however they are mounted on the car with the mount holes close to 45 Degrees which means there is a small area above the bleed hole(s) where air can be trapped.
So one would have to remove the front bolt and tilt the caliper more vertical, ensuring pads can't move out too far of course.

Now having said all this I need to bleed my own brakes again as can't recall if I did this last time! :)
Jack
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PostPost by: 661 » Mon Apr 17, 2017 7:38 pm

Lots of good advice, but please persist with the +2 calipers and discs in a non servo Elan. It works great.
You don't need a bigger MC.
Graeme
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PostPost by: Foxie » Mon Apr 17, 2017 10:43 pm

I would strongly second checking bearing play and disc run-out to minimize piston knock-back. Seal knock-back can be eliminated by fitting anti knock-back springs under the pistons, available from the usual suspects. :D
68 Elan +2, 70 Elan +2s
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PostPost by: tedtaylor » Tue Apr 18, 2017 1:20 am

"anti knock back springs under the pistons"???? Now i thought i've heard everything before, but that's a first for me. Wouldn't that keep constant pressure against the rotors and prematurely wear out the pads, let alone create drag?? Sounds scary to me.
TED
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PostPost by: UAB807F » Tue Apr 18, 2017 5:43 am

tedtaylor wrote:"anti knock back springs under the pistons"???? Now i thought i've heard everything before, but that's a first for me. Wouldn't that keep constant pressure against the rotors and prematurely wear out the pads, let alone create drag?? Sounds scary to me.


Hi Ted,

It's not as scary as you might think, they are very light springs and don't cause significantly increased wear. They're fitted on the Lotus Elise S1 and having done those calipers I did wonder if they'd make any difference on the Elan.

https://www.eliseparts.com/products/show/20/1022/anti-knock-springs/

It seems to me like they perform a similar function to a residual pressure valve in the system.

Brian
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PostPost by: vxah » Thu Aug 10, 2017 8:52 am

Ted, did you get the "double pump" issue sorted?
I did on mine, I found that Wilwood do a valve to keep 2 psi in the brake system. This keeps the calliper pistons from creeping back and giving the long pedal at first application

https://www.motorsport-tools.com/wilwoo ... l?___SID=S

I fitted it in the pipe between the servo and splitter piece, it sits near the vacuum spigot on the front cross member.. So far, good pedal every time!
Might be worth a try?
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