Printable Version of Topic
Click here to view this topic in its original format
914World.com _ 914World Garage _ Brake bleeding night mare
Posted by: mb911 Jan 14 2021, 04:27 PM
I have been struggling to bleed the brakes on my car and can't figure out what is going on. Here is what I have..
New pmb stainless solid brake lines
New pmb restored rear brakes
New pmb restored bias valve
New stainless steel flex brake lines(possible issue?)
New 914 rubber master cylinder (possible issue?)
New resealed 911 s calipers by me.
I have bled the system with a motive bleeder, old school method, gravity and had somewhat of a pedal but as I was pressing on it the pedal went to the floor like there was a leak. I have found no leaks.
So the question is could the stainless flex brake lines be the issue? Could the 914 rubber MC be the issue? I am just curious as I know they were semi new when I got mine..
Any insight? Any suggestions?
Posted by: Pops71Por Jan 14 2021, 04:34 PM
I have been struggling to bleed the brakes on my car and can't figure out what is going on. Here is what I have..
New pmb stainless solid brake lines
New pmb restored rear brakes
New pmb restored bias valve
New stainless steel flex brake lines(possible issue?)
New 914 rubber master cylinder (possible issue?)
New resealed 911 s calipers by me.
I have bled the system with a motive bleeder, old school method, gravity and had somewhat of a pedal but as I was pressing on it the pedal went to the floor like there was a leak. I have found no leaks.
So the question is could the stainless flex brake lines be the issue? Could the 914 rubber MC be the issue? I am just curious as I know they were semi new when I got mine..
Any insight? Any suggestions?
I put new 914 rubber upgrade Master and all around PMB breaks with all new rubber lines. Never could get it. Had to have it towed to specialist and he took almost a day to get it. Said not bench bleeding the MC was potential issue. My suggest taking off and bench bleed and then you know it would be only lines
Posted by: mepstein Jan 14 2021, 04:38 PM
I had one car that wouldn't bleed until I cracked the lines at the MC and then it worked fine. I also tapped on the calipers with a brass hammer while bleeding and got out a few more bubbles.
Posted by: mb911 Jan 14 2021, 04:39 PM
I am concerned that may have damaged the mc as my helper pushed all the way to the floor.
Posted by: Superhawk996 Jan 14 2021, 04:47 PM
All new cars are initially filled, automatically during assembly by a process called Evac & Fill.
Starts by 1st pulling a vacuum on the entire brake system at the M/C reservoir. Then locking out the vacuum. While vacum is maintained on the lines, M/C, etc., the brake fluid is introduced under pressure.
ABS and ESC systems introduce a lot of possibility for trapped air due to the M/C not always being the highest point in the system. 914 is similar in that the bias valve lines are higher than the M/C and are a prime place to trap air and notoriously hard to bleed.
Obviously it's not entirely possible to duplicate that sequence at home.
However, I've found a lot of success by using vacuum on the bleeder 1st and then apply the Motive style bleeder under pressure. Mighty Vac works well enough but I prefer to use a constant venturi vacuum source like HF vacuum bleeder or A/C venturi vacuum to keep constant vacuum on a bleed screw while brake fluid is introduced at the reservoir under pressure. Mighty-Vac has only limited vacuum capability and you need to keep constantly pumping it to try to keep up with the fluid introduced - sort of a losing game.
There is always the possibility of a cut seal lip internal to the M/C but is highly unlikely. Line flex is not the issue. Fluid is displaced inside the lines. The volume inside the line is more or less fixed regardless of whether the line is straight, bent, or flexing as you apply the brakes. Yes, there is a tiny variation in volume as a line flexes but it's insignificant and doesn't account for a soft pedal.
@http://www.914world.com/bbs2/index.php?showuser=9892
Posted by: 76-914 Jan 14 2021, 04:49 PM
I am concerned that may have damaged the mc as my helper pushed all the way to the floor.
That won't matter on a new MC. Did you bench bleed the MC prior to installation? Did you bleed the brakes in the proper order. Which method are you using to bleed the brakes? Self bleeders; long tube; ?
Posted by: mb911 Jan 14 2021, 04:52 PM
I am concerned that may have damaged the mc as my helper pushed all the way to the floor.
That won't matter on a new MC. Did you bench bleed the MC prior to installation? Did you bleed the brakes in the proper order. Which method are you using to bleed the brakes? Self bleeders; long tube; ?
I did motive 1st, then right rear pump and the left, then front right then front left. I did not bench bleed the master so that could be my issue.
Posted by: mepstein Jan 14 2021, 04:53 PM
I am concerned that may have damaged the mc as my helper pushed all the way to the floor.
I thought that is only a problem on used mc's that develop a ridge on the cylinder from the piston and then the ridge is damaged when hyper extended.
Posted by: mb911 Jan 14 2021, 04:54 PM
I am concerned that may have damaged the mc as my helper pushed all the way to the floor.
I thought that is only a problem on used mc's that develop a ridge on the cylinder from the piston and then the ridge is damaged when hyper extended.
I believe your right
Posted by: mb911 Jan 14 2021, 05:31 PM
One thing that is note worthy though there is no pedal feel the brakes do seem to work. Frustrating
Posted by: JOEPROPER Jan 14 2021, 05:41 PM
I had a similar issue. When i made the rear steel lines, I didn't flare the end 100% and it sucked air in and would only leak externally very slightly. I re-flared the line and bled the system without issue. Took me a little while to figure out because there was no external leak. i was using a BG Products vacuum bleeder kit.
Posted by: Olympic 914 Jan 14 2021, 05:58 PM
I used my shop vac to bleed my brakes initially,
Maybe try this and the Motive pressure bleeder.
http://www.914world.com/bbs2/index.php?showtopic=303639&hl=
Posted by: BillJ Jan 14 2021, 06:04 PM
i had the slightest of weeps at the banjo joint fitting due to a poor seal to the copper washer. May want to check that.
Posted by: bigkensteele Jan 14 2021, 07:07 PM
Are you absolutely positive you don't have a leak somewhere? I had the same problem a couple months ago only to discover that one of my rear lines was leaking slightly. Fixed that and all was good. Still need to set the gap on my rear calipers. Pedal should be very firm then.
Posted by: mb911 Jan 14 2021, 07:08 PM
Slite resolution.. took the cap off and heard a pressure relief . Realized I left the plug on the back of the reservoir.. now a decent pedal not awesome but that may require another bleed after a few miles
Posted by: TX914 Jan 15 2021, 07:12 AM
I had one car that wouldn't bleed until I cracked the lines at the MC and then it worked fine. I also tapped on the calipers with a brass hammer while bleeding and got out a few more bubbles.
I can't imagine pushing air in the mc all the way through the lines. I just replaced the mc and ABS valve body on the wife's Volvo. I cracked the lines on both several times while she pumped and now it's perfect.
Posted by: mb911 Jan 15 2021, 07:52 AM
It was the vent without doubt.. all good now.
Posted by: Frankvw Jan 15 2021, 08:29 AM
Hi Ben @http://www.914world.com/bbs2/index.php?showuser=9892
what vent do you mean ? You mean the cap of the brakefluid reservoir ?
Thanks for the additional info.
Posted by: mb911 Jan 15 2021, 08:35 AM
Hi Ben @http://www.914world.com/bbs2/index.php?showuser=9892
what vent do you mean ? You mean the cap of the brakefluid reservoir ?
Thanks for the additional info.
My reservoir is an early one so they have a vent to the back that a hose connects to.
Powered by Invision Power Board (http://www.invisionboard.com)
© Invision Power Services (http://www.invisionpower.com)