Can't Bleed Wilwood MC after adding brake light pressure switch

[skullandbones]

I've got a dual MC Wilwood setup with 3/4 inch MC and bias bar. There are about 3K miles on the roadster with no MC issues. Recently, after adding a pressure switch to the brake light circuit to replace the mechanical one, I can't get the MC bled. I don't know what else to do as I have tried using a syringe and line on the bleeder on top of the MC to evacuate the air but no luck. I can't get the pedal to stay up. Now I'm wondering if the MC is failing. I just don't know for sure. I hate to disassemble it if that's not it (not the easiest job with the tight quarters). However, I don't know what else to do at this point. Has anyone had similar problems? Was it a bad MC or some idiosyncrasy in the bleeding of this MC that I am missing? As I remember, I installed the MCs without any issues regarding bleeding. In other words, I don't think I had to bench bleed them. I just let the fluid drain into the MCs by gravity and bled the air out of the system. This is the front MC that is causing the issues.

This problem has got me completely perplexed.:confused::mad::confused::(

Thanks in advance,

WEK.

[skullandbones]

Bump. I know I'm not the only one who's had Wilwood Master Cylinder problems.

[2bking]

I had to bleed mine at the wheels the old fashion way. I tried the vacuum method and pulled in air at the calipers. If the reservoirs are lower than the MC you could have lost the siphon there and the MC is sucking air.

[skullandbones]

Hi King,

I did check the two forward calipers and both bled fluid when opened (no air). It's the front circuit that is affected. The remote reservoirs are above the MCs. I am still concerned that a bubble of air be in the line or area just where the line enters the top of the MC from the remote reservoir. Don't know if that is possible or not. So one more thing I will try tomorrow is to force fluid down through the reservoir to force any air out of that area. I'm not sure if there is a leak in the MC piston that keeps it from pumping pressure to the system. I've never had this much trouble bleeding a system before now. I was having trouble with the brake switch keeping in contact with the pedal so the brake lights would remain on. So in hind sight maybe the MC was loosing pressure all that time. Don't know at this point. If the next little experiment doesn't work, I guess I will have to order a new MC. I suppose after this trial, I will become a MC expert of sorts. I would rather spend my time getting good at other things like paint/body work or some other useful discipline. If anyone else has some ideas, you are welcome to chime in.

Thank you,

WEK.

[2bking]

I have ABS and a lot of places where air can be trapped in high places. I had to open the bleeders and force the fluid quickly through the lines to get the air past the traps. This method will force the air toward the calipers. I used a catch can with the hose immersed in the fluid so no air came back when the pedal came back up. I don't think the MC is at fault if it doesn't leak fluid but a stoppage or slow feed of fluid from the reservoir could cause the MC to suck air past the piston seals on the return stroke.

[skullandbones]

I have ABS and a lot of places where air can be trapped in high places. I had to open the bleeders and force the fluid quickly through the lines to get the air past the traps. This method will force the air toward the calipers. I used a catch can with the hose immersed in the fluid so no air came back when the pedal came back up. I don't think the MC is at fault if it doesn't leak fluid but a stoppage or slow feed of fluid from the reservoir could cause the MC to suck air past the piston seals on the return stroke.

I'm hoping you are right. I didn't work on it today but will try to purge the air again tomorrow. I don't care if I get air in the calipers if this works. I would trade bleeding the calipers any time. Thanks for the discussion. I would rather work on this assuming it's still air in the line rather than give up and have to disassemble the MCs.

Thank you,

WEK.

[CraigS]

Have you looked at MC pushrod adjustment? Similar to a pedal pushrod. You need just a little bit of free play in the pushrods or the MC piston won't return fully to allow fluid to seep down from the reservoir to in front of the piston seal. See the diagram and ignore 'piston #2' as this is a standard OE dual MC.
http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http%3A%2F%2Fwww.gomog.com%2Fallmorgan%2FMASTE RCYLINDER.htm&ei=CoH9VPPZG8mZgwS64ILQDA&bvm=bv.87611401,d.eXY&psig=AFQjCNGAbjF7qTZCkPFmeeunLtpOJ2M_lg&ust=1425986145854629
The port that allows the fluid to flow in front of the piston seal is very close (maybe 1/32 inch) to the seal. It needs to be. If it were further away you would have a huge amount of free play at the top of your brake pedal. So, if your pushrod is just 1/32 too long, the fluid port will be covered by the seal and fluid won't be able to get in front of the seal. Also, when bleeding the double MC system manually, many have found it good to bleed one rear caliper and one front caliper at the same time. Otherwise you can get to where most of your pedal stroke simply puts an angle into the balance bar but doesn't move the MC much.

[skullandbones]

Craig S,

I've noticed the MC reservoir has not gone down very much during the several bleeding attempts. So are you saying the pressure needs to be released from the other MC to allow for the push rod to have a little more play? If I release the bleeder in the rear caliper with a line on it so it will not suck air back in, that may take pressure off the balance bar to allow the front MC pushrod to rebound far enough to let fluid from it's reservoir go into the cylinder. I haven't been able to figure out how to get some free movement in the balance bar up to this point and have been concerned that the front MC pushrod would not return. I just thought it was because the MC needed more fluid in it so I continued the bleeding process. What normally would solve the problem is more or less an exercise in frustration. I will try taking pressure off the other system. I guess it's a balancing act (ha!).

I'll let you know if this works.

Thank you,

WEK.

[CraigS]

Here is a pick I stole from GWL post years ago and edited a little. I like it because the boots are not installed so it's easy to see the MC pushrod adjustment w/ the threaded rod and jam nut. The red arrow.
http://i3.photobucket.com/albums/y91/craig-s/a42d9dde-4a46-4ee8-a72f-f16de4ee9dae_zpsoty7xxie.jpg
With the pedal fully released the black blocks that the pushrods thread into are all the way forward. I would put a bungee or similar on your brake pedal to pull it toward the driver seat and then feel these pushrods to see if they have any freeplay after you have loosened the jam nut. If one or both are tight adjust it/them so there is just a little play. Also look at your brake light switch. Mine is the plunger type that pushes against the back edge of the pedal arm. The spring in it is strong enough that it will keep my pedal from returning fully. I have an extra tension spring on the brake pedal pulling it up so the switch will collapse.