Brakes- loss of pedal, no apparent leaks.

[mat in tn]

Coincidentally I started getting the same symptoms over the weekend.

Still not sure what's going on, but I'm thinking it's the master cylinder.

Brakes are adjusted, and I haven't done any brake line work since last year so I have no reason to suspect air in the system...

However when I was going through the diagnostic procedure in my shop manual, I noticed in the rear brake reservoir:

- If I press the pedal slowly, I am seeing the fluid level rise slightly then go back down when I let go which indicates a problem with the master.

- If I press and release the pedal more quickly I am getting a geyser which indicates air in the line.

Is it possible the master is letting air in?

normally if air could be drawn in then fluid could be pushed out. I'm more suspicious of the master seals not sealing. i went through three on my bronco last year just to get one reman to bench bleed.

[Orkea6]

for bleeding I used both the vacuum bleeder system, and followed with the old fashioned two person pump and bleed- starting at the closest to MC (LF) and ending at the far right wheel. Thing is- the pedal pumps up with the truck not running. Start the truck, and it disappears.

I do have a Motive pressure bleeder and I need to get a adapter plate for this type MC. An air pocket doesn't make sense as they don't just wait 5 weeks to suddenly show up.

Thanks for the help.

The vacuum bleeding if from a hand pump is a wast of time in my book.

I have one that uses shop air to make vacuum and that was only a little better.

When bleeding ALWAYS start at the farthest wheel and working to the master.

Check the rear brakes to make sure they are adjusted if not that can through off the whole system.

Get the needed MC cap and pressure bleed the system.

If the rear is adjusted and the pressure bleeding did not help I am thinking the new MC is bad.

If you can fid an empty lot get up to speed and lock out the brakes and see what marks are left.

If all is good you should have 4 even marks.

If only 2 wheels lock, front or rear, then you know where the system has the issue.

Dave ----

My vacuum bleeding was with a compressor- but started at the nearest line to the furthest. I'm used to working on Mitsubishi and that is how they do it- but they are different (only three bleeders on my Mitsu trucks). It sure seems like it must be air- just odd that I had a firm pedal - never "squishy" right up until this symptom started. All else fails, I need to review the factory manual procedures and bleed some more- starting at the furthest this time.

I have bench bled the original MC and reinstalled- same result.

Thanks to all for the comments and suggestions

[Gary Lewis]

My vacuum bleeding was with a compressor- but started at the nearest line to the furthest. I'm used to working on Mitsubishi and that is how they do it- but they are different (only three bleeders on my Mitsu trucks). It sure seems like it must be air- just odd that I had a firm pedal - never "squishy" right up until this symptom started. All else fails, I need to review the factory manual procedures and bleed some more- starting at the furthest this time.

I have bench bled the original MC and reinstalled- same result.

Thanks to all for the comments and suggestions

Have you found the page here: Documentation/Driveline/Brakes? Might click on the Overall and then the General Brake Service tabs and see the section from the factory shop manual there.

[Orkea6]

Have you found the page here: Documentation/Driveline/Brakes? Might click on the Overall and then the General Brake Service tabs and see the section from the factory shop manual there.

Thanks Gary- I have that downloaded now for reference. Appreciate the work you've done here.

[Gary Lewis]

Thanks Gary- I have that downloaded now for reference. Appreciate the work you've done here.

[Orkea6]

Thanks Gary- I have that downloaded now for reference. Appreciate the work you've done here.

Update- followed the FSM troubleshooting guide and found the right rear self adjuster came loose. Not sure why exactly but it might be the cable is too long as it went back together loosely. The self adjusters are new and made by Stromberg Carlson- or so I thought. The replacement self adjuster kit is Carlson too- this one says "Made in China" - I think the crimp on the cable may have slipped. I thought I was getting good parts. Seems they are all made of Chinesium. The adjuster lever fell off and rattled around in the drum- so now I need two new drums and shoes as well. Oh well. Thanks all for the help and suggestions

[JohnC]

Pedal builds pressure with truck not running- not with it running. I think I may have just answered my Q right there.

Bleeding started at closest -(LF) to the furthest (RR).

Shoes were seated, adjusted by rotating the wheel until it stopped, then backed off 20 clicks. Then checked again after first day test drive.

My method for setting the rear brakes is different than yours. I adjust the star wheel until there is just a bit of drag, noise mostly. I have self-adjusting rear brakes. I just back up and hit the brakes with more force than normal. They should be set then.

Sorry, I have no info for your actual issue.