M35A2 6 wheel lock up!

[wiggall]

Looks like I am back to square one! I got my master cylinder replaced, brakes bled! Step on brakes, and all 6 are locked up! any idea?

 

[GopherHill]

Looks like I am back to square one! I got my master cylinder replaced, brakes bled! Step on brakes, and all 6 are locked up! any idea?

Check and make sure the brake linkage has a small amount of free play before it contacts the master cylinder piston.

 

[jeffhuey1n]

A full lockup seems to indicate a central point of failure. You indicated you’ve rebuilt the master cylinder? If so, might want to pull it and verify the parts you put in stayed where they’re supposed to be. If the master cylinder is good to go, check the air pack. When’s the last time it was worked on? I seem to recall a similar issue somewhere in my past. I started at the furthest wheel cylinder and go through each one. Check the lines for kinks, especially around the master cylinder and air pack. Question: what type brake fluid have you been using? If it’s DOT 3, you could have some rather nasty corrosion issues.

 

[wiggall]

Check and make sure the brake linkage has a small amount of free play before it contacts the master cylinder piston.

Thanks!

A full lockup seems to indicate a central point of failure. You indicated you’ve rebuilt the master cylinder? If so, might want to pull it and verify the parts you put in stayed where they’re supposed to be. If the master cylinder is good to go, check the air pack. When’s the last time it was worked on? I seem to recall a similar issue somewhere in my past. I started at the furthest wheel cylinder and go through each one. Check the lines for kinks, especially around the master cylinder and air pack. Question: what type brake fluid have you been using? If it’s DOT 3, you could have some rather nasty corrosion issues.

I replaced the Master Cylinder with a new one. So I think that is out! DOT 5

 

[wiggall]

Check and make sure the brake linkage has a small amount of free play before it contacts the master cylinder piston.

I loosened it up today . I turned the Master Cylinder rod all the way into the linkage! I am running DOT 5 Brake fluid in it. As soon as I have air. and step on the brake all six wheels are locked up!

 

[wiggall]

A full lockup seems to indicate a central point of failure. You indicated you’ve rebuilt the master cylinder? If so, might want to pull it and verify the parts you put in stayed where they’re supposed to be. If the master cylinder is good to go, check the air pack. When’s the last time it was worked on? I seem to recall a similar issue somewhere in my past. I started at the furthest wheel cylinder and go through each one. Check the lines for kinks, especially around the master cylinder and air pack. Question: what type brake fluid have you been using? If it’s DOT 3, you could have some rather nasty corrosion issues.

The Master Cylinder is bran new.

 

[wiggall]

Thanks!

I replaced the Master Cylinder with a new one. So I think that is out! DOT 5

The brakes work without air. Could it be the air pack?

 

[Jeepsinker]

The brakes work without air. Could it be the air pack?

Yes. Sounds like the relay valving is sticking, or the air piston itself is. Get it to stick, then open your service gladhand valve and see if they release immediately. If so, probably the relay valve. If not, open the emergency air gladhand valve and see if they release.

 

[wiggall]

Yes. Sounds like the relay valving is sticking, or the air piston itself is. Get it to stick, then open your service gladhand valve and see if they release immediately. If so, probably the relay valve. If not, open the emergency air gladhand valve and see if they release.

Thanks! Iwill try that.

 

[wiggall]

Thanks! Iwill try that.

They only release when the air pressure gets below 5# So it looks like I need a new air pack.