Bleeding 970 brakes, huge pressure difference.

[petebert]

I've been posting about the stuck brakes on my 970. Quick recap, bought a used 970, both brakes stuck in activated position. Heated pins with torch, left side now works. Right side is so-so. I put some stronger springs on the right side and that seems to help.

I decided to bleed them. The method in the manual says, run tractor at 1500rpm, turn steering left/right at least two times. Open right side bleeder, wait until air escapes. It also says to have someone hold down the the right side pedal before closing the bleeder. I was by myself so I did not do this.

The right side went pretty smooth, had a little 6" arch of fluid, had some air come out. Tightened the bleeder after it smoother out. On the left side it came out with enough pressure to hit you in the face, and I was standing behind the axle. When I retightened the left side the pressure caused the brake cylinder to activate. When I returned the engine to idle the cylinder slowly came back down.

Here's a video from the left side. This is the 2nd time I tried the left side so notice the cylinder is in a raised position and lowers when I open the bleeder. Wondering if the big difference in pressure between the sides means anything or could be why there's some brake issues.

https://www.youtube.com/watch?v=IiY7q-PydiY&feature=youtu.be

Here's the video from the right side.

https://www.youtube.com/watch?v=0AiK-qGIUKA&feature=youtu.be

 

[mEl]

Sounds like the boost spool is stuck in the power brake valve, it is located in the brake valve underneath the fitting that the brake line fastens to, remove the line banjo fitting and the fitting right out of the valve, the spool is in that bore,you may be able to work it loose as it is spring loader out the hole. once you get it out flush the bore with Brake kleen and wipe the nylon seal to make sure there is no grit on it. You may want to change the filters as grit is getting in there. Before you do the above make sure the nylon retainer has not failed where the spool from the valve fastens to the piece hooked to the pedal, if you can see a ball on the spool end it is bad. If the spool is not pulled clear out by brake spring pulling the pedal clear back that can cause the issue also, also weak pedal spring not pulling the pedal back all the way can do it also or a rusted pedal pivot

 

[petebert]

Finally got around to opening it up and yes the LH boost spool was stuck in there. The only things that came out were the spool and a spring. I haven't sprayed brake cleaner in there yet, have to run out and get some. After getting it out and wiping it down it still gets stuck when I put it back in. What do you think about using gun cleaning supplies on it? Figure a bore mop wouldn't hurt. Would a brass brush be too aggressive?

Oh and as far as the filters, the previous owners was running the filters without the valves in them. That was one of the first things I fixed.

 

[mEl]

The reliefs were probably the cause of the sticking, look closely at the seal to see if its scored or has metal ground into it. the seal would probably have to be sourced through Case , A brass brush would be ok. repeated moving in and out may help to free it.