M35A2 not building pressure with full brake reservoir

[mstepchinski]

Hi,
I looked around, but didn't see anything that matched my situation exactly, so I thought I would send a post out. I had an empty brake reservoir yesterday (deuce sat for 3 weeks), so I filled it with dot 5. Pumped for 30 minutes and no pressure builds at all. I know the system will need a bleed down, but pressure should still build, right? I let sit overnight and reservoir is still full. Pumped another 10 minutes or so and still absolutely no pressure builds.

MC bad? Something else?

Thanks in advance - if I missed a post that details this I apologize. I searched through a few pages and found nothing.

Mike
1968 M35A2 - still new at this

 

[drmerc]

Did you try bleeding the system?

 

[mstepchinski]

Did you try bleeding the system?

No Pressure will build at all. Won't push anything out.

 

[porkysplace]

No Pressure will build at all. Won't push anything out.

I would crack the bleeder on the air-pack a try bleeding , it could be air locked or at least tell you if the MC is bad.

TB43-0002-87.pdf TB43-0002-87 Brake fluid replacement procedure.
TB-9-2300-426-20.pdf TB-9-2300-426-20 Hydraulic and Air Hydraulic Brakes preventive maintenance.
TM9-1827c Ord. Maint. Wagner Lockheed Brakes Manual for repair and maintenance of Hydraulic brake systems illustrated.

 

[drmerc]

I would crack the bleeder on the air-pack a try bleeding , it could be air locked or at least tell you if the MC is bad.

That's what I was thinking... if you can't bleed it probably need to rebuild/replace it

 

[m-35tom]

such a big system has to be bled. but first you need to fix the leak!! something 40+ years old should be completely torn down and checked. it's part of the responsibility of having a big truck.

 

[mstepchinski]

such a big system has to be bled. but first you need to fix the leak!! something 40+ years old should be completely torn down and checked. it's part of the responsibility of having a big truck.

Thanks, and I agree. I will try cracking the bleed valve on the airpack to see if I can get anything out of it. I guess if nothing comes out with a full reservoir, the MC is shot.

 

[Jeepsinker]

Or just buy another one. Replacement masters are still relatively cheap for our trucks.

 

[rosco]

If you build/have a pressure bleeder, you can hook it up to the MC, then by yourself, go crack the Booster, then to the fartherest WC, etc., working your way back. If you don't have the pressure bleeder, then you have to have "soldier 1", pump the brakes, while "soldier 2" uses the bottle with the hose, & cracks the booster, etc., doing the whole drill. The pressure bleeder is easy to build, cheap, & is by far, the most positive & faster to use!

 

[M-1028]

I've had good luck gravity bleeding my trucks, takes a lot longer but no choice when I'm by myself.

 

[rolling18]

Thanks, and I agree. I will try cracking the bleed valve on the airpack to see if I can get anything out of it. I guess if nothing comes out with a full reservoir, the MC is shot.

I also have this problem.. the pedal goes straight to floor after sitting months filled a empty res.

when I open the bleeder valve on air pack .. fluid comes out... not air.. this system worked perfectly before it sat.

thanks!

 

[tommys2patrick]

I recently had this problem as well. A couple years ago I rebuilt the air pack and did the service /bleed/etc. it worked fine afterwards. I put in a remote fluid reservoir but after sitting for a long while the fluid would slowly draw down. I suspect a leaking fitting or cracked pipe. will have to tear into it from top to bottom. anyone have suggestions/experience with similar?

 

[Floridianson]

I recently had this problem as well. A couple years ago I rebuilt the air pack and did the service /bleed/etc. it worked fine afterwards. I put in a remote fluid reservoir but after sitting for a long while the fluid would slowly draw down. I suspect a leaking fitting or cracked pipe. will have to tear into it from top to bottom. anyone have suggestions/experience with similar?

Myself I pull back the rubber boot on the end of the push rod of the master. Need small tool to get under the rod /rubber end but pull it down and push on the rubber boot and see if you get fluid. If I remember on the air pack if you disconnect the discharge air line and it has fluid there then the air pack is leaking out fluid.

 

[rolling18]

WHEW!!
I lucked out... nothing more to do than have someone pump the brakes, (yes even with no resistance pressure) and I blead the air pac got some air out a few times and they the brakes are back to normal!!

Mental note: GET A REMOTE FLUID RES. setup!!