bleeding the hydro-vac

[loosewrenchcowboy]

i swapped rockwell toploaders into my m-135. hooked everything up, but can't seem to get the brakes to bleed out. they worked fine before i swapped the axles. now the pedal is spongy, and i get intermittent brake pressure that changes wheel location every time i hit the whoa pedal. i have the service manual for the m-135, and everything else except the axles was untouched. any secret tips? and the manual is a little vague as to which bleeder to open first on the air-pack. help?

 

[M543A2]

I have had the best luck using a pressure bleeder. Connect it to the master cylinder then work down from the master cylinder opening bleeders in consecutive order, ending with the wheels.
Regards Marti

 

[loosewrenchcowboy]

ok. thanks. i used a vaccum bleeder setup the last time, and it helped a TON, but still room for improvement. i'll try that. TY

 

[badgmc56]

It can be done the old fasion way but pressure bleeding is the way to go.Thats how I did mine.Bleed hydrovac first then the farthest wheel away from master cylinder and work your way forward.Left front wheel being the last one.That's how I have done it for years.Take your time and you shoud be fine.If your truck has two wheel cylinders per wheel make sure you bleed bottom one first

 

[acetomatoco]

One thing to be careful of is the nomenclature of stuff... A M135/M211 Deuce has an Air Pak for the brakes which is a Air over Hydraulic booster using a compressor. The Hydrovac is a Vacuum booster for brakes which was used in WWII on Halftracks and CCKW etc... Air pressure not vacuum is used to boost the brakes on most M series vehicles. Brakes are among the most talked about accessories on this forum.. Be sure to search well and take heed of the advice given... Do not reuse brake fluid..!! Dot 3 takes on water in solution when exposed to air and Dot 5 is usually very contaminated with water globules when bled from systems.

 

[badgmc56]

Thanks ACE for correcting me.I did mean AIR-PAK. Sorry for the miss info.

 

[acetomatoco]

Gotta keep you Jimmie Guys straight...brakes are the most important component to keep up on MV as they are usually only single systems and on the GMC M135 et al...only one cup in one of the 12 wheel cyls has to fail and there are no brakes...with or without the Air Pak.. whoops.. on the M35 series only half the possible failures...but the same result. Remember if you break the brakes...something else will break and it will not be pretty.. But as they say in Da Bronx, dems da breaks... Remember to take a break when you are working on the brakes before you break something... Happy Veterans' Day to all us old Soldiers...