Rebuilt airpack w/ yellow retrofit sticker

[Rokhead]

The time came this weekend to replace the airpack on the deuce. I had soft brakes (truck needs to be bled wvery 2-3 months from a leak) so I make a pressure sprayer bleeder and it did a fine job bleeding out the dot 3/4 and neon yellow silicon brake fluid blend that was in the truck. I pushed new DOT 3/4 they the system since that's what I'd prefer to run and flush the system every year or so.

after the bleed session, I started the truck and had brake fluid blowing out the vent line on the passenger fire wall and couldn't make more than 30 psi air pressure. Traced it back to the airpack and I figured something was worn out. My buddy down the road had a rebuilt airpack I swapped in, but is has a big round yellow sticker that reads "retrofit". Anyone know what this means?

i opened the old air pack and there was gummy orings that were in pieces....problem identified. Just like ethanol eats carburetor rubber

What would have caused the oring deterioration? Dot 3/4?. Does retrofit mean there is old style orings that modern brake fluid could eat? I haven't hooked up the hydraulic portions of the brakes yet.....looking for advice. Run dot 3/4 and flush it again in a few months, or go DOT 5 because yellow retrofit sticker means I have too.

thanks!

 

[212sparky]

Did you change all the seals when you went with dot 3? There was a thread a while back talking about how going from dot5 to dot3 swells all the seals and could lead to catastrophic brake failure. Dot 5 will turn yellow over time. I have never seen a retrofit sticker, unless it means it is the newer style airpack.

 

[ptg530C]

Mine has the retro-fit sticker in the cab.

 

[welldigger]

Did you ever figure out why your brakes were leaking before you switched to dot 3/4? You also need to disassemble and probably rebuild all 6 wheel cylinders. Simply bleeding the brakes won't flush all of the dot 5 out of them. The bleeder valve is on top of the wheel cylinder and you can have dot 5 sitting on the bottom. The 2 different fluids will react and turn to gel. Very bad.

 

[Rokhead]

With a specific gravity for DOT 3/4 at ~1.04 and DOT 5 at ~0.96, it is clear that the dot 3-4 would displace any dot 5 and make the dot 5 rise. Dot 3/4 would also make water (sg of 1) rise. I get that some dot 5 may "get stuck" but I don't fully understand how. I was hoping I could flush the dot 5 out since it floats on dot 3-4. I'm worried the dot 3/4 could eat old seals that have been exposed to dot 5 for several years.

The original leak was from the airpack leaking air into the brakes. Pressure bleeding the lines pushed brake fluid into the air lines.