New Master Cylinder question

[Bronze Mist 64 Riviera]

I'm installing a new master cylinder on my first gen. I've installed M.C.s on several vehicles and each of them came with instructions to bench bleed the unit prior to installation. The new M.C. I just got has a big orange (maybe yellow?) label on it saying to absolutely NOT bench bleed it or damage will occur, but to bleed it on the car. 

 

Anybody have any ideas on why this would be the case?

 

 

Jeff Bean 

ROA 13051

[Jim Cannon]

I have no idea!  I have always bench bled before installing. 

 

One new MC that I received even included some small plastic fittings to screw into the side of the MC and 2 short lengths of hose to direct the fluid back into the fluid reservoirs as you bled it.

 

Perhaps they are concerned about you pressing in on the piston too far, bottoming it out, and damaging something.

 

[Bloo]

No idea. Bench bleeding saves time. It is not technically a necessity.

[OldGerman]

I aggree with Jim. 

When I bleeded my new single master I did the mistake to just push the piston in as deep as possible.

the piston overtravel a bore and fluid dripped out the cylinder. I think I ruined the Innern rubber seal Lippe that way. The brake pedal creates  a limited travel of about 1“ at the push rod. 

The next time I did the bench bleed, I‘ve limited the travel by adding shims over the screw  driver, to limit travel to max 1“.

 

[crowvet]

For the win.

https://www.amazon.com/Cardone-10-5000MCB-Master-Cylinder-Bleeder/dp/B002JSM7HA/ref=asc_df_B002JSM7HA/?tag=hyprod-20&linkCode=df0&hvadid=312026024613&hvpos=&hvnetw=g&hvrand=12116603271893787164&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033094&hvtargid=pla-491509626214&psc=1