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I have disassembled and rebuilt the Easamatic unit on my '52 300, thanks to the useful guides on this site, and I'm getting ready to re-install it. The service manual says after pressing the pedal to the floor, it should return to its start position.

How fast should it return? Mine does return but takes 30-seconds or so. There's no brake lines connected yet or vacuum lines - not sure if this will make things quicker.

I'm debating stripping it down again to see if I can speed up the return - but before I do, I thought I'd check if slow return is expected.

Thanks in advance.

JB

It should pop back fairly quickly so be sure that your pedal arm isn't binding in any way and that it is lubricated at the pivots.

Also, when you had the unit out, were you able to press the diaphragm in my hand? It would be tight but not so hard that it can't be pressed. Did it return immediately?

I don't think the pedal arm is binding. I get about the same response when I push it in by hand.

I could press the diaphragm in by hand when the unit was partially disassembled. But it didn't pop back up easily then. I did lubricate the inside of the piston housing, but perhaps I didn't do it enough?

I get about the same experience as in this rebuild video (around the 28m 15s mark:

youtube.com/watch?v=LKbnYmPj9a8&t=1695s

JB

The one I just rebuilt but haven't yet installed is 550 miles away so I'm going from memory but I recall it popping back quickly. Maybe one of the Easamatic specialists will chime in.

I would wonder if the lube used on the power piston assy was too heavy or the leather seal is damaged, or out of position. The recommended lube for the leather seal and vacuum canister is vacuum cylinder oil so a fairly light material. Is the condition of the canister interior smooth with no trace of any brake fluid that might have leaked in and gotten gummy. Anyl of those situations would cause a lot of drag on the piston the return spring might not be strong enough to overcome.

Should pop back in just a few seconds and you should be able to hear the air going back in.

It is often helpful to take the cover off the can and loosen the cover plate screws on the power piston. Wiggle the piston about and cycle the unit a couple of times before re-tightening the screws. This will get your leather nicely centered and seated.

Thanks for the advice. Mine was definitely not returning in a couple of seconds. I took it back apart - it wasn't the leather sealed vacuum piston, but the small hydraulic piston. It was very hard to move back and forth.

Looks like I didn't lubricate it enough with brake fluid during the reassembly. After a liberal application of brake fluid to the cup seal, it started to move freely.

Once re-assembled, I can push it in and get a strong puff of air of the outlet and then it returns back within two seconds with an audible in-rush of air as well.

JB