Master Cyl
 

Getting my MC ready for a refresh and I noticed it does not have bleeders. From what I read it should. It’s a Delco,has the right numbers and I believe was original to the car. In looking closely I am trying to determine if the date code is 18 or 184. My car is an April 16 LA build, the 18 might be a bit early and the 184 is too late. Is this a service replacement?

https://hosting.photobucket.com/3d51...720&fit=bounds

https://hosting.photobucket.com/3d51...720&fit=bounds

https://hosting.photobucket.com/3d51...720&fit=bounds

What is the Julian date it should have bleeders

MC
 

Julian date is either 184 or 18 , see last photo.

The julian date is stamped on the machined surface where the brake lines screw in

I have had some with out bleeders a asked the same thing it may be for a automatic

The original 346, WT master cyl is still on my 1968 Z/28 that I've had for 50 years. It has bleeder screws & no date code.....Joe

There is no reason to believe manual/automatic masters were different. Both show code CU in box #56 on the Body Broadcast Copy.

Vintage road test photos (PHR March '69) show automatics with bleeders.

From JM’s 67/68 Z28 book confirming 5460346 WT master with bleeders.

Other things I’ve noted regarding the 346 master are that there are 2 front styles for the WT stamp and that some masters have an upside down cast number.
I believe that both versions of the WT stamp are legitimate although beware that reproductions (or restamps) do exist as stated in Chick’s build thread.
I also believe that both versions of the casting number are legitimate. I do wonder if Defiance had more than 1 foundry and if that’s the reason for the different casting number orientation and stamp font?

If you’re also looking for a lid you’ll need one without a SAE stamp. There are reproduction lids out there but it’s easy to spot them since font and word spacing is different.

Nice looking master here. Perhaps still available.

https://www.yenko.net/forum/showthre...hlight=5460346

My understanding is the bleeders were due to the tilt of the MC, and was to eliminate any possible air that might get into the brake line.

From: The First Gen Camaro Assembly Process by John Hinckley

The chassis then passed into the fluids area, where the power steering system was evacuated and filled automatically, and the brake system was evacuated-and-filled automatically through the master cylinder - the bleeders on the master cylinder and at each wheel were never touched.

From my observations of original cars and research in the original 60's parts books --

- Any car with power brakes which the booster orientation resulted in the Master Cylinder NOT being level / horizontal received a MC with bleeder(s); and

- Any car that had a MC that WAS level / horizontal received one without bleeder(s). That could be manual brakes, or it could be power brakes with no booster tilt.

Despite there not being any need to bleed them on the assembly line, the issue was future service. If the MC were removed and serviced and reinstalled, or if fluid got low enough to get air in the top of the system before refilling, then there can be an air bubble just above the line attachment caused by the tilt of the MC. The bleeder(s) allow elimination of that bubble at the MC, rather than having to try to push it all the way down the brake line to get it out. A level MC did not create that issue.

As for service replacement MC's, after some period of time of servicing both styles of a given MC, they typically stopped selling the version without bleeder(s) and only offered the version with bleeder(s). That may not be true for all of them (such as a MC that was never used in a tilted application). But if you trace the part number supercessions through the parts books, that was usually the case.