C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette

'69 Master Cylinder Identification

 
Old 04-15-2019, 09:16 AM
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Bergerboy
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Default '69 Master Cylinder Identification

Hi Folks,
Doing a complete refurbish of my Brake system, including rebuilding my M/C.
I have a manual brake car, which I've never been happy with its braking performance, so I'm replacing all the lines, replacing the Proportioning Valve, and replacing the pistons and seals in the M/C.
I've cleaned up the M/C, removed the pistons, springs, and seals, and painted it in the nice Cast Blast gray.
This M/C has NO Bleeder valves.

HOWEVER: From researching the serial numbers on the casting of the M/C, I seem to have a POWER M/C installed, rather than a manual.

Can you experts verify this for me please? Pictures attached.

My research:
1969 Manual M/C: # 5455509
1969 Power M/C: # 5460346
Also, the stamped numbers on the machined pad read: CN9041 - not sure what the "CN" indicates, but I'm suspecting the 9041 is a Julian date for the 41st day of 1969, which would fit with my July 1969 VIN.

So,
#1) Do I have an original 1969 M/C on my car?
#2) Is it, in fact, a Power M/C?
#3) Is this a problem to be operating on my Manual Brake car???
THANKS!!





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Old 04-15-2019, 10:52 AM
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MelWff
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measure the bore size of the cylinder, manual is 1", power is 1.125. They can not be interchanged and function correctly. The numbers you mention are correct for power versus manual.

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Old 04-15-2019, 11:17 AM
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Bergerboy
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Originally Posted by MelWff View Post
measure the bore size of the cylinder, manual is 1", power is 1.125. They can not be interchanged and function correctly. The numbers you mention are correct for power versus manual.
Thanks Mel for the quick reply.
I'll check the bore size tonight when I get home.
By "function correctly", what do you mean? If this ends up being truly a Power M/C, what would I perceive in the brake performance? Or would it not operate at all? (there is no booster present)
I'm currently getting "OK" braking, but lack-luster at best. Replaced all pads and rotors recently, but still am never able to get full lock-up of the wheels, even when burying the pedal.
Was always thinking this was just Me, getting used to manual brakes again, but now I'm more suspicious.

If the Power M/C has a bore larger by 1/8", then I would think maybe slightly better braking power with the same pedal effort. But not sure.
Hard to imagine the M/C being mis-numbered, as those are in the casting when the part is formed, so very slim chance of mis-marking.
Also - is the fact that this M/C is lacking the bleeders any hint into what I've been running with?
Thanks - another mystery to get to the bottom of! Really want to make sure I'm running safely.

EDIT: Had my son at home measure the bore, and it's a 1" bore.

So - mystery continues: Manual 1" bore size, on a M/C with the Power part number of 5460346. Anyone offer any clues?



Last edited by Bergerboy; 04-15-2019 at 11:35 AM.
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Old 04-15-2019, 11:27 AM
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Peterbuilt
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Default Something else to check

Some M/C's have a deep hole and some are shallow.


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Old 04-15-2019, 11:39 AM
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MelWff
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The power master on a manual system will generate less pressure at the brake caliper piston. The surface area of a power master piston is larger,1.125", so the PSI applied to it by your leg will be less.
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Old 04-15-2019, 12:17 PM
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Originally Posted by Peterbuilt View Post
Some M/C's have a deep hole and some are shallow.

Thanks Peterbuilt. Those holes you're showing are part of the inner piston, not the bore itself, right? So, that depth would affect the pusher rod stroke, not really the hydraulic advantage?
Still trying to figure out how I got a M/C with the 1" bore for a Manual, but showing the casting part number of a Power?
Ponderous Man, Frikkin' Ponderous!
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Old 04-15-2019, 01:02 PM
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Here are some better photos of the M/C in question.
Is there such as thing as an insert sleeve to reduce the bore from 1.125" to 1"? If so, can that be detected from the photos?
That's my only plausible explanation for the 1" bore on a M/C with a Power part number in the casting.





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Old 04-15-2019, 01:17 PM
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BB

The master cylinder you show is not original to the car. An original 1969 master cylinder would have bleeders above the ports.

John
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Old 04-15-2019, 02:23 PM
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Originally Posted by JC68 View Post
BB

The master cylinder you show is not original to the car. An original 1969 master cylinder would have bleeders above the ports.

John
That's true!


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Old 04-15-2019, 02:36 PM
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So, what are we looking at? A bad fake?
Why would a part be made with a 1" manual bore, but with a power part number in the casting?
Unless it was re-sleeved down to 1" at some point? If thats even a thing.
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Old 04-15-2019, 06:23 PM
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As JC68 said, it is not a 69 MC, because it doesn't have any bleeders.

Between 68 and 82, there were 4 different versions of the "346" power MC, and 3 versions of the "509" manual MC.

The variations of the 5480346 Power Master Cylinder are as follows.

68-72 5480346 casting
1 1/8" bore, 2 bleeders, and "PG" stamped in a half moon shaped machined pad on the front of the casting. Some 72 346's have been seen with an "MK" stamp, instead of the PG. The 346 with the PG stamp MC, was also used on 67's with J56 Heavy Duty brakes.

73 and First Design 74 346 Casting
1 1/8" bore, 2 bleeders, but no pad or stamping on the front.

Second Design 74 to 76 346 Casting
1 1/8" bore, no bleeders, no pad or stamping.

77-82 346 Casting
1 1/8" bore. no bleeders, no pad or stamping, with shallow piston.

The variations of the 5455509 Manual Brake Master Cylinder are:

68-72 5455509 Casting
1" bore, 2 bleeders, and "DC" stamped on a half moon shaped machined pad, on the front of the casting. Some 72 509's have been seen with a "ZC" stamp, instead of the DC.

73 and First Design 74 509 Casting
1" bore, 2 bleeders, but no pad or stamping on the front.

Second Design 74 to 76 509 Casting
1" bore, no bleeders, no pad or stamping.

Power brakes became standard in 77, and only the 346 casting was used from 77 to 82.

The 5480346 master cylinder was also used on other GM cars, when equipped with power front disc brakes. When the 346 was used on a disc/drum application on a regular GM car, I believe a reducer was added to the rear line fitting, to balance the front to rear brake pressure. 67-68 Camaro 346's were stamped with "WT", and 69 Camaro's used a 346 stamped "US".

Because there were so many variations of the master cylinder castings, often when they were turned in as cores, and came back as rebuilt MC's, they often ended up on cars they never were intended for.

Your 69, with manual brakes, should have the 509 casting master cylinder, with 2 bleeders and "DC" stamped on the front of the master cylinder.
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Old 04-16-2019, 10:19 AM
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Thanks GB Vette - very informative.

However, I'm now even more puzzled as to how I have a power 5480346 casted M/C with a manual 1" bore, and without bleeders???
I was thinking that this may have been one of those core returns that you mentioned, that somewhere along the way, got "re-bored". Seems like a lot of work to go through to re-purpose this bore. I didn't detect any obvious sleeve insert or anything like that, and even so, wouldn't a sleeve also require a very intricate operation to re-drill the port holes from each fluid chamber?
The stamped number of CN9041 on the machined pad may be some form of rework marking?

Sorry I went to all the trouble of trying to rebuild this M/C with the piston and seal kit, as well as cleaned it up thoroughly and gave it a nice gray cast paint job. Maybe it will make a nice planter for my wife's herb garden!
I've gone ahead and ordered a new re-pro M/C from Corvette Central, but in the meantime, this is one of those mysteries that I find entertaining to try to solve.

Thanks,

Last edited by Bergerboy; 04-16-2019 at 11:01 AM.
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Old 04-18-2019, 11:53 AM
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My new reproduction M/C arrives today from Corvette Central.
Will be installing and finishing the brake rebuild this weekend to see if any performance improvement is noticed (new Prop Valve, new Braided lines, new front Hawk pads, new lines all around, and the new M/C that is proper for a Manual car).
But I still am intrigued by the existing M/C that I've removed.
Power part number in casting, but a 1" bore and pistons?? Has anyone heard of a re-sleeving operation to create a Manual M/C out of a returned core casting from a Power unit?
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