Jhiltonn

Hello, I thought my Master Cylinder was original to my 72 Coupe, 350 sb with power brakes, but looking closely at it, the stamp on the front is "WT". not PG, or anything else that's listed in my 5th edition Ncrs judging manual. It doesn't have any Julian Dates stamped either. Does anyone have any idea what year this is from? Sorry I couldn't get the WT to show in any picture as its lightly stamped but it is definitely stamped WT, off to one side, it's not centered at all, if that matters.

So about a year ago I thought that I'd simply buy a new MC made by GM Restoration Parts that had the correct 5460346 casting number with a 1 1/8" bore that's stamped PG and be done with it. After receiving the new MC, I was recently looking at why the cap/cover doesn't fit like it does on my original MC. On the original MC, the cap, once put in place, has very little 'side to side' or 'end to end' movement !! Nice, right? But the newly made GM authorized MC is different.... The cap will slide around with at least triple the 'side to side' and 'end to end' movement!! Yes, triple!! Yikes!!! What's this all about!!? I even tried putting my vintage cap on the new MC....same results...way too much play!! It's got so much play in it that I don't want to try and trust it in my car!! So I'm back to utilizing an original MC that was made in the 1970s. Can't go wrong there I know! If my "WT" MC isn't correct for my car, then I'll try to find one that is.

Finally,
I'd now like to locate an original GM Master Cylinder from 1971ish that I could rebuild. So if anyone has an original GM MC for a 11/10/71 build date car please let me know. It must be a vintage GM made MC....

Thanks,
Joe in NH

Alan 71

Hi Joe,
Is it the configuration of the bails that are allowing the slide?

Maybe this from a Camaro site?

Bore
1967 1968 1969 Size
---- ---- ---- ----
Manual drums * BS/CT BS BS 1"
Power drums * BS BS BS/CT 1"

Manual J65 drums AU - - 7/8"
Power J65 drums ?? - - 1"

Manual discs AD - - 1"
Power discs WT WT US 1 1/8"
JL8 4-wheel discs - - US 1 1/8"

Regards,
Alan

For some reason the column alignment is screwed up by the copy/edit.
WT…in 67 and 68 cars with power disc brakes.

gbvette62

67-68 Camaros with front disc and rear drum brakes, used the same "346" master cylinder casting, as 67-72 Corvettes. The Camaro 346 was stamped "WT", while the Corvette one was stamped "PG". The master cylinders were different though, because the Camaro WT had a valve in the rear port to regulate pressure to the rear brakes, that was not used in the Corvette PG's. The valve was used in all disc/drum master cylinders, but often seem to get left out when the master cylinders are rebuilt.

69 disc/drum Camaros used a "309" casting master cylinder, with a "US" stamp.

Here's a break down of all 67-82 master cylinders, that I posted on the C1/C2 Forum, a few days ago.

67 Corvettes equipped with J-56 brakes, and 68-72 Corvettes with power brakes, used the 346. The 67-72 346 can be identified by a "PG" stamp in the machined half moon surface on the front of the casting, and bleeders over each line fitting. 73-74 346's still have the bleeders, but no PG stamp. Late 74-82 346's, don't have the stamp or the bleeders.

67 Corvettes with either manual or power brakes, without J-56, used the "509" master cylinder. The 509 has 2 bleeders and is stamped "DC" on the front of the casting. The DC 509 was also used on 68-72 Corvettes with manual brakes. A 509 with bleeders but no DC stamp, was used on manual brake 73-74's, and a 509 without bleeders was used with manual brakes from 74-76.

The main difference between the 346 and the 509, is the bore. The 346 is 1 1/8" bore, while the 509 is 1".

Tooch1

Interesting stuff here guys,
Joe,
I've been doing some research lately on the C3 master cylinders. It all started when I was trying to get the correct bail handle broadcast code letters label for my 73 manual brake car. One of the popular vette venders listed 'YA' or 'HC' as being correct depending on the car's build date, these letters were also mentioned as being correct in the Prince Restoration Guide. However, the 73-74 NCRS judging manual said the correct bail handle label should be 'YA' for the MC with casting number 5455509. I have yet to find any proof that the 'HC' was ever used. Hopefully someone will come forth with some documentation and pictures.
Getting back to your 72 MC. It appears that the 72 had the most variations used for broadcast codes. Earlier 72's had a PG or DC stamped into a flat area on top of the MC (pictured below), then the later 72's had the letters stamped on the flat surface by the front line fitting along with a date code. I will post those example below too. Here are what I've found as possible broadcast codes found on the 72.
Most with power brakes had a 'PG', some could also have'MK'.
Most with manual brakes had 'DC', and some also could have 'HC' or 'ZC'.
Then, the later 72's had 'TG' which carried over to the 73's and on.
Confusing to say the least, and to add to this confusion during this earlier C3 period the bail handle label didn't always match what as stamped into the MC.
This all stopped in 73 because they did match up. And the broadcast codes printed on the build sheets were the same as the labels.
First pic below shows the earlier broadcast letter stamping and location. DC for manual brakes and PG would have been for power brakes.

Tooch1

This is a photo of a late 72 and possibly an early 73 manual brake MC. It shows how the stamping location changed. Also note the two letter broadcast code in front of the date codes!

Tooch1

This is a photo of an early 73' power brake MC. It could be found on a 72 too! Just want to show the two letter broadcast code and the date code and where it was stamped on the MC.
Regards,
Jimmy

Jhiltonn

Thanks guys with all this great information! It really helps clarify things!

Alan, the slop in the cap is because the original MC is at least 1/16" wider and over 1/16" longer than the newly made GM Restoration Authorized Parts MC!! See pics below... Maybe it won't matter much once the bails are in place, but...

I still want to find an original GM master cylinder 346 PG for my 72... If anyone has one kicking around I'm interested!

Alan 71

Hi Joe,
Very interesting find about the size of the castings!
Is the repro you're measuring one those supposedly "correct" reproductions available?
Regards,
Alan

Alan 71

Hi Jimmy,
Interesting to read about the work you're doing and SEEING examples of what you're finding!!!!
Regards,
Alan

Jhiltonn

Alan, that's exactly what it was touted as ... a "correct reproduction" Master Cylinder.

QIK59

Hi Jimmy,
I have a 346 cylinder with bleeders that looks to be very close on stamping to yours : IG or 1G 2356 - what do you make of that ?
Thank you,
Jerry

HeadsU.P.

Note the dates above.

eboggs_jkvl

At 7 years of age, I see a lock in the future.