'68 Brake Master Cylinder

[William S.]

I have a '68 with power brakes. The casting number, which is quite legible, is 5460348. This differs with the Tech. Info and Judging Guide which lists 5480346. I searched the NCRS Archives, and found 5460346 also. I read in the Archives that the same casting number was used from 1968-1976. So:
1) What is the correct casting number ?
2) I see no date code on the unit, and no Delco logo on the side. What might I have ?

[Joe L.]

Re: '68 Brake Master Cylinder

William------

I am convinced that the number is 5460346. I have done some research on this issue and I cannot find that Delco Moraine ever actually utilized or issued any part numbers in the 548XXXX range. Plus, I've examined several of these casting numbers under high magnification and they all appeared to have a "6" in the third position.

I've never seen one without the Delco logo. However, it's very possible that some were produced. GM might have manufactured master cylinders for ultimate sale under other brand names. If so, they would likely have omitted a GM trademarks on those. Actually, the casting number, itself, is a GM trademark but most folks would not so-connect it and that might otherwise have been necessary for casting identification purposes. Actually, it would be illegal for anyone else to manufacture a brake master cylinder casting of this configuration with that number on it (unless, of course, through the "GM Restoration Parts Program").

Of those examples I've seen with bleeder screws (used from 1967 through at least 1972), the only ones that did not have a manufacturing date stamped into the forward brake line fitting machined surface are those from 1967. However, the 1967 usage of the 5460346 casting was Corvette with J-56 only.

Does it have a two character broadcast code stamped into the "semi-circular"
machined surface on the front and, if so, what is it?

A photo of it might be helpful, also.

[Anthony S.]

Re: '68 Brake Master Cylinder

Bill,

I have a '68 w/ J-50 and I was very confused by these numbers too.

When I bought my car, it had a non-dated 5460346 master on it, but it did not have the two bleeder srews or the "PG" stamped on the machined surface. It must have been a service replacement. The numbers truly looked like 5480346 on this unit.

After trying to find a rebuildable original 5480346 unit I turned to Lone Star Calipers who told me pretty much what Joe Lucia has said, that the casting number really is 5460346.

I bought a repro unit ($80) from Lone Star that is one of the truest reproduction units that I've ever seen. It has the two bleeder screws & the "PG" stamp. However, I have no idea how it will do on the judging field.

Good luck,

Anthony

[William S.]

Re: '68 Brake Master Cylinder

Joe,

I'll go with 5460346. I have the 3rd edition of the JG manual. Hopefully, later versions will have the casting number corrected.

There is what must be a split ring mark located 1"-2" ahead of the casting number--I thought it was some kind of broach mark because of its small size. Using a mirror, I found a number on the fender side of the master cylider under the front bail wire. The top line was 718 and in bigger characters below it was D5. The unit has a separate proportioning valve (3 fittings) below it. For what it's worth, the large booster unit attached to the master cylinder also has a number 143A902 on the top. The car is a 400hp automatic with a late June, 1968 build date.

I appreciate your help in sorting all these numbers out.

Bill

[Dick W.]

Re: '68 Brake Master Cylinder *NM*

[Joe L.]

Re: '68 Brake Master Cylinder

Bill-----

The "split ring" is the Delco logo; there is usually no other reference to Delco on the castings other than the "split ring".

The "D5" denotes the Danville, IL foundry where these master cylinders were cast and the pattern number.

Does the master cylinder have bleeder valves and does it have a 2 alpha character stamping on the front?

[William S.]

Re: '68 Brake Master Cylinder

Joe,

Other than the D of the D5, there is no alpha character anywhere on the unit. There is no bleeder valve anywhere, only the two lines that come from the unit and go immediately to a proportioning valve (below the master cylinder) that is held by a bracket off of the master cylinder-brake booster junction.

To correct an error, the number on the side is 178, followed by the D5 below it, not 718 as I earlier reported.

Bill

[Dick W.]

Re: '68 Brake Master Cylinder

I do not know what happened to the info that I typed in my last post, anywho, probably where the 5480 came from is some bad castings that Moraine did. The "6" looks just like an "8". I have one of those laying around here somewhere. The manual revision (whenever that is done) will make the correction. We have be accepting the 5460 for a long time

[Joe L.]

Re: '68 Brake Master Cylinder

Bill-----

The lack of bleeder valves indicates that it's a 1973-74 or later unit. It may be a SERVICE replacement. The later cylinders did not usually have the 2 alpha character stamping on the front of the cylinder as there was usually no machined area on those units. However, they may have had the 2 alpha character coding stamped elsewhere on them.

[William S.]

Re: '68 Brake Master Cylinder

Joe,

Thanks for the info. I'm still curious about the 178 number above the D5. It has every indication of being a date code in that it has the marks on either side of the number suggesting that it was from a plate attached to the casting mold. But how is this number interpreted ? Is the 178 the day of the year ? If so, what year? Is it month and day and year ? If so, how exactly is it decoded ? The JG manual gives no insight(p. 58, 3rd edition) on how to decipher the date code, which the manual acknowledges exists. Thanks.

Bill

[Anthony S.]

Here's a good examle

Of a 546 that looks like a 548........

http://cgi.ebay.com/ebaymotors/67-68-69-Camaro-Corvette-Disc-NOS-GM-Master-Cylinder_W0QQcmdZViewItemQQcategoryZ33566QQihZ014QQitemZ330207157599QQrdZ1QQsspagenameZWDVW

[William S.]

Re: Here's a good examle

Anthony,

Thanks for the reference. In reviewing the JG manual and the available Archives, I wonder if the PG, DC, and SA designations "mean" something or other, or if they were just arbitrarily chosen letters to distinguish the different applications for the 5460346 casting.

Bill

[Joe L.]

Re: '68 Brake Master Cylinder

Bill------

The number series "178" MAY represent a julian date code. However, if it does, there is no year indicated. You will also find the same sort of date coding on some Corvette calipers manufactured during the 65-72 period when these were being cast at Danville, IL. Later calipers, which were cast elsewhere, have a date code which does include a year. The "yearless" date coding, if that's what it actually is, is something that the Danville foundry practiced with some regularity.

I once checked these "date codes" on the calipers on my original owner 1969 for which I obviously know that the calipers are original to the car. My car was built in September, 1969. Presumably, any calipers used on this car would have been cast during 1969. However, there was not a "9" to be found anywhere on ANY of the calipers.

In any event, assuming that the number series found on the master cylinder in question is a date code, without a year it's fairly meaningless. It's not judged, either.

[Joe L.]

Re: Here's a good examle

Anthony-----

I totally agree that the "546" does often look like "548". However, I'm virtually 100% convinced that it's "546". Like I mentioned, I can't find any indication that any part numbers in the "548" series were ever actually used or released by Delco-Moraine. Plus, there are quite a few known brake part numbers which are in the "546" series. On top of all this is the fact that the master cylinder in question was released in late 1966. I can't see any reason that Delco-Moraine would have been using a "548" series part number at that time, assuming they ever used them.

[Joe L.]

Re: Here's a good examle

Bill-----

The 2 character stamped numbers are not "abbreviations" for anything. They are simply a broadcast code which relates to a particular master cylinder FINISHED PART NUMBER. The 5460346 casting was used for several master cylinder finished part numbers, for Corvettes as well as other GM cars. Variations in the final machining and included parts determined the finished part number for the assembly. It was much easier for assembly plant personnel to identify the correct part to be installed by a 2 alpha character code than by complete finished part number. So, the broadcast coding system was used. It was also used for MANY other components installed on the assembly line.

In fact, the build sheets used for later Corvettes (after about the mid 70's) had a series of boxes on them for a myriad of components to be installed on the assembly line for any particular car. Within the boxes was printed the broadcast code for the component to be installed.