JL8 master cylinder

[bertfam]

309 MC with US Stamp is the correct one

Dave, 5468309 is the CASTING number of the master cylinder and has no real bearing on the application. That casting number was used on multiple models and even multiple divisions in 1969 with different part numbers and codes, depending on the application.

Ed

[69Z28-RS]

It *seems* to be a fact that the JL8 factory installed brake system included the '309' cast MC with US stamp, and of course, as Bert points out, this doesn't necessarily mean that the parts are assembled the same.  Any differences should be reflected in the bill of materials (BOM) for the part number (PN).  But.. in this case, the same MC part number used on Camaros with  either JL8 OR J52 disk/drum brake systems.  I would assume that these 'master cylinder assemblies' were assembled completely at Delco-Moraine prior to delivery to Norwood or VanNuys, which raises the question as to 'when'how' were the differences in the residual pressure valve (an internal part of the assembled Master cylinder) accomodated?  Did Delco Moraine build them two different ways (with and without the rear brake residual pressure valve)?  OR did they build them with the valve and the assembly plant remove the valve from the rear outlet??  OR were the valves, springs, seats included as loose parts in the MC package, and the assemblers used what they needed to?  (curious minds want to know!)..

The CRG archive/reports section on brakes says this...
"1969 J52 disc brake systems and JL8 four wheel disc brake systems used similar master cylinders. The only difference between the master cylinders was the J52 master cylinder (code US) had a check valve in the outlet for the rear drum brakes, whereas the JL8 master cylinder did not have any check valves."

Since the same PN MC (5463751 ) was used for both brake systems, how was this difference accommodated?   The only answer I can come up with is that the differences associated with  the 5463751 master cylinder would have to be accommodated at assembly time??  but wouldn't the AIM reflect that?  (I just took a quick look at the AIM and didn't see anything on this issue?)...

[bertfam]

Since the same PN MC (5463751 ) was used for both brake systems, how was this difference accommodated?

Gary, the assembly line part number was different than the service part number which is what I posted above.

For example, the assembly line part number for the 69 Camaro J52 master cylinder, as called out in the AIM (UPC J52, Sheet A2, item 1), was 5468165. This included not only the master cylinder, but the booster as well and it came to Norwood/LA as an assembly from Delco.

The same goes for the JL8 master cylinder. It would have come from Delco to Norwood/LA as an "assembly" (master cylinder and booster) with it's own part number (which is unfortunately unknown since the AIM doesn't show it).

Therefore, it would have been Delco that would be building the "assembly", and in the case of the JL8, not installing the RPV in the master cylinder.

Ed

[JKZ27]

Doesn't the service manual describe the check valve usage and, possibly, letter code usage? Also, it should show the RCV(residual check valve) service procedure per application since they're removable. Install only one check valve for front disc or no valves for 4 wheel disc.

[jdv69z]

Since the same PN MC (5463751 ) was used for both brake systems, how was this difference accommodated?

Gary, the assembly line part number was different than the service part number which is what I posted above.

For example, the assembly line part number for the 69 Camaro J52 master cylinder, as called out in the AIM (UPC J52, Sheet A2, item 1), was 5468165. This included not only the master cylinder, but the booster as well and it came to Norwood/LA as an assembly from Delco.

The same goes for the JL8 master cylinder. It would have come from Delco to Norwood/LA as an "assembly" (master cylinder and booster) with it's own part number (which is unfortunately unknown since the AIM doesn't show it).

Therefore, it would have been Delco that would be building the "assembly", and in the case of the JL8, not installing the RPV in the master cylinder.

Ed

So was "US" stamped on master cylinder the same as the broadcast code for J52 master cylinder on the assembly line? If the JL8 cylinder is different, then the broadcast code would have to different. But is it possible that at Delco they used the same "US" stamped cylinder without the residual pressure valve rather than having it stamped differently? But then attach a tag (I'm assuming there was a broadcast tag attached to the assembly at Delco) with the correct broadcast code to the complete cylinder/booster assembly before shipping to the assembly plant? Is the broadcast code for the JL8 known?

[bertfam]

The Broadcast Code for front disc brakes/rear drum brakes was CU, and for 4 wheel disc brakes it was CX, so yes, they're different, and yes, the tag on the bail wire would be CU (front disc) or CX (4 wheel disc).

I don't have a service manual for 1969, so maybe someone could look that up. I'm not sure it mentions the 4 wheel disc brakes though.

Ed

[JKZ27]

In the 1969 Chassis Service Manual, there is a chart listing the master cylinder codes and their usage. Here's a few;
Camaro and Nova with power disc.......US
Chevelle with power disc....................BA
Corvette with power disc....................PG
"The two-letter identification stamp on the end of the master cylinder indicates the displacement capabilities of that particular cylinder."
There are no special service procedures for the master cyl in the 4 wheel disc section as it simply refers you to the Duo-Servo Brakes section.

[bertfam]

There are no special service procedures for the master cyl in the 4 wheel disc section as it simply refers you to the Duo-Servo Brakes section.

Yeah, I didn't think there would be.

As for the same code being used for front disc/rear drum and 4 wheel disc master cylinders, I believe (and this is my opinion only) that since the JL8 option was rarely called for, if Delco got an order for the JL8 master cylinder/booster, they would simply pull a CU assembly, remove the RPV and retag it as a CX. This would explain why both master cylinders are stamped US.

Ed

[bcmiller]

That makes sense to me Ed.

[ZLP955]

That is a good theory, especially as it seems the JL8 cars were scheduled in batches.

[69Z28-RS]

OK Ed, that tells us how GM handled the difference in the factory (via a *different PN*) for a higher level assembly (and tag CX, CU, etc), but for someone with 4-wheel disk brakes on their car, who go into the parts department to purchase a replacement MC (for whatever reason), the service MC being the same PN would mean they got the same part.   Did that part include the RPV or not?  IF the MC PN does not include the RPV, springs, and seats, then the repair person would remove those parts from the old MC and install them in the new MC (problem solved), BUT.. if the MC PN (5463751) included those small items - which only seem reasonable to me - then people repairing a 4-wheel disk system with a new service PN would find themselves with their rear brakes not working correctly after replacement with a GM service part.   Is there any means to find how how that PN was defined??

In my experience, the PN *defines* the complete bill of materials for an item... and I don't know how a company's manufacturing and delivery system would function if this wasn't true.

[bcmiller]

Is there any means to find how how that PN was defined??

I doubt it.

May have been included in a service note somewhere, but it is such a low volume item - it probably don't get much press.

Servicing one is covered well starting on page 5-16 of the 1969 Chassis Service Manual.  Mostly.

"No check valve is required for disc brakes" is specified - but they only mention the front, saying "the outlet boss to the front brakes will not contain a check valve and spring".  I guess I would read into that - those two items are not required in the outlet boss to the rear brakes either - if you have rear discs. But maybe I am assuming too much.

That's about all I can find if you want something in written format.

[bertfam]

I agree with Bryon, and would go on to say that there may have been a "Chevrolet Dealer Service Technical Bulletin" or one of the monthly "Chevrolet Service News" editions that mentions this.

Ed

[bcmiller]

I looked in all of the 1969 Chevrolet Service News monthly publications, but could not find anything on JL8 Master Cylinders.

I will try to look in the Service Bulletins - but I don't remember there being any from when I looked through all of the ones I have about a year ago. But I don't have access to them all.

[big iron]

There are no special service procedures for the master cyl in the 4 wheel disc section as it simply refers you to the Duo-Servo Brakes section.

Yeah, I didn't think there would be.

As for the same code being used for front disc/rear drum and 4 wheel disc master cylinders, I believe (and this is my opinion only) that since the JL8 option was rarely called for, if Delco got an order for the JL8 master cylinder/booster, they would simply pull a CU assembly, remove the RPV and retag it as a CX. This would explain why both master cylinders are stamped US.

Ed

How would they handle a JL8 replacement in the field? Would need some kind of work instructions for the dealers or P&A would have side note explaining the removal of the valves. I think the side note in the P&A would have been used as the parts person would pass the information to the mechanic.
No side notes in any of the P&A's, so must be another explanation or maybe that is the explanation.
Bob