J76 Park Brake Park Shaft

[dagnabbitt]

So I am trying to get my 1968 C20 on the road - build thread coming soon I hope - and it's getting interesting.

The truck has numerous odd features for a vehicle purchased by some Canadian farmer 50 years ago, but the one that is stumping me is the J76 code in the thread title. Very little mention of this code in the forum except that it is considered quite rare and most people seem sure that it was only offered on C30s.

I understand the basic concept of a prop shaft ebrake, but I don't really know what I am working with here. It seems like it is missing some pieces... for example I have no idea what it is supposed to look like, much less how to engage it: is there a handle or a lever somewhere?

If I am unable to repair or restore it, can I just add a regular old drum e-brake?

Does anyone have any knowledge of this component, pictures, anything at all would be appreciated.

[LockDoc]

Originally Posted by dagnabbitt

So I am trying to get my 1968 C20 on the road - build thread coming soon I hope - and it's getting interesting.

The truck has numerous odd features for a vehicle purchased by some Canadian farmer 50 years ago, but the one that is stumping me is the J76 code in the thread title. Very little mention of this code in the forum except that it is considered quite rare and most people seem sure that it was only offered on C30s.

I understand the basic concept of a prop shaft ebrake, but I don't really know what I am working with here. It seems like it is missing some pieces... for example I have no idea what it is supposed to look like, much less how to engage it: is there a handle or a lever somewhere?

If I am unable to repair or restore it, can I just add a regular old drum e-brake?

Does anyone have any knowledge of this component, pictures, anything at all would be appreciated.

There are some threads on that type of brake on here. If you type "drive shaft emergency brake" or "drive shaft parking brake" into the Google search box at the top of this page, click on the circle in front of "67-72chevytrucks.com", and click on the google button you will see them.

LockDoc

[dagnabbitt]

Thank you LockDoc, I will search with those parameters, I was looking under the SPID code and couldn't find much.

In the meantime and in-between-time, if anyone has anything new to add lay it on me please.

[dagnabbitt]

So after searching the forums I still haven't found a 67-72 C20 with this setup, just a school bus and a '63. But looking at the second link there is a picture from someone with just two posts which shows me that I am likely missing some parts: I do not have a lever coming off the 4-speed tranny through the cab, for one thing.

All the past threads end the same way: what the heck is this thing and where can I find parts. Hoping someone on here might be familiar with this and can help me. Alternatively, I guess what I will eventually do is put in a regular old drum ebrake in place.

http://67-72chevytrucks.com/vboard/s...d.php?t=664961
http://67-72chevytrucks.com/vboard/s...d.php?t=622541

[toolboxchev]

Cool that you found a C20 with this. I have seen it on the C50's.

[dagnabbitt]

I'm starting to get the impression that this was only offered on light pickup trucks built in Canada, ie at the Oshawa plant.

I'd still like to see some pictures of this set up if anyone has some. I am trying to figure out if it used the standard under the dash handbrake or if it had the brake coming out of the trans hump next to the 4 speed stick.

I guess there isn't any particular reason why I can't install a conventional wheel drum ebrake, but it'd be nice to make it original. Once again, any clues to how this would have looked from inside the cab would be appreciated.

Wonder if parts from a C50-60 with the same set up would just bolt on?

[chewychevy67]

I've had quite a few and know many others who have them in Canada and I've never seen this on a half or 3/4 truck. I'm sure yours isn't the only one though. Post some pictures of yours if you can for those who don't know. May help in the search. How big is it? It must almost rub on the bottom of the cab. The larger trucks cabs sat higher on the frames.

[dagnabbitt]

Took me long enough to post this picture, I know, but I really figured the next post would be of me solving the problem. No such luck, this is a weird option for a light duty vehicle. I still believe that they were only offered at the Oshawa plant.

To catch up, I parted out a couple of 67 GMCs this year and one thing I did was rob the entire cab-to-rear emergency brake assembly from one of them. I still have no idea if the J76 had the underdash handle like all other 68's (some of this style brake came off the trans hump on other vehicles), but it does now.

The problem I have is that the cable comes up a little short, it doesn't quite reach from the dash to the prop brake. Looking of options on extending the cable, seems to me that something like that is available somewhere.

Aside from the dust and cobwebs, the drum on this contraption is in good shape so I think I am almost there.

As I have mentioned in other posts if anyone has seen a J76 brake before, I would be interested in any info and pics you might have. The most difficult thing about restoring this option is just trying to convince people that it is original and I am not crazy.

[dagnabbitt]

Still trying to get this one on the road!

I think that the drum itself is fully functional and ready to be used, but the entire assembly going to the cab was missing. So I scrounged a dash mounted parking brake handle and cable from a 1967 and installed it... but it comes up a bit short, like about 6-8 inches.

Is it possible to lengthen a parking brake cable by attaching another section to it, or is that inadvisable. Is there a place that anyone recommends who would custom make a cable?

Of course, if anyone has seen this setup before I would appreciate your advice.

[Luvlegs]

Could it have used an "eared" tab like most vehicle emergency brake cables under vehicles... Each end ( the one you have now and the extension, having a ball on the end of the cables) The ones that look like a folded over washer with slot/holes for the balls to go into?

Try typing that description out of your head... Whew!

[firedemon]

you might try custom harley cables 75-76 sportys used a cable similar to our parking brake cable and its been a few years but i know you could get them made to custom lengths . possibly might be able to buy a kit to make your own

[dagnabbitt]

Originally Posted by firedemon

you might try custom harley cables 75-76 sportys used a cable similar to our parking brake cable and its been a few years but i know you could get them made to custom lengths . possibly might be able to buy a kit to make your own

Thanks I will check that out!

[dagnabbitt]

I've been doing some more research and keep finding little bits of info that are tantalizingly close to what I am looking for. It appears that in 60-66 trucks this setup was relatively common, and it was controlled by a handbrake next to the gearshift. Picture 1 is pretty much how it goes.

Picture 2 is my trans hump, there is/was no provision for a handbrake - I even removed the rubber boot to be sure - so it remains a mystery to me how the propeller brake was engaged. I am going to have to guess that it was from under the dash like all other 67-68s, using a cable.

I am going to look into the custom cables suggested above, but am wondering if I can get a 60-66 handbrake and make a hole in the appropriate spot to engage it that way directly, no cable necessary. I need to pull off the trans hump or crawl under to see if there is a linkage mounted to the side of the transmission to accept it.

[dagnabbitt]

I finally pulled the trans hump off of the cab to get a better look, and the trans does indeed have the specific top cover that has the provision for a handbrake. Someone decided they did not need it anymore or it broke and they just left it as is.

After scraping about a pound of muck off and spraying it down with cleaner I was able to read the following numbers, 3830574, and A2364. What I think I have here is an SM420 that was cast on January 23, 1964. Perhaps someone can confirm.

So this is a conundrum, kind of, but here is what I know or am pretty sure of:

• This truck does indeed have the J76 Prop Shaft Park Brake option on the SPID, ie. from factory. If it wasn't right there on the SPID I wouldn't have believed it and thought maybe this transmission was an early swap.
• This type of J76 parking brake was somewhat commonly offered on light trucks as late as 1966, but I have seen only two or three 1967-1972 C10 or C20's that have it after searching 20 years of discussion in this forum.
• ALL of the few that I have found were made in Oshawa, Ontario Canada, including mine.
• Despite being a 1968, it has a transmission that to the best of my knowledge was discontinued in 1967. I have never seen it's replacement, the SM465, with a prop shaft brake attached to it.
• Even more odd, the transmission that is in it is stamped 1964. I have absolutely no reason to believe that this transmission has ever been out of the truck: the truck is in horrible, original condition.
• Assuming that all of the above is true I am going to guess that the Oshawa plant was using up old transmissions for a few years. My 71 year old Chevy mechanic friend says that this is plausible, he started his first job around this time and (he thinks) he remembers this happening at the Oshawa plant.

I don't know if the trans hump is original... looking at it I wonder if it was originally blue, I see some red underneath: regardless, it has been removed and reinstalled at some point, maybe because it was replaced with one that eliminated the beside-the-shifter handbrake slot that was common up until 1966. Or, maybe it is original and the brake was operated from under the dash like all 67-68s were, with a special cable and different routing... I am doubtful of this, though, as the trans clearly has a spindle that the handbrake rotates on, and it does show wear from use. Regardless, I am thinking of installing a handbrake next to the shifter as I have seen all pics of this set up do, and make a spot in the trans hump for it to go through.

I feel like I am solving a mystery of sorts, it's too bad that this extremely rare option doesn't make the truck more valuable, just more difficult to restore. Feel free to chime in, this all started because of a "rare option SPID" thread and I got curious about what the heck this was.

[Accelo]

It looks like the hump cover on you truck may have been replaced. I am assuming there is no other provisions for any type of parking brake. I am confident a parking brake was required. This setup was likely used to avoid the complexities of adding a parking brake to the rear wheels. I have seen this on school buses and all sorts of heave equipment. I agree it may be rare on a C20. It appears to be the correct transmission as it matches the SID. These transmission typically outlast the truck they are in. Another reason I believe it's likely an original. it is unlikely GM would have used more than one method of operation for the same brake.

[dagnabbitt]

Originally Posted by Accelo

These transmission typically outlast the truck they are in. Another reason I believe it's likely an original.

That's a pretty good point I had not thought of, who breaks one of these? Thanks!

[dagnabbitt]

I have run the casting numbers on the 292 (build thread in signature, more pics there) and found that it was made on May 4, 1964. So it probably belongs with the transmission since they were made a few months apart.

Does it make any sense that an engine and trans would be cast but lie around for 3-4 years before being put into a truck? Does my theory that this truck with a weird option, common in 60-66... and which seems to have only ever existed in Oshawa-built trucks... was built with driveline parts from the previous generation, hold water? Was the Oshawa plant the repository or dumping ground for a bunch of J76 driveline parts that did not get used in the previous gen?

Hopefully someone can chime in, it has been fun researching this and I am imagining someone finding this thread in 2038 and getting their own questions answered.

Anyway, the very good news: I have all the various parts that were missing installed, and it works! Thanks, BigBird. Handbrake might be from a big truck, though: it is longer than ones I have seen in my small collection of photos. Wondering if there was a shorter one for light trucks?

Also, I finally took a look and sure enough the backing plates on the rear brakes have no holes where you could attach a parking brake cable. So this is a J76 truck, alright. The mystery of the casting dates continues, though.

[CG]

Interesting read. As long as Ive been on the board I somehow missed these things even existed.

[Steeveedee]

I worked at a repair shop in Idaho in the mid-'70s. I seem to recall that those were mostly on Dodges, but a few Chevies had them. All farm trucks.

[BigBird05]

Lock at your firewall and see if there is a hole for the hand operated parking brake cable or for a block off plate in the hole.

[dagnabbitt]

I don't see a block off plate, of course it might been there at one time. Lots of the rubber grommets on the firewall have fallen off or been removed.

[Ironangel]

Interesting read, just when you think you've seen it all, a J76 shows up!