"Papa Smurf" - 1966 GMC 1500 Custom

[GMCNUT]

Originally Posted by Funky61

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Looks to be the rare Sport truck option one year only. Congratulations.

Funky, I had a copy of that ad many moons ago and I took it to the framing shop and they destroyed it. Not getting into how and become irate again, but they destroyed it. Very poor communication between the owner and the idiot who ruined it. Anyway, I am going to guess you don't want to sell yours, but would you do me a solid and post a WTB ad in the marketplace on this site showing your ad in a clear picture so we can see who else has a copy they might sell?

[Funky61]

Hello GMCNUT, That is just a copy and paste saved from a thread at the 67-72 Forum or an old eBay ad I don't recall, but I don't have the actual ad.

I will post up the WTB for you.

[LordNatedawg]

It has been a while, but I'm back with another update. Working on more family cars has kept me busy. They take priority over Papa Smurf, unfortunately. Also, I bought a new-to-me GMC 1500. That one is 46 years too new to talk about on this forum, lol. Anyways, I also have an update on Papa Smurf.

I completely rebuilt both rear hubs and gutted the old drum brakes. I installed new wheel bearings and races, new seals, and new studs and lug nuts. Next logical step would be to install the new brake hardware. Just need another day of decent weather so I can do that.

Here are some part numbers if anyone needs them. I have a Dana 60 rear diff. that came out of a Jeep J20. Keep in mind that there were a few variants of the Dana 60 that these parts may not fit.

Wheel Bearing (Inner): Timken 28678
Bearing Race (Inner): Timken 28622
Bearing Race (Outer): Timken 18620
Wheel Bearing (Outer): Timken 18690
Wheel Seal: Timken 455860
Axle Shaft Flange Gasket: Fel-Pro 55350
Axle Nuts and Washer Kit: QK4763
The axle nuts require a 2-3/8" socket.
Lug Stud: 6413166 (Napa)
Lug Nut: Dorman 611161
My lug nuts and studs are 9/16". I believe every other truck had 1/2" studs.

[FetchMeAPepsi]

Good job on the part numbers. For the other projects, you can put them in the

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. I put my woodsplitter build in there and even installing my water heater.

[POWERSTROKE]

Since we're talking full floating rear axles, 25 years ago now I was fretting over getting a half or 3/4 ton truck. And I'm not sure why but almost 25 years later and 320,000 miles later it still has the factory installed bearings and seals. Guess I made the right choice all those years ago.
Never stops amazing me how these GMC trucks were built! Not many common parts with a Chevy, but I bet it's almost easier to get the GMC parts today than the Chevy parts.

[LordNatedawg]

Finally got around to assembling my rear drums. Without any detailed photos to reference, I have to assume that I followed my service manual's directions correctly. It got too cold and dark to actually adjust them, so I put the old drums back on for now. Sometimes later I'll have to finish installing brake lines to the wheel cylinders, put on the new drums, and get everything adjusted properly.

If you see something wrong in my photos, please let me know. This is my first time doing a full assembly of drum brakes. The pictures are showing the passenger side drum assembly.

Part numbers:

Rear Drums - ND 4401202 (12" x 2.5" / Lug holes are meant for 9/16" lug studs)
Self-Adjusting Hardware - Carlson H2555/H2554
Drum Hardware - Raybestos H7128
Wheel Cylinders - Centric 13462016/13462015
Brake Shoes - Raybestos 127PG (Semi-metallic pads)

And a note. The golden bracket you see in the photo is not replaceable. Earlier in this thread I mentioned how it was missing. I was able to track one down (Dorman HW2553) and then I had it copied and mirrored by a precision metal shop. It wasn't cheap to do. Don't throw them out!

[Funky61]

LND, here is a link with some drum brake assembly photos.



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[LordNatedawg]

Originally Posted by Funky61

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LND, here is a link with some drum brake assembly photos.



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Thanks for this. Based on these photos, I have no reason to believe anything is assembled wrong. I even followed my service manual step-by-step. Shouldn't doubt myself too much.

Unfortunately, there is a problem somewhere in the braking system. Today I adjusted my drums, installed the last two pieces of brake line, and then vacuum bled everything. Ran about 2 quarts of fluid through the system. Haven't had a single air bubble all day, but the pedal has a lot of travel. It goes down about half way to the floor before it gets stiff. With the truck running, there almost isn't a brake pedal at all.

The last time I had an issue like this was on a Saturn Ion. I had just replaced the master cylinder, it experienced these symptoms, and it turned out the the new master cylinder had a bad internal seal.

Too many factors to consider on my truck. I replaced every single item you can possibly replace in the brake system. I have no way of knowing if all the parts are compatible or not. I'm relying on aftermarket manufacturers correctly labeling products.

My truck has some braking power, so I plan on taking it on a very slow road test to see if anything changes. If nothing else, the parking brake seems to work. It's super tight and I can only get 3-4 clicks out of it.

As much as my dad would hate me for doing it, I could always borrow the MC out of his 74 just to see if mine is the issue or not. I could only see the problem being either the:
1. Master cylinder
2. Proportioning valve
3. Improperly adjusted push-rod
4. Non-compatible MC bore size

On the bright side of all of this, it has enough braking power that I can probably move my truck to the driveway and get it out of the slanted gravel pit.

Sorry if the post is jumbled. I'm a bit frustrated.

[Funky61]

That’s got to be very frustrating LND;
Sorry to hear that...

Here’s a link from CPP on figuring out brake issues that might help you.



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[LordNatedawg]

Vented my frustrations, read through CPPs troubleshooting sheet, and then did some research on braking systems.

Here's what I came up with:

After looking at old part numbers (**** glad I documented part #s), it appears that I ordered a MC and brake booster kit for a 1/2-ton truck. Meaning the bore of the MC is too small to push out the required volume of fluid needed for 3/4-ton disc brakes. It explains why my pedal has a good amount of resistance, but goes to the floor. The MC is currently producing pressure, but not volume.

The bore I have on my MC is likely 1" or 1-1/8". The solution is grab a MC and proportioning valve off of a 1979 GMC 3/4-ton (to match the front discs). They used a 1-1/4" bore. This will allow me to meet the volume needs of the heavy duty disc brakes.

Essentially what we're looking at is the difference between JB5, JB6 and JB7 braking systems. JB5 systems are on light duty 1/2-tons (your typical GMC 1000 or Ch*vy C10). JB6 systems are on heavy duty 1/2-ton and light duty 3/4-ton. JB7 is for light duty 1-ton and heavy duty 3/4-ton. I mixed and matched JB5, JB6 and JB7 parts. My truck has a GVWR of 7,500 which would put it in the JB7 category (7,500-8,400).

So, I'll be ordering a new master cylinder for a JB7 system and I'll see where that gets me. Probably a new proportioning valve too, just to be on the safe side.

*This post is a compilation of everything I researched today. It is accurate to the best of my knowledge.*