Newbie - 78 GMC Sierra Classic 25 Camper Special

[BuckB78GMC]

Howdy guys, I'm new to the forum and the proud new owner of a 1978 GMC Sierra Classic 25 Camper Special 2WD. It has the 454, TH400, Corporate 14 bolt. It has a few dents and the original Burgundy or Maroon paint is a bit faded. The interior is in pretty darn good shape for a 32 year old truck that was I bought from a farm in the hills above Snohomish, Washington. It has a tilt steering wheel, AC (that still works), full gauge package and I believe as part of the Camper Special thing a HEAVY duty tow hitch, dual saddlebag style fuel tanks. 20 gallons each, I think, big radiator, auxiliary tranny cooler and it was wired for a bumper pull trailor, fifth wheel trailor and slide in camper. I do have a few of the known issues with this type of truck, though. The doors have to be slammed hard and lifted to close and even when closed they rattle when going over bumps. Are there adjustments I can do or pieces that can be tightened? I need to pull the passenger side door panel off and knock out a dent, anyway. The fuel gauge looks to be reading correctly for both tanks when I flip the switch on the dash but, I found out the hard way that my tank selector valve was not switching my tanks. So, I need to get that troubleshot down to a switch, selector valve or wiring issue. I now have it just feeding off the driver's side tank which is all fine and good because the previous owner couldn't find the key to the passenger side locking gas cap...so, I will be removing that the hard way unless one you knows an easy way to get them off. I was thinking a drill or BFH but, both of which could cause a spark and ruin my whole day....lol. Also, as stupid as I sound. How do I get the rear brake drums off of that full floater Corp. 14? I'm guessing take the bolts out of the flanges and pull the axles first. The secondaries aren't opening on the Q-Jet 4bbl carb which from the numbers I looked up appears to be the original put on in 78. However, the Motor is painted and still shiney Goodwrench crate motor black. There is also no engine ID number on the little plate in front of the passenger side head. Both of these lead me to believe I have a replacement engine which I have no clue what the specs are. It has a fare bit of lope to it at idle but not much in the way of neck snapping torque or HP that I can feel. I'm not sure how much of that is Carb, issues. Like I said, the secondaries don't open at all and it's leaking fuel out of just about every place it can and still run. So, I'm guessing the whole thing is one big vacuum leak. Probably why my secondaries won't open. If any of you sould help me out with troubleshooting for the fuel tank selector or the secondarie issue with the carb. or pulling the rear brake drums it would be very much appreciated. I also have the brake grabbing issue that I've read about with these trucks in the rear brakes. I just re-packed my front wheel bearings and put new pads on the front brakes so that area is all good. From what I can tell it needs new balljoints and tierod ends, too. One of the previous owners put a very stupid or cheap exhaust system on it, too. It has 2.5" pipes running from the manifolds to the Cheesey (ballooned) turbo muffler. Then, it has tiny little 2" tailpipes exiting behind the rear wheels. As soon as I can afford it, I will be getting glasspacks or Flowmaster 40s with 2.5 inlets and outlets and 2.5" tailpipes put on. I'm guessing a 454 + small tailpipes = the "exploded" as my local muffler shop called them, mufflers. That could be part of my aparent lack of power, too. Bad air and fuel mixing on the way in and blocked up exhaust can't possibly make for a very happy 454...lol. I flipped the stock air cleaner lid for more air. That was an old trick I learned way back in the day. I'm not even sure if it's benefiting my truck at all or not. Oh, also, does anybody know what a truck set up like mine would have for a rear ring and pinion gear ratio. I can jack it up and do the old count DS to tire revolutions and figure it out for myself but, I was just curious if anybody knew. I guess that's about it for now. My name is Brian Buchanan and I live in Oak Harbor, Washington. I am a 24 year Navy Chief Petty Officer. I will be retiring this summer and going to work for the Northrop/Grumman Corporation as a Weapons Systems Instructor (government contractor) on the new EA-18G growler tactical electronic attack jet fighter aircraft. Thank you so much ahead of time for any help I get. I will definitely share what I learn as I tackle my issues with this truck so others can learn from my wrenching.

[gchemist]

Welcome to the site.

Pictures please!!

[ray_mcavoy]

Welcome Brian!

Yeah, post up some pics

The door issue sounds like worn out hinge pin bushings. With the door open, try lifting up on the latch end. If the bushings are worn, you'll be able to feel the door wobble up/down a bit on the hinges. Replacing the pins & bushings usually fixes the problem.

Also check the striker bolts in the door jambs. They have a built-in plastic bushing that often wears out and makes the doors hard to close without slamming.

The tank selector valve for this year is a simple 1-wire hookup. All the other wires in the dual tank harness go to the gauge/sending units. The wire is green if I remember correctly. To run off the main tank, no power is applied to that wire. When you switch to the auxillary tank, power from a jumper that plugs into the fuse box is fed (through the dash switch) to the green wire leading to the solenoid valve. Use a test light on that wire to see if the dash switch & associated wiring is okay. Also make sure the solenoid valve is securely bolted to the frame and that the connection is free of dirt/rust since that's the solenoid's ground connection.

The ID stamping on some big blocks is on a pad above the timing chain cover (instead of on the pad in front of the pass side cyl head).

Q-jet carbs have a lockout mechanism that keeps the secondaries from opening up while the engine is still cold. It's tied into the choke mechanism. So make sure the choke is opening all the way and not sticking.

The secondary throttle plates are hooked via a linkage rod to the primaries. Unless the lockout mechanism is holding them, they will always open (even with the engine off). However, the secondary air doors (up on top of the carb) only open based on airflow demand. Just reving the engine up (no load) won't make them open. You should be able to push the secondary air doors open by hand though (against slight spring tension) ... if not, check for something that's binding/sticking.

The grabbing rear brakes could be due to a leaking wheel cylinder or axle seal that's contaminating the brake shoes with brake fluid or gear oil. If I remember correctly, the wheel studs are pressed through the brake drum, then through the hub, connecting the two together. So to remove the drum/hub assembly, you have to unbolt and slide out the axle shaft. Then remove the snap ring, key, and nut. That'll allow you to pull the whole drum/hub assembly.

[BuckB78GMC]

Ray, Thank you so much for all the good information. I really had my eyes opened when I bought this truck. I was thinking old chevy, I've owned many...Well, cars that is. Trucks are a whole different ballgame. I've also never owned a big block chevy. I've alway just tinkered with small blocks in the past. I will get some pics posted as soon as I take a few.

[BuckB78GMC]

I threw this one pic I have of my truck up so you guys can check it out. I'll take some better ones of it and add them soon. This was before the addition of the new mufflers and 2.5 inch tailpipes but the tailpipes still come out in the same place.

[C10Silverado79]

Regarding the locking gas cap with no key, I would suggest you stop by a Lock Smith and have them remove the cap. I doubt it would cost much and much better than creating a spark or dropping parts into the tank.
JMHO

[BuckB78GMC]

Thanks for the words of wisdom.

[munice]

welcome! but....

[78 Big10 454]

Hey, Brian, welcome from Socal and thank you for your military service. This is the best Board around with definetly the most knowledgeable people (and I'm not talking about myself!). Good luck with your truck - gotta love those 78's!

[BuckB78GMC]

Well, I've been addressing the bigtime wobbles I have at highway speed. I got all 4 tires balanced which the technician said were waaaaay out. That helped a little bit. I also changed out the right side outer tierod end which was so wasted I could grab the tire sides and wiggle it about a half inch in and out or more.

[DrMr]

I have an 82 GMC Sierra 2500 Camper Special. The rattling of the doors can be fixed by cutting off 3/4" of 1/2" pex pipe, splitting it with a box cutter or a saw, spreading it open so it fits on the striker post like a sleeve. This replaces the original part and makes the doors latch easily. No more slaming or rattling.

There are tons of sites discussing Q-jet issues associated with the secondaries. A good one is: http://www.thecarburetorshop.com/Troubleshooting.htm