My New '68 GMC ... kinda Ouch - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Droff · 02-06-2017, 12:03 PM

My first post with a question or two. I've searched and read, searched and read. I want a nice looking/good running truck, not a show truck. I think I've got a decent start down that path...

I picked up a '68 GMC 3/4 ton yesterday, first truck I've owned in this age range, still learning what the particulars are to suspension and braking with an 8 lug. It's got a 350 ('86 age range) and 350 auto transmission, column shifter. A few bubble spots/rust spots with the clear coat coming off but a good 20-30 footer for the most part. Drum/drum brakes with no booster, not used to that at all, so that's my first (maybe second fix) on the truck.
I test drove it, rode like a 50 yr old truck, ran it up to 65, steering was fairly solid, not too much play. All seemed good enough. Paid the man, got the title and a full tank of gas and headed out.

Got out on the road, ran it up to 65 and it starts cutting out, losing power and speed, like it's choking for fuel. I pull over and let it idle for a few minutes, no sputter or cough, sounds and feels smooth and even. Take off again and climb to about 60 and the problem re-starts. Process repeated for about a half hour until I can get it to the house, just at dark.

I figure a couple new fuel filters and most likely cleaning the Edelbrock carb on it and then see where things go from there. It doesn't look like the original tank but I'm not sure what one would look like, this one just looks 'newer'. Could be trash in the tank too, don't know yet. The PO drove it, it wasn't a sitting truck. So that's my first fix unless I should be looking another direction?

Once I get it going, I need help getting it stopped (second fix). I want to drive it so I don't want a lot of down time or too much cost initially. I figure just add a booster and that should help stop the right leg workout. I don't know that I need Captainfab's booster bracket, not too concerned with room in the engine compartment, I just need a booster I can bolt to the firewall, the MC and then to the pedal. I THINK I've got that worked out, still looking around at what to pick up.

Anyway, don't know how much I can add to the knowledge base that's not already here but it's nice having a place to go for some help.
Thanks.

**Boog** · 02-06-2017, 01:31 PM

Since it has an 86 engine it should have the big hei distributor. Use a volt meter to see if it has a solid 12 volts going to the distributor. The old points type distributors used less voltage like 7-9 or so. Hei will not provide enough spark to run very well at that lower voltage.
Next id look at the fuel supply. Filters and such.

Droff · 02-06-2017, 02:23 PM

Quote:

Originally Posted by Boog

it should have the big hei distributor

It does have one. My truck is still about 2 hrs away but it's in my son's driveway. If he gets the time, he'll most likely change out the filter, should be able to check the voltage as well. Otherwise, it'll be at least a week before I can get back up there.
Thanks.

**LockDoc** · 02-07-2017, 12:46 AM

Quote:

Originally Posted by Droff

It does have one. My truck is still about 2 hrs away but it's in my son's driveway. If he gets the time, he'll most likely change out the filter, should be able to check the voltage as well. Otherwise, it'll be at least a week before I can get back up there.
Thanks.

Welcome to the board.

If it is a stock tank there should be a sock filter on the end of the pickup tube that may be partially pluged up. Quadrajet carb will have a small filter in the fuel inlet also.

LockDoc

LongBox · 02-07-2017, 01:46 AM

Great that you got your 68, and these are good vehicles, so once you work out the kinks, all should be well. The posts above point to the standard approach: ignition, then fuel supply.

As for the brakes, my 69 has manual drums, and I personally do not find that it needs excessive pressure on the pedal to produce a reasonable stop.

Keep the thread alive, as we all learn from each other, and we'd like to know what caused the cutting out problem.

wbc409 · 02-07-2017, 03:57 AM

Double check your timing, and it could also be the mechanical fuel pump is starting to go bad.

Droff · 02-07-2017, 09:02 AM

Quote:

Originally Posted by LockDoc

If it is a stock tank there should be a sock filter on the end of the pickup tube that may be partially pluged up. Quadrajet carb will have a small filter in the fuel inlet also.
LockDoc

I'm not sure on the stock tank, the PO did install a new sending unit in the 2 yrs he owned it. I suppose the pickup tube is removable? There's an Edlebrock carb on the truck now but no filter from the fuel pump to the carb, I plan on adding one in there. There's a barrel looking filter inline from the tank to the fuel pump.

Quote:

Originally Posted by LongBox

As for the brakes, my 69 has manual drums, and I personally do not find that it needs excessive pressure on the pedal to produce a reasonable stop.

I feel like I need more than what I should need to get stopped, I haven't looked anything over on the brakes though. I can bleed them and see if it makes a difference.

Quote:

Originally Posted by wbc409

Double check your timing, and it could also be the mechanical fuel pump is starting to go bad.

PO told me he installed a new fuel pump, should be under 2 yrs old, but if nothing else is helping the problem, that's something to consider. I can check the timing, will need some internet help on that one. Last time I did/watched a timing check was around ...... 30 years ago.

**LockDoc** · 02-07-2017, 10:17 AM

Quote:

Originally Posted by Droff

I'm not sure on the stock tank, the PO did install a new sending unit in the 2 yrs he owned it. I suppose the pickup tube is removable? There's an Edlebrock carb on the truck now but no filter from the fuel pump to the carb, I plan on adding one in there. There's a barrel looking filter inline from the tank to the fuel pump..

Pickup tube is part of the sending unit. The Edelbrock will not have the fuel inlet filter. I would go ahead and change the inline filter, they are cheap and easy to change.

LockDoc

Bigdav160 · 02-07-2017, 09:19 AM

By chance is the brake master cylinder new(ish)? Using a power brake master cylinder in place of a manual brake master cylinder will increase the pedal effort.

4 wheel manual drums, when properly adjusted should stop fine without too much effort depressing the pedal.

James the III · 03-01-2017, 09:05 AM

Quote:

Originally Posted by Bigdav160

By chance is the brake master cylinder new(ish)? Using a power brake master cylinder in place of a manual brake master cylinder will increase the pedal effort.

4 wheel manual drums, when properly adjusted should stop fine without too much effort depressing the pedal.

For a person that never driven a manual all drum vehicle.. it can feel like to much effort. after being used to a power brake disc /drum or all disc vehicle..

First time I drove a all drum manual vehicle (71 chevelle) it felt like it needed more effort than normal.. but was normal, just I was spoiled and always had power brakes..

Droff · 03-01-2017, 09:31 AM

Quote:

Originally Posted by James the III

For a person that never driven a manual all drum vehicle.. it can feel like to much effort. after being used to a power brake disc /drum or all disc vehicle..

I've driven a manual brake vehicle before, but many years ago. I can agree with what you're saying but there were definite issues with these brakes. When I first drove it, by the time I got the truck stopped, I was pretty much out of the seat, standing on the pedal. You can see how nasty the fluid was when we drained the MC and bled the brakes for the first time.
Once I got the new wheel cylinders and was able to get all 4 corners bled, I can get stopped with just a little more pressure than a power brake setup.

I'm going with discs regardless though.

Droff · 02-07-2017, 10:18 AM

There's always a chance it's a new(ish) MC, but I don't really know and can't get an eye on it right away. Just by appearance, what would I be looking for? I've read a manual MC has a smaller bore than a power MC, but that's pretty much all I've gotten on the subject.

Droff · 02-08-2017, 10:55 AM

There are things I'd like to replace or get done on the truck other than what has been mostly obvious once I drove it.
As this is a '68 without the original motor, is there any easy way to buy engine parts at Autozone or O'rielly's without the guys there getting confused? I'm thinking plugs, oil filter, etc.
I figure a 350 is pretty much a 350 but then again....

LongBox · 02-08-2017, 11:39 AM

Easy way to check fuel delivery is to disconnect fuel line at carb, and hold end of line over a container, like a coffee can. Have someone crank the engine (Might want to disconnect centre distributor lead) and see how much fuel is delivered into the container.

I'm sure the specs are out there somewhere, but I don't have them.

If that checks out, time to go after the ignition. Pull one plug lead, and hold it near the exhaust manifold. When the engine is idling, there should be a strong spark, with a distinctive sharp noise.

These are very basic tests, but they might help you isolate your problem, and don't cost anything to perform.

Droff · 02-13-2017, 07:01 PM

OK, she's still about 100 miles away, haven't gotten her home yet but did a little work over the weekend.
We changed the fuel filter from the tank to the pump, nasty looking stuff ran out of it when we pulled it off. We also added another filter between the pump and the carb, a clear one so we could see how bad the fuel was looking.
Once that was done, we got after the brakes a little, drained the MC and was able to break 3 of the 4 bleeders loose, couldn't get a wrench on the fourth, it was right up against the rubber brake line coming into the drum. Bled three wheels, nasty looking stuff again, got a lot better pedal but still feels off to me, not sure why though. It would be best to pull the wheels and see if there is any shoe material left, just need the time. We did get on the road a little, once the brakes felt better. There was no throttle stumble, it responded to the pedal regardless of speed, so I'm thinking the filter had a big part in that problem. Haven't done anything with the timing yet.

There's a couple things that need attention and I'd like some input.
1. Brakes, swap to a disc setup, (boneyard or CL), or keep what I have and rebuild the drums/shoes as needed? Just to keep in mind, not too far down the road I'll need some suspension work, it all looks tired and old (ball joints and most other connecting parts). Opinions?
2. I need seat belts, I have none. Anything that's kind of a direct fit from a newer truck I could pick up at a boneyard?
3. Need front shocks, was thinking Bilstein's, only due to what I've read, not much shock experience with a 3/4 ton. Any other good choices?
4. The tailgate rattles a lot, are there bumpers or anything available to help it fit tighter or not rattle so bad?
5. Either clean the gas tank or get a new one and move it under the bed. I know there are plenty of threads on it, just undecided at the moment. Don't want to pay to get the tank cleaned, along with pulling it if I'm replacing it...
6. on the rear diff, is that a Dana 60 or 70? I didn't clear anything off to try and find a number, thought someone could tell from the pic. There may be or was a leak at the yoke on the front as well as the rear seal, not sure but something through some fluid around the underside.

Anyway, that's my update, thanks for the input.
I've attached a few pics. That's brake fluid, not coffee or Coke.

Droff · 02-16-2017, 04:41 PM

Still looking for some input....

Concerning the swap to disc, I've found that 73-87 year donor truck parts will fit, just need to change out the ball joints and tie rod ends. Would this also include a Suburban in the same year(s)?

I found a guy that will sell me the spindles, calipers and rotors, off of an '85-'86 Burb, in good condition for $200, just wanted to confirm. I want to stay with the 8 lugs I have, his rotors are 8 lug as well.

I haven't found any local salvage yards that carry trucks that old, haven't checked with a Pull-a-Part yard though.

Thanks.

Droff · 02-28-2017, 12:46 PM

I got the truck home last week, we worked on the brakes enough so they were driveable/useable but still not the greatest. I had noticed the tail lights being more white than red, as they were really washed out. Other than needing replaced and being a really bright white, they worked as required. Of course it got dark on the drive home and of course I got pulled over for not having red tail lights. And no tag light. Which led to verifying I didn't have insurance verification yet. A bit of a trifecta going on but she was nice and just warned me to get things taken care of.

Once home, I pulled the rear wheels and the shoes looked nearly new, so something wasn't right. I cleaned everything up and installed new wheel cylinders, pulled the front pax wheel and was able to get to the bleeder on that side. I got all 4 wheels bled and have much better brakes now, like night and day, figuring there was an issue with the wheel cylinders on the rear.

I painted the tail lights with some transparent red paint and they look like new. Replaced the turn signal socket up front on the drivers side so now all 4 corners are working, just no back up lights yet. I have a tag light to install, that will be done soon. I also replaced the exhaust so it runs to the rear and doesn't dump the Flowmasters out right under the cab.

I picked up a front end out of an '86 3/4 ton over the weekend. Booster, MC, A-arms, sway bar, tie rods, spindles, calipers, rotors - pretty much all of it. Everything needs cleaned up and I need to get some new rubber parts but it should do the job.

No fuel delivery issues have come up again.

Need some seat belts, shocks and a few fluid leaks resolved but so far so good otherwise.

68Gold/white · 03-01-2017, 11:52 AM

Quote:

Originally Posted by Droff

I got the truck home last week, we worked on the brakes enough so they were driveable/useable but still not the greatest. I had noticed the tail lights being more white than red, as they were really washed out. Other than needing replaced and being a really bright white, they worked as required. Of course it got dark on the drive home and of course I got pulled over for not having red tail lights. And no tag light. Which led to verifying I didn't have insurance verification yet. A bit of a trifecta going on but she was nice and just warned me to get things taken care of.

Once home, I pulled the rear wheels and the shoes looked nearly new, so something wasn't right. I cleaned everything up and installed new wheel cylinders, pulled the front pax wheel and was able to get to the bleeder on that side. I got all 4 wheels bled and have much better brakes now, like night and day, figuring there was an issue with the wheel cylinders on the rear.

I painted the tail lights with some transparent red paint and they look like new. Replaced the turn signal socket up front on the drivers side so now all 4 corners are working, just no back up lights yet. I have a tag light to install, that will be done soon. I also replaced the exhaust so it runs to the rear and doesn't dump the Flowmasters out right under the cab.

I picked up a front end out of an '86 3/4 ton over the weekend. Booster, MC, A-arms, sway bar, tie rods, spindles, calipers, rotors - pretty much all of it. Everything needs cleaned up and I need to get some new rubber parts but it should do the job.

No fuel delivery issues have come up again.

Need some seat belts, shocks and a few fluid leaks resolved but so far so good otherwise.

Did you get the frame cross member that the control arms bolt to???
You may need it, not sure if the 86 stuff will bolt up to the 68 cross member.

Going disc is the only way to go, although many here are satisfied with drum brakes...

There's a number on the block behind the driver side head that identifies the engine. If it is actually a 86 engine, it may even have "5.7" in same area also. I hope you don't have a 305...

Next best modification after getting proper brakes is getting the gas tank out of the cab. There's many choices, I like the Boyd's Tanks, I've seen here.

I was wondering if the lug studs are the same size on the 86 stuff. I'm only asking because my 3/4 ton knowledge is minimal, something you'd want to make sure of...

My brother lives in SW Oklahoma City.

Droff · 03-01-2017, 12:48 PM

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