68 gmc c2500 396 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Chknlyps2 · 05-01-2016, 05:51 PM

I picked up a 68 GMC with a 396 a couple months ago. It was at my friends place for a few years (along with 2 others, both 70's but that is for a later thread) and he only started it every couple months and the gas was starting to smell bad. I siphoned out all I could and added 5 gallons of fresh gas and got it running. It ran real rough, like on 5 or 6 cylinders but it idled and still drove ok but had zero power. Master cylinder was dry and the brake pedal went to the floor so we filled it up and bled the brakes several times and got them to work so so.

I hopped in and drove it 3 miles home on back roads, it ran rough, has a pretty harsh 2 to 3 shift on the 4 speed tranny but it drove nice and straight and the road feel felt good.

I figured the rough running was one or more of the following. Bad gas, carb needing rebuilt, plugs, wires or points. I have a couple HEI's so I thought I would put one in with plugs and wires to rule out the ignition system. The plugs were terrible, 3 were light brown/tan and the other 5 were so black and covered with fried oil buggers that I am surprised it ran at all. Below is a couple pics of the truck and a few of the plugs good to bad.

Chknlyps2 · 05-01-2016, 06:07 PM

Well it runs better with the new distributor and plugs but still not great. still sputters and a general lack of power. Cleaning the fuel tank and going through the carb is next when I get time. I pressure washed the motor a little to get some of the grime off (It cleaned up pretty good!) and I found on the left inner fender some chalk marks of an old compression test. 120 / 90 / 120 / 110. The worst plug was from #1 cylinder which said 120. On the pass side I can make out 120 and 110 but that is it. I will do my own test to see what I get later on but the low numbers don't look to promising.

The last pic is the cast iron distributor that was in it. It has a tach drive but the build tag is missing. I figured it was swapped some time back.

35boulder · 05-01-2016, 06:14 PM

Good luck with your build. Plugs look nasty!

Chknlyps2 · 05-01-2016, 06:31 PM

Do any of you guys know where to get the plug wire separators that push on to the metal tabs on the valve covers in the first pic? I am missing the passenger side. I found them one night a few weeks back and thought I saved the web site but can't find it now.

The carb tag numbers are pretty warn off and the tags are different that the other Q-jet carbs I have. On the bottom tag I can see 7153AA then below it 24389264190 I think. The top tag is faded all together.

Is there a specific kit for big blocks or are the kits the same as small block's?

Chknlyps2 · 05-01-2016, 06:35 PM

Quote:

Originally Posted by 35boulder

Good luck with your build. Plugs look nasty!

Thanks and I agree they do!

Chknlyps2 · 05-01-2016, 07:10 PM

Couple of odd/interesting things in the cab, the rear view mirror and a brass tag above the radio. Is the mirror aftermarket? I have never seen one like this. The paint is all crackled and looks cool and the bracket is strange, looks like a threaded center support with a lock nut but the side supports look welded.

I need to clean the brass tag a little to see what it says, There is some faint stamping on it but hard to make out. #ILK#FS TEXACO

At some point the rear end was swapped out with a 14 bolt unit and a flat bed was installed. The VIN shows it came as a V8 fleetside made in Fremont CA. Did 68's come with only an Eaton or was a Dana 60 an option? I have the Dana 60 that was on the 72 GMC frame & bed behind the 68 that I could put in it to replace the 14 bolt.

**dutchmanz** · 05-01-2016, 07:12 PM

I think those carb numbers are something else. I'd guess it's not the original carb or its a rebuilt version. Qjet numbers should be stamped vertically on the drivers side rear of the carb.

Chknlyps2 · 05-01-2016, 07:19 PM

Quote:

Originally Posted by dutchmanz

I think those carb numbers are something else. I'd guess it's not the original carb or its a rebuilt version. Qjet numbers should be stamped vertically on the drivers side rear of the carb.

I kinda thought it was a replacement also. My other Q-jets have vertical numbers but in the same place as these tags. Rear drivers corner.

Chknlyps2 · 05-04-2016, 09:38 PM

I don't know what I was thinking, the numbers for the carb were right there. 7045213, according to Cliffs Quadrajet site http://www.cliffshighperformance.com...carb_ID_2.html it is a 1975 body. I will order a kit this weekend.

Anyone remember who sells the wire separators that clip on the valve covers pictured above?

05-01-2016, 06:07 PM	#2
Chknlyps2 Registered User Join Date: Feb 2016 Location: Anza, CA Posts: 160	Re: 68 gmc c2500 396 Well it runs better with the new distributor and plugs but still not great. still sputters and a general lack of power. Cleaning the fuel tank and going through the carb is next when I get time. I pressure washed the motor a little to get some of the grime off (It cleaned up pretty good!) and I found on the left inner fender some chalk marks of an old compression test. 120 / 90 / 120 / 110. The worst plug was from #1 cylinder which said 120. On the pass side I can make out 120 and 110 but that is it. I will do my own test to see what I get later on but the low numbers don't look to promising. The last pic is the cast iron distributor that was in it. It has a tach drive but the build tag is missing. I figured it was swapped some time back. Attached Images Last edited by Chknlyps2; 05-01-2016 at 07:27 PM. Reason: spelling

05-01-2016, 06:14 PM	#3
35boulder Registered User Join Date: Oct 2015 Location: Dallas Texas Posts: 1,380	Re: 68 gmc c2500 396 Good luck with your build. Plugs look nasty!

05-01-2016, 06:31 PM	#4
Chknlyps2 Registered User Join Date: Feb 2016 Location: Anza, CA Posts: 160	Re: 68 gmc c2500 396 Do any of you guys know where to get the plug wire separators that push on to the metal tabs on the valve covers in the first pic? I am missing the passenger side. I found them one night a few weeks back and thought I saved the web site but can't find it now. The carb tag numbers are pretty warn off and the tags are different that the other Q-jet carbs I have. On the bottom tag I can see 7153AA then below it 24389264190 I think. The top tag is faded all together. Is there a specific kit for big blocks or are the kits the same as small block's? Attached Images

05-01-2016, 07:10 PM	#6
Chknlyps2 Registered User Join Date: Feb 2016 Location: Anza, CA Posts: 160	Re: 68 gmc c2500 396 Couple of odd/interesting things in the cab, the rear view mirror and a brass tag above the radio. Is the mirror aftermarket? I have never seen one like this. The paint is all crackled and looks cool and the bracket is strange, looks like a threaded center support with a lock nut but the side supports look welded. I need to clean the brass tag a little to see what it says, There is some faint stamping on it but hard to make out. #ILK#FS TEXACO At some point the rear end was swapped out with a 14 bolt unit and a flat bed was installed. The VIN shows it came as a V8 fleetside made in Fremont CA. Did 68's come with only an Eaton or was a Dana 60 an option? I have the Dana 60 that was on the 72 GMC frame & bed behind the 68 that I could put in it to replace the 14 bolt. Attached Images

05-01-2016, 07:12 PM	#7
dutchmanz Knuckle Buster, Instructor Join Date: May 2010 Location: Pantego, NC Posts: 562	Re: 68 gmc c2500 396 I think those carb numbers are something else. I'd guess it's not the original carb or its a rebuilt version. Qjet numbers should be stamped vertically on the drivers side rear of the carb. __________________ Current classic fleet: 72 K5 Blazer CST, unrestored factory Orange paint...mostly 69 C10 factory SWB, 454, TH400, Saddle tan, Rust-o-ration 53 Studebaker M35 w/331 Reo gas I-6, Air Force Strata Blue

05-01-2016, 05:51 PM	#1
Chknlyps2 Registered User Join Date: Feb 2016 Location: Anza, CA Posts: 160	68 gmc c2500 396 I picked up a 68 GMC with a 396 a couple months ago. It was at my friends place for a few years (along with 2 others, both 70's but that is for a later thread) and he only started it every couple months and the gas was starting to smell bad. I siphoned out all I could and added 5 gallons of fresh gas and got it running. It ran real rough, like on 5 or 6 cylinders but it idled and still drove ok but had zero power. Master cylinder was dry and the brake pedal went to the floor so we filled it up and bled the brakes several times and got them to work so so. I hopped in and drove it 3 miles home on back roads, it ran rough, has a pretty harsh 2 to 3 shift on the 4 speed tranny but it drove nice and straight and the road feel felt good. I figured the rough running was one or more of the following. Bad gas, carb needing rebuilt, plugs, wires or points. I have a couple HEI's so I thought I would put one in with plugs and wires to rule out the ignition system. The plugs were terrible, 3 were light brown/tan and the other 5 were so black and covered with fried oil buggers that I am surprised it ran at all. Below is a couple pics of the truck and a few of the plugs good to bad. Attached Images

05-04-2016, 09:38 PM	#9
Chknlyps2 Registered User Join Date: Feb 2016 Location: Anza, CA Posts: 160	Re: 68 gmc c2500 396 I don't know what I was thinking, the numbers for the carb were right there. 7045213, according to Cliffs Quadrajet site http://www.cliffshighperformance.com...carb_ID_2.html it is a 1975 body. I will order a kit this weekend. Anyone remember who sells the wire separators that clip on the valve covers pictured above? Attached Images



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