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Newbie on diesels - Need advice on diesel swap

R

rd durham

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Need some advice. I've never owned a diesel, though I've run and maintained a few over the years as part of work.

I've acquired a 1979 GMC Jimmy that use to have a gasoline 350 V8. The Jimmy is missing the engine, transmission and transfer case, but has the drive shafts. It also has a ten bolt front axle and a twelve bolt rear axle (ratio unknown at this time). I've also purchased a low miles (15,000 miles approx.) 6.2 diesel out of a CUCV Blazer, along with the TH400 automatic transmission and 208 transfer case. The 6.2 also came with the diesel radiator.

I plan on putting the diesel drive train into the Jimmy. I know I'll need to swap the starter, but any advice as to what problems will crop up or what I need to be looking for? Also will the axles hold up to a the 6.2 diesel? Do I need to change/modify the radiator support to accommodate the larger diesel radiator?

Thanks in advance.

R. Dale Durham
Colorado Springs, CO
 
Welcome to the site! You have come to the right place. You might want to PM TrustyK5. I am sure he will post up here soon. He did the exact same swap and will give you plenty of advice. You might want to look for a parts truck to donate all of the little items that you will need. Good luck with your swap! /forums/images/graemlins/thumb.gif
 
do you have the wiring harness to the 6.2? The swap is'nt that hard if you have the wiring harness.You will also need glow plug relay .The hardest part is defently the wiring.Your axles should hold up ok if your tires are36's or smaller.The radiator should fit with little modificaion.
 
The wiring harness was just cut at the firewall. Since the engine doesn't have all the glow plug control system, I had planned on using a Ford starter or RV battery solenoid to activate the glow plugs, possibly wiring into a ten second delayed cutoff relay. Then use the coil wire for the fuel shut off solenoid. I am not sure what else I would need for wiring.

I don't know how much off road use this truck will get. I have an IH Scout II/Terra that I use for hauling and most of my off road use. More than likely the Jimmy will get tires from 31" to 33", but not much bigger, as it won't be off road all that much. Primarily this will be my daily driver, though the wife is hinting she might be interested in having it if it cleans up nice.
 
Things you'll need if you do not have a donor truck.

All the hydroboost stuff for the brakes
Seeing as it's a 79 you'll either need to modify the rad support or you could swap a 81 and up front clip on as the rad support for those has all the correct holes and stuff for the big diesel rad (and every other rad avaialble at the time)

The diesel throttle cable is about 16" longer than the gasser version.

Motor mounts work just fine.

Second battery tray, second battery.

For the TH400 there is an electric kickdown switch inside the cab near the gas pedal that makes the tranny downshift and stuff. Pretty simple, easy to miss, and might be a pain to drive without it.

The motor itself should have the glow timer and stuff right on the motor so I don't see a need to 'build one' even without a proper harness. Haynes has a good book for diesel's that has a rather large section on wiring and the different variations between the years. I just unplugged the harness from the firewall and plugged the diesel harness in. Couldn't have been simpler for me. The relay is an easy part to find at any parts store.

Starter...I can't stress enough the importance of a strong fast starter for the 6.2. The 28MT gear reduction starter is the better of the two styles. With a poor starter you will pull your hair out trying to start it...especially cold. I sacked up and bought a brandy new one and it'll spin fast enough to start from cold without the glow plugs in 50F weather.

The diffs in your truck should be just fine. The M1009 the motor came out of had 10 bolts front and rear with 3.08 gears and 31x10.5s stock. If your truck has gears deeper than 3.08's you might want a slightly taller tire to compensate and keep freeway RPM's down.

Hopefully you have all the accessories and brackets for the 6.2. They are all very different from the sbc and bbc.

If I think of more I'll add to this.

Rene
 
All the brackets are on the engine, but both alternators are missing. Did the CUCV use a Delco SI alternator? Delco 12si, 15si or 17si by chance? If I remember correctly the power steering pump is on the engine.

The engine does have a vacuum pump installed at the rear of the engine. So would I really need to swap to hydroboost at this time?

Sounds like I will need to locate a junkyard diesel to at least find the kickdown switch and wiring, or see Chevrolet will sell them at a reasonable price.
 
[ QUOTE ]
All the brackets are on the engine, but both alternators are missing. Did the CUCV use a Delco SI alternator? Delco 12si, 15si or 17si by chance? If I remember correctly the power steering pump is on the engine.

The engine does have a vacuum pump installed at the rear of the engine. So would I really need to swap to hydroboost at this time?

Sounds like I will need to locate a junkyard diesel to at least find the kickdown switch and wiring, or see Chevrolet will sell them at a reasonable price.

[/ QUOTE ]

I am not sure how good the vacuum pump is on these engines, but I thinm it can activate a 350 or 700 tranny, I wouldn't trust it on my brake booster though.
Maybe someone that has this pump can give a better opinion.
 
I think you could probably run a large accumulator for the short term. Hydro-boost is much better though.

Rene
 
[ QUOTE ]
Which hydroboost is best? The one off of a pickup or will the one off of a all wheel drive GM Astro van work for something as large as a Jimmy?

[/ QUOTE ]
I would go with one from the pickup just because for sure it's a straight bolt on.
Maybe the one in the astro is the same but since I don't know I go with what I know.
/forums/images/graemlins/thumb.gif
 
You can use the vacuum boost, but I wouldn't recommend it. These vacuum pumps tend to wear out over time, so you'd probably need a new one anyway, so that's another $100 or more right there. Then, you'll need an accumulator/resorvoir/tank, whatever you want to call it, to store enough vacuum to make the brakes work right.

I've been running vacuum assist brakes on my '81 since 1996. The only problem I have is that I don't have any power brakes for a few moments after the engine is started...it takes a while for the vacuum to pull down and get to working. The hydroboost setup is instant. Also, if you step on the brakes several times in a row, you start to lose assist. If you don't have the reservoir in the system, you can only step on the brakes three times in a row until you're out of vacuum: not safe when backing up to a dock or trailer or something like that. You'll run into something for sure.

Hydroboost is better, but you can always try the vacuum setup and see if it works.

Casey
 
I noticed on my donor truck that the 400 torque converter had 6 bolts, not 3. Also, the diesel flex plate has an extra weight attached to it. The sock in the fuel tank is made of different stuff. There are 12VDC electric motor driven vac pumps available. I saw an old Furd p/u with a Cummins in it and the guy was running vac brakes and an electric vac pump.
 
[ QUOTE ]
I noticed on my donor truck that the 400 torque converter had 6 bolts, not 3. Also, the diesel flex plate has an extra weight attached to it. The sock in the fuel tank is made of different stuff. There are 12VDC electric motor driven vac pumps available. I saw an old Furd p/u with a Cummins in it and the guy was running vac brakes and an electric vac pump.

[/ QUOTE ]

Yeah all diesel autos have 6 bolts on the TC and the diesel is externally balanced like most BBC's.
And as you know diesel reacts to some plastics different from gas.
 
Some sources for electric vacuum pumps used on other vehicles are:

Ford Escort & Mercury Lynx Diesel powered cars, part number: E4FZ-2A451-A

Various General Motors cars & trucks, part number: 22034995

These normally cost anywhere from $100 and up and were used to supply vacuum to power brakes. I've seen them used on older Jeeps and Scouts that used vacuum wipers.
 
Went shopping this week at a local Pic N' Pull and got a number of items for my converting my '79 Jimmy to diesel. Local boneyard had two early '80s GM diesel vans. Pulled the brackets and some of the pulleys off both engines. The AC bracket was cracked and/or broken on both engines so figured might need a spare. Also pulled the alternator brackets off both engines. Didn't get two complete sets as some or the AC brackets, on the AC were just too far gone to fix. Did get a starter and the stock alternator (61 amp), both look like they have been recently installed. Starter and alternator were nice and clean with rebuild stickers, while the engine was dirty and oily.

Pulled both hydro boost systems. On one of the vans someone had cut up the front of the van and wrenched out the rod from the hydro boost to the brake pedal arm, but I think I can fix it. Also pulled hoses and grabbed a 21si 100 amp alternator off of a Cadillac DeVille.

The 21si alternator fits the alternator mounting bracket on the CUCV engine & lines up with the pulley, but it is too tall for the adjusting arm. I am thinking about modifying another adjusting arm that I have to accommodate the 21si alternator. If worse comes to worse I can just use the 12si alternator I pulled off the diesel van. I also kept every single nut and bolt, especially the intake manifold bolts that are used to mount the AC bracket.

Is there anything else that I might need off these vans? Any suggestions? Will the hydro boost bolt right up to my '79 Jimmy or do I need modifications? I know the lines will have to be modified, but there is a local shop that will do the work if I bring in the old lines from the Jimmy and the vans. All I have to tell them is which ends go where, how long and get the checkbook out.

The yard also had a 1987 GMC pickup with a really nice front clip. I'm assuming that this will bolt right onto my Jimmy and let me use the diesel radiator without modifications to the radiator support. It also would let me get rid of the rust front fenders. If it won't work for the radiator let me know.
 
[ QUOTE ]
Went shopping this week at a local Pic N' Pull and got a number of items for my converting my '79 Jimmy to diesel. Local boneyard had two early '80s GM diesel vans. Pulled the brackets and some of the pulleys off both engines. The AC bracket was cracked and/or broken on both engines so figured might need a spare. Also pulled the alternator brackets off both engines. Didn't get two complete sets as some or the AC brackets, on the AC were just too far gone to fix. Did get a starter and the stock alternator (61 amp), both look like they have been recently installed. Starter and alternator were nice and clean with rebuild stickers, while the engine was dirty and oily.

Pulled both hydro boost systems. On one of the vans someone had cut up the front of the van and wrenched out the rod from the hydro boost to the brake pedal arm, but I think I can fix it. Also pulled hoses and grabbed a 21si 100 amp alternator off of a Cadillac DeVille.

The 21si alternator fits the alternator mounting bracket on the CUCV engine & lines up with the pulley, but it is too tall for the adjusting arm. I am thinking about modifying another adjusting arm that I have to accommodate the 21si alternator. If worse comes to worse I can just use the 12si alternator I pulled off the diesel van. I also kept every single nut and bolt, especially the intake manifold bolts that are used to mount the AC bracket.

Is there anything else that I might need off these vans? Any suggestions? Will the hydro boost bolt right up to my '79 Jimmy or do I need modifications? I know the lines will have to be modified, but there is a local shop that will do the work if I bring in the old lines from the Jimmy and the vans. All I have to tell them is which ends go where, how long and get the checkbook out.

The yard also had a 1987 GMC pickup with a really nice front clip. I'm assuming that this will bolt right onto my Jimmy and let me use the diesel radiator without modifications to the radiator support. It also would let me get rid of the rust front fenders. If it won't work for the radiator let me know.

[/ QUOTE ]

Well I have the van with the 6.2 and a truck with the 6.2
There are some differences in the accessories between them.
The hydraboost is not the same different backing plate.
Might work but it's not the same.
I think the crossover pipe is also different if you want to get the engine.
I was going to get one for my Van and never found a van with a 6.2 so I looked at the trucks.
It's not a big deal if you have the original where you can get the oddball pieces from your old engine but you want to change.
Just thought I'd let you know.
/forums/images/graemlins/thumb.gif
 
Are you planning on single or dual exhaust? The '83 diesel Silverado I just picked up has dual, my '77 gas has single. Is it dual becuase it's a Silverado or because it's a diesel.

Rich
 
I have the Y-pipe from the 350 that was in the Jimmy and it looks like it will fit the diesel with very little modifications. So I was planning on a single exhaust. Go from two 2 1/4 inch pipes into one 3 inch pipe.
 
[ QUOTE ]
Are you planning on single or dual exhaust? The '83 diesel Silverado I just picked up has dual, my '77 gas has single. Is it dual becuase it's a Silverado or because it's a diesel.

Rich

[/ QUOTE ]

Stock for the diesel was 2 1/4" duals.

I run a single 2.5" system right now...I have some H1 headers that I'll likely install and then I'll run better exhaust.

Rene
 
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