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Discussion Starter #1
Hey guys. I just joined up. I have a 1986 GMC Jimmy K5. It came with a 305 in it. I have done several upgrades such as a cam, headers, dual exhaust, and a new carb, but still am not happy with the power. I have a 21 foot boat I usually use the Jimmy for. I found a 1984 Chevy K10 with a 6.2L diesel with a 4 Speed T10 manual trans. It as 104,000 miles and runs great. I'm thinking about swapping the diesel into my Jimmy as the trucks body is shot. It also come with a working plow. The guy wants 1000 for it. Is this a good price and a good idea for me to switch? Also will I have everything needed to do the swap since I will have the whole truck? Is this a straight swap or do I need to do fabricating? Also I want to keep my auto trans, I hate launching my boat with a manual, is this possible? What all should I look for when checking out this engine. I have done some searching but was hoping for some answers tailored to my situation. Thanks for your help.
 

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welcome to dieselplace. everything you need is on the donor truck, direct bolt in to your current truck.
T10? chevy/gmc dont use a T10. if its a 4 speed with a low gear, its an sm465, damn near bullet proof tranny. if it is a 4 speed with overdrive, its an 833.

you can use your auto, bellhousing pattern is the same on the 6.2 as it is on all small block chevy's. you will need a diesel torque converter though.

brake system from the diesel is better. what you need from the diesel for the brakes is the power steering pump, and the hydroboost assembly that is bolted to your brake master cylinder.

radiator from the diesel is needed as well. the engine will bolt up to your motor mounts, making this even easier. you will either need the exhaust from the truck, or fabricate your own.

as far as if the truck is worth the price, depends on where you live. where i am, it would be worth more than that. if you live up north you might be able to find others for a cheaper price.
 

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Discussion Starter #3
Thanks for the help. I live in Columbus, Ohio. The body on it is usable I guess, but not something I would want around, nor my neighbors (I hate the suburbs). After I swap it all, I will either put the 305 back in the truck and try and make some money back or just sell the truck for scrap.
 

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MattD86K5;1584516; said:
Hey guys. I just joined up. I have a 1986 GMC Jimmy K5. It came with a 305 in it.
Just keep in mind that the 6.2 doesn't have any more horsepower or torque then your 305 (actually less) - but it will be a lot better on fuel.

1986 stock 305 gas engine has 245 lb. ft. of torque at 1600 RPM and 155 horsepower at 4000 RPM.

1984 K10 6.2 diesel has 240 lb. ft. of torque at 2000 RPM and 130 horsepower at 3600 RPM.

Price does not sound too bad with a working plow - same setup around me in New York would sell around $500 at best for a rustbucket. I've got an 82 K10 with 6.2 diesel, fisher plow, four-speed manual overdrive trans (New Process 833) and traded 50 bales of hay for it (hay is one dollar a bale - i.e. $50). It's rusty but runs great. I've been thinking of fixing it up - but I know it will be useless for towing - especially with the 3.08 axles.
 

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I just think the diesel will last longer too, where as my 305 has 150,xxx miles on it so I know its old and worn. I think this would be a more worth while swap than replacing the 305.
 

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Just slap a turbo on it and you'll anihilate the old 305. You are definitely right about being able to get more miles out of the diesel. If you have the time you could even do an overhaul on the diesel before dropping it in since you still have a running 305. Headstuds and gaskets anyway.
 

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Welcome to the forum! :welcome:

You can swap the diesel in pretty easily. It is virtually a bolt-in installation, no cutting or modifications like that necessary. You can use your current transmission. You can actually use the existing torque converter and set up the governor for the diesel and it will work fine, although the diesel torque converter would be a little bit better. You will need to get a flexplate for the diesel if you want to use the automatic, but they are fairly cheap.

Diesels are great... They have lots of torque and get great fuel economy.

I'd swap the motor into the Blazer, put the 305 in the truck, and sell the truck... That way you get some of your money back. :cool:

Welcome again! :welcome2:
 

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MattD86K5;1584863; said:
I just think the diesel will last longer too, where as my 305 has 150,xxx miles on it so I know its old and worn. I think this would be a more worth while swap than replacing the 305.
Yeah - most 6.2s should outlast a 305 (but not always!). Some 6.2s diesels die early with broken cranks and main-bearing webs - but that is not common. My 87 diesel Suburban got to 520,000 miles before the block and crankshaft broke in many pieces. I say "should" because many stop getting used first time the injection pump craps out. I've bought many in that condition. Owned by someone who pays for all repairs, gets an $800 or more estimate to put a rebuilt pump on - and dumps the truck instead.
On an older gas engine - you don't see that sort of thing happen -since there is no ONE component I can think of - that locals can't work on - or that is very expensive.

The injection pumps had short life spans until 1985 when they were upgraded. Any older pump that is still being used has probably been upgraded already. The pumps after 1985 rarely will leave you dead on the road somewhere, they wear out slowly. After 100K the fuel timing advance gets sluggish. It can be adjusted on the vehicle and usually made to work - but eventually it requires a tear-down.

I bought a low-miles 86 diesel Blazer recently. The injection pump went and the guy burned up the starter trying to get it going. Local shop gave him a $1500 repair estimate. He sold it to me instead.

What trans. are you using? If that manual is the NP 833, it's really not rugged enough for towing, and certainly isn't if you ever add a turbo. It's only rated for 260 lb. ft. of torque. Also, transfer cases come with two different splines - one for T400 and SM465s, and the other for TH350s and 700R4s.
 

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Discussion Starter #9
I want to use the one that came in my Jimmy. Its an auto with overdrive. I have not yet looked up the specifics, but I think it is a 700r4, maybe.
 

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since its an 86 it is a 700r4, plenty of aftermarket upgrades for it to make it alot stronger.
 

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Yeah, it should be a 700R4. If it is all stock it definitely isn't the strongest tranny to run behind a diesel (especially for towing), but it will work. Aftermarket upgrades would definitely be good if you want to run it behind a diesel, but in stock configuration many of those transmissions lasted a long time. Since you do plan to tow with it I would recommend a transmission upgrade at some point although it isn't absolutely necessary.
 

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Discussion Starter #12
What kind of upgrades to the trans should I do? How about gears? I still want to be able to use the 4WD some.
 

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High Sierra 2500;1586000; said:
Yeah, it should be a 700R4. If it is all stock it definitely isn't the strongest tranny to run behind a diesel (especially for towing), but it will work.
It doesn't have anything do with being hooked to a diesel or gas - it's just a matter of max. engine torque. A stock 6.2 doesn't make enough torque to be a big problem, whereas a 6.2 or 6.5 with a turbo could be. A 305 gas engine with a good cam and turbo would be just as problematic. In fact, the 305 was designed to be a high torque engine with the long stroke taken from the 350 - quite different than the older 307s or the HP 302s.

The weak-link - even with a modified 700R4 is the lock-up converter. The heavy-duty upgrades eliminate it - which kind of defeats the reason why many want it - better fuel mileage. But, a careful driver can just make sure OD and lockup is not used when towing.

With the Ford automatic-OD setup, there are high-torque, mutliple clutch lock-up converter kits along with larger studs where it all bolts to the flywheel. Also, once electric controls came into use - and the 700R4 became the 4L60E or 4L65E - torque-shock between shifts and line pressures are monitored and adjusted on an ad hoc basis.
 

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MattD86K5;1586016; said:
What kind of upgrades to the trans should I do? How about gears? I still want to be able to use the 4WD some.
If you buy a $15 700R4 repair manual, it will give you a current, piece by piece explanation of upgrades available. I'm sure you can find the info on-line also. Number one - I assume you don't know for sure what year your trans. is - without reading the ID code off of it (it's stamped into the passenger-side rear). And, even when you determine the year - you might not know how many upgrades it has alreay had. The early 1982 - 1984 transmissions can be made just as strong as the newer ones, BUT require more large parts changes - and thus more money spent.
Using 4WD has nothing to do with most of this - since the weak-link in the 700R4 is the fourth overdrive and the lockup converter - and neither will be engaged when you are using 4WD anyway. They also shouldn't be used when towing.
For the most part, the heavy duty upgrade parts are cheap. What to do with the converter is another issue - since I assume you cannot take it apart to check it. It has to be cut apart and then welded back together. That's why it is usually standard procedure to just buy an exchange unit.
 

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Discussion Starter #15
I know not to use the 4WD when towing, but It does help when coming up steep ramps with my boat behind it, especially slick ones. What I meant about the gears is if I change the rear gear to a taller one, do I need to change the front one too? Thanks again for all the help guys, diesel and 4WD is still fairly new to this garage tinkerer.
 

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What kind of upgrades to the trans should I do? How about gears? I still want to be able to use the 4WD some.
There are many failure points and corresponding upgrades that can be done to a 700R4 to help it hold up and last a long time. It all depends (as usual) on how much you want to spend and how involved you want to get. You could start with the basic shift kit and leave it at that, you could go all the way and do a complete buildup for the application, or you could do something in between... Your choice.

If you wanted to build an awesome transmission to go behind the diesel, you'd want to start with a late model transmission out of a 4WD truck (if your transmission is the original it should be pretty good). In general with the 700R4, the newer the tranny, the more upgrades are on it already. There were slight differences between the different 700s... 4WD truck transmissions had the strongest cases. You'd want the later model with the larger input shafts. Then you'd want to add a good, strong pump. The list goes on... The problem with this is you can get a pretty large parts bill really quickly. You can easily spend $1000 in parts building a good quality 700R4 for a diesel.

As far as gearing goes, most Blazers came with 3.08 gears. That's great for fuel economy when you are running empty, but not very great for off-roading, towing, or your 700R4 (the 700 doesn't like torque and you need a lot of torque to tow with those gears). 3.42 or 3.73 gears would be better for towing and light off-road use. If you've got a really heavy load you might even want to gear it lower than that... That said, if I were you I think I'd see how I liked it with those gears and the new engine before going to the trouble of changing the gears.

EDIT: And yes, you definitely need to gear the front the same as the rear...
 

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Discussion Starter #17
Sounds good, I'll get it swapped first before I worry about the gears. I have only taken it off-road once. I mostly use the 4WD for boat ramps and snow. My boat is said to weigh 2800 pounds, but I'm not sure I believe that. My Jimmy REALLY struggles with it. So either my boat weighs a lot more than they rate it at, or my engine is very tired.
 

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Well, gears will help with that. It's going to be hard to tow anything at all with 3.08s. Still, I'd wait until after the motor swap before you mess with the gears...
 

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MattD86K5;1586071; said:
I know not to use the 4WD when towing, but It does help when coming up steep ramps with my boat behind it, especially slick ones. What I meant about the gears is if I change the rear gear to a taller one, do I need to change the front one too? Thanks again for all the help guys, diesel and 4WD is still fairly new to this garage tinkerer.
There's no problem with towing in 4WD - but there IS with driving in 4WD on hard pavement - towing or not. The transfer case that gives you 4WD has a torque rating that greatly exceeds any other part of the drivetrain.

In regard to putting in a different rear axle ratio? Will not work. Ideally, the front axle ratio is supposed to be slightly different and turn faster than the rear - the idea being that - when in 4WD - the front is always slightly pulling - and the rear NEVER pushiing. That's what keeps you going straight down the road on ice and/or snow. Don't worry about the math - just make sure the front axle "stated ratio" matches the rear. If you ever have tires with uneven wear, always install the newest looking with the largest OD on front - otherwise handling on slippery roads will be screwed up.

When it comes to 4WD and overdrives - it can sometimes be a problem. For example, the most expensive overdrive system on the market - made by Gear Vendors - when in OD - only change your rear-axle ratio and NOT the front - so 4WD use is NOT permitted in OD mode. It attaches to the output of the transfer-case.

On the other hand, Ranger makes an overdrive gearbox that hooks up before the transmission and is fully operational in 2WD or 4WD - but it is only available for standard transmissions.

That's the nice thing about a unitized overdrive trans. - like the 700R4, or an updated TH400 that became the 4L80E. Also the NP833, NV3500, NV3500HD, or the NV4500. Most can be installed without shortening or lengthening driveshafts like most of the OD add-ons require.
 

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MattD86K5;1586097; said:
Sounds good, I'll get it swapped first before I worry about the gears. I have only taken it off-road once. I mostly use the 4WD for boat ramps and snow. My boat is said to weigh 2800 pounds, but I'm not sure I believe that. My Jimmy REALLY struggles with it. So either my boat weighs a lot more than they rate it at, or my engine is very tired.
Many boats weigh a lot more than they are supposed to once they get old - especially if fiberglass. Fiberglass boats use a lot of wood inside the hull where you cannot see it. My 20 footer - a 1970 Glastron got really heavy - and finally when the transom got kind of shaky, I cut the floor out, and split the boat in half and repaired it. I was really suprised at how much wood was below running the entire length of the boat - and also - how incredibly water-logged and heavy it all was. I re-did all the lower wood with white oak - and it now trailers - and cruises much better. In fact, it acts now like an entirely different boat and sits much higher in the water.
That's why a boat is always supposed to be stored with the nose up in the air, and the rear transom water-plug removed.
 
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