A New-be to diesels'

[hdshadpar]

Hello everyone! Just made the leap to my first ever diesel and am excited yet nervous. Been reading some the threads already and seems like if you maintain them they are very efficient and economical. My 81 720 is a short box, sd22, with 229,000.

I also got a 83 in the deal which has a sd25 motor and is a long box, its all there except its rusty. My question is, what parts are interchangeable between the motors, running gear or body wise? Looks like the bumpers and glass are the same, which is good. I also got a sd22 head with the 83 as the guy was going to change heads account the sd25 has a crack but wouldn't fit???

The 81 runs fine, shifts fine and I'm going to change all the fluids once I see what types I need. The guy said he got around 40 mpg which is better than 16 in my El Camino. I will keep reading the threads but if there is something else I should know I would be pleased if you can advise. Tks JP

[waynosworld]

Welcome JP, I do not come here everyday but I try to check in every few days.

I would run the SD25 engine if it is good, the transmissions are interchangeable, but from the clutch cover forward there are differences, some things interchange and some don't.
The body parts themselves, hood, fenders, doors, windshield do interchange, but the stuff connected to them only interchange depending on the year, 1980 thru 1982 stuff interchanges as long as it is the same body type(1-regular cab/short box, 2-regular cab/longbox, 3-kingcab, regular cab and kingcab rear windows are different, 1980 thru 1982 grills interchange, 1983 thru 1986 depends on what it is, you can ask me and I will tell you if it will interchange and how to do it, like 1981 on you can put any grill you want on your truck, but if you want to put your 1983 grill on your 81 truck it might just bolt on or you may have to remove all the front sheet metal, lower the headlights 1 inch(holes are already there), and put all the sheet metal and grill on yours, it depends on the build date, 1984 on you would have to change out everything.
The 720 had a major change in 1983, the cabs were made a few inches longer and the boxes were made a few inches shorter, so even if you had a 1981 longbox truck, the 1983 longbox might be shorter and the cab might be longer depending on the build date, kingcabs are all the same length, so are the kingcab boxes, they all interchange.
If you ask me something I will try to answer if I can, do not scrap that SD25 engine, people will buy it and have the crack fixed in the head, SD25 engines are hard to find and have more power but get the same mileage, I actually have a SD25 block with a bent rod but a good head as far as I know.

Where are you located?

[hdshadpar]

Tks for the reply, Wayn, I am from Saskatchewan and about 10 miles from the Montana boarder (1 1/2) from Glasgow.

Ok, I plan on keeping the 83 until the parts that do interchange are off, so I did find out that the water pump will not interchange as the guy I bought it from has to change the sd22 pump and the sd 25 is different so he says, before he gets my money. How about the injection/fuel system, brake system etc.? The 83 cab is a regular cab like the 81, but it has cruise, tilt and power steering where the 81 doesn't. How about the front end components? I guess one needs to get a manual. Anyway, sd25 head is cracked, the guy bought a sd22 thinking it would fit. It ran when he parked it. The sd22 runs very nice and will probably just leave as is for I'm going to use it just for running around in the summer and park for the winter. One other important thing, what fuel additive should one use and do you add every time you get fuel? Like I said its my first diesel and know nothing of them....

[waynosworld]

I have never heard of a diesel truck with cruise control, if it really does have cruise control it likely has this electrical thing on the front cover somewhere below the water pump.
I thought all the water pumps were the same, but I don't know everything.
The power steering will interchange unless one of them is a 4WD, you need to use everything from the 1983 and it is a pain to transfer over as that power steering pump is below the injection pump if it is stock, you have to use everything, column, steering gear, all the piping, the pump and associated brackets, the reservoir, you need everything.
If it was my SD25 head I would take it to someone that specializes in fixing heads and see if they could fix it, that 10 more horse power is noticeable(SD22 61hp/SD25 71hp), that is what I would do.
As far as I know the SD22 and SD25 injection pumps are different, but I could be wrong, maybe it is the injectors that are different, I do not have an answer for that question, but Canada received VE injection pumps also, so I don't really know what injection pumps you have, were the injection pump lines coming out of the top of the injection pump or did they come out the back of the injection pump?

The 1983 depending on build date might have vented rotors, if it does they are better brakes than your 81 has, they will easily bolt right onto your 1981 truck, you just unbolt the ball joints from the upper and lower control arms, remove the brake hose from the hard line on the frame, remove the tie-rods from the spindles and put it all on your 1981, bleed the brakes and your good to go.

The 1981 and 1983 wiring might be different, I have had to change out complete wiring harnesses from one truck to another to have special stuff, you might have to do that to have power steering as the columns are different, your combination switch(headlights/turn signals/wipers) on you non tilt column will not fit on a tilt column, you will have to use the 1983 column combination switch unless the plugs are the same on both switches, that is something you will have to look at yourself, I have made combinations switches to fit my harness, but I had maybe ten 720s in the wrecking yard to choose parts from to make it work, I do have a few of them in my parts tub but I need what you need so I will not likely be selling something I might need, this is a complicated subject that is hard to explain, as the years went by the combination switches changed, they do not interchange a lot of the time, it depends on the build date, since the truck has an SD25 I expect it is a late build date, that is good for upgraded brakes, it is bad for electrical stuff.

Finally I shall address the cabs, the easiest way for me to know what truck the 1983 is is for you to measure the distance between the back of the door and the back of the cab, if they are the same you have an early build date and the column electrical stuff might interchange(except the cruise control) but the front brakes are likely the same and not an upgrade, if the 1983 is longer then it is a late build date with likely better front brakes but to have the power steering/tilt column/cruise control you might have to use the 1983 wiring harness in your 1981 truck, and the cruise control depends on if you SD22 has the spot to put the electrical thing into.

This is stuff I learned over years of messing around with these diesel and gas trucks, I likely have forgotten a lot of stuff that you need to know to start moving stuff around between the 2 trucks, if you ask questions I will try to answer them, but lets see if you get the trucks at all, maybe it will not work out and everything I will have wrote will have been a waste of time.

[asavage]

The SD25 has the VE-style Distributor type IP; the SD22 uses the "bulletproof" Inline type.

While there are a lot of good things to say about the SD25, I do not like the VE IPs, as the vane pump wears fast and causes all kinds of trouble, including lack of timing advance. The SD22's Inline IP has the problem of the pneumatic governor diaphragm now being nearly unobtainable, and "nobody" ever lubricated it. When they crack and leak, things don't work right anymore.

[hdshadpar]

Well its been awhile so thought an update would be appropriate The little diesel now has 280,000 kms on it. Had a few issues that I thought were corrected or need to be attended to in the Spring.

#1 A dead spot in the starter, so I purchased a new starter but the problem still continues but only when it is very warm out (80f or more). When I let it sit and cool down it starts. So I also ended up changing the battery account gone bad and have not had this issue since so maybe.....

#2 My gear shift seems to rattle more and am wondering if there is a fix for this? Hate for it to wear to a point that may do damage where I can't shift. I can move it around and find a spot that it won't rattle but thats annoying Any thoughts??

#3 Injectors just started to leak a little, haven't researched it yet but it is in storage for the winter and will have to be attended to in the spring once I know the fix again any thoughts?

Other than that, damn good little truck, haven't had to use my parts truck yet. Getting about 45mpg Been asked to sell it several times but that's not happening.

[waynosworld]

I did not see this post or if I did I forgot hdshadpar, sorry for the late reply.

I have had that starter thing going on for years, since I turbocharged my engine the starter is very hard to get to, removing and replacing the starter is an all day project as I have to remove and replace the alternator also to make a hole to get the starter out, I would put a rebuilt starter in and within a week the starter solenoid would start messing up again(clicking or just not doing anything), the starter motor worked just fine every time I removed the starter, so I gave up and created a work around, I installed a relay on the firewall and wired it directly to the battery on one side, the other side went to the starter motor post, I wired the exciter to a button on the dash, when I turn the key to the start position and nothing happens I hit the button and the engine starts turning over, after I get the engine turning I can let off the button and it keeps on turning until the engine starts, I have been using this method for a few years now without any issues, the clicking and nothing happening got real old fast, I figure the China made solenoids are garbage.

Your shifter lever bushings might be toast where the shift lever connects to the transmission, I have parted out so many 720s over the years I have always had a bushing around to replace the worn out one, I have no extras, I also do not know what shift lever you have as there are more than one type of bushing, is your shift lever silver or black? They are interchangeable to a point.

If my injectors start leaking I normally just tighten the offending injector tighter, if it continues to leak I remove the injection line/lines and clean everything and put it back together, it normally does not leak anymore after doing that.

I cannot drive 55mph, so I get around 30mpg going 75mph, I got 35mpg once doing under 60mph on the way to pick up an engine, it drove me crazy and I drove 70+ on the way back(without turbocharger at that time), I suspect I also could get close to 45mpg or better with the turbocharger if I could only drive 55mph.