HELP, I need somebody.

[allistor80]

Hi guys. I have a few questions for you. First I am a hevy equipment mechanic. so most things will not have to be over explained. I have picked up 2 f-250's
One a 1990 xlt lariat 4x4 with a 7.3. the other is a 1987 xlt lariat 4x4 with a 6.9
I need to know what truck had the better frame if there is any differences. what truck had the best trans or are they the same. what diffs. I plan on a ground up resto. I ABSOLUTELY GET SICK when I see these new trucks that cant haul a bag of feathers. have ridiculous emission crap, and just all around suck. Old iron all the way.
Also Should a use the 7.3 or the 6.9. what components are interchangeable.
Both trucks drive. Although the 6.9 has a bad injector and the 7.3 was driven home without cooland. The guy hit a deer punctured the rad. I got it for cheap, figured do a blow by test if the rings are good, plane the heads and go with it.
any help would be greatly appreciated

 

[blacksnapon]

Hi guys. I have a few questions for you. First I am a hevy equipment mechanic. so most things will not have to be over explained. I have picked up 2 f-250's
One a 1990 xlt lariat 4x4 with a 7.3. the other is a 1987 xlt lariat 4x4 with a 6.9
I need to know what truck had the better frame if there is any differences. what truck had the best trans or are they the same. what diffs. I plan on a ground up resto. I ABSOLUTELY GET SICK when I see these new trucks that cant haul a bag of feathers. have ridiculous emission crap, and just all around suck. Old iron all the way.
Also Should a use the 7.3 or the 6.9. what components are interchangeable.
Both trucks drive. Although the 6.9 has a bad injector and the 7.3 was driven home without cooland. The guy hit a deer punctured the rad. I got it for cheap, figured do a blow by test if the rings are good, plane the heads and go with it.
any help would be greatly appreciated

Pretty much the same engine, just an evolution from one to another. The 7.3 is the better bet. The automatic behind is a better bet unless the 6.9 would have a C6.

 

[allistor80]

Thanks for the quick response. They are both standard trans. What numbers would tell me what they are I could get them and post. also you didn't mention the diffs. how do I find out what they are for you. or are they all the same danas

 

[allistor80]

ok looked in the door the 90 says trans c axle 35 and the 87 say trans p axle c9

 

[allistor80]

well with some minor google searching I was able to find out that the 87 has the best diffs, and likely a good idea would be to drop the 7.3 and 5 sp into it. ?????? would the 3.55 and the 5 sp be too much of an over gear. would that limit towing ability.

 

[Fellro]

The 6.9 is a good motor as well, and has thicker cylinder walls, less likely to cavitate, which if the PO didn't keep up with the SCA's and quality coolant, could become an issue on the 7.3.Both can be turbo'd equally, and will perform fine. The 7.3 can not have the walls bored and run, you must sleeve them, which since they were not designed for sleeves, can be an issue. The 6.9 block can be bored with no issues. These motors will be more efficient if you spin them slower, and I see reports of near 20's with the overdrives and 3.55 gearsets. As far as diff design goes, they should be the same axles, the only change would be limited slip, or gears themselves. The 87 has the limited slip, so that is worth a bit in itself. (the alpha code tells that, assuming it is still in there)

 

[nobodyspecial]

I thought this was going to be about The Beatles...

 

[allistor80]

Ok so here is the consensus then ? Keep the 6.9 as the 7.3 undoubtedly has been abused her whole life. I believe your right in saying that a rebuild likely isnt in her future. And I should use the 5 speed from the 90 to keep the rpm down and should have a reliable fuel efficient truck ? Thats easy enough. Just need a paint guy and ill be set.

 

[Fellro]

The 87 is a 4 speed? That was the first year of the overdrive manuals. Otherwise, if you want to build it, I would go with a 5 speed swap, largely a bolt and go swap from what I understand. Injectors can be had for around 100 for a set, get the return line kit when you do it. i was getting 10 -12 mpg out of my 86 with the 4 speed, 4wd, and 4.10 gears. pulled pretty good, just don't expect to get there fast. I hauled a loaded horse trailer up the New York and southern West Virginia mountains with it, wasn't doing any passing going up, but was able to stay with the semi trucks.

 

[allistor80]

Yeah. 87 has 3.55 gears in it according to the tag. I pulled these trucks home with my half ton. 351 2wd auto. It had a tough time of it but it was ok. Burnt alot of fuel though. Hoping this 87 is the answer to my truck woes. Are things like glow plug relays and the timing advance the same on both trucks . The guy who owned the 87 has switches rigged up on the dash for them.

 

[Fellro]

They will be the same on those years, as 87 was the first year of the new style controllers as well.

 

[flareside_thunder]

The only thing that will be different on the 6.9 harness is the GP connectors. The 6.9 uses blade style connectors and the 7.3 uses bullet style. It wouldn't be a big deal to swap the GP controller harnesses.....especially since the 7.3 GP's are a little more readily available.

 

[Fellro]

Nope, on the 87, they used the bullet connectors, only year 6.9 that had it.

 

[flareside_thunder]

Ah GTK....

 

[allistor80]

So there wont be a problem changing everything over ? The glow plugs can be switched?the relay? Are. the injectors interchangeable.how about the pump.

 

[flareside_thunder]

Yup, everything is interchangeable....

 

[Fellro]

Theoretically everything swaps. I however have recently encountered a problem with a 7.3 pump on my 86 6.9. It behaved like the timing was off, but it was dead on, but it just acted like it was one tooth retarded. I haven't finished with putting the 6.9 pump back on, just haven't had the time to get back to it. It is also entirely possible the pump really wasn't that good, and considering the initial source it came from, I wouldn't doubt that it actually was not a good motor as presented. The truck was parted to the point the motor and body are about all that is left, makes you wonder, huh? I don't make a habit of yanking pumps to see if it will swap properly, but it is the same pump. Part of the problem was that the guy helping out my friend that was using my truck took the timing cover and gear with the pump, so it throws in a lot of questions, like the possibility of a mismarked pump gear that had been corrected for, but not marked at the correct location. That is why I pulled the 7.3 pump back off, and put my 6.9 gear and pump back on (not to mention, I don't think it was ever a IP problem). I just have to finish the swap and see how it goes.

There were a few variations through the years, but overall, it is supposed to swap ok. The late model injectors with turbo were able to deliver more fuel, beyond that there isn't any real difference. The 7.3 has slightly larger head bolts, and redesigned valve guides to reduce oil usage, and the rockers are a little bit more ratio, but that largely is the only differences. It is common to put 7.3 rockers on 6.9 motors, adds a bit more lift.

 

[allistor80]

Silly question perhaps, but if the 7.3's major improvement was the head. can the be easily swapped. or are they totally. different. i suppose its a bigger bore so its out of the question. I just need to know what to save on the 1990 before I scrap it. I live in the city at the moment so my neighbors LOVE the old vehicles I keep. LOL I try to keep them to a minimum and when a new one comes I like to strip it, put the parts on a shelf and get it gone ASAP.

 

[Fellro]

I would pull the heads. I have seen it go two ways, some get the special head studs that make the 6.9 accept the heads with no issue, and I have seen use normal head bolts/studs that are the slight bit smaller, and it works too. The crank is the same as well, just the bore and the head setups changed.

 

[allistor80]

Alright so just scrap the block. Put the crank and heads on a shelf. Got it. Fly wheel ?