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Just bought k5 , is the 6.2 really that big of a turd?

82detroit diesel

82detroit diesel

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Hello guys, I’m new to 4x4 and I’m learning. I just got a 1982 k5 with a 6.2 ,turbo 400 and a 14 bolt in the rear and stock 10 bolt in front. The thing tops out at 50mph if I’m lucky.Long story short it’s got stock gears and heavy Humvee wheels with run flats. I could Not get it into 4 low which is another problem I’ll deal with but I was in 4 high and tried to climb a hill( not crazy) and it just had no guts and didn’t go anywhere lol. Get gears front and back and figure out getting into 4 low and I should be good??? Thanks guys any help would be much appreciated
 
82detroit diesel said:
Hello guys, I’m new to 4x4 and I’m learning. I just got a 1982 k5 with a 6.2 ,turbo 400 and a 14 bolt in the rear and stock 10 bolt in front. The thing tops out at 50mph if I’m lucky.Long story short it’s got stock gears and heavy Humvee wheels with run flats. I could Not get it into 4 low which is another problem I’ll deal with but I was in 4 high and tried to climb a hill( not crazy) and it just had no guts and didn’t go anywhere lol. Get gears front and back and figure out getting into 4 low and I should be good??? Thanks guys any help would be much appreciated
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Well let's start with solid information:
You say k5 with 6.2 14bff and humvee tires.
14bff is not stock on a k5 so do you know the gear ratio?
The tires, are they the 36" tires?
The 6.2 is not a monster,but not a turd either but geared improperly it's going to struggle like any other engine.
You say barely can make 50 mph, but couldn't climb.
I wonder if you actually are stuck in low gear because 50 mph is pretty much max in low gear or your speedometer is not calibrated to your gear/tire combo and showing the wrong speed.
I you can get this information but to answer your question, no the 6.2 is not that bad.
 
Not going to climb something in 4H, big tires, and wrong gears. Just piss of the torque converter :D
 
My 6.2 burb with th400 and 3:73s did 70 all day long....if you have a 14bff I'd bet its out of a cucv with 4:56s. Unless the as Issam mentioned your tranny is not hitting 3rd gear.
 
The guy I bought it from said the gears are 3:42’s “stock gears” in the back , i used gps on my phone and yup it’s not getting above 50mph, and they are 37” tires good year mtr’s, and it struggles to even get up to 50mph if there is any kind of hill
 
82detroit diesel said:
The guy I bought it from said the gears are 3:42’s “stock gears” in the back , i used gps on my phone and yup it’s not getting above 50mph, and they are 37” tires good year mtr’s, and it struggles to even get up to 50mph if there is any kind of hill
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There's your answer, 3.42 with 37" tires not even a good gas engine is going to be good there.
With the diesel you want to keep it conservative because it will not go more than 3600 rpm so keeping that in mind see what top speed you want and work backwards from that to figure out what gears to get.
And if it was me, I would switch to a 700r4.
All the civilian k5 came with one for a reason taller first gear and overdrive to get higher speed.
Once you get your gears done you can look at the engine, it might need some tuning too
 
My '82 GMC K2500 has pretty high gearing,I don't know the exact ratio,never had the diff cover off it,but going by my experience with other trucks that had 3:08 gears I'd guess it has either 3:23 or 3:42 ratio gears,it can hit 60 in second (TH400) before it hits the governor and upshifts into third..

It is no ball of fire taking off from a dead stop on a steep hill,it feels like a straight six,but it'll eventually get up to 35 mph or so in a reasonable distance..it certainly does not feel like a 379 cubic inch V8 !..but it'll go 80+ mph on the highway in third if it has too..just takes longer to get it up there compared to a 350 or larger gas engine would..
The 6.2 is about equal to a 2bbl 305 as far as torque and HP,and the truck weighs over 6200 lbs empty--you cant expect blazing performance with a 140 HP engine with 240 ft/lbs of torque..
A K5 might weigh less,but not that much..

Most of the diesel trucks came factory with high gearing to increase fuel economy,and the fact the diesel tops out at 3600 rpms before the governor holds it from revving any higher..the military ones had 4:56's to increase low end power and the fact they usually aren't needing to go highway speeds over 55 mph or so..

If you were stuck in 4 lo,the thing would take off like a dragster and top out around 45 mph..

Also my truck has 245/75-16" tires ,I noticed a pretty large drop in power and hill climbing ability when I put 265/75-16's on it...37" tires would really bog it down I bet,I would try putting "stock" diameter tires on your truck and see how you like it before going too crazy changing gearing or transmissions..
 
37's, th350, 3.73 gears. I can do 70mph but i'm at like 4000rpm and she's a dog all the way there. Needless to say, you need gears. Personally, I'm going for 4.88's.
 
Turn the tire and count the driveshaft rotations. In my case, one spin of the tire should be 3.73 spins of the driveshaft. It's a rough way to do it but about the only way unless you want to pop the cover off and count ring and pinion teeth.
 
The ring gear should be stamped with numbers like "41:12" --divide the larger number by the smaller one to get the ratio..that would be a 3:42 ratio diff..or you can try counting the teeth,but the pinion gear is kind of tough to see..
 
Keep in mind that with an open diff, if only one tire is turning, the effective gear reduction is cut in half. So with 3.73 gears, 3.73 revolutions of the driveshaft will be 2 rotations of one tire, or 1 rotation of both tires. Best to do more rotations that that, though. With things like slop in the spiders and backlash counting fractional driveshaft rotations can leave you guessing between 2 ratios.
 
The 6.2 is a great engine if you learn how to maintain them properly. You just have to understand its limitations. It's meant to be an economical engine. I would just return your rig to stock and get some 31x10.5 duratracs and you're set. You can get 20 mpg or better out of a 6.2.
 
I think you just open it up and count the teeth on your ring, I was thinking 5:38 gears because eventually I want to get 40’s and sac swap some day
 
I think mybtires may be too big, if that’s possible. Might go from 37 down to 35....

If you run 37’ shouldn’t you add that ORD steering box weld on brace? Or can the regular spot take the play of the steering box with bigger tires? What is the tipping point for stock bracing without support? 35” tires 40” tires?
 
Looks like I’ll re gear it, and look at the linkage so I can get it into 4 low and start from there. Thanks for the info guys. This k5 was bought just for fun, I have a lot of trails minutes from my house with out getting on the freeway. It’s been a while since I’ve been on forums and would post a pic of my rig but can’t figure it out lol the 6.2 has long tube headers and a custom intake with dual cone k&n filters
 
Become a supporting member($), recommended and you can upload pics all day long. Other than becoming a supporter you’d have to use an offsite pic hosting platform that is prone to bugs and viruses if clicked on....

One thing we all agree on... Support the CK5 site, you won’t regret it.
 
6.2/6.5 fan checking in here. Along with what's already been said, poor performance can be caused by a clogged fuel and/or air filter. Even if the fuel filter is fairly new it could be clogged, especially if the truck sat for long periods of time.

Others include faulty lift pump, clogged fuel tank sock, IP timing, severely worn timing chain and lastly, incorrect expectation of what the mighty 6.2 was designed to do. :haha:
 
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