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It's normal for my 86 Blazer to be slow right lol

Just keep it in D, the trans will do the rest. As for towing, you will need to judge for yourself if D or 3 works better. For the hills, hunting gears sucks, so 3 would be best.

If this is more of a driver rig, with towing a for sure, I would guess 4.10s would be a good choice. Without the towing, it would be good as well but 3.73s in a cruiser is pretty nice too. My truck had the tired '85 350, 31.5" tires, 700, and 3.73s. Felt really happy on the freeway doing 60-75. Didn't mind a 21' boat much either, just no long hills.
 
I think D is 3 on mine...If I remember correctly it went O/D,D,2,1...not positive though...
 
Id say go 4.10s. And if im not mistaken a 3/4 ton swap is pretty much a bolt in deal.
When im not in school I live not too far from Arlington, and always willing to lend a hand and learn too!
 
wilpetty said:
If I do upgrade, will 4.10's still let me cruise at 70 with a safe rpm that won't hurt the motor? The truck has 33x12.5 mud terrains on there btw. I will be doing a lot of highway driving for the truck to pull the boat or the hour and a half drive to the deer lease, so this is a concern for me.
Click to expand...

Really comparing apples and oranges here, but your question struck a familiar chord.
My Ford is running a C6 transmission, no overdrive, 205 transfer case and 4.10 gears sitting on 12.50-33s.

The 351 engine in it turns up at about 3K at highway speeds. And did so for better than 250k miles.
Of course, a lot of that was offroad and not highway, but I used it for a DD for several years with lots of highway stuff.

When I swapped the engine out, it was because of a coolant leak between two cylinders.
Water pump exploded and I think it either put a hairline crack in the head or block when it dumped all the coolant in seconds.

When I pulled it, after that many miles at those kind of RPMs, it had good compression on all cylinders, and 40# oil pressure at idle.

Used no oil between changes of about 5K each.

I used Amsoil for about the last 3/4 of its life.

Of course, it is a Ford, so you might not do as good.........:whistle:
 
OUCH :shame: lol just kidding. I have no problem with ford or chevy. Good to know. I have quite a bit of work ahoead of me to make it a DD. Hopefully all of that work will get done next week. And then I can focus on making it a bit quicker.
 
If you can swing an engine, you can swap axles. An engine swing is much more work, and much more complicated. Just look for a deal on a set of 3/4 ton axles.

You really need to find out what you actually have now though. If you haven't changed the axle grease since you owned, now is a good time to do so, and find out what gears you have for sure.

Martin
 
Will do Martin. I am not afraid to do the axle swap, but I think it is something that will happen after I get everything in better working order
 
It's honestly a few hours work to swap axles. I would check what gears you actually have tomorrow if you have the time.

Martin
 
Won't be in the blazer until thursday when I go buy a boat...Does the rear diff have the gears stamped on there?
 
jack it up and spin the tires
as long as both tires spin the same, you can count the number of turns the driveshaft makes per one tire revolution
if both tires don't spin evenly forward, you wont be able to accurately count driveshaft rotations

if it's an open diff, you might be able to set one tire on the ground and spin the one in he air, counting rotations. If the driveshaft rotates 2.73 times for each tire rotation....you have 2.73 gears.
 
K85 Octane said:
jack it up and spin the tires
as long as both tires spin the same, you can count the number of turns the driveshaft makes per one tire revolution
if both tires don't spin evenly forward, you wont be able to accurately count driveshaft rotations

if it's an open diff, you might be able to set one tire on the ground and spin the one in he air, counting rotations. If the driveshaft rotates 2.73 times for each tire rotation....you have 2.73 gears.
Click to expand...

You are forgetting about gear reduction through the spider gears. One tire on the ground will not give an accurate number of turns on the d-shaft vs the gear ratio.

Without popping the cover and reading the numbers on the ring gear, next best way is to get the "G" codes from the glove box door. Research them via google, type in "RPO codes". This will tell you what gears are in the axles as long as they have never been changed out, and the way you describe, they probably are original. You can double check your findings by jacking BOTH rear tires up and supporting the axle. With trans in N crawl under and turn the d-shaft by hand and watch, making sure BOTH tires spin about evenly. Coax a slower or non spinner with your other hand or foot just get them moving together (yes, I've done this) and count the d-shaft revolutions vs ONE rotation of the tire.

If your G codes came up with 3.08 gears, expect to see just barely more than 3 shaft revs to 1 tire rev. 2.73s would be less than 3 revs. 3.5 revs would mean 3.42s but I doubt, from what you describe, your truck would be so equipped. My truck with it's stock 3.42s and 33s would do brake stands and lay rubber but would hunt between 3 and 4 on highway uphills.

Highly recommend 4.10s for a K5 with the 700R4 and 33s that will be towing. 3.73s would get you by but 4.10s would be optimal, not only for the engine but the trans too. Oh, and invest in a good trans cooler to save the trans. A shift kit would be on my list of "wants" too.
 
like everyone said, 3/4 tons are a bolt in deal, only thing you might need to screw with is if you want your e brake to work(should hook up but don't quote me, my lines were rusted solid) and a conversion u joint for the rear.

depending on how good a shape your rear is in, you might still have the little tag attached to one of the diff cover bolts which would tell you what ratio you have. most people don't have it, i'm surprised my dana 60 still had it but that thing was rust free and pulled out of a truck i think in the late 90's. if not i'd pull the rear cover and replace the fluid just as a general maintenance procedure while checking the ratio.
 
K85 Octane said:
jack it up and spin the tires
as long as both tires spin the same, you can count the number of turns the driveshaft makes per one tire revolution
if both tires don't spin evenly forward, you wont be able to accurately count driveshaft rotations

if it's an open diff, you might be able to set one tire on the ground and spin the one in he air, counting rotations. If the driveshaft rotates 2.73 times for each tire rotation....you have 2.73 gears.
Click to expand...
If both tire turn the same way count the driveshaft revolutions.
If one turns double the count.
Knowing the ratios available I can tell the gears without opening the cover.
 
after doing all this transmission work, swapping some axles seems like cake.. i think im going to do this as well during the summer... :waytogo:
 
wilpetty said:
I put in a rebuilt 350...Thought it would have more pep than it does. I floor it and it will put you back a little but on the highway I am slammed on the gas to speed up. I was kind of worried until I saw that the 86 350 had 165 or 185 HP. Im not worried about power as long it is normal for it to be slow
Click to expand...

I will say this one thing:
I worked on a friends 86 k5 that had stock 3.42 gears and 33" tires.
Stock engine CA truck and it ran like a raped ape compared to my older 70's era k5s.
 
What he said (martin). Some jack stands, floor jack, loosen some bolts and roll em out of there wheels and all. If you haven't gone through your current set up, might as well gets some 4.10s and go through those instead
 
Thats the best way. Find a set of 4.10 3/4 tons and go through them. Replace brakes, seals, fluids, repack bearings, axle joints, and ball joints if needed. Even clean and paint if you're into that sort of thing. Then, when they are 100% and you have new u-bolts, swap them in.

I had mine all ready to go with a lift kit and installed it all in one weekend by myself.
 
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