GEAR RATIO IN 86 GMC posi?

[tupac]

hey guys i need help i got a 86 gmc shortbed and id like to find out if it has posi rear end and the gears im gonna swap motors and im gonna put a 383 stroker roller motor in it and i was wondering if anybody can post a website where i can get informatin about this also it has a 700r4 trans would it be a good idea to keep the trans or should i put a 350 with a shiftkit that i have im not gonna race the truck to often i want to be able to cruise on weekends and keep it streetable

[petey_z24]

youll probably have to check you rpo codes for the gear ratio, should be able to find them in your glove compartment, as for the tranny, if your not going to be beating on it to harshly i would keep it till it goes to hell and then upgrade

[SloNlo_350]

well the overdrive with the 700 is real good, and if your new motor breaks it just build it up. And as for the rear end... if you spin 2 tires you have a posi, if you spin one you have an open (or worn out posi). And then for the ratio, look for a code GU2, GU4, GU6, or GT4. That would be 2.73, 3.08, 3.42, and 3.73 respectively. I can't remember the code for 4.10, but you probably dont have those anyway. If the code is other than what I mentioned (namely a GU with higher than a #6 or GT with # higher than 4) it is probably 4.10.

[amac209]

jack up the rear end so both tires are off the ground & rest it on jackstands. now with it in park try turning one of the tires if it's very hard to turn it you have a posi. another way is remove the diff pan, the oil probably needs to be changed anyways. now count the number of gear teeth on the ring gear & pinion gear, simple math will give you the ratio r=(ring teeth)/(pinion teeth) and you'll be able to see the clutch packs if you have a posi. this would be a good time to check the axle seals too if you have a semi floating diff (axles held in with c-clips).

[tupac]

hey SloNlo 350 .does those codes apply for all years?

[SloNlo_350]

Not all, but I am 99% sure that they would for an 86. I had a friend that bought an 85 Chevy wagon that had the GU2 code, so they should be right for yours. If you don't have one of the codes I mentioned, you might have some weird ratio, or they may not apply. But, like I said, I am pretty sure they do. Why do you ask? Did you not have one of those?

[badguy in bowtie]

I have an 86 1/2 ton 2wd shortwide bed also, It came from the factory with a 305, 700r4, and 2.73 gears. I would put money you either have the same gears or 3.08. Those where the standard ratios for these trucks. The 700r4 trannies are just as strong as a 350 turbo as long as you don't try pulling a load in overdrive. as far as the codes go if you can find the rpo code for the rear axle I can tell ya what the gear ratio is. And yes the codes are the same for all years even from car to truck.

[pind]

I have an 86 2wd out here in the yard, just for lack of something to do, I checked. it too has a 2.73 rear and a 700r4. Long bed model though. came with a diesel, now has a 355 small block in it.

[badguy in bowtie]

GM installed 2.73 gears in most of these trucks to improve gasmilage. I swapped mine out for 3.73 gears and with the 700r4 I actually got better gasmilage over the 2.73's. With a turbo 350 the 2.73 gears would be a good choice for milage.

[bowtie1]

The RPO code for the posi unit is G80 for all gm cars and trucks I have a dealers RPO quick reference guide stoped to ask the same question and they gave it to me.