GM 14-Bolt FF 3.21 gear ratio?

[mountainexplorer]

I had a '78 2wd Crew Cab... pretty much not screwed with... had the original sticker in the glove box stating "Rear axle- 4.10 ratio"... seemed like 4.10's. Just last night pulled the cover. The date code reads the 9th month of 1978 on the ring gear pretty much verifying it's the original rear gear set.

The numbers are 14 and 45. That divides out to 3.21.



I've had a very rare 3.42 ratio full floater 14-bolt before. But 3.21? I checked and double checked, divided those numbers over and over, looked at the stampings again and again. It's 14 and 45.

I have as yet to actually count the teeth as I pulled the cover with it cover up as to keep the gear lube in and didnt try looking at the pinion yet.

Anyone have any input here or heard of a 3.21 ratio?

 

[YZEATER]

i've read here somewhere, that someone had a 14bff with that ratio in it. i've never seen one though.

 

[resurrected_jimmy]

yep, not very common but they do exist, there is a WTB ad in the for classified section where someone was looking for this gear set

 

[Xtremegmc80]

i was looking at a dump truck a few months ago, took the covers off the rearend, it was 3.21.. they are out there, i was confused at first.. but yep there are 3.21 out there in a 1 tons, even the dump truck i was lookin at. a 1974 c35..

 

[howdiy]

I cant even find a 14 bolt at all

 

[tRustyK5]

u2slow has a 14 bolt with factory 3.21's that he runs in a diesel Suburban around here. They do exist, but weren't common at all.

rene

 

[thatK30guy]

Yep, that ratio is like hens teeth in the 14FF.

I had an '80 K20 once and I remember well the owner telling me it was geared high, very high. I was thinking it had 3.73's but when I sold the truck and the new owner had it up on a lift to inspect the axles/gears, you can imagine all of our shock when we came up with the same numbers you did.

I have seen WTB ads and also saw a few of these ratio sets on eBay selling for high prices, used.

 

[oakknight]

I have a set of 3/4 ton axles out of a 79 K20 D44 front 14 btff rear on my blazer. I have the old diffs and gears in the shed . they are in fact 14 pinion and 45 ring as well. I am thinking they were installed behind a low geared 3 spd or something .. late 79s maybe for highway mileage , who knows ..lol

 

[dyeager535]

I've got the front 3.23 ring/pinion out of a 10 bolt/14FF combo in my garage.

I say 3.23, but that's what I *thought* GM called it. Guess not, they used both 3.21 and 3.23 lol.

http://brochures.slosh.com/1981/pickups20.jpg

 

[mountainexplorer]

The thing I can't figure out is why the truck had 4.10 listed as the factory gear ratio on the options list in the glove box. Every other option listed was accurate and it was the right sticker for the truck.

It also didn't ever feel too gutless or high geared when towing. I suppose that motor had more power than I thought.

 

[dyeager535]

That does seem odd, only thing I can guess is that maybe back then based on the fuel situation, the owner had the axle swapped out.

If the speedometer was accurate, pretty unlikely it was just a tinkerer that did it.

 

[mountainexplorer]

The thing that's odd is the date code on the ring gear is for September of 1978 which is the same year as the truck, so if it was swapped out long after the truck was made, they happened to get the same year ring gear as the truck. Or if the truck was actually made earlier in '78 or in late '77, perhaps the gears were switched out right after the 1st owner purchased it and decided he wanted higher gears.

I can't remember the actual production date of the truck now, but it's a '78. Had the date on the ring gear said 76 or 80 or something, I'd have more easily thought someone else swapped gears around some time in it's life.

 

[dyeager535]

Yeah wasn't gas sky-high in the late 70's? Only thing I could think of if it looks "natural". Bought it, decided for whatever reason the 4.10's weren't cutting it, and had them swapped by the dealer, thus a date of the axle that matches. Or blind luck lol.

It would seem odd for GM to turn a vehicle out with an incorrect RPO tag, but they made all sorts of errors.

 

[oakknight]

I was looking thru the brochures on the link .. cool stuff by the way!

It looks like the 3.21 was offered only in the 2wd before the 1980 model year on the K20regular duty had to go to the HD to get 3.73 , 4.10 and 4.56. Maybe he went in after 1980 and had them both switch ed out and they used the 1978 shelf stock for the rear 14 bolt and what the new was for the front D44 im assuming .

all guess work of course .

The guy i bought mine from said a 79 K20 .. but it was more likely an 80 model with a 79 build date ..


interesting i just went out and checked the front .. it is 13 and 42 tooth count D44 . calcs out to 3.23 which is probably close enough not to tear things apart . maybe it is a 79 after all shrug

 

[mountainexplorer]

Mine was just a 2wd C20 crew cab. But yeah probably switched out by the dealer I would guess not long after it was bought new. If I remember right the speedometer worked and wasn't too far off. I didn't think it would have been a valid ratio they made for front ends in 4x4's but appearantly so if they did a 3.23 for a 44 or 10-bolt. I guess I will now have to change what Ive told people that 3.40 was the highest gear ratio for a FF 14.