Gears

[bikerbuck]

Anyone tell me their gear setup, sounds like most are running 373's , courious cause someone told me iwas running 343's does that sound right.

[Longhorn Man]

we need to know more about your ride to tell you if those gears sound right.
What RPM at 60?
What engine and tranny was original?
What series burb... C or K?
What size burb, 10 or 20?
3.43 was never offered as original.
4.57
4.10
3.54
3.73
3.07
That's pretty much all you'll find in these rigs. At least, that's all you'll find that's original anyways.

[bikerbuck]

Ok well i cant remember the rpm at 60..guess ill have to drive it,originally i believe it had a 350-350, now its a 383 700r4, has a 12 bolt posi 5 lug,

[bikerbuck]

Whoops, just realized i posted on the burb board,, I got a 70 C-10 pickup

[Monte Carlo Man]

It doesn't matter.

The 1970 - with a 307 and TH 350 should have 3:07 gears.

The 350 V-8 with the TH 350 / 400 might have either the 3:54 or the 3:73

The L-6 250 / 292 would definately have either 3:73 or 4:10 / 4:11 gears.

The Big Block could have most any gear, but the most common I saw was 3:73

TH 350 / 400 would have the same gear ratio - final drive as a 700R4 in 3rd gear. 1:1

Tire size would dictate speedo and RPM's at X miles a hour.

As I remember it, with a set of P235/75/15 inch tires, my truck ran around 2500 - 2750 Rpms at 55 MPH!

I do not believe that there was a 4:57 - they were 4.56 , I never seen a 3:54 in a Pennsylvania pick up truck either.

[Longhorn Man]

moving to the truck board.
Quite a few errors on that list there. I don't have time for the specifics, but the general rules are;
C/10;
inline with a 3 speed 3.73
small block with a 3 speed, 3/73
small block with a 4 speed, 3.07
small block with an TH350/400 3.07
cant remember what a powerglide would get
big blocks were almost always automatic and got a 3.07.
Some of these are not set in stone, if memory serves, a 307 would get a 3.73 even with the auto, but I am not 100% certian and don't have time to look it up. Some inline/auto seem to have gotten the 3.54, but there's no factory lit to document this, only the handfull of seemingly unmollested trucks to verify.
C/20
inlines and small blocks with a 3 speed was 4.56
I think 4 speeds were the same, can't remember
small blocks with an auto got 4.10
big blocks with auto got 3.54
Again, we are going by my fuzzy memory and I don't have time to dig out all my books to list everrything per GM's lit.

[LONGHAIR]

Some of those "numbers" are kinda "fuzzy". They are not necessarily exactly by the math.
The commonly mis-used "3.08" is a car gear. "3.07" is the truck equivalent.
"4.10" and "4.11" same thing
"4.56" and "4.57" are a little different. 4.57 is out of and corporate (Eaton) axle and the others (Danas and 12 bolts) had 4.56.

[beatupbandit]

My truck is a 69 GMC 3/4 ton with a 350/350 set up, the guy I bought it from claimed 4:11's in the rear, I thought it was a bit suspect or is it a possibility.

[Monte Carlo Man]

I worked in a junk yard when those trucks were still in style, although the junk yards I frequented were in Pennsylvania - so the gears I mentioned were from my experiences.

Honestly, I don't recall seeing any power glides in pick up's, especially in a 4 wheel drive. But I can tell you that we had a 71 Blazer - 307 2 bbl engine and it had the 3:07 - 3:08 gears - 12 bolt posi. I know cuz I replaced it once and the front axle twice.

We owned lot's of those trucks back then for the company that my grandfather owned and we had lot's of spare parts trucks out back in the field.

The 3 on the tree transmission was the weak link of the whole thing in the half ton 2 wheel drive pick up. It wasn't uncommon for me to take 3 of them apart to make one good one back then. The slider gear always broke.

My buddy had a 1970 Chevelle with a 12 bolt posi and I took the gears and carrier directly out of a '72 Blazer and put it in his rear end housing - so saying this gear is a car gear and this gear is a truck gear is erroneous.

The proper way to explain it would be to say this was a 12 bolt gear and this was a 10 bolt gear. Or this was a 8 1/2 inch gear or this was a 7 1/2 inch gear etc.

[Shyguy]

My stock '71 C-10 with a 350 and 4 speed granny transmission has an option 3.73 12 bolt rear end.

The optional 3.73 rear-end is listed on SPID.

Danny

[Stocker]

Originally Posted by LONGHAIR

"4.10" and "4.11" same thing

I thought our trucks (mine included) had an actual 4:10 gearset -- 41 teeth on the ring gear, 10 on the pinion.

And I thought other diffs (don't ask me which) had 4:11s -- 37 teeth on the ring gear, 9 on the pinion.

No?

[Monte Carlo Man]

You divide the larger number by the smaller number and that is the approximate number given for the gear.

The 10 bolt rear ends were known for having 41 teeth on the ring gear.

It really doesn't matter because you buy gears in sets. You cannot mix and match gears. Gears are hobbed on a machine that cuts the teeth. I think that the term for the rear end gears is called Involuted.

But the actual process name for the gear is Spiral Bevel with helical teeth. I know because I worked for a company that cut gears.

http://en.wikipedia.org/wiki/Spiral_bevel_gear
The one gear is special cut for the other gear and when the two gears are finished they are put into a machine where the two gears are run in together and they polish the gears - one to the other.

If you look at the side of the gear there will be a couple of numbers scribed into the sides of aftermarket gears and they are there to tell you information about the gears, how much shim and lash and stuff like that - that they used when they ran them in. The height installed etc - just all depends on which manufacturer made the gears and what they tell you.

[Longhorn Man]

Originally Posted by beatupbandit

My truck is a 69 GMC 3/4 ton with a 350/350 set up, the guy I bought it from claimed 4:11's in the rear, I thought it was a bit suspect or is it a possibility.

4.10 is the base model gear ratio for that combo in a 3/4 ton

[71longbed-brew]

i went from open diff. 3.08 to 3.42 eaton posi .. and im happy with that ratio ... sometimes i'd like a lower ratio to get up and move alittle quicker but ... i think 3.42 is a great medium gear ratio

[beatupbandit]

Originally Posted by Longhorn Man

4.10 is the base model gear ratio for that combo in a 3/4 ton

Thank you.

[LONGHAIR]

Originally Posted by Monte Carlo Man

My buddy had a 1970 Chevelle with a 12 bolt posi and I took the gears and carrier directly out of a '72 Blazer and put it in his rear end housing - so saying this gear is a car gear and this gear is a truck gear is erroneous.

Just because someone has put them into the other housing do NOT mean that they are the same thing. There is definately a difference in the pinion shaft. Believe it or not the car pinion is bigger than the truck's. I can only assume that this is because of a "performance" thing, but at least at one time, GM was pretty good about interchangability.

BTW, they a "Hypoid gears" because the pinion is not centered on the ring.

Originally Posted by Stocker

I thought our trucks (mine included) had an actual 4:10 gearset -- 41 teeth on the ring gear, 10 on the pinion.

And I thought other diffs (don't ask me which) had 4:11s -- 37 teeth on the ring gear, 9 on the pinion.

No?

Yes, they are different, but I have heard lots of people call them out wrong.
A lot of the "names" that we as mechanic's/hobbyists use are not only regional to some degree, but GM never called them by that name in the first place. GM may have "adopted" the 10 bolt or 12 bolt wording, but it wasn't their's originally.