Gear Ratio ??

[Psycho71]

Wanted to see if any of you know what the standard gear ratio would have been in a '68 one ton dually? The only thing we can read on the spid is a 327ci motor. The rest is illegible.
This truck had a PTO winch on it, not sure if that was factory or not. But it had a 327, with 4spd tranny.
We checked the tire rotation method, and came out close to 5:1, then counted teeth on the ring and pinion, and came out to 5.14:1. So we're thinking around a 5.13 gear.
Does that seem right? That is an awfully low gear, even for a 1-ton. With a gear like that, all we can see is needing a 100 gallon fuel tank and a government style bail-out every time we drive this thing.


Thanks
Jay

[Orange]

What was the count on the teeth?

DLB

[Steelawork'n]

How about a 4.10

[Psycho71]

Originally Posted by Orange

What was the count on the teeth?

DLB

It was hard to count the teeth on the pinion (it is still installed), but we came up with 7/37. Which equates to 5.14.

[Longhorn Man]

5.13 was avalible as an option
4.56 was standard with that eng/tranny combo
4.10 came in the automatics, not quite sure off the top of my head if it could be had with the 4 speed.

[Psycho71]

Originally Posted by Longhorn Man

5.13 was avalible as an option
4.56 was standard with that eng/tranny combo
4.10 came in the automatics, not quite sure off the top of my head if it could be had with the 4 speed.

Thanks for the info. It looks like this thing does in fact have the 5:13 then.

Couple of more questions;

Would the PTO have been factory on this truck? Dealer add? Or completely aftermarket?

And exactly what rear end is in this truck?

We checked in the LMC book and it does not look anything like the Dana 44 or 60, Definitely not a 12 bolt. Does not look like a 10 bolt, but it has 10 bolts on the rear cover (which is completely rounded, with a filler plug in the back). And the axle tubes are cast as part of the center section. It also looks like a 9" (although we know it's not) in that the pumpkin looks to be bolted in from the front, but then there's the removable cover in the rear.

Any ideas?



Jay

[special-K]

It would have the Corporate HO72 rear.It`s a drop-out differential assembly.It is interchangeable with the HO52s,too,found in 3/4t trucks.

What`s the brand of the pto?Is it marked.I think there is a pto unit in the factory parts catalog.

[Longhorn Man]

special K is dead on right.
GM called it the Corporate, we genaricly call it the Eaton, but the full and proper is the corerate rear with the eaton HO72. When going to NAPA or whereever, normally saying non-dana is enough. They seem to think that a dana was avalible in a one ton.
I am pretty sure there were no factory installed PTOs, but there were plenty installed before they were sold from the dealer though.

[Psycho71]

Thanks for the info fellas.

I guess the next step will be to get her back on the road, and see just how horrible the mileage is. then maybe start looking for a new ring and pinion.

Thanks again,
Jay

[Steelawork'n]

Too bad you don't live up here. I have an Eaton 4.10 axle assembly that needs a home.

[factorystock]

From what I have learned,optional gear ratios were usually listed on SPIDs in 66, 67, and maybe 68. If there is nothing on the SPID, assume it has the standard ratio.A 1 ton would be 5.14. Around 68 or 69, it gets confusing, the ratio depended on the engine and trans used,and was not shown as an option on SPID, unless it was a special order ratio.I have seen many 66's and 67's C-20's with V8 automatics with 4.57's(standard ratio) when nothing was listed on SPIDs.

[WorkinLonghorn]

If you've got 31" tires you should be spinning 3058 RPM to go 55 MPH.



http://pitbulltires.com/calculate.php

[Longhorn Man]

ok, i just looked into this a little more.
any combo of engine or tranny (excluding the 396) would have a standard ratio of 4.57. (this chainged in 69) so regerdless of engine (250, 292, 307 or 327) and regardless of tranny, ( 465, 435 or automatic) it got the 4.57 gear.
The only way the base gear chainged without showing on the SPID, was if it came with daul rear wheels. Then, the standard gear ratio was 5.14.
Optional ratios were 4.10 in all combinations of engine and tranny, or a 6.17 (!!!!) if you got the 465 4 speed with any of the listed engines, and only with the 11,000 lb rear axle.
The big block only came with the 4.10 gears acording to the restoration book from GM.

[oldiron]

On my 68 1 ton I have the 5.13 ratio. At 60 mph I get 10 mpg.

[Steelawork'n]

Originally Posted by oldiron

On my 68 1 ton I have the 5.13 ratio. At 60 mph I get 10 mpg.

You need mine that I have laying around. I can even take a picture for you. Heck, I'll even bring it to you. Pulleez take it from me

Anyone is welcome to it. Just let me know.

P.S.

It is off a '71 3/4 ton and is an Eaton.

[Longhorn Man]

I'm able to sell open 4.10s for 100 bucks each all day long. I've shipped them to Cali, forida, and a few closer too.

[Steelawork'n]

Well, it was a freebee. Now I got $$ signs in my eyes.

[Psycho71]

It does have dually wheels on the rear. So yeah, 5.13 it most likely is.

It's not actually my truck. It's my boss' truck. He's just not real computer savy, so I'm asking here.

Thanks again for the info fellas

Jay

[Psycho71]

One more question and I'll leave y'all alone.

What kind of carrier/differential does this thing have? Open, Posi, Limited?

It acts like an open carrier (if my thinking is correct), but doesn't have the conventional spider gear set-up I'm used to seeing in 12 bolts and such. With both rear wheels in the air, if you rotate one tire, the other rotates the opposite direction. If you rotate both of them the same direction, then the drive shaft turns. With one wheel on the ground, rotating one tire turns the drive shaft.

My boss, and his family have used this thing for years around the family farm. He said there were times, pulling stumps, where he's had the front wheels 3-4' off the ground. I'd think that would be hard to do with a pegleg rear end. Not that it'd be easy with a posi, but still.....

Jay

[Longhorn Man]

with enough weight and traction and gearing... it could be done even with an open peg leg.
If there is no traction lock listed on the SPID, then it didn't have one originally. As far as not being what you are used to seeing, it's not a GM diff, it is another make, so it may differ a tad.
Sounds like an open diff to me.