The Stovebolt Site Forums The Shop Area Driveline Rear end gear ratio?

I’m rebuilding my rear end in a 59 Apache 31 and am trying to figure out what size ring I have. The numbers on the ring are 3087702 GM 10-39 3 59 2. No clue how to decipher! Lol

10-39 is the # of teeth. That makes it a 3:90 gear ratio. That is the normal ratio for the 1/2 ton models of that era.

George

Great! Thanks a bunch.

If I put a Saginaw 4 speed trans in front of it will it cruise nice on the hiway? I’m running a 235.

In other words, the pinion has 10 teeth and the ring has 39. 39 divided by 10= 3.90. The ratio between the two gears.

Some of the rest looks like date. Feb 1959? So the gears are original.

There are 4-5 different gear ratio available in the Saginaw 4-speeds...they are all direct drive transmission with 1:1 high gear, the same as the 3-speed you're probably replacing. The difference is in the lower gear ratios. The input shaft will have rings/grooves machined around the shaft that tell what gears are inside. Post the number of rings/grooves and we will have a better idea if that's a good choice or not.

Mike B

I haven’t bought the trans yet so which one should I look for? I’m also planning on running around 31x10.5 tires on it.

Almost all 3 and 4 speed trans. are direct in high gear, OD trans. are specified as OD. Cruising 'nice' on the highway had a lot of connotations, specify.

Ed

Scroll down on this web page for a list of all the gear ratios for many of the popular transmissions.

https://m.roadkillcustoms.com/transmission-gear-ratio-chart/

Hope this helps,

Mike B

In my opinion there is no 235 that cruises nicely on the highway with a 3:90 rear end. Best reason I can think of for an overdrive.
Fred

I ran that size tires on my 59 Suburban, with 3.40 gears in the rear end (79 Blazer rear axle) with an SM465 trans an loved it. I could cruise along at 90 if I wanted to and it pulled whatever I put behind it (broulght my bog bolts home, weighed in at 17,340 with the 59 behind it). That said, depending on how you are using it, and with the 235 , your 3.90 gears should be great!

Seems like that tall of a tire/wheel combination will place allot of strain on an old driveline.

Thanks Mike B. That website helped out tremendously!

sorry its been awhile. you are correct Mike B. I'm changing out the 3 speed for a 4 speed. the trans in it has a 2.85 first gear. I'm thinking a taller first gear in a 4 speed would be better? I would like to drive down the highway without overdoing it RPM wise- 2200 to 2500 RPMS. thanks

Three speeds and four speeds both have direct in top gear.

Ed

According to the 1959 truck resto pack your truck rear end had a Regular Production Option RPO 3.70 and 3.38
You could find a 3.38 ring & pinion 3rd member and install in the axle housing and you could drive at 70-80 mph all day long.
The Resto pack does not seem to show the RPO number for the 3.38 RPO, Teeth 13-44

1959 Resto pack PDF page 41.
1959 CHEVROLET TRUCK OPERATOR'S MANUAL 1/2 Ton Rear axle ratio spec. (bottom of page)

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