The Stovebolt Site Forums The Shop Area Driveline Spotters guide for an SM 319???

Having recently registered my 58 Suburban, I've finally had the opportunity to do some real driving in it. I made the 50 mile round trip to Classic Parts in Riverside, MO yesterday. It was a very enjoyable ride.

That being said, with the current tires (215/75/R15) and rearend (I assume factory 3.90) I'm running about 3000 rpm at 55mph. Its loud and extremely inefficient. I would like to swap out my current 3 speed column shift for a 3 speed overdrive.

That brings me to my question. I know they were an option in many cars from the 50s to the 70s. Is there any way to narrow the search. If I'm spending some quality time in the local salvage yards, how do I know what to look for? Is there a telltale shifter or knob or something that signals there is a 3 speed overdrive under the hood?

That being said, do salvage yards pull all the engines and trannies when the vehicles come in? Is this a wasted question? Do I just ask at the office?

I haven't spent anytime in salvage yards in 20 years so I'm a bit rusty on junk yard etiquette/operations.

yes, ask at the office, many yards do pull drivelines, and because they were optional there won't be any way to know what model/year to look for .... an OD will have a handle/knob under the dash that, if original, will have "overdrive" on it .... if you can find one from 68 or after it will have a syncro first .... and of course the other choice would be the 3.38 rear gears, not likely found in a yard but available new from Patricks

Bill

Bill;

Hooah. Thanks. I went on line and found a gearing calculator. Turns out that based on my readings for speed/rpm/tire size I have ~4.50 gears in the rear end. I haven't had the chance to see if that was an option in 58. Seems awfully low.

I may need to swap the trans and the rear end.

4.57 would be the 3/4T ratio, and that'd have 8 lug wheels, not likely in a burb unless someone swapped it out in the past, standard 1/2T would be 3.90, or 4.11 if it originally had the OD .... you can find the actual ratio by jacking up one rear wheel, chalk mark the tire and drive shaft, turn the wheel 2 full turns, count the turns of the drive shaft, or turn the drive shaft, count the wheel revs, multiply or divide by 2

Bill

Bill;

Roger. I'll do that when I get home tonight.

According to 58 sales brochure.

Series 31 offered 3.9, 3.7, 3.38 posi 3.92
Series 32 the same
Series 36 4.57
Series 38 5.14

I didn't see a 4.11 offering

the 4.11 may not be listed, because it was not a separate option but paired with the OD 3 speed trans, which was available from 55.2 on .... '58 was the beginning of a variety of optional rear offerings, and AFAIK the first year for the posi, but the 3.9 was still "standard" and any of the others would be a rare find nowadays, I've searched for years but never found a posi and the only 3.38 gears I've seen were NORS at a rear end specialty shop or the the current new production from Patrick

Bill

Ok. I did as bill said. I jacked up the left rear tire and left the right side on the ground. Put trans in neutral and marked the tire and drive shaft.

2 complete turns of the rear tire netted just under 4 turns of the drive shaft. That should mean 3.90 gears.

So, either the speedo is more wrong than I thought or the tach isn't completely accurate or both.

I'll have to go out on the highway with the GPS and try to dial in the speed. The tires are 215/75-R15. The website I found says they are 27.7 inches tall.

According to what the gauges show, at 55mph I'm turning 3000rpm. On 27.7 inch tires that calculates to 4.57 gears. With 3.90s, I have to figure out what variable is wrong.

All that being said, I still either need to swap the rear end or get an overdrive trans. I'm having a hell of a time getting a lead on an sm319.

your speedo will be off, the original tire sizes were taller, the GPS would be a good idea .... keep looking, and watch e-bay and the parts for sale forum here, they've come up regularly in the past .... if you don't mind the cost, the 3.38 gears are readily available, might even find a local place that could bring them in

Bill

I have some of those 3 speed overdive trans, these are out late 50,s -mid 60,s GM cars, I have some with rear trans mount and some without rear trans mount,
these trans are hard to come by as it was an optional.

Chevy Overdrives appear on eBay quite often. 55 through 65 pickup or passenger will work. 66-68 Saginaw will also work. Its a lot heavier transmission than the Muncie but they are rare. I found one here at a local swap meet a few years ago. The guy hadn't sold anything and he needed gas money to get home. I really don't think he knew what he had. Very few salvage yards have anything 50 years old any more. And fewer have anyone who knows what is what. They all rely on a computer. There are several on eBay right now including a Saginaw that I would grab if I didn't already have one. Just do a search with "Chevy overdrive".

I got one, but its more of a limited slip,has some clutch plates backing the differential side gears kinda like where the thrust bearings are. And its in an old style rear axle, like the 57's had. Hmm I guess that is what 58's used, 59 has a newer spread case design.

Juan:

I sent you a PM.

Crenwelge;

I had a bad feeling that would be the case if I went to a salvage yard. I'd get the trout look from some pimple faced teenager that didn't know what to do when the computer wouldn't compute.

'59 was the first year for the Positraction rear, which used the GMC Spicer 45 housing. It was a 1 year only for Chevrolet. If you have a Eaton HO33 with a Positraction using, it most likely originally came out of a '60-'62. The Positraction, or "Posi", isn't "more of a limited slip", it is a limited slip. Positraction was just the Chevrolet brand name for it. Other companies sold virtually identical limited slips under their own brand names, such as Sure-Grip (Chrysler), Powr-Lok (GMC),and Traction-Lok (Ford).

Did they drop the overdrive after '57?

MisterR - no, the BW 3 speed overdrive was an option until late 60's, after that the better Saginaw 3 speed OD was offered into the 70's

Bill