The Stovebolt Site Forums The Shop Area Driveline 1958 3200 Transmission

This summer, after 11 years for a total restoration, I finally got my 1958 Chevrolet Apache 3200 Fleetside licensed and on the road.

I assume that it has the original rear 3.90 axle ratio and a Muncie SM319 3 speed transmission. My VIN plate says that the GVWR is 5000 lbs. The owners manual says that it should have come with 7-17.5 tires/wheels, though when I got it, it had 2 non clipped newer 15" wheels on the rear, one 16" clipped front wheel, and one 15" front wheel. I bought 4 matching period 15" clipped wheels, and per a recommendation on this forum, I bought Yokohama RB215 7.00R15 tires, which have a diameter of 29.4", 706 revs per mile. It has a 235 'Frankenstein" motor, 56 car engine, but with mechanical lifters, camshaft unknown. Rebuilt cylinder head, but no upgrades or repairs to the bottom end. Had some rust in cylinder 4 bore, but doesn't appear to be smoking much. Seems to be running OK. Compression is improving the more I run it, presumably as rings start to free up from sitting for a long time outside in it's prior life. Now lives in a nice warm garage.

So I have some questions.
1. My speedometer seems to be reading low. Indicated 40 MPH seems to be 45 MPH per my GPS. It has a white nylon speedometer driven gear. Are there different transmission speedo gears that might give me a more accurate speedometer reading?

2. Are there any synchronizers in this vintage transmission. I learned to drive 55 years ago in my Dad's similar 57 & 59 panel truck. I don't remember having much gear clash going from 3rd to 2nd after rounding a corner for instance. Is this 'normal', and I just need a bit more practice or develop a better technique? My Dad also had a '64 panel and I think it might have even been able to downshift to 1st without coming to a near standstill. Are the newer 3 speed transmission backwards compatible to my 58 bellhousing with a 235 engine?

3. I don't have a tachometer, so not sure what the revs are at 50MPH/80KPH or 60MPH/100KPH, but it seems to be revving pretty high. What maximum real speed is my existing engine/transmission/rear axle/tire size combination comfortable with. Just want to set some expectations, and not destroy the engine. Is there a calculator that would tell me what the engine revs would be at above speeds?

4. The owner's manual suggests 25PSI front, 45PSI rear tire pressure. Yokohama says max load of 2040 lbs at 65PSI, obviously well over my 5000 Lbs GVWR (2040 x 4 = 8160). My truck is likely to never have much of a load in the bed. Any recommendations for proper inflation pressure for these tires. I'm currently using 35 PSI front and rear.

Appreciate any help you folks can offer.

John.

Hy John D, I'll try and answer your questions.
1. yes there are a multitude of different speedometer driven gears based on rear axle ratio and tire size. I think the main reason your speedometer is reading incorrectly is the change in tire diameter that you have made.
2. yes there are synchronizers in your transmission, it sounds like it may be time for a transmission overhaul. There are many choices for newer fully synchronized transmissions some even have overdrive so more speed at the same RPM.
3. I would say 3200 RPM would be where I would hold it if you were going to be at that RPM for a while. When your truck was new common "highway" speeds were 50 mph (80 kph) today traffic travels much faster and as I said you lost some speed at RPM by going to smaller diameter tires.
4.Tire pressures are quite a different matter today, they depend on tire construction, load and conditions. If the tire has a recommended pressure branded/cast into it I would use their recommendation or close to it. If it were my truck with a 65psi recommendation, I would run them at 50psi. Hope that helps.

It's possible to create a gear grinding problem on a downshift by using the wrong lubricant in the transmission. Some of the new synthetic gear lubes are too slippery to allow the blocker rings in the synchronizer to get a grip on the gears and match up the speeds during a downshift. Plain old 90 weight mineral oil is the preferred lube. Most farm stores sell a "Ford tractor" 90 weight lube that's the right stuff for a SM-319. There is no synchronization on 1st. gear on a SM-319. It uses a "low-reverse sliding gear". The later model Saginaw 3 speed used in the middle 1960's and later is a bolt-in swap to the bell housing for a 319, but it will probably need some modification to the shift linkage and possibly a different driveshaft to complete the conversion. The Saginaw has a synchro 1st. gear that can be engaged up to about 15-20 MPH or so.

Question- - - - -isn't the SM-318 the normally-installed 3 speed for your truck? A 319 has a Borg-Warner overdrive attached.
Jerry

Thanks for your replies.

3B.
I'm only guessing at the original tire size, based on the GVWR and owners manual. But if my tires are SMALLER than original, then my indicated speed should be FASTER than actual speed. But I have the reverse. My INDICATED speed is LESS than my ACTUAL speed.
I presume that you have to change the speedometer gears in matched sets, or am I wrong on this? I have a white nylon 25 tooth driven gear. Seems like I need to go to a 24 tooth gear ?

Jerry,
OK, I'll take your word for it that I have an SM-318, not a SM-319. Didn't know there was a difference.

On the oil side, I'm not sure what oil I put in the transmission. Probably a 75W90 or 80W90 I had at the time. Maybe from the final drive of my various shaft drive motorcycles of the past. I can't find the container to be sure, and it was filled over 2 years ago.
Due to growing COVID-19 numbers, we are in a bit of a lock down in Ontario, and I can't walk the isles of the stores to find the right stuff. Online, at the normal automotive shops, I can only find a SAE 90 gear oil for 'marine' use. Not sure if there is much difference or if that would work. I can find a 80W90, 85W140, Otherwise, I'll have to go to a farm machinery dealer and see if they have some straight 90 weight oil.

John.

John,
There are 3 speedometer driven gears currently available for the Muncie 3 speed or 3 speed OD transmissions: White 25 teeth, Yellow 24 teeth, and Green 22 Teeth. The drive gear does not have to be replaced to use either of them. I get the gears on ebay from Muttonhollow Chevy. He usually has the best prices.
Changing the gear oil is a good place to start but any grinding in 2-3 generally indicates a syncro problem. Don't rule out the clutch though.
Fred

Note: Earlier regular 3 speeds used a 19 tooth steel gear. They also use a different drive gear.
Also, the SM319 is a factory overdrive and would make a serious improvement in overall driving and also lower engine rpm's.

Back on this old post.
I've changed my transmission oil to a straight grade 90 oil I found in my supply cabinet. Still grinds a bit downshifting from 3 to 2.

I bought a replacement 235 engine that came with a 3 speed transmission. It looks the same as my existing original (?) transmission. Before I swap transmissions, is my replacement a good match? I tried looking for casting numbers online, but couldn't find anything.

Existing Transmission casting numbers:
Main Case: 3845122. 4 bolt side Cover: 3845157 Tail extension: 3707185
Replacement Transmission 4 bolt side Cover:3845044

My existing transmission has both linkage arms pointing downwards.
[img]https://imgur.com/s0Nfwid[/img]

Replacement transmission has 2-3 selector arm pointing upwards.
[img]https://imgur.com/T4S4rqa[/img]

The bell housing on the replacement 235 engine has a shaft on the drivers side with some linkage levers that my truck doesn't have.
[img]https://imgur.com/yZjLzqv[/img]

I have steering column "3 on the tree" gear selector. Would my replacement transmission have come from a COE or cab forward truck with different linkage?
Can I rotate my 2-3 transmission lever 180 degrees, or swap with my original transmission lever.

Any recommendations?

Thanks.

The replacement transmission and bellhousing are from a 55 first and or second series truck with a 235 engine. 55 V8 trucks and all later trucks used the configuration as in your first photo. Simply remove the side covers and swap them over. Be aware that the 2-3 shift forks are a common wear item. You can use the shift fork from the replacement if it is better or get a new one.
Fred

The info from the GM Heritage website says rear axle is a 3.90 or could be the optional 3.70.

I came across a Saginaw 3 speed transmission at a flea market. Cast Iron cases. Supposedly fully synchronized and in good shape. Came out of a 60's Chevrolet truck I think.
Would this be compatible with my SM318 transmission? Input shaft looked like a 10 spline. Not sure about the output end. Seller has a floor shift with it (Hurst?), but not sure I want to scrap my column shift.
Hoping seller can bring it over and I can put it beside my spare SM318 and see hot it measures up.

John D,

Any way you can get the seller to send you a picture???

If so, you could post here so someone can help answer your questions.

Thanks and good luck in your pursuit.

Dan