The Stovebolt Site Forums The Shop Area Driveline 1932-36 3-speed transmission

One of the ongoing challenges since I restored my ’36 Chevy PU in the early 1970s is finding something that matches the SAE 160 gear oil that was specified for the transmission “back in the day”. This matters because the primitive 1932-36 Chevy Master car and pickup 3-speed transmission has a small 3rd gear synchronizer that works poorly at best and becomes worse with less viscous oil.

It really bad with SAE 90 gear oil, a little better with SAE 140 and slightly better yet with so called “600W” oil that is not a gear oil at all but is a steam cylinder oil. I’ve prepared 2 different transmissions with new synchronizers shimmed to the middle of the specified 0.025” — 0.035” end play and new shift forks and they behave identically.

Pressing on I tried Mobil “600 XP460” gear oil with an ISO viscosity of 460 and that was actually worse than the “600W”. This oil is available in gallon quantities but the next step up in viscosity in this Mobil oil, XP 680, is available only in a minimum 5 gallon quantity, too pricey for a quick experiment.

Looking further I found that Lubri Plate has an ISO 680 oil packaged in quarts and Lubri Plate themselves and others sell it in 1 quart quantities. So I just got a couple of quarts of this oil to try. Its SAE viscosity is approximately 250. It doesn’t appear to be vastly more viscous than Mobil XP460 so maybe these viscosity numbers are not linear.

On a quick drive this morning of only about 5 miles the shifting did seem improved, but it was a pretty cold morning, about 40 degrees F. Only a longer drive where everything gets up to normal operating temperature will be conclusive. If anyone is interested in the results of this experiment please let me know.

Torque drive? Could you install a later trans? 420 for example.

Ed

Ed,

This is a restored '36 PU so keeping it original is a priority. It does have a torque tube. I have made some significant alterations like this:

http://vcca.org/forum/ubbthreads.php/topics/334876/1936_Chevy_3.55_rear_gear_conv

but they are visually undetectable.

If the present gear oil experiment doesn't solve the 3rd gear engagement problem I'll accept that the '32-'36 3-speed synchronizer design simply can't do any better. It's probably a design conceived in the late 1920s, nearly 90 years ago. That is part of enjoying any antique vehicle.

Synchronizing 3rd gear requires speeding up or slowing down not only the input shaft ("main drive gear") but also the countershaft gear ("cluster gear") and the reverse idler that are both always in mesh with the input shaft. The latter 2 gears are always below the oil line so the more viscous oil should at least help slow them down for the 2-3 shift. Time will tell.

I appreciate your interest.

If you decide to change transmissions, I believe a 1937-39 truck 3 speed would be a direct fit.

Dave,

That's an interesting possibility. Thanks!

It would depend on the bellhousing bolt pattern, transmission overall length, whether the output splines fit the '36 U-joint and whether the '37-'39 trans has lugs cast in the side for the pedal and master cylinder mount casting to bolt to.

Decades ago when the VCCA monthly magazine, Generator and Didtributor, was still a car magazine instead of the travel magazine it is today it had an article about updating '37 and up Chevy 3-speed transmissions with much later gears for improved shifting. That information did not apply to the '32-'36 transmissions like the one in my '36 PU so I don't remember any details.

It's pretty amazing what can be done to totally stock appearing antiques to improve safety and drivability.

Following your suggestion I used a '37 Chevy car rear end to allow use of OEM '50-'54 Chevy car 3.55 gears. Thanks again for that too. Nobody would know from looking at my PU that such a conversion was ever made. It makes the PU much more pleasant to drive.

My 2 current projects are adapting in a dual master cylinder and a '34-'36 truck fan shroud. Finding the upper 1/2 of the fan shroud was a 40 year search.

Transmission bolt patterns chart
Transmission length chart

Drive report:

The short version is that the SPO-288 gear oil has greatly improved the shifting. I tend to go into too much detail in explaining things and I won’t do that here.