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Hello Everyone.

I just bought a 1952 Chevy 3100 with an inline 6 and 4 on the floor transmission. I am very excited to start restoring this old beauty, but I need a little help. There is no dip stick to check the transmission fluid. Can anyone help? Also, any specific transmission fluid that I should be putting in an old truck like this?

I appreciate all your help!

~George

There is no dip stick.
To check tranny fluid level, there is a square head threaded plug on the passenger side of the tranny housing.
The fluid when cold should be a half inch below the threaded plug hole.
Fluid when hot should be level with threaded plug hole.
Use pinky finger on your hand to check level.
Use threaded hole to fill or top off fluid.
GM film strip Picture of square head plugs Slide 14

Type of fluid to use is 90 weight gear lube.

To drain fluid there is a square head threaded plug on bottom back of the tranny housing.

Capacity of 4 speed tranny is 6 pints 1952 OPERATOR'S MANUAL
If fluid seems to disappear, the torque tube oil seal may be worn and leaking tranny fluid down the torque tube into rear axle housing.

xfiles

Thank you !

I appreciate you help! The info was spot on!
You're the best!

Shouldn’t the gear lube be GL-3 , or GL-4, due to the corrosive nature of GL-5 on brass?

GL4 hard to find just was looking for it online in Canada anyway and looks like it is going to be pricey .Anyone know if you can use synthetic or am I just asking for trouble like leaks everywhere along the tube to the rear ended .

Synthetic leaking thru good seals is an internet myth. If the seal was good to start with, synthetic oil won't leak thru either.

GL-4 Gear Lube

90w Mineral gear oil, from NAPA is another way to go.

I looked up the same on amazon but shipping says 49.99 a no go for me

I agree with kl ,i use mobile 1 in everything and rope rear seal dont leak any more than regular oil and only change once a year

Yeah, a lot of stuff Amazon won't even ship to Alaska even though we're part of the same country.
Maybe you can find some locally.

Just learned about and purchased Penn Grade (formerly Brad Penn) Classic Multi-Purpose Gear Oil. GL4 safe for our stovebolts with synchronized transmissions. $8.00 a quart. I've been using their Classic Motor Oil for the last 6 years.
Chuck 52

Tractor Supply carries Ford Tractor Transmission Fluid, which is straight 90 weight Mineral Oil.

I have been using Royal Purple gear oil and now it is easy to detect the tranny leaks from the engine drips.

The four speed trans also has a separate reservoir to bathe the rear universal in oil while operating. From memory, I recall the fill plug being on the passenger side. Oil removal happens when the torque tube retaining plate is loosened.

Absolutely agree with the Traveller straight 90, and have heavy duty hand cleaner available before you start. Local parts stores will also have a lube transfer pump available that makes this job much easier.

I use Sta-Lube 85w-90 GL-4 gear oil in transmissions with brass synchros. The part number is SL-24239. It's $30/gallon on Amazon. Napa has it for $38/gallon.

https://www.amazon.com/gp/product/B000M8RYMC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

1952 OPERATOR'S MANUAL
Recommended lubricants
Transmission: S.A.E. 90 Straight Mineral Oil Gear Lubricant or S.A.E. 90 "Multi-Purpose" Gear Lubricant

S.A.E. 90 "Multi-Purpose" Gear Lubricant can be found at most auto parts stores.

In regard to "Hink" post, when flushing and changing transmission fluid to GL4 will the rear u-joint housing lube need to replaced also since it does not drain out with transmission lube?
Chuck 52

Primary function of that lube is to cool and lubricate the universal joint. Now that you know it's there, it's your call. But I would get a new gasket and replace that lube to ensure I have good, moisture-free fluid and take that opportunity to inspect the contact surfaces.

Learned a lot from this thread. Thanks to all of you for information and advice.
Chuck

Hink that is an excellent point. There is a small pipe plug on the bearing retainer. Does this always need filled separately from the transmission fill?

Yes, the rear universal joint area needs to be filled separately from the main transmission fill. Failure to fill this area will lead to near immediate universal joint overheating and failure.

The two fluid areas do not cross over.

How do you fill the u-joint enclosure ball/bell?

Transmission fluid "migrates" to the enclosed u-joint on 1/2 ton Advance-Design trucks.

Forgive these two rules of thumbs : after replacing an SM420 on a 3100:
1. warm transmission/fluid: fill the transmission up to the filler plug-hole on the upper passenger side of the SM420
2. cold transmission/fluid: fill the transmission to a thumb-length below the opening

The 1/2 ton u-joint-housing/u-joint-cover/bell slides back and forth on the outside of the torque-tube.
I clean/shine that surface so the torque tube can easily slide a little in-and-out with no/minimal leaking.

After a while, they all leak/drip a little : the old saying/joke was - if you have no leak at the torque-tube seal, you have low transmission oil.

It seems that the u-joint only gets filled separately on the 3-speed, and not the 4-speed (there's no mention of it). Doesn't the 4 speed use an open u-joint at the rear of the transmission and an open driveshaft?
From the Service Manual section for the 3-speed transmission used on 1/2 tons.
10. Remove the square head pipe plug, lubricate the universal joint bearings through the opening, and replace the pipe plug.
11. Fill the transmission with 1 1/2 pints of transmission lubricant.
The fill plug is in the actual gear case, not in the tail housing, so those are two separate operations.

Kevin, my '37 1/2 ton has the "optional" 4 speed with tube. only the 1.5 ton and up had open shaft. now I'm confused as all the previous things I have read regarding IF the rear tranny seal was bad the oil would migrate to the rear end then overfill it forcing it out the axle shafts ruining the brake shoes. So is there NO crossover to the U joint and beyond in a 3 spd but there IS in a 4 spd?

I see. Sorry for the misunderstanding. I was looking at the 47-52 service manual. If the earlier 4-speed has an additional plug in the tail portion, I would assume that there's no transfer between the main gearcase and the tail housing that has the u-joint. If that's correct, then there wouldn't be a problem with overfilling the rear axle UNLESS the seal in the torque tube is leaking. Again, I'm assuming that the earlier torque tube is similar to the ones in the AD 1/2 tons.

Welcome to the big adventure, it is habit forming. The people on this site are genuine and helpful. I thought I knew a lot when I joined in January but, that was not the case, they have taught me so much about my AD trucks. Doc.

This is an interesting thread. I know a couple of former co-workers that cautioned me against the 4-speed U-joint when I was swapping from a 3-speed to a 4-speed in my '53 3100. They claimed they had to replace their U-joints multiple times due to breakage. Maybe that was why...the small hole in the bearing retainer was not being filled with tranny fluid, leading to U-joint failure.

Going downstairs to the garage to check mine now...

To add to the confusion, the service manual for my '54 1/2 ton w/ torque tube and SM420 four speed says to remove the little plug on the torque tube ball joint and insert a "few"ounces of 90W gear lube AFTER rebuild. Because there is no rear seal in this transmission, it is assumed that gear oil from the tranny will leak into the torque tube ball joint and keep the u joint lubricated. There is a seal and a bushing around the internal driveshaft at the front of the torque tube that is designed to keep tranny oil from leaking past this seal and overfilling the differential. This bushing and oil seal can be removed with a special tool and replaced with a new integrated seal and bushing called an "Okie" bushing without disassembling the differential and removing the driveshaft.

Also, I find it easier to fill or top off my SM420 four speed by removing the gearshft and pouring gear oil into the top of the tranny until it runs out of the fill hole on the side of the tranny.

Or you can add oil through the "fill hole on the right/passenger top-side of the tranny" to about 1/2" below the hole (when gear oil is cold). I think this is described in the Shop Manual.

Wow, I just read this whole thread and would be confused as to what to do. I just finished rebuilding my SM-318 3-speed on my ‘52 and can tell you that there is no extra fill for the u-joint , the tranny migrates lube to the u-joint.

In reference to the four speed SM-420, the link to the ‘52 Operators Manual tells all. I would however, fill the u-joint cavity after a rebuild, but after that, the transmission oil will migrate to keep it lubricated.

http://chevy.oldcarmanualproject.com/chevyowner/52tom98.htm

kevinski Someone commented that synthetic gear oil may be too slick to let the synchronizer rings work,may grind more going in !

Hotrod Lincoln has mentioned that in this thread.
https://www.stovebolt.com/ubbthread...ssion-grinding-in-first.html#Post1374964