VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 36 High Speed Diff

A fellow member I know has told me he has a NOS 3.55 gear set for a 36 truck. I have been told the truck, and master in 36 used the same differential. He also has a differential out of a 54 powerglide car. I have seen a post on the web site about converting the differential to the later style 3.73. My question is two fold - doesn't the later style look significantly different being a hypoid style, and how difficult is it to change the gear set in the original 36? Any challenges? This is a fairly high point car.

If it is a "high point car" then why change it? I enjoy my two 1936's as is, original.

maybe he likes higher speed driving turning a whole lot less RPM.
Also would get better gas mileage with 3.55 as motor is not turning over as fast.

Longer engine life due to less stress of tighter rpm.

mike

A 3.55 ring gear was never made for a 1936 truck or car. I would question that one.
The differential for 1937 and up cars is completely different and comes with the torque tube so length can be a problem
Anything can be dome with a lot of machening and tools.
There was a optional 3.82 made for 1935 and 1936 Masters. Very rare.
A 3,82. or 3.73 would reduce your RPM,s from 7 to 10 percent. 10 percent with the 3.73 would gain you 5 MPH at 50 MPH.
If the engines are in good condition then can be driven at at least 55 MPH......going 60 wwith a 3.73 will be very little gain and traffic will still be flying by a 70 + MPH.

If you can ever get up to 70 with the original stuff, I would like to hear about that one. At 60 it should start to "get light" and go air born. On coming traffic on a two lane U. S. Highway passing would cause the car to rock, especially a semi rig. The air blast would hit the car hard.
Who would want to go that fast? Just plain scary and dangerous to exceed the car's design. Not that I haven't been above 60 but in my younger days and only for a short while. A sustained 60+ driving any distance is ill advised. (The most Dad ever drove on the open highway was 55 and up to 60 in short bursts. Then back to 55.) I do not go on the Inter State Highway. 45 and 50 is more like it for this type of vehicle.

Remember the higher the gears the less power you have.

I agree with the above with one minor exception. You will find that the Master with knee-action is much more stable feeling at high speeds.....and if in good shape will hit 75 on the speedometer.....and 55 to 60 is a comfortable crusing speed after you get accustom to driving an old car.

Beach,

As this article demonstrates the project you are contemplating is easily accomplished in a home shop that has basic machining and welding equipment:

https://vccachat.org/ubbthreads.php/topics/334876/1936_Chevy_3.55_rear_gear_conv

It will have no effect on the "high point" status of the car because once completed it looks original. The judges simply aren't knowledgeable enough or energetic enough to crawl under your vehicle and say "Ah ha, that's a hypoid differential, not a spiral bevel differential. You're caught buddy".

I know from personal experience that the judges won't catch it. My '36 PU won Class T-2 at the 1976 VCCA National Meet with obvious safety upgrades like modern tie rod ends on the tie rod and a home made drag link with those same modern tie rod ends. Those modifications, made to eliminate steering linkage slack, went unrecognized.

If you'd appreciate less engine noise and a 17% drop in RPM/increase in cruising speed there's no reason not to go for it. My '36 pulls the 3.55 gears easily with no engine modifications except a rejetted '39-'40 carburetor and a paper element in the air filter.

Ray W

All 1936 Trucks are straight axle. So no riding like a Master Car. More like riding in a diesel 18 wheeler.

The pick-up truck and even the Standard passenger cars are a few hundred pounds lighter than a Master sedan so the "high speed gears" would limit the acceleration and hill climbing power in a Master.

There was another member at the recent NW meet who has the 3:55 gear set in his 36 master coupe. He said it made a lot of difference in the driveability of his car. I am still in the investigation stage, we will see.

How did he do it? Did he use Ray W's method?

I have a 36 Pontiac, and it uses the same differential as a 36 master. I have been down this rabbit hole in every way possible, and I am fairly sure no 3.55 ring and pinion sets were ever made for this differential. I would absolutely love to be proven wrong.

To the best of my knowledge, Ray W's method is by far the cheapest and least invasive way to get 3.55.

If you can find out how that guy at the NW meet did it, please let us know!

The 1936 Pontiac 6 had a 4.44 ratio and the 8 had a 4,55.
The 4.11 from a Chevrolet would already be an improvement.

Gene- Thanks to a very helpful forum member, I am building a 3.82 third member. My Pontiac has the optional 4.88 gears (the 4.11 Chevy gears were also optional). It is a six, and yes if it had the standard setup it would be 4.44.

Have you ever actually seen 4.55? My shop manual says the Pontiac Eight is 4.55, but I have come to suspect it is a typo. I have never (yet) seen any part number for a 4.55 ring and pinion.

SEEN guys down here jump on the freeway and hit 75/80 MPH! THEY ARE MOVING! very unsafe on So. Cal freeways
for me 45/50 mph at the most

"All 1936 Trucks are straight axle. So no riding like a Master Car. More like riding in a diesel 18 wheeler."

That's a fact Terrill. I've had that '36 since I was a 20 year old college kid in 1965 and now at age nearly 73 I still love driving around in it. It's bouncy even with optional shock absorbers. And the multipiece cab sheet metal nailed to a wood frame squeaks like a haunted house on the bumpy country roads around where I live. I love it and wouldn't change a thing.

If I wanted a Lexus I'd get one. Grin!


"To the best of my knowledge, Ray W's method is by far the cheapest and least invasive way to get 3.55."

Bloo,

I think you would be impressed with how totally original is looks. I can say with confidence that even if I pointed it out to you you'd say "Really". Let me know if you'd like to see a photo.

It would be really easy to do another now that I've done the job once.

"The pick-up truck and even the Standard passenger cars are a few hundred pounds lighter than a Master sedan so the "high speed gears" would limit the acceleration and hill climbing power in a Master."

Gene,

There is an 11% grade near my home a couple of miles long. With the 3.55 gears my '36 won't pull that hill in 3rd gear but it pulls it easily in 2nd. Even with 4.11 gears my '36 couldn't pull that hill in 3rd. Now that I've run the same '36 with both gear ratios the 3.55 gears seem better in every way. If this were 1936 and I was hauling loads that might not be the case. Today it hauls only a cooler and a couple of lawn chairs.

Ray W

I have had my 1936 truck since 1964 some 53 years. I am the second owner. I am 70 years old and also would not change a thing about this bouncy old gal. She has overload springs and can still haul a one thousand pound load over these hills on dirt roads out here in rural Mississippi. Yes, I use second gear to pull 11% grades. She is not fast but still a very good truck.

"Yes, I use second gear to pull 11% grades."

3 speed or 4 speed "crash" box? Mine's a 3-speed. If yours is too I found the perfect equivalent of the 160 gear oil recommended back in the day. It's a Lubriplate product, not the "600W" steam cylinder oil sold by some vendors.

I'll send you an emailed PM.

Ray W

The 1938 Pontiac parts book list ring gear and pinion set, 544266, 4.55 ratio for a a '35 P/8 after axle number 8-1452022 and all '36 P/8.
Also the 1934 P8 and early 1935 P8 had a 4.55 but the change was to the roller bearing in mid 1935...same change made to the Chevrolet differential.

Ray, Going by my 1939 the change from the 4.22 that would pull any hill in high gear to a 3,73 didn't kill the power too much with just the driver but with 4 people in the car the speed would drop off on larger hills requiring the use of 2nd gear.Empty the '39 was a couple hundred of pounds lighter than a '36 Master and the 216 developed more torque.
With the 3.73 it would cruise smooth and quiet at 70 MPH.

I've just read through this thread and found it interesting. Gene has pointed out all the things one would need to know before attempting a change of differential gearing. For instance:

a. As you lower (you know go to taller gears) the engine will turn over less for the miles driven.

b. There is a trade off with the above gears. The taller the gears the less hill and highspeed power you will have. That is to say you will experience what is called deminishing return or trade off. The engine will suffer pulling power the taller the gear.

c. If you go to taller gears then you will need to increase the horsepower in direct coorelation to the gear ratio to engine horsepower.

d. As I understand it a 1950 Frod without overdrive will run at top speed about equal to the one with O/D. The slight difference owing to the speed and direction of the wind the vehicle is going through.

If one wants a good performing old Chevrolet then don't screw with the product as manufactured. If you don't then one thing will lead to another. A 1941 with the 4:11 is a good all-around gear. It premits good level travel whild having good incling climbing power and engine braking assist.

We always want to tinker and try to outdo the factory engineers, but they were and are smarter than most of us. So I believe.

Just my two cents worth.

Charlie

BTW: The old saying about doubling the speed of an airplane was that you had to quadruple the horsepower. Interesting, huh?

Charlie have you considered that the environment the cars are now running in are much different than when the engineers designed them? You are correct that they were very smart however they did not have a crystal ball and know the conditions in which they are now being driven or the products available to maintain them.

Thanks. Always good to have somewhere else to get products. I use Case International Harvester products on mine.

"Gene has pointed out all the things one would need to know before attempting a change of differential gearing."

Charlie,

This is not a hypothetical for me. I've actually done that 4.11 to 3.55 conversion and I can enthusiastically recommend it to anyone. The bone stock 207 engine pulls the 3.55 gears no sweat and the reduced engine noise and more comfortable highway running are huge pluses.

A '37 car rear end, 3.55 gears and access to a lathe and welder are all it takes.

Ray W

I owned my '35 Std coupe for 43 years, and have driven it
every where, including on the Interstates! The stock 4:11
rear axle is adequate for most driving situations. I have had
her up to 60 mph, but not held for long! On Interstate driving
I usually cruise comfortably at 50 mph. The minimum speed on
most Interstates is 40 mph, and at 50 the car cruises easily
and within safe braking limitations! I wouldn't put too much
faith in those brakes at higher speeds! I don't feel I have
ever been a hazard to faster moving traffic, but there is
always the idiot who will cut you short when passing! The joy
of driving an antique is staying within its limitations!

Thanks!

Also, I think the 4:88 kept the old bearing right up to the end. One parts book I found online said 1936 4:88 used a ball bearing instead of the Hyatt. I suspect it is the same one used in 1934 to early 1935.

Do you know if the any of the machining changed on the case when they changed to the new bearing?

In other words, can you put the 34-to-early-35 pinion in a late-35-to-36 housing (or vice versa) as long as you use the correct bearing for the pinion?