VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Change 4:11 ring gear and pinion to 3:55

I have heard that you can change the ring gear and pinion (only) from a 1951 - 1952 Power Glide Chevrolet (3:55 ratio) to a 1941 Chevrolet rear end without changing any other rear end parts. If this will work what would be the gain in terms of speed. One fellow told me that I would not gain very much from the change. I don't want to change the whole rear end unless absolutly necessary.

With every thing except the rear end ratio being the same, going from 4.11 to 3.55 will increase your speed at the same engine rpm from 50mph to 58 mph a change of 115.8%
I consider it very much desirable specially if the engine is a Chevy inline six.

MrMack I think you mean it will be a 11.58% change.Changed gears on my 1939(4.22 to 3.73)This enables me to cruise at 68 mph with ease where as before 60 mph was my usual speed.Gas milage went from 15 to 16 up to 17 & 18 mpg .There is a power loss on hills,mainly under 50 mph but if you do a lot Interstate driving its worth it. Also the speedo. will be off unless you change the speedo gears or use an adapter or just figure a 12% error.

P.S. That would be 1950 thru 1954 Power Glide.The 1953-54 sticks used a 3.70 rear end this makes a good choice also especially if you live in a hilly area.

Thanks Gene, What I meant to say was 115.8% of what speed you were doing before or a 15.8 increase in speed. The math is simple:

4.11/3.55 = 1.1577464

Thanks Mr Mack and Chev Nut for your reply and information. Chev Nut did you change ring gear and pinion only on your 39? Also will the ring and pinion from 1950 to 1954 Power Glide work on my 41 without any changes or alterations? Were all 50-54 power glide ring gear and pinion 3:55.?

Automobile Archives - http://www.automobilearchives.com has 'Differential Ring and Pinion Gear set, 37-9 ratio, 1940-52 Chevrolet Passenger' (Featured parts - $95) (3:79 gears) This was a stock option for 41 - the 'Economy gearing'. Much cheaper than 3:55 sets (which run around $400). Also, about as much as you'd probably want with a 216.

Jim

My calculator must be on the fritz For a 37-9 ratio Ring and pinion I come up with 4.11 which is the STOCK ratio and not the optional????????????????

I don't know much about what you might call archivial documentation but if you count teeth and come up with 9 on pinion and 37 on the ring 37/9=4.111111111111111 and 32/9=3.5555555555, did you ever wonder why someone came up with 4.11 to 1 and not 4.25 to 1 and why 3.55 to 1 and not 3.50 to one? 35 tooth ring / 9 tooth pinion =3.8888
and 36 /9=4.000 34/9=3.7777777 or ??? I always wondered why 9 teeth on the pinion gear (maybe harmonic vibration is less???)then came up with 360* / 40=9 !!! I guess it is easyer to index 40* than to index 36* or 45* I still don't see why they use 9 teeth on the pinion do you?,... think about it for a while and then read another book, and get back with us , please!!!!


Yeah!

Yes,I changed the ring gear & pinion only on my 39.Had a new one in the box for years when I began using the car for long distance travel again I made the change.The 1939 parts fit 37-39 only and the 3.73 ratio was standard in the lower priced Master series.If you change your 41 most people I know used the complete center section and torque tube (enclosed drive shaft )from the P.G. and bolted it in to the rear axle banjo.If you remove the gears from the P.G.you must use the case that the ring gear bolts unto .The bearings should be inspected anyway so it would be advisable to dissasemble the rear end and put just the gears into (and case) your present unit. There was an high speed or economy ratio available for 1941 thru 1949 as a factory option. It also was the 3.73 ratio with 11& 41 teeth.

Yes 11 and 41 teeth is not a pleasure for the older gear cutting crowd but with todays materials and heat treating methods well within standards...... anyone come up with the reason for 9/37,9/32 and11/41 tooth combinations yet? there may be a prize for the best answers, Billy Barker may give you an award! LoL (Lots of Luck!)
:confused: :arrow:

MrMack, Here is a few more things you can ponder.As an example Ford used a 4.10 ratio(with O.D.)Studebaker and others used 4.09,Chev had 4.11,.These were all common ratios in these years. Why did no one ever offer a 4.00???Also Chev changed from 3.54 in 1954 to 3.55 in 1955.(11&39to9&32) and yes the diff. was a complete different unit. Also why did Chev.go to a 3.70 in1953-4 sticks when they had used 3.73 earlier.The 3.70 being 37&10.This set up also used the diff case of the PG cars as mentioned in my previous post.When the 53-54 sticks were new we had some with noisy rear ends that they could not correct and as a last resort Chev. suggested to install the old 3.73 ring gear & pinion with the earlier case and this would make them Quiet.

Well, why you ask grasshopper??, any ways grad you asked grasshopper!!, It was revelled to me by long time gear guru that in a helical gear setup arways use numbers of teeths so that same teeths and same teeths on pinion gear and ring gear never run together all the times, such as if it were 4 and 36 (4.00:1) that teeth repeating to run together is not so good, causes wear patterns that are un acceptable and something to do with harmonic vibrations comeing down road in later days. and that is my story , grasshopper.......

:rolleyes: :p :arrow:

Look at web page < http://la.znet.com/~c1937/RPM.htm > for more details that you wanted to know about Chevrolet rear end ratios. Click here for rear end ratios: &l...PM.htm]http://la.znet.com/~c1937/RPM.htm >[/url]

Automobile Archive (http://www.automobilearchives.com) also has the RING, PINION GEAR DIFFERENTIAL 41-11 (#604397) for $125.

Jim

if anyone is wanting to make a change they should jump on this.This is a rare item & the price is right

OK, I've got to ask... is there any hope for someone with a '37 1/2 ton truck? I have both a 3 speed and 4 speed transmission available, but I think both of my diff's are 4:11, and I'd like to go to the 3.5 to 3.7 range. :confused:

I have some g00d news and some bad news.Yes there was an economy ratio offered for 1937-39 1/2 tons.The ratio was 3.82 (11-42 teeth)The part # was 602477.This was and is a rare part.In my years of digging out old parts in the 70's I found only one & don"t recall seeing any ever being advertised in the G&D.The same gears also were used in and available for the 35-36 Master cars 1/2 tons.

Thanks, I saw this ratio in the service manual.

When you say it was and is rare, do you mean in 37's only, or also in the 35 & 36 cars also? A few weeks ago there was a '38 1/2 ton that sold on E-bay that had been converted to a 5 speed transmission... I wrote and asked if the truck retained it's enclosed driveshaft, and the seller said it did, but did not elaborate on how this was accomplished. I wouldn't want to deviate from the original transmission design, but this was an interesting idea.

It was rare for all of those years for cars & trucks.

also it was the same part number for 1935-36 Master cars and 1935-39 trucks.This would give less than a 10% engine speed reduction so it would be only a 4mph speed gain at 50 mph.This would be a good application for someone to make a set of 3.50 gears for.Sorry for the delay I missed your post from the other day.

Thanks Chev Nut. You're right, the 10% reduction wouldn't be worth the trouble. For now, I'll do well just to get something of this pile of parts back on the road, then I'll worry about saving the engine.

I have a 38 1/2 ton with 3 speed but am not sure what ratio the diff was (now absolutely stuffed with water). I wondered if they were made with 4 speed now I know.
Pity you are in USA or we could discuss the exchange of differential ownership but the cost of getting it down under prevents that possibility.

OK guys, I'm new here and am in the process of finishing the restoration of my 1940 Chev Master Deluxe Sedan. (The body, upholstery and chrome are already done). I believe this is going to be a very helpful forum.

So, will the topic 'ring and pinion' change also work as a "drop-in" without further modification on the 1940 models? I would at least like to sort of keep up with the flow of traffic and at 55-60 you can't do that without getting run over.

DocB

If you can find the torque tube out of a '40 Master 85 you can slip the complete unit it your ''40.They will be 3.73 gears.If you can come up with a 50-54 Power Glide rear end you can use only the ring gear and pinion plus must use the case the ring gear is bolted to.Dido on the 53-54 stick but will be a 3.70 ratio.Any of these ratios will allow you to run at 65 mph if engine is good.

Hey Chev Nut -Shade Tree Mechanic from West Allis, thanks for the response. After I get the steering gear replaced (about a half turn of 'play', and the clutch throwout bearing (fully functional, but noisy), the next item will be the lower (higher?) differential gear replacement.

Since we are both from the same part of the country - I'm a native of southwest Minnesota and that's where the car presently resides - on the family farm, I may e-mail you later.

Doc