3:78 vs 3:54 ring and pinion

[Al 29Tudor]

I'm planning to do some repairs on my rear-end this summer and would like some comments on changing to a higher speed rear end ring and pinion.
In south Florida there are no hills so I'm wondering how drivable the car would be taking advantage of the engine torque while staying in a safe RPM range. The engine is stock except for .090 over pistons.
I'd like to hear about your experience with this type of change.
Thanks much for your help.
Al Leach

[lindy williams]

My experience is that its a minor change and maybe not worth the price unless you need a new ring gear and pinion for some reason.

[Jim/GA]

You won't hate it. You will hardly notice the difference. Running around on flatlands is pretty much what this gear was made for, back in the day.

It is a 6% overdrive. Any overdrive is about using the engine HP to give you slightly higher speed for the same engine RPM.

Instead of going 40 MPH, you will go 42.5 MPH at the same engine RPM. The sweet spot on my Model A was around 47 MPH; this ring/pinion would move it to 50. Hardly a mind-blowing difference. Hard to make much of a safety case for the change. But if you are installing new R&P anyway, sure, why not?

[H. L. Chauvin]

Hi Al,

South Florida, maybe mild inclines on certain highways, changing ring & pinion .... 3:27 is what I did & would recommend.

At 45 mph, driving 1,800 mile per year, your engine would rotate 4.6 million rpms per year with a 3:78; however, your engine would rotate only 3.9 million rpms with a 3:27; hence, 700,000 rpms less wear per 1,800 miles. Try jumping up & down 700,000 times to a year to experience this experiment in physics.

At 1900 rpms, if one obtains 43 mph with a 3:78, approximately 51 mph with a 3:27 or 8 mph faster ...... with an 8 hour drive, one travels 64 miles further, gets there quicker & can take one's time to eat dinner ..... plus additional savings in gas mileage.

Per your question in #1 above:

"I'd like to hear about your experience with this type of change."

Many Model A owners never listens to "actual" past experiences; however, with humility, some of us continue to make Forum suggestions based on past "actual" experiences as opposed to continue quoting what others have written over the years.

My "so-called" heavy Town Sedan loaded with people has no problem with a 3:27 even in hills ..... 20 mpg in stop & go traffic.

[Tom Wesenberg]

I would also go with the 3.27 ring and pinion, and hope to do that with my spare rear end when I get around to it.

[H. L. Chauvin]

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If anyone calls Steve at Bert's, (maybe others), he has a torque tube mounted device for converting speedometer rpms for a 3:27.

And just in case one has a vegetable or flower garden to plow, with a 3:27, no doubt one can still pull a plow in first gear with your wife driving while you hold on to the single wing plow handles.

[diomed]

I went from 3.78 to 3.54 and am very happy with it. The car happily cruises at 55mph on the freeway and will cruise at 45 in the city like a modern car. I'd recommend the switch to 3.54 or 3.27

I didn't go with 3.27 because I do see hills often enough. I drove it up a mountain road last year with the local club and it wasn't pleasant. It was a 2 lane road with modern cars trying to do 65mph+ while I struggled to do 35mph. 35 was right about the rpm where I'd normally shift between 2nd and 3rd so it was either lug or over-rev

[Ron in Quincy]

One thing you might consider is installing a Snyder 5.4 high compression head, this is one thing most notable and pored bearings will handle it OK, then you get better performance when you install the 3.54 gears when you rebuild the rear differential.

I have a Touring engine in my 30 Coupe with 3.54 gears in the differential, I live in the mountains but climb hills without having to shift down due to the additional horse power, sure like the arrangement and a lot cheaper than installing a overdrive.

Just my opinion,

Ron

[Big hammer]

Originally Posted by H. L. Chauvin

If anyone calls Steve at Bert's, (maybe others), he has a torque tube mounted device for converting speedometer rpms for a 3:27.

And just in case one has a vegetable or flower garden to plow, with a 3:27, no doubt one can still pull a plow in first gear with your wife driving while you hold on to the single wing plow handles.

Having an accurate speedometer would be a must for me, once a got a speeding ticket 27mph in a 25 speed zone and a warning ticket for loud exhaust. The new muffler and tail pipe was in the back seat.

[Mitch//pa]

For your terrain Go with the 3:27's... we have flat and hills combined and I'm sorry i did the 3:54's....not enough inprovement

[1929]

Originally Posted by Mitch//pa

For your terrain Go with the 3:27's... we have flat and hills combined and I'm sorry i did the 3:54's....not enough inprovement

X2, I can repeat all of the above stated.

[Peyton]

I've thought long and hard about what I'd do if my 3.78 went out. With a stock engine and flat land driving it would be nice to cruise at 50 with no effort. A 3.54 would certainly allow that. You don't encounter many hills in Jacksonville so a 3.54 would do great here.

Most of my driving has been on flatland but some has been in mountain country. A good test of Model A climbing prowess is Grandfather Mountain NC. There's some real grade there and I can assure you that we would have never made it to the top with our stock engine and a 3.54. No way --- it was tenuous with the 3.78 which was a very roadworthy ratio for the 20's and 30's. You could say that the 3.78 was a high speed ring and pinion of its day. Most cars (including luxury ones) had much higher ratios --- 4.11 to 5.50, etc.

Just me, but I'll stick with the 3.78 if need be.

[H. L. Chauvin]

In my opinion, as late as the mid 1950's, traveling along at 40 mph on back roads was still patiently tolerated by far more patient drivers back then. Besides, one could even still see an occasional slow moving horse drawn or mule drawn wagon on these back roads where nobody went into a rage.

Appears today, chugging along at 40 mph on back roads in a 55 mph zone causes today's many drivers to become very impatient.

Sometimes to show their rage, they will pass and almost clip your Model A front bumper.

Stepping up to at least 50 mph with a 3:27 appears to somewhat refrigerate their underwear.

[Synchro909]

I've read the advice above about 3.54/3.27 ratios but observe that by going from 3.78 to 3.54 gives you about an extra 6.8%. I notice your avatar is a '28 or '29 model so I will base the rest on that. Fitting 5.25x 21" tyres gives you another 5% and a better grip of the road. By doing both, you have gained nearly 12%. Going from 3.78 to 3.27 ratio gives you 15.6% and still on the skinny tyres.
I've run 5.25 tyres in conjunction with a 26% Mitchell O/D and liked them. I was towing a camper that weighed nearly as much as the car at the time. In the same car without the camper following me, the extra road grip was very reassuring.
The 3.27 gear set is more expensive than the 3.54. If you put the extra towards the tyres, you get the safety of the extra grip for not very much. I know what I'd do!

[updraught]

Do those 5.25x21 clear the brake rods? How does it effect the brakes?

[Al 29Tudor]

Very helpful Guys.
So not much gain going to the 3.54:1 gear set. ($450) (not worth it)
5.25 tires adds a little more speed which I hadn't thought about but like the look of the skinny tires. ($450-$635 + 4x $160 for tires = $640, $1,100-$1,600) +$100 ship.
3.27:1 sounds good for Florida without hills. ($635) +50 ship.
This brings me back to the 26% Mitchell overdrive. ($2,700) +50 ship. one and a half to four times as much as the other configurations but with six speed ranges.
Thanks for all the information from everyone. This helps me to organize thoughts based on your experiences. I've also thrown out my original idea.
Thanks for your help.
Al

[Synchro909]

Originally Posted by updraught

Do those 5.25x21 clear the brake rods? How does it effect the brakes?

Updraught, I only had them on the back but others I know have put the all round with no problems. No effect on brakes other than harder to lock up the wheels. I also think they last longer. I towed the camper from Melbourne to Darwin and back on a back and they are still well and truly roadworthy. They will go back on when I finally remove the ones that are there now.