Rear end ratio change

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Model T Ford Forum: Forum 2015: Rear end ratio change
Top of pagePrevious messageNext messageBottom of page Link to this message  By Bruce Compton on Monday, November 23, 2015 - 10:08 pm:

I need advice on changing the rear end ratio on my 25 coupe from 3.63 to 3.25. I have a very nice recessed 39 tooth crown, and would have to find a suitable 12 tooth pinion. I live in a fairly flat area and do most of my driving on paved secondary roads, but still feel that I'm holding up traffic although I don't want to join the two-piece crank club. The motor is basically stock (0.020 over with a Z head) and it runs strong and smooth with a rebuilt OF Stromberg and TW timer. It also has good working Lockwood outside brakes, 5:1 steering gears and a short pitman arm that really helps the steering control. The change would be about 9% , dropping the RPM from 2000 to 1820 or increasing the speed from 45 to around 53 at the same RPM. Any thoughts???? Thanks : Bruce


Top of pagePrevious messageNext messageBottom of page Link to this message  By Terry Woods, Richmond, Texas on Monday, November 23, 2015 - 10:31 pm:

Bruce, I have a heavier 27 coupe that my Dad and I restored back in the late sixties. Without asking anyone for advice, I decided to change the rear gears from the original 4 to 1 ratio to a 3 to 1 gear set, since the 4 to 1's were totally worn out and had to be replaced anyway. The block was a .040 over 1922 block but all the rest was parts from the original 27 engine, except intake, exhaust, and carburetor. I am currently re-restoring it correctly with a 27 block and vaporizer setup, and changing the rear axle to a Ruxtell, but keeping the 3 to 1 gears. The Ruxtell will allow me to gear down under the 3 to 1 ratio for hills, but like you, most of my driving is on flat terrain. In the 20 years the car was driven before my Dad passed, we never regretted going to the 3 to 1 gears.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Allan Bennett - Australia on Tuesday, November 24, 2015 - 05:26 am:

The 3:1 gear set is OK in light cars, but is dangerous without upgraded brakes. That ratio tends to drive the car down the road, the standard Ford transmission brake being really inadequate.

Hope this helps avoid some trouble.
Allan from down under.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Tuesday, November 24, 2015 - 05:45 am:

Odd Allan, I haven't had the least bit of trouble with the brake in my light primitive pickup with a narrow kevlar brake band and 3:1 in the rear axle?
The tall 3:1 gear is great in my light car even on hills with a Prus high compression head, 7.5 degrees retarded timing gear and a 3/4 race reground cam shaft. Only problem is the need for slipping the low band a tad when starting, especially when starting on an incline like from a underground garage ramp up onto the street, so for a heavier car than my 1400 lb pickup a Ruckstell would be recommended. 3.25:1 might be a better compromise, haven't tried that.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Terry Woods, Richmond, Texas on Tuesday, November 24, 2015 - 07:28 am:

Allan, I know everybody says what you did, but the key is knowing your car's limitations and driving it to stay safe. (Like Clint Eastwood said, "Everyone's got to know their limitations"). Yes, I may hold up a few driver's at the speeds I drive, but in the 20 plus years the 27 coupe was driven by my Dad and I, neither one of us came close to having a problem or scare, and the rear E brakes weren't even hooked up, in fact it didn't even have E brake shoes in the rear hubs. All we had was the transmission brake and never in all those years did we have to adjust any of the bands, regardless of the use we put on the transmission brake. To each his own thoughts, but I wouldn't leave home without 3 to 1 gears. I am restoring our coupe again and along with the Ruxtell and 3 to 1 gears, I will have rear E brakes and a brake equalizer. On my 26 fordor, I have SureStop hydraulics, but have them as a extra security feature since the car is heavier and can carry more people.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem - SE Michigan on Tuesday, November 24, 2015 - 09:07 am:

To Allan's point, I would not say that the 3:1 ratio makes the brakes "dangerous" but, it definitely does reduce the effectiveness of your stock Model T transmission brake. Just as your engine has to work a little harder to accelerate the car with 3:1, so to does your brake have to work a little harder to decelerate it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Tuesday, November 24, 2015 - 11:57 am:

3-1 would be OK in flat country. In fact it would be an advantage for country driving in Kansas or other flat places. However in hilly country, you will have a hard time starting out in low. One of my 3 Model T's has 3-1 and I live in Southern California where it is either hilly, or heavy traffic or both. I need to use Ruckstell to start out from a stop because even on the slightest upgrade it is hard to get a start in low and then to shift into high lugs the engine. However once it gets going it will pull a 6% grade in high as long as I can keep it over 30 mph. But on tours the other T's will usually go up those hills at 25, so I still need to shift down.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Tuesday, November 24, 2015 - 02:17 pm:

I think that Norman has touched on an important point when he mentioned the Ruckstell. I would only consider changing from the stock 3:63 to a 3:25 or especially 3 to 1 with a very light "T" and only in an area that is pretty flat. (The Ford engineers knew what they were doing when they settled on the stock 3:63 to 1 rear end ratio.) However,.....I believe the Ruckstell makes all the difference! Especially in the area of starting out from a dead stop which of course necessitates the "slipping" of the low band. Driving a Ruckstell equipped Model "T" allows the car to be normally driven just like you would drive a more modern three speed standard transmission equipped car. You can shift while accelerating from a dead stop, just like you would in a modern three speed stick shift. Start out in low Ruckstell/low pedal, then high pedal while leaving Ruckstell in low range, then upon additional acceleration, shifting the Ruckstell to high. Works great and very easy on the low band when first starting out. FWIW,......harold


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bruce Compton on Tuesday, November 24, 2015 - 02:44 pm:

Thanks for all the input guys. It's hard to dispute Henry's original choice of 3.63, but that was in 1909. To me the biggest difference today is the road surface and traffic conditions, not to mention improvements in engine components and especially lubricants. I don't want to set or break any speed records, just fit in a little better with my surroundings while not beating up my engine. Some of you have commented assuming that I'm considering a 3:1, not a 3.25:1. I tried a 3:1 in a '15 roadster and was very unhappy with the loss of braking, but in this case I have accessory outside brakes and a 3.25 possibility. Keep the comments coming .Thanks again : Bruce


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Weeds on Tuesday, November 24, 2015 - 04:31 pm:

A friend imported a 13 runabout, its very light and I've only driven it the once but it has a 3-1. Not easy to drive, takes about a block to pull away when changing up. Once going on flat ground its great as it just chugs away but you have to get going first! any hill would be an issue and a long drive in low gear.
3-1 Ruckstell would be perfect as Harold has suggested.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Constantine in Australia on Wednesday, November 25, 2015 - 09:35 am:

3.25 when compared to 3.63, or any other gearing, will always be better AND worse.

There is no one "silver bullet" ratio that will beat all others, all of the time.

If it really matters to you and you have the $$$ then consider 3.63 + Ruckstell + a KC Warford optioned with custom gears to suit your exact car and needs.

Roger mentioned 3:1 works for him (except when taking off...?), here he is:



No fenders, no running boards, no splash guards, no windscreen and I would guess Roger is also wearing shorts to cut weight being he lives in not so warm and sunny Sweden. Am I correct Roger?

So there you have it, drive a naked car while in the nude and 3:1 gear will work well...except when taking off.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Wednesday, November 25, 2015 - 09:44 am:

Ha ha, Constantine, not nude here - that was the only ride this summer when I used shorts, summer temperatures doesn't last long here. The primitive pickup weighs 1400 lbs with driver fully clothed, tools and a full tank. Add three passengers and it'll still pull strong uphill, but the Watts clutch will slip at full throttle, something it rarely does when I'm alone in the car.

If I had the money I would import a Ruckstell axle for better flexibility, but as it is now it's OK for what it's used for - I'm building another car instead for other uses :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Wednesday, November 25, 2015 - 10:20 am:

Even in flat country I like the idea of keeping what transmission braking I have. Sometimes doofus driving occurs in front of me and I need to stop quickly. I also like the idea of taking it easy on my crankshaft. Even in flat country there are places where you have to accelerate up a hill from a dead stop, and I don't like lugging. But don't I want to go faster? No. I'm driving a Model T. If I want to go faster I'll drive something else.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Wednesday, November 25, 2015 - 10:34 am:

And that's what's great with the Universal car - with all the accessories available it can be better suited to different terrains and different driver's various uses and wishes. I like to be able to drive it faster than they had to do in the 20's due to bad roads back then.

When the roads are free from salt again, I'll try to check how fast it really can stop from speed with both the transmission brake and the emergency brake. In ordinary driving it isn't a problem since I tend to keep distances and let off the gas in time - but there are those unpredictable modern drivers..


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jon Allen on Wednesday, November 25, 2015 - 07:33 pm:

Bruce,
I have a Ruckstell set-up with a 3.25 rear end in my '14 Runabout. Stan Howe did the rear end rebuild for me , and he did an outstanding job. I would highly recommend the 3.25 ratio. It is a great compromise ratio for a T on the road. If you have a bit more power by virtue of a Z-head as you have, it is the best ratio.
The only downside to the 39/12 ratio is that the 12-tooth pinion will not fit through the differential housing hole if the differential is bolted together. So you have to separate the housing to get the pinion in place. I did it myself with no help except that Stan had it ready to go when he shipped it, so it was not too bad to do myself.
Regards,
Jon


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bruce Compton on Thursday, November 26, 2015 - 05:46 pm:

Thanks Jon. I don't have a Ruckstell so I want to be pretty sure before I deviate from Henry's first choice. I very much appreciate your input and would really like to hear from someone with a 3.25 and NO Ruckstell. Thanks again : Bruce


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