Rear End ratio...

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Model T Ford Forum: Forum 2015: Rear End ratio...
Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Menkhaus on Sunday, May 31, 2015 - 08:29 pm:

Is there an easy way to determine which ring gear ratio you have in your car? I can usually keep up with the fastest T's on the open road, but cannot get going out of low shifting into high. I'm thinking I might have a higher ratio ring gear than I want. Is there an easy way to check?

I'm thinking if I jack up the rear wheel, put the car in high, and rotate the crank, can I count the wheel revolutions to determine which ring / pinion set i have? Or am I smoking something? :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Weeds on Sunday, May 31, 2015 - 08:37 pm:

A friend of mine imported a 13 and we got it going a few weeks ago. It was completely different to my 27. 1st gear was really usable where mine is a crawler to take off with however it took about 7 houses to pull away after changing into top, just kept chugging and making no headway. Once up and cruising at 30 mph on the flat it was just ticking over. The guys on here suggested it had a 3-1 ratio diff and these can put extra strain on your crankshaft.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Menkhaus on Sunday, May 31, 2015 - 08:56 pm:

Kevin that pretty much describes mine. I'm thinking a STIPE (?) CAM might be an answer? Actually, I have no desire for Top End Speed. I would downsize the Ring and Pinion if I found out I had a Higher Ratio one if it would give me better High speed takeoff and hill Pulling Power..


Top of pagePrevious messageNext messageBottom of page Link to this message  By HARRY A DAW Troy, Mo. on Sunday, May 31, 2015 - 09:01 pm:

Yes you can Doug. Just remember that if only one wheel is allowed to turn, you will have to divide the turns by two.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Garnet on Sunday, May 31, 2015 - 09:13 pm:

Crank it by hand and count turns for one wheel revolution. A two speed rearend helps a lot with a speedier takeoff.

Regards,
Garnet


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Sunday, May 31, 2015 - 09:38 pm:

Garnet - .....and more importantly, starting out from a dead stop, a 2-speed rear end in "low" range will let you slip the low band for only a couple feet max until you can lock it up for no more slipping than that! Done properly, low band can be made to last a long, long time!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Monday, June 01, 2015 - 06:35 am:

If you jack up both wheels, each wheel may turn differently depending on drag from hand brake, etc. I would jack up just one wheel and check how many turns with the hand crank were needed for one revolution. The differential action makes a single wheel turn twice the ratio when the other is stopped, so you'll only need to crank 1.5 turns for 3:1 and about 1.8 turns for std 3.636 ratio.
(Since there are four claws on the crank ratchet, four quarter cranks makes one full turn of the engine)

Considering your driving impressions it's very likely you have the 3:1 ratio. In my 1400 lb pickup with a prus head and a 7.5 degrees advanced cam 3:1 works just fine for most driving - it's really strong uphill. It's just stating from standing still that needs some more slipping of the low band than with a std ratio


Top of pagePrevious messageNext messageBottom of page Link to this message  By Larry Smith on Monday, June 01, 2015 - 09:57 am:

When I first started driving my '13 roadster, I noticed the rear end gears seemed a little tall, because I have two other T's with standard gearing. Late last year, I pulled the rear end apart, and sure enough it had 3-1 gears in it made by the Republic Gear Co. The person who put them in had to really work at it too, because they even used the studs in the driveshaft bearing spool to put it back together! (The pinion gear is too large to fit through the differential when it's together). I recall, it took me an afternoon to get it apart. Well, it now has stock gearing, all Ford script too!


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Monday, June 01, 2015 - 05:34 pm:

One wheel off the ground, The other on the ground. Count how many times the crank turns for 2 wheel revolutions.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Monday, June 01, 2015 - 08:54 pm:

What Garnet said. Take the spark plugs out to make it easier. No jacking or math just counting. :-)


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