Different R&P combos, help me understand

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modernbeat
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Different R&P combos, help me understand

Post by modernbeat » Fri Mar 22, 2019 12:11 pm

Novice T owner here. I'm considering re-gearing the final drive in the Ruckstell during an axle rebuild. Don't know what's in it now, but it's a pretty high gear, and likely too fast for the truck it will eventually end up under. I've read the MTFCA Axles and Ruckstell booklets, but not the Chaffin book.

I'm reading up on ring and pinions, and came across the "Ruckstell" 40-tooth and 39-tooth ring gears in Chaffin's catalog. As far as I can tell, they are thinner versions of the ring gear that work with larger diameter 12 and 13 tooth pinion gears. Is this right? Will they work in a standard, non-Ruckstell differential? I've read about the interference issue and solutions between the 39-tooth ring gear bolts and the pinion teeth when these parts are used.

Can the standard depth ring and pinion gears be used in the Ruckstell axle? I have not read anything definitive, but also no warnings that you have to switch gears when building up a Ruckstell from an existing axle. And replacement gears were/are not supplied with the base kits.
Jason McDaniel

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Steve Jelf
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Re: Different R&P combos, help me understand

Post by Steve Jelf » Fri Mar 22, 2019 11:23 pm

I would call Chaffins. Glen wrote the books. I expect he and Dave can answer all Ruckstell questions.
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Re: Different R&P combos, help me understand

Post by Allan » Sat Mar 23, 2019 9:37 am

Jason, I had a 13/39 combo in my speedster and it was light enough to handle such a tall ratio, but the standard brakes were dreadful. When I put that Ruckstel in my new roadster, I mated the 39 tooth ring gear with a 12 tooth pinion to kick the ratio back a bit. It is an ideal combo in a light roadster. Both were straight-up fittings requiring no modifications.

Allan from down under.

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Re: Different R&P combos, help me understand

Post by Ruxstel24 » Sat Mar 23, 2019 10:10 am

My 24 touring has a Ruckstell with 13-39 GR...
The engine is not stock, but nothing major...HC head, aluminum pistons, oversized valves.
Around here, most hills it does well, terrain has a lot to do with the choice of GR.
I recommend at the very least, to have 26-27 rear brakes or auxiliary brakes, with ANY Ruckstell or auxiliary transmission.

Related question, what is the GR of the Ruckstell in low axle (high transmission) ? With 13-39 gears = 3:1 in high...


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Re: Different R&P combos, help me understand

Post by Les Schubert » Sat Mar 23, 2019 11:19 am

I will add a thought.
What elevation will you be driving at. Around sea level and you could be fine with the 13 tooth or 12 tooth pinions. Where I live at 3,000 ft in a stock body roadster and a stock engine the 11 tooth pinion (with a 40 tooth crown) seems optimal.
I have a 12 tooth pinion that I plan to try with a 39 tooth crown in a Ruckstell. Probably the engine will be “warmed up “ a bit!!


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Re: Different R&P combos, help me understand

Post by modernbeat » Sat Mar 23, 2019 1:41 pm

Looks like I didn't make my questions clear.

Is the "Ruckstell" style ring gear thinner to accommodate the special high-tooth pinions they work with, and only with those pinions? From reading, it sounds like they are thinner, and only work with the special, larger, pinion gears.

Will standard ring and pinion sets, like a 40/11, not the "Ruckstell" thin rings, work in a Ruckstell axle?

Will the "Ruckstell" thin ring gear sets work in a standard, non-Ruckstell axle?

For the record, these parts are going in a moderately heavy canopy express, on 31" tall tires, with a load of camping gear which will be run up and down mountain passes in Colorado down to the Mojave Road in California. So elevations from 13,000+ feet down to to 4,000 and eventually down to sea level. The motor is a high compression counterweighted stroker with a Holley 1904 downdraft. Already have a Ruckstell, and will be adding a new Warford and disc rear brakes. Not looking for gearing recommendations, but want to know what parts are compatible.
Jason McDaniel


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Re: Different R&P combos, help me understand

Post by Nv Bob » Sat Mar 23, 2019 4:01 pm

Where I live a mile up high desert BIG hills long flats 12/39GR (3.25/1) roadster or 12/40 (3.33/1)touring
With a ruckstel
Best ir not are my gear sets of choice


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Re: Different R&P combos, help me understand

Post by Wayne Sheldon » Sat Mar 23, 2019 4:42 pm

Generally speaking, somewhere out there may be an exception? However, generally speaking, any gear sets that fit in the standard Ford rear end will fit and work in the Ruckstell, and visa versa. The spacings and offsets were designed to be absolutely compatible.

The high speed ring gears are offset farther to allow for the larger pinion gear necessary. While the "gear" area itself is not really thinner, the offset does cut in from the back side and is in effect thinner in a small area of the gear, between the gear teeth and the mounting bolts.

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