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| | | | Joined: Sep 2013 Posts: 14 New Guy | | New Guy Joined: Sep 2013 Posts: 14 | Considering replacing my original 4.10 differential gearing with the aftermarket 3.55's that are available. I'm wondering if anyone who has done this swap (on a 3100 with a three on the tree) can comment on drivability after doing the swap. While I'm looking forward to more comfortable and achievable highway speeds, I'm wondering how it will drive at low speeds around town, considering that it can't be downshifted to first gear with my non-synchro three speed. Any thoughts? Thanks, Charlie | | | | | Joined: Jun 2012 Posts: 1,747 'Bolter | | 'Bolter Joined: Jun 2012 Posts: 1,747 | Still have the 216? Might get a bit tall for any thing but flat or gentle slopes. A 235 will love it. None of the early 3 speeds have a synchronous first gear, but most of the time a shift to 2nd will get you going from any thing that is not a complete stop. The 3.55 is a popular update, but it depends on how you use your truck. Mine still works. Hauls, and carries. The 4.11 is fine, and highway speeds around 60 to 65 mph are comfy. A bit noisy but the engine is just over 2000 rpm. Cheap Tach so I can't say for certain. About as fast as I want to stop. Brakes must be kept in good adjustment. Any faster, and I would consider, updating the MC and I might look hard at disk fronts. But I never need of a push much to consider time and money on my truck. Kinda fun for me.
Steve H
| | | | | Joined: Oct 2006 Posts: 1,847 'Bolter | | 'Bolter Joined: Oct 2006 Posts: 1,847 | | | | | | Joined: Mar 2010 Posts: 10,281 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,281 | I'm thinking that the 3.55 to 1 ratio was chosen as an upgrade for these trucks to be in the optimal middle ground of low enough ratio to achieve highway speeds, yet not so low of a ratio as to effect getting out of its own way from a dead stop. I haven't heard anyone say that they were sorry that they made the swap. Now if they wanted to use the truck to pull stumps, as it was originally designed, they might have some reservations about the swap.
Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Oct 2006 Posts: 1,847 'Bolter | | 'Bolter Joined: Oct 2006 Posts: 1,847 | one other reason 3:55 was chosen is there is no more room left on the ring gear to make any further change. And no, I have no regrets. (well maybe a few, but none that has anything to do with changing the gears) | | | | | Joined: Jan 2013 Posts: 1,518 'Bolter | | 'Bolter Joined: Jan 2013 Posts: 1,518 | One thing worth mentioning here, is if you don't mind filling up the fender wells a bit, a modern light truck radial LT215/85-16 or 700-16 bias will give you about the same effect of this axle change- speed versus rpm. Heck of a lot less expense and installation cost too. Just saying.
Last edited by sstock; 01/14/2015 2:17 PM.
1953 Chevrolet 3100261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY GalleryVideo of the 261 running1964 GMC 1000305 Big Block V6, sm420, the next cab off restoration
| | | | | Joined: Mar 2010 Posts: 10,281 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,281 | One thing worth mentioning here, is if you don't mind filling up the fender wells a bit, a modern light truck radial LT215/85-16 or 700-16 bias will give you about the same effect of this axle change- speed versus rpm. Heck of a lot less expense and installation cost too. Just saying. Do those tires have a riding diameter of 31.68 inches? I did the math and that is what it would take to equal the 3.55 swap. Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Nov 2006 Posts: 2,544 Shop Shark | | Shop Shark Joined: Nov 2006 Posts: 2,544 | If you change to a 3:55 gear and use the original 6:00-16 tires you should have no trouble getting your truck to move with its 3 speed transmission. If you have a big load in your truck is might be a little sluggish starting out. You just need to practice and be careful not to ride or slip the clutch when taking off. | | | | | Joined: Jan 2013 Posts: 1,518 'Bolter | | 'Bolter Joined: Jan 2013 Posts: 1,518 | Do those tires have a riding diameter of 31.68 inches? I did the math and that is what it would take to equal the 3.55 swap.
about 30-1/2"
Carl [/quote]
1953 Chevrolet 3100261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY GalleryVideo of the 261 running1964 GMC 1000305 Big Block V6, sm420, the next cab off restoration
| | | | | Joined: Mar 2010 Posts: 10,281 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,281 | 30 1/2" diameter tires on a 4.11:1 axle would equate to a 3.74:1 gear ratio. Still a significant improvement compared to 28" tires on 4.11:1 axle.
Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Mar 2014 Posts: 4,501 Moderator, Electrical Bay | | Moderator, Electrical Bay Joined: Mar 2014 Posts: 4,501 | Please note: if you use a larger diameter tire on the rear (or a smaller diameter tire on the front), you will alter the caster angle in the front end--the angle will become more positive. While using a large diameter rear wheel is one way to lower your overall gear ratio, a more positive caster angle will always cause your truck to wander more. The closer you get to a caster angle of 0 the more you will wander, and re-shimming the front axle is the only way to remedy this.
Jon
~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
| | | | | Joined: Mar 2010 Posts: 10,281 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,281 | There is another factors to take into account.
-Are your rear springs currently holding your frame at stock height? (No sag?)
If the amount of sag is equal to the increase in tire diameter, your castor will be fine.
If you have no sag, you could add lowering shims similar to what GM used on the passenger side axle on 1953 pickups with the optional driver side bed-mounted spare tire. (That shim countered the additional sag on the driver side rear spring caused by the weight of the spare tire and bracket.)
Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Jan 2001 Posts: 1,424 ODSS President | | ODSS President Joined: Jan 2001 Posts: 1,424 | Do those tires have a riding diameter of 31.68 inches? I did the math and that is what it would take to equal the 3.55 swap.
about 30-1/2"
Carl
~ Cosmo
1949 Chevy Half Ton
Rocinante, like Don Quixote, he is awkward, past his prime, and engaged in a task beyond his capacities.
"...my good horse Rocinante, mine eternal and inseparable companion in all my journeys and courses." ...Don Quixote, Cervantes
"If you come to a fork in the road, take it."...Yogi Berra
"Rudeness is the weak man's imitation of strength." ...Eric Hoffer
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