The Stovebolt Site Forums The Shop Area Engine Shop 3 Speed Transmission

I finished my truck last month and during that restoration I installed 3:55 to 1 ring and pinion gears. My truck has a 4 speed transmission (was originally a 3 on the column) and I don't think I am getting the speed that should come from the transmission with the new gears. Does anyone have any guesses or suggestions on how much extra speed I could get by converting back to a 3 speed transmission. I think if I change it back to a 3 speed the new 3:55 gears will work better with the 3 speed. I think the 4 speed is just geared to low for highway driving. I have a guy who I can trade my 4 speed for the whole 3 speed setup. Any thoughts on this or am I wrong?

Both the 4 speed and the 3 speed are 1 to 1 in high gear. Another way to go is find a 3 speed over drive tranny. High gear in OD would give you a 30% reduction in RPM on your engine.
Just some info to confuse the issue. All this is assuming that the truck has an open drive line.
Tom

Truck has the closed drive line.

That doesn’t make sense. You should have seen a huge difference with the new gearset and as was stated a 3 or 4 speed are 1 to 1 ratio in high gear so that makes no difference. Are you sure you got 3:55 gears and not a replacement 4:11 set? You should be able to cruise at 60 mph with no problem.

Curt B.

I'm assuming that I got the right gears which came from Chevy Duty. Only thing I can think of is that I'm traveling faster MPH than I thought. My speedodometer says 55 and feels like thats pushing it. Maybe I'm going faster but have not had a chance to check the speed. (ice storm here) Will check that with my GPS to get the exact MPH. At 60 mph it feels like I'm pushing it. Engine runs smooth and everything. I have 15" tires on the truck. Just does not feel right.

"assuming"? ya didn't count the teeth?
if the original rear was 3.90, there won't be a lot of difference - even if it was 4.11, without doing a comparison with a tach, you might be fooled by the sound and "feel"

Bill

go to www.randysringandpinion.com and use their caculater.it works well.

My dad has a '55 2nd series with 3.38 gears and even that seems like it's winding high at 55 to 60 mph.
16" wheels and tires will help you slightly.
They would have been standard on your truck anyway.

zenish, my old ring and pinion gears were 4:11 (37 teeth on ring and 9 on pinion) that calculates to 4:11. The new gears are 3:55, at least thats what I ordered as advertised as 3:55.
It may be the tires that make a difference. Once I am able to check the mph, and tire heighth, I can calculate my rpm's. Only other thing maybe is what Red58 said, maybe I am being fooled by the sound and feel. This is a fresh rebuild and sometimes to much caution on a test run may have done me in.

Did you recalibrate the speedometer when you changed the gear ratio? If not, you're still indicating the same speed as before for any particular engine RPM, but the truck is running faster than the speedo indicates. Do a stopwatch check over a 1-mile run. 60 seconds/mile equals 60 MPH.

Where is Missouri are you located?? There are a few Bolters in the Kansas City area.

Thanks for the info. I've been wondering if someone made this device.

BigSix302, I'm located in Mid-Missouri about 25 miles east of Jefferson City.

HotRodLincoln, no, I did not recalibrate the speedometer when I changed the rearend gears. I think you are right, probably am still indicating the same speed as before but am actually going faster. I will take the advise of the replys received when I get a chance.

One more thing, did any of you see the 52 Chevy that had a $36,000 bid on eBay and did not sell because the reserve of $39,950 had not been met. I think my truck is close to the one that did not sell. I should sale mine and buy another if I could get that much for it. Wow!

Jon,

As stated above, with a 3.55 conversion to a 4.11 rear-end, the speedometer would be reading about 14% lower (55 mp would really be around 63 mph).

If you have original optional 15" wheels and original-style light truck tires, you might find that they are larger diameter than 16" tires, depending on brand and profile. The 15" original tires were larger diameter than the original 16" tires. As you mentioned above, the best way to check this is to measure the tires. However, if you used the same tires before and after, then this is not the reason for not feeling "a difference" after the conversion.

Also, I recall that someone once posted a link to a company that makes speedometer correction gears (adapters?) that work on our trucks. I will see if I can find the post.

Tim

Earler posts have recommended United Speedometer Service for speedometer ratio adapters. I will be contacting them before the spring and will post my results here. Maybe someone else who has bought an adapter from them will post their experience?

Patrick's (the company who supplies all the 3.55 and 3.38 conversion gears) sells speedometer adapters; however, his adapter is for stock diameter tires. If you are going to spend the money for an adapter ($60-$100?), you might as well get one that matches the tires/gears on your vehicle.

The first thing to do is establish what percentage of error there is between indicated speed and actual speed. Time a measured mile, and jot down the indicated speed. 60 MPH indiccated makes a good reference point in most cases. Let's say you run a mile at an indicated 60 MPH, and it takes 50 seconds. 60 divided by 50 equals 1.2, indicating 1.2 miles per minute, or 72 miles per hour. That's a 17% error at that speed, so you would need to speed up the speedometer cable by that much. I doubt if internal gears are still available to make the correction inside the transmission, so you'd need an external gearbox to drop the cable speed by that amount. Simply figuring the amount of error at a specific speed will give the vendor of the correction box a reference point to start with. If you want the correction factor at a lower speed, driving a mile at 30 MPH should take 2 minutes, etc.
Jerry

United Speedometer Service describes three methods (ratio tests) for obtaining the correction factor.

mine use to have the 3:55 ring and pinion, also ran the patricks sagnaw four speed conversion with the enclosed drive train,, pretty quick but even at 60 mph or more I was turning 3,000 plus rpm.. always felt like I needed another gear to shift into.. the shift were close and quick........I now have the s-10 conversion,etc............

Joker, is the S-10 conversion both the rear end and transmission. How difficult is that to do.

Jon mentioned his truck used to be a 3 speed and that it has an enclosed driveshaft. Aren't the 3 speed and 4 sp. trannies different lengths?