Question about gear ratios

Parker

Parker

Well-known member
Evening y'all. This old car of mine loves to smoke its clutch when taking off from a standstill. This ain't operator error. It's either stall, or smoke. I've got 2.75 gears in the back, with a wide ratio toploader. That is, 2.99 first, 1.75 second, 1.1 third. It's that first gear a screwing me up. Whenever I start out, it nearly smokes my clutch. Reverse is even worse. What would be an appropriate rear end ratio to run for easy starts and town driving, while keeping decent fuel econom (low RPMs on highway)?
I've got my eye set on a 3.25 gearset in Tennessee.

What ratios are you running? What transmission? Do you have any preferences? I'm building this car for mostly town use but with double nickle crusing in mind from time to time.

Edit: If anyone has a third member 3.25 for a Ford 9" near WNC, let me know. I'm in the market.
 
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If thats a fairlane or galaxie, 2.75 is too high, 3.25 or even 3.5. You have a 3 speed toploader, would be OK with a really torquie engine.
 
I'd personally never change a 9 inch axle ratio.


I'd grab an SROD 4.9 Big Six gearbox with it's 3.29 ratio first gear.

Basically like running a 3.00: 1 axle. Its a Top Loader 3 speed with rehashed ratios, an SR4 nylon shifter sled, so it's easy to find and fix.


If you break it, pop your 3 speed Top loader back in while you source another. You get an 0.81 overdriven top, equivalent to a 2.26 axle ratio.

Source:
There are many sub-variants in Tremec SROD transmissions in other model lines, but with the US made Foxes and F-trucks and Econoline Vans, there are two ratio sets, the I6 EA suffix Ratio #1 got an 0.81 overdrive, the 5.0 V8 EM suffix Ratio #2 an 0.70 top in the Fox.

RUG EA D*** ***** XXXX Ratio #1: 3.29 1st, 1.84 2nd, 1.00 3rd, 0.81 4th, and 3.29 Rev.
RUG EM DC17 E2ZRAA 2914 is Ratio #2: 3.07 1st, 1.72 2nd, 1.00 3rd, 0.70 4th, and 3.07 Rev.
 
aussie7mains said:
If thats a fairlane or galaxie, 2.75 is too high, 3.25 or even 3.5. You have a 3 speed toploader, would be OK with a really torquie engine.
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I've got a healthy 300 6 so no problems taking off. I just don't like burning the clutch to get going.
This car actually came with a 2.75 optioned from the factory. My guess is that the guy wanted his '74 to not be so much of a gas hog since this was ordered during the oil crisis.
 
xctasy said:
I'd personally never change a 9 inch axle ratio.


I'd grab an SROD 4.9 Big Six gearbox with it's 3.29 ratio first gear.

Basically like running a 3.00: 1 axle. Its a Top Loader 3 speed with rehashed ratios, an SR4 nylon shifter sled, so it's easy to find and fix.


If you break it, pop your 3 speed Top loader back in while you source another. You get an 0.81 overdriven top, equivalent to a 2.26 axle ratio.

Source:
There are many sub-variants in Tremec SROD transmissions in other model lines, but with the US made Foxes and F-trucks and Econoline Vans, there are two ratio sets, the I6 EA suffix Ratio #1 got an 0.81 overdrive, the 5.0 V8 EM suffix Ratio #2 an 0.70 top in the Fox.

RUG EA D*** ***** XXXX Ratio #1: 3.29 1st, 1.84 2nd, 1.00 3rd, 0.81 4th, and 3.29 Rev.
RUG EM DC17 E2ZRAA 2914 is Ratio #2: 3.07 1st, 1.72 2nd, 1.00 3rd, 0.70 4th, and 3.07 Rev.
Click to expand...
I would have put that transmission into my car, but unfortunately, they cost $1,000 locally, while a 3 speed short tailshaft costs $100. I can buy 7-10 good trannies with slightly taller gearing for the price of one of the RUGs. A gear swap would set me back between $150 and $800, depending if I but a used third member or not.

I'll keep an eye out for the tranny though! Thanks for letting me know about the ratios. It will help a lot I'm sure.
 
Parker said:
I've got a healthy 300 6 so no problems taking off. I just don't like burning the clutch to get going.
This car actually came with a 2.75 optioned from the factory. My guess is that the guy wanted his '74 to not be so much of a gas hog since this was ordered during the oil crisis.
Click to expand...
3.70:1 is a good street gear. Would be turning just under 2700 @ 60 mph.
 
I think Ford used a 3.50 in cars with a 6 and 3 speed unless something else was ordered.
 
Parker said:
This car actually came with a 2.75 optioned from the factory.
Click to expand...
This is ok for that car if it were left an automatic. I would say start out with a 3:25 ratio if your keeping the trans right now. If you get the overdrive go for something around a 3:70 ratio.
I also would not want a 9 inch diff in there. It also draws from your power more and is just plain heavy for what you need. It looks like you are good at making stuff fit where you want so an 8.8 could be a good choice; there are plenty of them and way more affordable
 
RUG CL AE 12 in D8 1978 model year Econoline form is a pretty good Ratios 3.2508 Ist, 1.9213 2nd, 1.00:1 3rd, 0.7837 OD top transmission, only the tail shaft length differs.


I did a Four speed and Axle ratio and driveshaft swap in my 1958 six cylinder 3 on the tree Vauxhall back in 1987 when I was still at school. I learnt that as long as first gear overall ratio, Axle gear times First ratio...if it matches the factory set up for a six, you were golden for gearing. I saved a lot of gas by going to a 3.46 axle ratio.

As long as we aren't putting you in the poor house with shifter, for ve shaft and gear swaps you didn't intend on doing, going to a commonly available 3.5:1 or 3.25:1 pumpkin would work three ways.

1. Improving over all lower first gear,
2. and then giving you a loping top gear like you currently have in 1:1 top in a 2.75, only better.
Thirdly, it gives you the ratio spread you get in a modern T5.

I'd personally recommend going for 3.25s, and get the standard 240 with 3.50 axle style of first gear with your SROD..
You effectively end up with a 2.55 ratio top gear.


I did road load calculations and mpg calculations using the Snook formula the Australians used for the Mobil Economy Run in 1979. Ford Australia decided to make a 2.53 axle ratio option available on the 3.3 liter 114 HP 1bbl Falcon in 1981, and it did 35 Imperial miles per gallon at 62 mph Highway figure,


This 81 and 82 Model year Falcon XD 3.3 Economy Pack was only a 2985 pound car, so it didn't need a 10.55 overall first gear. It actually had a 3.47, 2.00, 1.43 and 1:1 non SROD single rail. Your 3.9 liter Big Six with 3.25 axle and SROD would really be nicely geared with overall ratios basically, exactly the same. Perfect for the modern world.
 
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