Determining Rear End Ratio - L-112

I have searched the net, and this site, and can't find a concise answer for what I am looking for.

My '52 L-112 has a BG241 engine, a T-9 four-speed (non-synchro) transmission, and a previously swapped-in Ford 8.8 rear end with an unknown gear ratio. I'm trying to determine the gear ratio of the rear end, because the ID tag of the rear end is missing - and even if the tag was there, I can't be certain it would be correct. The questions I have are:

1) I jacked the rear wheel off the ground. When I hold the input shaft of the rear end steady, and rotate one of the rear wheels forward, the other wheel rotates backwards. If I read everything correctly, that means I have an "open" rear end. Is that correct?

2) Assuming it is an "open" rear end...I secured one wheel, and turned the other wheel one complete revolution. The input shaft of the rear end turned "two" revolutions for every revolution of the wheel. Based on what I read for an "open" rear end, I then doubled the number of revolutions on the input shaft (2x2) - giving me the number "four". Based on the available options for a 8.8, that should mean that my current rear end has a 4.11:1 gear ratio. Is that correct?

3) Assuming the ratio is in fact 4.11:1...that's may not be an ideal ratio if I plan to use the truck on the highway, and not get rear-ended on the on-ramp by a guy on a Vespa smoking a cigarette. This ratio may also not be good for fuel mileage. Should I swap this rear end out for a different ratio since I will be using it about 25% of the time on the highway?

4) Assuming I should swap the rear end out...I have read on this forum where others have swapped in rear ends with a ratio of 3.73:1. If the 4.11:1 ratio I have is not ideal for highway driving, and I have to get a rear end with a different ratio "anyway", what would be the ideal ratio to look for? Is it 3.73:1? Is there a better ratio for highway driving and better fuel mileage? Is the 4.11:1 good enough to leave in the truck as is?

5) I have no idea what the gear ratios of the existing T-9 transmission are yet. How do the gear ratios of the transmission factor into the selection of gear ratios for the rear end? Should I even worry about that?

Thank you VERY MUCH in advance - I really appreciate everyone's patience!
Heinz

Most all rears have the tooth count marked on the head of the pinion, Drop the driveshaft and clean the head of the pinion and find the tooth count, divide the bigger by the smaller for the ratio, no guessing or hoping involved.

Here is a link to lots of good information. http://content.wisconsinhistory.org/cdm ... c/id/36853
Your only axle ratios offered were 3:73, 4:10 and 4:77. Lots of luck with finding a 3"73.
The information I found on the transmissions shows the top gear to be 1:1
The situation you have with using the OEM engine is this. There may not be enough power to make your truck respond the way you want if the axle ratio is changed to 3:54 after installing a Ford 8.8. 3:73 will make a noticeable difference and this may not give you what you want.
Going quicker can be measured in cubic dollars.

I have an R-100 with an SD220, so less horsepower than you have. Same ratios in the transmission, although mine is synchronized in 2nd through 4th. And a rear axle with a 3:55 ratio. And about as tall of radial tires as I could put on the 15" rims. There is a lot of speculation that with the aerodynamics of a wall, these pickups won't go down the road with anything higher than a 3:73 rear end. I've driven mine about 50,000 miles in the last 5 or six years, from Canada to Texas, and from Savannah, Georgia to the west coast, across the Rockies. I can tell you that if I had it to do over, I'd go for something in the 3:20 to 3:30 range with the 220 engine. But you have to determine what will work for you. If you are only going to be on the open road 25% of the time, you may want the extra grunt. Keep in mind that when you do finally have to downshift on the long hill, there's a wide gap between 3rd and 4th, and with the 3:73 gears, you'll be at about 35 miles an hour.

I think you both missed that the rear had already been replaced with the Ford, and he wanted to know the ratio because the tag was missing.

I was just concerned about the guy on the Vespa smoking the cigarette rear-ending him on the on ramp.

Seems to be a rash of “What’s the best...” going on lately. You’re the only one that can answer that... Perhaps you should get your truck running the best that it can as is. Spend some time with it and get a feel for what it is willing to do and where it’s happiest. This isn’t a 2015 Whatever. There is no imperical data saying “this” is a good setup and will make 90% of people happy because every truck is at its own stage of “worn out”. What works for me and my needs for a truck ( towing/hauling) may be the complete opposite of your needs (carrying a loaf of bread and a gallon of milk home from the store. These trucks were built to work and they were never even intended to travel at today’s speeds. Highways around here are 70mph. My truck only goes down state routes for now as the speeds are more reasonable (55mph posted). Your brakes likely suck at best even compared to a dodge K car from the 80s. Hurdling down the highway at 70 could end poorly if your braking system is up to snuff if you could even get to that speed. Find some online calculators if you don’t know the math already to figure out your theoretical top speed in 4th given the tire size you have, rear end, and a comfortable cruising rpm for the engine- likely 3000 or less rpms. The highest strung SD/BD/BGs redlined at 3600 and I believe yours is 3400.

Pull the diff cover and count the teeth. Remove all doubt. It’s not hard. It’ll give you a chance to see what’s in it and decide if it’s even worth messing with. A little research can get you a “better” rear end for very short money at a wrecking yard if you know what you’re after. R+Ps are cheap for these axles as well. Like less than $250 for the gears and an install kit.

S
Pull the diff cover and count the teeth. Remove all doubt. It’s not hard. It’ll give you a chance to see what’s in it and decide if it’s even worth messing with. A little research can get you a “better” rear end for very short money at a wrecking yard if you know what you’re after. R+Ps are cheap for these axles as well. Like less than $250 for the gears and an install kit.

Don't have to pull the cover and drain the oil, the tooth count is on the head of the pinion, when the r&p are mated, the tooth count is etched into the pinion, along with some other numbers.

on't have to pull the cover and drain the oil, the tooth count is on the head of the pinion, when the r&p are mated, the tooth count is etched into the pinion, along with some other numbers.

On the fords as well? I didn’t notice that on mine.

I could be wrong, most mfg do it that way, I haven't looked on my cars, But it is much more reliable than stampings on housing, and tags can and do get lost.
Most of my experience is medium to heavy stuff.