Folks Of Interest Rear gears for flathead and t5

Alright guys so I have the '49 Ford with the 8ba in it. I picked up an S10 T5 with the .76 overdrive. Now I'm on the hunt for a rear axle but I'm trying to figure out the best gear ratio to use. I've used the calculators and all that but numbers on paper are a lot different than the real world. On my '51 Chevy I used a 3.73 rear with the t5 but that 235 had 140 hp/215 pounds of torque. This flathead has 100 hp/190ish pounds of torque. I'm sure someone on here's done it before so what is the best combo

 

Well you need to know what gears are in that T5 other than the final OD. I have a 4:10 QC behind my 8BA and T5 and I plan to go to 5:30s or something to actually utilize 1st gear properly. 3:73 gears and you will be able to start off in 3rd... which saves on shifting.

 

All the S10 T5s with a point .7x od (it might be .72 as opposed to .76 like I said but I really can't remember off the top of my head. Either way it's one or the other as they didn't offer both) have the same 1st thru 3rd gear. Of course 4th is 1.00. In the Chevy if I ran a 4.10 rear axle I wouldn't have had to touch 1st gear ever, and probably could have started in 3rd on flat-ish ground. Maybe I'm misunderstanding you but you want to go to a 5.30 rear gear to make 1st gear more usable? Not trying to be an *** but I think your numbers are backwards. If you go to a 5.30 gear you'll be able to start off in 4th gear probably And you'll get up to a cool 20 miles an hour hour before the motors ready to explode. Again if I'm misunderstanding what you mean I'm sorry

 

On most of the customer ch***is I have built with a T5/Flathead combo I have used 3.78 rear gears. Most of the builders have been using a 30/31 inch tall tire. With the .72 OD and a 31 inch tire you'll be turning in the 2000 rpm area at 70 miles an hour. All the controversy about the low 1st gear, I've sold many rebuilt 85-92 rebuilt S10 trans with the stock gears and the customers seem to be pleased with the way the car comes off the line. I realize your not going very far in 1st but it'll be a rocket off the line.

 

I got a T5 with 0,84 OD behind my 255ci flathead, driving a 3,09 rear axle, have 7.00 x 16 tires. Nice ride and still enough power to accelerate even in OD. Topspeed not yet tested as I need a lot better brakes and better steering....

 

I’m with @StefanS on this one.

‘splain that Lucy!

Ray

 

I guess I should have specified tire size...I'm running 205/75-15s. I think they're 27.1" tall if I'm not mistaken. So if I run a 3.73 rear I should have a bit more "torque" and should be good to go..?

 

I was referring to this chart that shows a few different gear sets being used in S-10 T-5's. They are not all created equal as posted above.

In regards to my comment about the 1st gear, it is almost unnecessary behind my flathead. Mine is the 4.03 first. I do expect more performance than most out the running gear and I don't like the way it comes off the line with the 4:10s in back. I get 70mph at 2000rpm with 30" tall slicks but I would gladly give up some of that for more performance off the line.

 

Don't forget this one:


It is the largely unknown fourth model found in the S ch***is.

I have one on the bench now.

 

Also, 5th gear sets are interchangeable, so you can roll-your-own top gear.

 

^^^Roll your own. Hee hee

 

If you look at that chart though, all the .72 and .76 gear ratios are the same respectively. I used the tape method to figure out the overdrive ratio and the 1st gear ratio but I can't remember what they were. It's got the Chevy bolt pattern and its world cl*** so I think it's a '95 if that gives any hints.

 

A lot of good info but it is going to come down to the rpm that that flathead is happy running at ____ MPH on the highway. OD ratio / rear gear ratio / tire diameter all factor in.

 

Don't forget that the OD ratio is dependent on the first gear ratio. The OD gears from a 4.03 first T5 will produce a different overdrive ratio in a 3.76 1st T5 box.

 

Correct, but you can compute the new potential ratio if you know the original ratio and the tooth count of the before and after 5th gear set.

 

Why not keep the same ratio it had? Then o.d. will help on the road.

 

Nobody said that it had to be changed, just that it could be, if needed.

It is important to know your options when building or fine tuning.

 

I get that. I was just wandering why you would go higher or lower gear than what it came with.
If you keep close to original gear then o.d. will be better.
If you go lower gear then o.d. puts it back to stock so no real advantage in gas mileage or less rpm on engine.
If you go higher then engine may bog down from to little rpm in high gear.
You need to know the power band on engine and gear properly.

 

There are many variables to take into consideration, working with what you have. I can only answer your last question in relation to what I have. I have spent a lot of years experimenting with gear ratios best suited for taking advantage of limited engine output. You want to plant yourself right in the usable range.
I opted for a T-5Z Ford and paid up for it to get what I considered to be the best option for my purposes. It really is a case of apples verses oranges and only posted to show what is possible.
Same 239 cu. in. flathead engine with moderate performance upgrades in a lightweight (2400 lbs est.) '30 Model A coupe. I have 30" tires, a 3.80 rear gear.
The T-5Z gear ratios are 1- 2.95, 2- 1.94, 3- 1.34, 4- 1, 5- .63OD. This puts 1st gear in a better "usable" position and at 70 MPH RPM is at 1877. I don't believe there is a better combo readily available for a flattie.
Hopefully you will get more input from someone better matched to your car. Good luck!

 

It is not as simple as you are trying to make it sound.

You cannot take a transmission from a dissimilar vehicle, with whatever ratios that it happens to have in it, and expect that you are going to achieve perfection on the first try. You might be pretty close. You might think that things are "good enough". They are often not, and could be quite a bit better. Go to a T5 identification page and you will see how many different ratio sets that GM used in JUST the S truck platform. Then have a look at all of the other platforms and marquees. There was a reason for each of them.

In most cases, a transmission is chosen because it could be found, and it fit in the hole.

It is not often possible to determine the exact performance effect that a major change like a transmission will make, in advance.

As an automotive engineer, even I would have trouble doing it solo, and would have to resort to using a simulation program.

Why? There are far too many variables in play. Everything from camshaft profile, coefficient-of-drag, ride height, to tire type and tread pattern. Something as simple as lowering the car 2" will necessitate that you do the calculations all over again, because you altered the aerodynamics. Same with having a louvered hood. Got a windshield visor? That counts too. The list is nearly endless.

Of course, all of the variables need to include a crankshaft dyno sheet, and a ch***is dyno sheet.

Even after all of that, the driver might not be happy.

There are countless threads here that say something to the same effect: first gear is too low and I don't use it, the first 4 gears are pretty good, but the top gear is too high or low, etc.

All of these are good examples of a transmission and rear end gear combination that are not properly matched to each other, the vehicle, and the habits of the driver.

I ran my Falcon through the simulator at GM. The result is a 0-60 time of 6.2 seconds, a top speed that is over the 120mph that I had room for, and a 75mph freeway mileage of 33mpg. All of this is with a 6-cylinder, with a 6-speed transmission.

All a regular hot rodder can do is try, and make changes based on the outcome. Hence the reason why I pointed out that 5th gear can be tweaked independently if the driver is not happy with the initial results. If this helps the user choose a unit with more appropriate base ratios, knowing that they can change the overdrive ratio.

For the record, I have put Word Cl*** 5th gear sets in Non-World Cl*** T5's, so the possibilities for change are enormous.

 

I do this often enough that there is an actual T5 5th gear set under my bedside table.

 

LOL...that's OK, as long as there isn't a set under your pillow.

 

Everything on the bed is white. If it made it in there, everything would be red.

 

The car has Aerostar coils and dropped uprights in the front, 4" lowered leaves in the rear, it will have 2" dual straight pipes and one day a visor when I can find one that isn't $600. The trans has no tag on it to identify it. As soon as I'm done feeding the baby I'm going to go do the tape test again to get an accurate 1st and 5th gear ratio. OD is either .72 or .76 so it either has the 3.76 or the 4.03 first gear. Actually I'll get all the gears ratios and post back.

 

S10 t5, World cl*** (1995?)
1st: 3.76
2nd: 2.18
3rd: 1.42
4th: 1.00
5th: .72

 

If it is a 1995 T5 it will be World Cl***, and would have the FORD pattern on the front, even though it came from a GM vehicle. It also would have the 4.03 gear set.

By 1995 they were all World Cl***, and almost all were going into Fords. The decision was made to not have separate production run for GM cases, to save money.

You have a GM pattern World Cl*** setup S10 setup. The last of the great T5's. I think there were some of these in the transition of BW moving over to Ford pattern cases for everything, but that would have been earlier than 1995, if memory serves. No matter, just trivia.

On the case parts there should be year indicators that look like this:

Look on the side that has the fill and drain plugs on the main case.

So long as you can live with the electronic speedometer sender, or have it converted, you managed to score about the best S10 T5 that can be found.

At one point HAMBER @Kato Kings was doing manual speedometer conversions on these, and might still be. It's worth asking, and cheaper than any electronic drive box. Once converted, and you get the correct plastic gears, it would just run your original speedometer.

On my T56 I run a Dakota Digital ECD-100 speedometer drive. These have been replaced by the ECD-200BT. It works well, but it was not cheap.

 

The T5 that I had in my 51 Chevy was electronic drive as well. I just stayed with the flow of traffic on whichever road I was on and it always worked out perfectly. I was going to buy the Dakota digital set up for that car but I couldn't justify the 260 or 70 or however much it was. I probably will Spring for the new version on this Ford though. I'll look for the year indicator on the case as I thought they switched over to the Ford bolt pattern in '96. So knowing my plans for the car and and the transmission gear ratios what was your suggested rear end wise? I'll most likely stick with 3.73, I just know once I hit 5th gear in the Chevy on any type of incline I wished I had 4.10s.

 

Looks like it's a '92.

 

The year of manufacture does not really matter at this point, except for record keeping sake. You got a good one.

The Dakota Digital boxes are now about $350, so keep that in mind. The mechanical speedometer conversion is cheaper, as far as I remember.

Rear ratio will depend on tire height. Somewhere between 3.73:1 and 4.10:1 is probably the sweet spot, but that would depend on your terrain. If you mostly run around the Bay, you can probably do wine with the taller set. If you like to see the sights up near Backbone Mountain, you would need the deeper set. If you do both, then the deeper set for sure.

When given the choice of a rear gear, one a transmission selection has been made, it is better to turn an engine a little faster, with more mechanical advantage, than it it is to turn an engine a little slower, with less mechanical advantage.

Operating an engine at a mechanical disadvantage puts a whole lot of strain on it. Flatheads have fewer main bearings than more modern engines, and therefore have a lot more of the crankshaft unsupported. Putting extra constant strain on an engine like that can be literal murder on that crank and its bearings.

Another thing to consider is carburetion. If you put your freeway cruise RPM too low, the velocity through carburetor(s) for proper fuel metering to happen. Airflow through the venturi needs to be fast enough to produce a significant reduction in pressure to draw the fuel out of the float bowl through the jets, and into the air stream. Too slow and this will not work efficiently. You might be trying to cruise on the idle circuit. Every engine has a floor under which it won't be happy operating.

You see all sorts or modern engines that have freeway cruising RPM's of 1600-1800, but they all have EFI, where fuel is pumped in by high pressure, under computer control.

My miracle Ford cruises at a very low RPM, and it can get away with that because it has 7-main bearings, in comparison to the 3 on a flathead, and it has EFI, which we cannot discuss publicly.

 

Run it!

I often hear from folks that "5th is too high. Every time I hit a hill I have to downshift into 4th."

My answer is: so? I have to do this on all of my factory-built manual transmission cars, and the automatic ones do it, too, except for the turbo diesel.

Not saying that this is you, but a whole lot of folks seem to to think gear selection is solely based on vehicle speed, when it is load vs. available torque (all other conditions considered equal).