Need new gears - help

richabilly · Post by **richabilly** » January 10, 2011, 3:05 am

Hello all. My 61 f100 has undergone some major transformations over the past year. I swapped in a 302 from a 93 mustang, along with the 5 speed that came with it. The problem is that the stock rear end has such tall gears that I can't take advantage of the power of the new motor -- not to mention I have yet to see 5th gear. My slick came with a 3 speed on the column.

Anyway, anyone know what the gear ratio of my truck is now? and what would be the ideal gears for my truck? (I'm interested in power and performance - I won't be towing anything).

Off hand I'm thinking somewhere between 3.50 - 3.83'... Would you guys agree? I don't know what the stock mustang ratio is.

Also, stupid question for some, but will my rear axle take new gears? I would rather not swap in a new axle if i don't have to.

Thank you so much!

MY OL 66 · Post by **MY OL 66** » January 10, 2011, 7:42 am

Stock gear ratio for the '93 Mustang is most likely a 3.08...

PFM-64f100 · Post by **PFM-64f100** » January 10, 2011, 9:27 am

My 64 (9") had 3.93 gears in it. You might be able to get by with 3.25... just a guess on my part. My 65 (Dana 60) has 4.56 gears in it. Maybe you still have a tag on your pumkin?

richabilly · Post by **richabilly** » January 10, 2011, 10:27 am

I'll look for the tag. The gears are super tall -- the truck bogs down when I take off from a dead stop.

Also do you know if any rear end can or cannot take a new gear set?

Sarg · Post by **Sarg** » January 10, 2011, 10:43 am

Answered on the "other" site, but figured I would answer here as well so that the guys here get the same answer

Yes you should be able to put new gears in it. There are some crazy number crunchers here that if you get the door tag, they should be able to tell you the axle that is in it.

richabilly · Post by **richabilly** » January 10, 2011, 1:02 pm

Okay cool - I will do some digging today to see if I can find out the ratio.

Also, is it true the higher the number, the quicker the car will be (not top speed, but out of the hole)?

62galxe · Post by **62galxe** » January 10, 2011, 1:48 pm

my 63 had 3:89 gears. im runnin a 292 T5 setup. even with 3:25 gears it accelerates ok. Im goin back to the 3:89s.

Sarg · Post by **Sarg** » January 10, 2011, 7:16 pm

richabilly wrote:Okay cool - I will do some digging today to see if I can find out the ratio.

Also, is it true the higher the number, the quicker the car will be (not top speed, but out of the hole)?

It is a mechanical ratio of the rpm vs the wheel speed. So yes, if you had say a 4.10:1 gear you will be able to accelerate quicker, but will lose top end as your engine will run out of rpms quicker. A 3.23 gear will not accelerate as quick but will have better top end.

Tires also need to be taken into account. Putting on larger tires effectively lowers your rear end number. By switching to smaller diameter tires you are effectively raising the number.

Think of it this way. a 4.10 gear has a mechanical advantage or torque advantage of 4.1 units of torque as the engine is spinning 4.1 times for every 1 time the rear wheel spins. A 3.23 would spin 3.23 times for every one time the rear wheel spins, so it would not be putting down as much torque but would not run out of rpms as fast either. That is a pretty over simplified version of what it does. You also have to take into account the gears in the transmission.

Also remember that if you gear it too low (higher number) cruising on the highway could turn into a nightmare. Think 4500 rpms at 70 mph.

MadMaxetc · Post by **MadMaxetc** » January 10, 2011, 7:21 pm

What is the OD ratio?

What RPM you you want to cruse in? and at what speed?

What id the Diameter of your rear tires? (or just the size)

I can run a spreadsheet that I made for my 67 when I put the T5 in.

R Pope · Post by **R Pope** » January 10, 2011, 7:28 pm

First you have to find out which rear end you have. A 9" has a separate "chunk" that comes out the front, a Dana 44 has a back plate where the gears are. Those are the options for a half ton. The 9" is the easiest to swap ratios, just bolt in another center section. The Dana requires some detailed adjustments to swap gears.

MadMaxetc · Post by **MadMaxetc** » January 10, 2011, 8:28 pm

I have the gear ratios for the T5 from a 93 stang with a 5.0

I need to know if it was a cobra or not.

Here is a sample of what I can show you...

richabilly · Post by **richabilly** » January 11, 2011, 11:22 am

MadMaxetc wrote:I have the gear ratios for the T5 from a 93 stang with a 5.0

I need to know if it was a cobra or not.

Here is a sample of what I can show you...

Not a cobra -- just a GT. The tires are close to a 31 -- I will get the exact size for sure. I will also take a look at that spread sheet. I thank you jfor taking the time to help.

MadMaxetc · Post by **MadMaxetc** » January 11, 2011, 10:22 pm

31" Tires 93 GT Trans

Unibodyguy1 · Post by **Unibodyguy1** » January 11, 2011, 11:25 pm

If you want to use a great site to figure out gearing and what your RPM's at a certain speed would be, check oout Richmond Gear and use ther "street calculator" its very accuate. www.richmondgear.com

Michael

charliemccraney · Post by **charliemccraney** » January 11, 2011, 11:36 pm

The rear end probably is not stock if it is bogging that engine and transmission. The T5 will give you a much shorter 1st gear than the 3 speed and that later 302 actually should have enough torque to move the truck around well. Those two factors mean it should be at least as good and probably better than it was. Assuming the engine and transmission are up to the task, the rear end can't be stock.
You aren't driving it like the 3 speed and starting in 2nd are you

I did that a couple times after I swapped mine.

qwertyd10n · Post by **qwertyd10n** » January 12, 2011, 12:47 am

I had always planned to put 3.55 gears in the 8.8" rear on my 5.0... but I never got that far. Think my '87 GT had 3.08 gears in it and my thought was that 3.55s would smarten up the bottom end without making highway speeds unbearable - the 5th gear OD helps with that.

Just my two cents worth...

Cheers,
Dion

MY OL 66 · Post by **MY OL 66** » January 12, 2011, 7:39 am

qwertyd10n wrote:I had always planned to put 3.55 gears in the 8.8" rear on my 5.0... but I never got that far. Think my '87 GT had 3.08 gears in it and my thought was that 3.55s would smarten up the bottom end without making highway speeds unbearable - the 5th gear OD helps with that.

Just my two cents worth...

Cheers,
Dion

I did that exact swap a few years back on my '93 SVT Cobra and it sure made it an even more enjoyable ride!

MadMaxetc · Post by **MadMaxetc** » January 12, 2011, 8:09 pm

Just remember that the tire size is another "gear ratio" that you need to worry about.

A mustang/car has a lot smaller tires than a truck.

R Pope · Post by **R Pope** » January 13, 2011, 7:53 am

I agree with C Mc, the rear has probably been swapped to a lower ratio, maybe from a truck that had an automatic. Something like a 3.08 or so. The good news is that means it's probably a 9" rear! The Dana's are too much of a pain to work on for most people to swap gears.