58 TBird 9" question

[RustyNCa]

Just checking if anyone knows what the spline count would be on the rear end in my 58 TBird?

If anyone has a deal on different gearing and or a limited slip or locker I be happy to hear about it.

Cheers
Bryan

[Dakota Boy]

28 splines.

I have a 28" tall rear tire with 3.50 gears. C6 transmission. 70 mph is around 2800 rpm.

[RustyNCa]

28 splines.

I have a 28" tall rear tire with 3.50 gears. C6 transmission. 70 mph is around 2800 rpm.

See you are down the road I was thinking. 3.50 gears with a Trak-Lok and I have a C6 to install. Need to decide what stall I want in it. What are you running for stall?

What is your tire size? I am running 275x40x17s I think.

[simplyconnected]

Bryan, consider this...
A sun gear from an E40D fits nicely in a C-6. That swap lowers first gear by 20%, and it lowers second by about 15%. Third remains 1:1. It widens your ratios.

This is a great improvement off the line but doesn't affect highway driving so you get the best of both worlds. Another way to do this is by lowering your RE gears with an AOD. - Dave

[RustyNCa]

Bryan, consider this...
A sun gear from an E40D fits nicely in a C-6. That swap lowers first gear by 20%, and it lowers second by about 15%. Third remains 1:1. It widens your ratios.

This is a great improvement off the line but doesn't affect highway driving so you get the best of both worlds. Another way to do this is by lowering your RE gears with an AOD. - Dave

Interesting, I've never heard that. I would assume the 3.0 ratio is still very high tho.

[simplyconnected]

I guess the question is, do you want more torque at the rear wheels? Other than changing engines, the only way to get there is through your drivetrain's transmission, rear end gears and tire diameter. RE gears and tire heights are set in stone but transmissions offer a host of options.

I am a 'Ford guy' and have done this swap on my C-6. It works well and it's still a three-speed automatic. I'm passing this information to you. California should have many good transmission shops. They usually have a good supply of parts and the knowledge to assemble them. Get ahold of some old transmission shops and talk with the rebuilders.

Most Ford transmission changes were done in small steps because engineers were very mindful of 'backward compatibility' issues. A good, experienced Ford transmission guy will be familiar with the E4OD as it was an overdrive attempt OF a C-6. Many Ford transmission parts are identical from the Ford-O-Matic, all the way through. That means, rebuild kits often include the same parts that wear. - Dave

[RustyNCa]

I guess the question is, do you want more torque at the rear wheels? Other than changing engines, the only way to get there is through your drivetrain's transmission, rear end gears and tire diameter. RE gears and tire heights are set in stone but transmissions offer a host of options.

I am a 'Ford guy' and have done this swap on my C-6. It works well and it's still a three-speed automatic. I'm passing this information to you. California should have many good transmission shops. They usually have a good supply of parts and the knowledge to assemble them. Get ahold of some old transmission shops and talk with the rebuilders.

Most Ford transmission changes were done in small steps because engineers were very mindful of 'backward compatibility' issues. A good, experienced Ford transmission guy will be familiar with the E4OD as it was an overdrive attempt OF a C-6. Many Ford transmission parts are identical from the Ford-O-Matic, all the way through. That means, rebuild kits often include the same parts that wear. - Dave

Well, I am replacing the trans with a C6 for sure, I'm pretty sure the COM won't live long behind what I have done to the motor in the TBird. And it seems terrible form to have a car with a roots blown motor and not have a limited slip. So, changing the gearing also seems prudent.

But, I like the idea of having larger gear splits.

Thanks
Bryan

[Dakota Boy]

The stall on my converter is around 2600-2800. Tire size is 275/60-15.

[scumdog]

Regarding those 'tall' gears as mentioned a couple of posts back:

I run a C-6 fitted with a shift kit but running a stock torque-converter behind the mild 429 in my '55 F100
I run an 'open' rear end with 4-spider 2.75 gears in my 9".

And the combo spins the 305/50/15" T/A's easily - at times too easily...

So if your motor has torque and you're not after the ultimate 1/4 mile time 2.75 gears will be OK.

(Stock gearing in the C-6 gives me just over 100mph in 2nd gear.)

[simplyconnected]

Tom, by 'open' do you mean you have non-limited slip (non-positraction)? And by 'four spider gears', are two splined for your axles and two are on the carrier pin? I guess I'm asking if this is a regular conventional setup or something that is custom.

The only reason we use low ratios (like 3.9:1 or 4.30:1) is for launches. Tall gears (like 2.75) tend to come apart when 400-500 HP tries to spin slicks off the line. I've seen axles twisted a half-turn as a result as well.

A 4.30 ratio will easily transfer 500 HP because more ring and pinion gear teeth are engaged at once and torque is doubled over a 2.75 just because of the ratio. I've seen 'tall' gears explode upon launch.

Bonneville cars use tall gears because they are looking for 'maximum top end speed' regardless of how long it takes to get there.

I don't know why but Ford puts tall gears in convertibles. When my Mustang was stock, the 5.0/AOD got me to 150 MPH but it took a very long time to get there and there was more elbow room left on the tach. The engine simply didn't have any more to give. Not bad for 'stock' but I wasn't satisfied with acceleration so I built a 351W. - Dave

[scumdog]

Tom, by 'open' do you mean you have non-limited slip (non-positraction)? And by 'four spider gears', are two splined for your axles and two are on the carrier pin? I guess I'm asking if this is a regular conventional setup or something that is custom.

The only reason we use low ratios (like 3.9:1 or 4.30:1) is for launches. Tall gears (like 2.75) tend to come apart when 400-500 HP tries to spin slicks off the line. I've seen axles twisted a half-turn as a result as well.

A 4.30 ratio will easily transfer 500 HP because more ring and pinion gear teeth are engaged at once and torque is doubled over a 2.75 just because of the ratio. I've seen 'tall' gears explode upon launch.

Bonneville cars use tall gears because they are looking for 'maximum top end speed' regardless of how long it takes to get there.

I don't know why but Ford puts tall gears in convertibles. When my Mustang was stock, the 5.0/AOD got me to 150 MPH but it took a very long time to get there and there was more elbow room left on the tach. The engine simply didn't have any more to give. Not bad for 'stock' but I wasn't satisfied with acceleration so I built a 351W. - Dave

Good comments Dave.

And yes Dave, it's a non-posi rear end, it has four spider gears, two on the normal pin that goes through the carrier and the other two on short pins that go into the centre 'block that the long pin passes through.

When one wheel is spinning it shares the load on the side gears with four gears instead of two.

And I've seen teeth shred off a real low geared set (5:13 etc) pinion because of the small diameter of the pinion so there's give and take I guess!.

But I like my 2:75 gears as it gives a semblance of 'economy' (huh!) and I have never run out of revs in top gear.