Can you swap a 2005+ 5 speed auto transmission in place of the 4R70W????

[007]

Anyone done this? Whats that tranny called? Is it do-able? Does the 05+ transmission have a up/down shifting function?

I'd like 5 gears instead of 4. I'll probably go T56 but my wife doesn't drive manual trans so this is an interesting option.

 

[04YELLOWGT]

Its called the 5R55.

I don't know of anyone doing it but I'm sure its possible. The only question is why would you want to. The 4R70W is a great transmission and there are quite a few 05 guys with the 5R55 that switch to the 4R70W.

 

[007]

For the extra gear - to keep you in the power band. Same effect as running steeper rear end gears but you still have the top end because you have the xtra gear.

 

[Flghtmstr1]

The 5R55 is a medium-duty trans. If you plan on making serious power, stick with the 4R70W.

 

[scupking]

As other people have said the 4R70W will hold more power then the 5R55. Not saying the 5R55 can hold a lot of power. A buddie of mine is makeing 435rwhp on his 5R55 and thats with 4.10 gears.

 

[TGJ]

The 2005+ Auto Mustangs have a 5R55S transmission.

You could probably make it work but is it worth it?

The 4R70W is a stronger transmission that will handle more abuse than the 5R55S. You won't much or anything with the 5R55S. I posted this before but here are the gear ratios for both transmissions.

5R55S:

1) 3.22
2) 2.29
3) 1.55
4) 1.00
5) 0.71

4R70W:

1) 2.84
2) 1.55
3) 1.00
4) 0.70

You will be able to launch a little harder due to the lower 1st gear, but you have an extra shift to deal with. The 4R70W will shift to 1-2 at the same MPH as the 5R55S shifts 2-3 at WOT and shift at the same point after that. It is track proven, the 5R55S does not have any performance advantage over the 4R70W.

There is no advantage of the 5R55S over the 4R70W once the 5 speed is in 3rd gear, in fact it will cost you a bit of gas mileage when both are in Over-Drive...

 

[007]

The 2005+ Auto Mustangs have a 5R55S transmission.

You could probably make it work but is it worth it?

The 4R70W is a stronger transmission that will handle more abuse than the 5R55S. You won't much or anything with the 5R55S. I posted this before but here are the gear ratios for both transmissions.

5R55S:

1) 3.22
2) 2.29
3) 1.55
4) 1.00
5) 0.71

4R70W:

1) 2.84
2) 1.55
3) 1.00
4) 0.70

You will be able to launch a little harder due to the lower 1st gear, but you have an extra shift to deal with. The 4R70W will shift to 1-2 at the same MPH as the 5R55S shifts 2-3 at WOT and shift at the same point after that. It is track proven, the 5R55S does not have any performance advantage over the 4R70W.

There is no advantage of the 5R55S over the 4R70W once the 5 speed is in 3rd gear, in fact it will cost you a bit of gas mileage when both are in Over-Drive...

Good info. Thanks.

That is disappointing. 1st is fine as it is (I have 4.10s of course), 2nd could be shorter and third is way too long. Looks like they added an extra gear into the 1-2 range which is early. Once you hit 2nd gear speed in the 4r70w theres no gain at all. They should have spread the ratios more evenly.

Fair enough. Waste of time. I'll get the T56. Its what I have always wanted anyway, but I thought this was interesting.

 

[wmburns]

I did not see anyone mention the most compelling reason why the swap is not practical. Both transmissions are computer controlled transmission. An ECU designed to work with a 4 speed 4R70W will not know how to tell the transmission to shift at the correct points.

I think it is likely that the electrical wiring harness connections are different.

Not to mention, the 5R55S is longer thus requiring a custom drive shaft/slip yoke.

Should you attempt such a swap, then some sort of external transmission computer control would be needed to control shifting.

I would suspect that re-engineering the stock ECU to work with a 5 speed 5R55S would be beyond of the abilities of most shade tree mechanics.

 

[Flghtmstr1]

I did not see anyone mention the most compelling reason why the swap is not practical. Both transmissions are computer controlled transmission. An ECU designed to work with a 4 speed 4R70W will not know how to tell the transmission to shift at the correct points.

I think it is likely that the electrical wiring harness connections are different.

Not to mention, the 5R55S is longer thus requiring a custom drive shaft/slip yoke.

Should you attempt such a swap, then some sort of external transmission computer control would be needed to control shifting.

I would suspect that re-engineering the stock ECU to work with a 5 speed 5R55S would be beyond of the abilities of most shade tree mechanics.

You make a good point, but it can be done by using a standalone ECU with trans control, like a MegaSquirt.

 

[SilverFoxbody]

swapping in the 5r would be a downgrade IMO...as you can see from the gear ratio charts posted, you get the same 1:1 and OD ratio anyway...just just have to slap the shifter one extra time to get there...gay....do what you can with the 4R.