3.55s to much for me?

[CheeseSteakJim]

How is your experience affected, if at all, by your old automatic having the wide ratio gearset? I guess the Overdrive gear is the same, though First is a bit deeper IIRC.

More importantly, how is it with the 5speed? I forgot which has which, but I know between the T5 and AOD one has .68 OD and one has .63.

[Blaze86Vic]

AOD has a .67 4th,
4R70W has a .70 4th,
T5 has a .68 5th,

For first gear, the wide ratio trans and a 3.55 final, is the same as an AOD with a 4.20 final (I know that's not an available ratio, but it's between a 4.10 and a 4.30)

For second gear, the wide ratio trans and a 3.55 final, is the same as an AOD with a 3.73.

For 3rd gear they are both the same ratio.

For overdrive, the wide ratio trans and a 3.55 final, is the same as an AOD with a 3.73.

[1987cp]

Nice way to describe it. Makes me wonder whether I should keep my 3.27s and build a wide-ratio AOD. Mike made a comment about messed-up shift points with the wide-ratio, though.

[1980c10]

I had 4.10's in my 90 mustang and got 25mpg consistantly <--- spell check - with that and speedo corrections at around 60-65 mph. but also had no smog - A/C - and electric fan so maybe that was part of it? who knows. I wouldn't worry to much if I wore you 1-2 mpg at the most.

[gabegt90]

I guess I'll be the opposite voice here. Yeah as a fun car, and a tow car, 3.73's are the way to go. But for what my car used to be, a highway cruise and 50+ mile daily driver, I wish I had put the 3.31's in there. I plan on getting another crown Vic in the future for taking long trips, and I'll either put 3.31' of the 3.27's in. City mileage is probably better with the 3.55, but highway mileage is all about keeping the revs down. The 2.73 is the absolute best on the highway, but it's such an extremely low gear that every time you have to get up to accelerate it destroys your mileage.

Though I do consistently get 1-2 MPG better in my Vic, I have never been able to get within 3mpg of my highway record that I made when I had 3.01's (25mpg). But I have gotten up to 22mpg with the 3.55's.

yeah I get around 18-19 city with my 3.55's the best I ever gotten highway was 23.5 the 3.55's are perfect for city driving plenty of take off at the lights. but for mileage 2.73 and 3.08's are better

[pantera77]

Alright, I have another quick question. Assuming I bought a brand new trac lock from summit, and new carrier bearings, if I just took out my open carrier, and in the process took out all the shims and marked which one went where, and swapped my ring gear over to the trac lock carrier, and put it all back together the way it came out would I be safe? Sorry for all the questions but I really don't know that much about diffs.

[Blaze86Vic]

No, it would likely need to be aligned again since you changed carriers. It could work out fine, but probably not.

[Pirate]

No, it would likely need to be aligned again since you changed carriers. It could work out fine, but probably not.

More than likely....not.


Another suggestion might be to add a Detroit mini-locker or Powertrax locker setup (the base model). I'm not too impressed with the Ford diff, as it's a bit of a lightweight that needs to be modified right out of the box. The lockers make the car a little spooky handling at first under acceleration in corners, but nothing that will send the car hurtling off of the road....but you will have full power to both rear tires at all times under acceleration.

So far as the 'spooky' handling, you get used to it rather quickly, as it only occurs if you accelerate in the middle of a corner. The only thing the car does is try to nudge back to center if you nail the gas.

Other than that....you'll never notice it.

You're wasting your money on the Ford piece, however.

[87gtVIC]

All you guys worry about fuel economy too much.

[pantera77]

More than likely....not.


Another suggestion might be to add a Detroit mini-locker or Powertrax locker setup (the base model). I'm not too impressed with the Ford diff, as it's a bit of a lightweight that needs to be modified right out of the box. The lockers make the car a little spooky handling at first under acceleration in corners, but nothing that will send the car hurtling off of the road....but you will have full power to both rear tires at all times under acceleration.

So far as the 'spooky' handling, you get used to it rather quickly, as it only occurs if you accelerate in the middle of a corner. The only thing the car does is try to nudge back to center if you nail the gas.

Other than that....you'll never notice it.

You're wasting your money on the Ford piece, however.

Ugh. Now I have no idea what to do. The only thing I was relatively sure on I now I'm not sure on.

Is this the Powertrax locker you were talking about:
http://www.summitracing.com/parts/PW...R/?image=large

I really like this part

Powertrax lockers replace the spider gears in your differential carrier without affecting your ring and pinion settings. The whole job can be done in your driveway with common hand tools in a couple of hours.

I've pretty much decided against the 3.55s for now anyways.

[Pirate]

Ugh. Now I have no idea what to do. The only thing I was relatively sure on I now I'm not sure on.

Is this the Powertrax locker you were talking about:
http://www.summitracing.com/parts/PW...R/?image=large

I really like this part


I've pretty much decided against the 3.55s for now anyways.

Any rear gear installation must be properly installed, and must always be considered in any rear gear upgrade.

Me personally?

I'd do the 3.55 gear swap, simply because it gets the engine rpm closer to the 302's torque peak during cruising. If you live in Texas, or only drive on flat interstates, then I'd live the 3.08's in.....otherwise, shitcan them as soon as possible.

[87gtVIC]

Any rear gear installation must be properly installed, and must always be considered in any rear gear upgrade.

Me personally?

I'd do the 3.55 gear swap, simply because it gets the engine rpm closer to the 302's torque peak during cruising. If you live in Texas, or only drive on flat interstates, then I'd live the 3.08's in.....otherwise, shitcan them as soon as possible.

[pantera77]

or only drive on flat interstates.

Honestly, about 70% of my daily driving is this.
If I leave my 3.08's in, and just bought that Powertrax locker, I'd be able to install it with out needing to re shim anything right? At least from the small amount of researching I did that's what I got out of it.
Really the main reason I wanted to change the gears was because I wanted some form of a limited slip diff for all the snow we get up here. I'd kind of rather leave my current gears in If I don't have to mess with them.

[Blaze86Vic]

Any locker like that is going to be odd handling as Pirate said. It's nice that it works without having to re-align everything since you aren't changing the carrier, bearings, or gears, just internals of the carrier.

However, for a daily drive I'd strongly suggest against it. Essentially, every time you hit the gas it's going to act like you welded the diff. Great if your car tends to oversteer (spin out or loose in nascar terms), or if you do a lot of drag racing, not for improved traction in low traction situations like rain or snow. It also leads to snap oversteer. That is that It will understeer (plow or tight in nascar terms) under throttle, until you break the traction of the rear wheels and it will snap the tail around, where as a weak LSD which will slowly start to step out on you giving you time to react.

[1987cp]

There's also the fact that the Powertrax unit costs something like $400-$500 (ouch!). I scored a rebuilt Trak Lok center off someone at the Corral for like $85, and by looking at lots of pics I took, Scott helped me verify that it does indeed seem to be OK.