3:42 vs 3:73 gear

[Blake442]

And here's something else you should know. It's gonna be about a $200 bill to get the speedo re-calibrated.

Sorry Phoenyx, but you got boned! I hope they bought you dinner or at least a drink or two first!

As long as you know the gear ratio that you're installing, whether it's a 3.42 or 3.73, all you have to do is buy the appropriate speedo gear for that gear ratio, swap it out, and call it a day. Total cost depending on your source for the gear, about $15.

 

[Phoenyx]

Also depends on if ur running stock size tires too I think.

 

[dogsht]

Phonix, Custom442 was referring to going from 3.42 to 3.73 not from 2.29. Is it worth it to change ring and pinion to go from 3.42 to 3.73 probably not with his transmission and goals or use of the car.

 

[jonnyslick]

I had 3 mustangs in the past, all 5.0 5 speeds. One had 2.73's, it was a dog off the line, but amazing on the freeway. Like 2,500 rpm at 100mph was pretty cool. Switched it to 3.73's and it was way more fun launching and accelerating, but started winding out pretty hard on the top end. The other two had 3.08 and a 3.55. Both of them were just average IMO, although the 3.55 was a good blend for town/highway.

The Cutlass has a really high gear, 2 somthing. It's horrible on acceleration, but get 27 mpg on the highway so I'm not complaining at this stage of what I'm doing.

 

[NAILS]

I just got a hold of a 8.5 grand national rear end with a 3:42 eaton posi unit. I was wondering if the difference in performance between the 3:42 and 3:73 were worth the price of a new pinion and ring gear? Just plan on doing some in town type racing with a 350 ci 87 el camino.
Thanks.

to answer your question plain and simple no, it absolutely is not worth the expense. you will not "feel " a gain at all. if you were racing at a track, you may "see" a small decrease in your 60' and maaaaybe your et - but thats not what your stating your intentions to be. in all honesty, if that 350 is just a stock or mild crate motor- you dont even need that gn rear- keep the 7.5 and throw a good posi and some 3.42/3.55's and call it a day. a 7.5 that has some decent internals will definitely hold up to 300 hp. if your 350 motor is in fact worked, even just cammed for a 350-375 hp motor then you prob will see that 7.5 take a sh*t.
im assuming your upgrading from a non posi 7.5... that be the case, once you slap that rear into your car, changing gears wont even be a thought in your mind. upgrading from a one tire fire aughta be enough to make you cream your pants good. good luck either way

 

[NAILS]

I had 3 mustangs in the past


that sucks...im sorry to hear that 🙁

b*tches!!

 

[kartrac3r]

In both of my aerocoupes (stock from factory) they are 305/auto w/OD/3.73 open end. IS it normal to be pulling 3000 cruising at 60? interstate speed lmitit here is 75 (which really means 80) and it rolls at 3400 then. Actively looking for a 3.42 posi. Hate to pirate this thread but would I be doing the smart thing by swapping for the 3.42 for the not racing minded driver car?

 

[Blake442]

Is it normal to be pulling 3000 cruising at 60?

No, it's not normal.
I run about 3000 rpm at 60 mph, and I have a TH400 and factory 3.73's.
When I still had the 200-4R in it, it would spin about 2200 at 60 IIRC...

I would venture to say that something may be misadjusted with your shifter linkage, and it's not going into overdrive.
But that's just a guess...

 

[kartrac3r]

I thought that was the case too. I took it to the transmission shop a couple of years ago to see what magic they can do. and whatever they did didn't do much. it kicked it down 100 rpm woooooo totally worth it!

 

[dogsht]

That is so far off I would say you are running a three speed or in only three gears. Count your upshifts from a stop. You should get three plus sort of a 4th when the converter locks up.