ykp53

when i purchased my 77 i was informed that it has 3.70's in it. well i was playing with the rear end claculator at smokemup.com and it looks like i have 4.xx. i run 68 ish at 3500 rpm and 74mph at 3800 rpm. i know i can jack up the car and count the revelutions of the drive shaft but where exactly are the identifications #'s stamped at? and what are they?
thanks


[Modified by ykp53, 11:07 AM 12/14/2001]


[Modified by ykp53, 11:09 AM 12/14/2001]

gerry72

If someone really put 4.11s in that thing, they must have been sadists (your car didn't come from the factory with that ring and pinion). At any rate, the axle code is on the bottom rear of the housing. You'll have to get on your back -most likely with a scrub brush and flashlight- and read the first two alpha characters. It will be something like AW. You need a reference to decypher the code (like a Chilton's). Don't know how much good that's going to do you though since those gears didn't come in that housing.

ykp53

it wouldn't suprise me they have changed everything else. it was origanily silver with a 350 and 3.08's when the work was done they did a good job. what all is required to put in 4.xx in a car. wouldnt you have to change out the entire pumkin?

FeedVaal

Remember those calculations vary with tire height. I was similarly confused until I realized my speedo was wrong due to short wheels.

ykp53

i run 255/60/r15's all around. i have thought about that but doing some calculations there should only be 2 or 3 mph differance. is hter any way to check my calculations? what were stock tires for a 77?

FeedVaal

I run 245/60/15 on really crappy looking aftermarket mags. My spare which I believe is the original is a 235/70/15 but I've never measured it. Hopefully someone will chime in here with the specs for it.
My 245's are 25.5 inches tall.

Sorry should read 225/70/15. Found an online calculater that says it should measure 27.4 high. http://www.ring-pinion.com/calc-tire.html


[Modified by FeedVaal, 2:25 PM 12/14/2001]

Gordonm

I was running 4.11 gears and a 245 60 15 tire. I think they are 26.6 tall. I would get about 3600 rpm at about 70. I just switched to 3.70 gears and don't have any speeds yet to talk about. Still have the wrong gear in the tranny

DeenHylton

What other modifications were made? If your running an automatic and the previous owners installed a higher stall converter, that could account for some of the differance in your speed/RPM calculations and what your actually seeing on the street. I have a 4,000 stall converter and show around 500 RPM of "slip" compared to a similar car equipped with a manual tranny. Just a thought...

Golden80

4.11's if you want to say goodbye to gas mileage! I'd only want 4.11's if I was making my car a street/strip only car. Not good for street use. But that's just my opinion. I'd stick with the 3.70's. It's a good gear for street use with a little strip use.