rt 440 8 3/4 diff gears

[Long Island RT]

This is probably why I was not going to rebuild my car unless I could afford an Overdrive.
The Tremec is probably the best thing I did.

Imagine cruising the side roads and stop and goes with 4:11 4 speed. 
Then get on the highway and slap in into 5th - 2050 rpm @ 65mph and at 75mph only @ 2400rpm!   

[Brass]

Of course a Gear-Vendors unit would be great too.

[Wicked72]

from what ive heard the gear vendors isnt all that great. But thats coming from rival trans companies.  So you gotta 5spd with 4.11s and only running 2050rpm at that spd? imagine a 6 spd which is what im looking at...maybe ill go with a 4.11 instead of 3.91

[Long Island RT]

from what ive heard the gear vendors isnt all that great. But thats coming from rival trans companies.  So you gotta 5spd with 4.11s and only running 2050rpm at that spd? imagine a 6 spd which is what im looking at...maybe ill go with a 4.11 instead of 3.91

That depends on what the overdrive ratio is on your final gear.

What are the ratios on that 6speed?

[Wicked72]

Ill have to check. I am currently looking at a T56 with a bit of an upgrade to handle my hp output.

[doctor4766]

I'm about to swap out my 2.76 to a 3.23.
I do a lot of highway driving on our club runs, but like Troy said it's tough to get moving but great for long distance cruising with the 2.76 ratio.
Just this weekend we took a spin down south with the club. I sat on 2000 rpm at 62mph (100kmh) for 200 miles and the temp sat at a steady 180 all the way.
Having never ever changed a diff ratio in any of my cars it will be very interesting to see the difference it makes off the mark.
I've been told that with my camshaft and new gear ratio combo that even @ 100kmh if my revs go up to 2400 the engine will be running more efficiently and may even be better on fuel.
Can't wait to try it out.

Well, just tried it out and wooohooooo!!!!
Can't believe how much difference the new gears have made. It's really transformed my car from a lumpy sounding old slug to a bitchin wheel spinner!!
Turns out that my 2.76 was in fact a 2.71.
Now she chirps into gear not only from 1st to 2nd, but from 2nd to third!!



Do I sound excited??

[elacruze]

Well done! Nothing left now but the 200 mile weekend trip and a mileage report. 

[hemi24]

i use to run 3.91 with M-50-14 tires on my charger it was just a little to low for hwy use great on the city street though.

[RIDELIKEHELL]

I have 3.23's in my 68 from the factory so that is what we've chose to leave in the for now. I had planned on putting a 4.10 with an overdrive setup but finances won't let that happen. I plan on driving this car on the hiway to shows etc next year so I hope I have made the right call here. I put a 2500 stall in so that should let me chirp a wee bit

[doctor4766]

Well done! Nothing left now but the 200 mile weekend trip and a mileage report. 

Actually it looks like we might be heading down south again on the 28th to the same town we visited last weekend.
There's a big car show on so could be worth the trip. Let yas know.

On a side issue, I think my speedo is outta whack now as it just doesn't seem to correspond with how fast I'm travelling.
Should I be looking to change the cog in the box?

[Troy]

Well done! Nothing left now but the 200 mile weekend trip and a mileage report. 

Actually it looks like we might be heading down south again on the 28th to the same town we visited last weekend.
There's a big car show on so could be worth the trip. Let yas know.

On a side issue, I think my speedo is outta whack now as it just doesn't seem to correspond with how fast I'm travelling.
Should I be looking to change the cog in the box?

Well yeah. If you changed the rear gears you need to match the speedometer pinion (in the transmission). The tires are spinning faster now so you need to slow down the speedometer.

Troy

[doctor4766]

So with 295/50/15's and a 3.23 rear end what should I be looking for?

[Troy]

Probaly something in the 30-31 spline range. There's a reference somewhere but I don't have time to find it (sounds like something useful to add to the site huh?). Google "mopar speedometer pinion chart" and you'll find a table with tire sizes, gear ratios, and the appropriate pinion.

Troy

[doctor4766]

Thanks Troy.
I did find a link for a formula a bit earlier on here but or course can no longer locate it.

[greenpigs]

Here ya go http://www.moparts.org/Tech/tech/pages/speedo.html

[Troy]

This is better since most used gears are sold by color instead of part number:
http://www.mopartech.net/showthread.php?p=439

Formula:
http://www.moparchat.com/forums/showthread.php?s=&postid=372505

Troy