[68jjf]

what is a good rear gear for my .68 O/D TKO? I was thinking a 4.88 what kind or R's would that be? what about 4.33? 411?

[Mike68RS]

Jaiden, It depends on what you're using the car for, weekend cruiser, strip car, etc.
What is your rear tire diameter? you need that to calculate rpm's.

Mike

[Steiner]

Holy Lord. Really? It's going to be a four speed because first will be about useless.

Try this:
http://www.keislerauto.com/speed_analyzers.php?sa=gm_5


...

[TMessick]

yeah, really need more info here but I'd go with a 3.73 AT THE ABSOLUTE MOST with the TKO500 and even that is pretty darn deep with a 12.2:1 overall 1st gear.
1st gear is 3.27 on the TKO500, so if you start running a lot of rear gear, 1st bear becomes kind of useless....

With 3.73's and a ~25.7" tall tire, you'd be at 1960 RPM at 60mph in 5th and 6000 RPM in 1st would be ~36mph.

3.08's are the normally recommended gearset for the TKO500, which nets you 1700 RPM at 60 and 1st gear would top out at ~44mph. Even with these "shallow" rear gears, you end up with an overall 1st gear that's the same as a M20 with a 4.00 rear or a M21 with a 4.58 rear .

Maybe run 3.36's if you want a little more around-town go power.

This gear/RPM calculator is also a good one:
http://tri-5.chevyrides.com/rpm.php

[68RS-SS]

Good thing you asked before spending the dough. I have TKO w/.64 O.D. and 3.73s. It's about perfect but 3.50s would even be just a tad more perfect for a "super-cruiser." If mostly drivin on the street strive to meet that objective at the sacrifice of a couple 1/10ths when you go to the track. You won't regret it and will save you from changing them again later.

[ace's68]

With 4.88's your going to be shifting as much as a semi truck driver, and I have seen 4.88's used on the street that create a lot of heat, burn things up, and start to leak.
4.10's would be great 3.73's are ok, it depends on if you want a good first gear, or you want the car to be able to still pull in o/d.
I know 4.10's in a T-56 are perfect, I've heard people going from 4.10's to 3.73's in the t-56's and they didn't like it... I know the trans are different, just giving you something to go off of.
My vote is 4.10.

[Steiner]

Originally Posted by 68RS-SS

Good thing you asked before spending the dough. I have TKO w/.64 O.D. and 3.73s. It's about perfect but 3.50s would even be just a tad more perfect for a "super-cruiser." If mostly drivin on the street strive to meet that objective at the sacrifice of a couple 1/10ths when you go to the track. You won't regret it and will save you from changing them again later.

I hear you. I've got a 600 and debated for like a week over what gear to get.....even called up and changed to order on my Moser from a 3.73 to 3.42 after playing with the speed calculator over and over. Of course, my truck has a 0.74 and a 3.42 so I knew roughly what it was going to feel like and I'm building a smaller cam 383 as the car is 100% street driven.

[67CamaroRS/SS]

Originally Posted by 68jjf

what is a good rear gear for my .68 O/D TKO? I was thinking a 4.88 what kind or R's would that be? what about 4.33? 411?

Personally I think a 4.88 is too low. I run a 4.10 and 1st gear is pretty short. Ideally you are looking for a 9:1 ratio for 1st gear. With a 4.88 you will be at 14:1. With my 4.10, I am at 11.7:1. Still too high, but no where near as bad as if it were a 4.88. If you run a 4.88, 1st gear will be like a granny gear. Absolutely pointless. You will be shifting out immediately or you won't even be able to use it. You will have to leave in 2nd. Most guys are running 3.73's. Even that is giving you a 10.7:1, but still a good overall ratio. I like the 4.10. It gives me an INCREDIBLY hard launch and I still "need" it(1st gear) to take off from a light. With a 25.1" tire, the 4.10's and a the TKO 600(.64 od), I run at 1900+rpm @55mph. 70mph is at 2455rpm. Just a little food for thought.

[68 Ragtop]

Originally Posted by 68jjf

what is a good rear gear for my .68 O/D TKO? I was thinking a 4.88 what kind or R's would that be? what about 4.33? 411?

You should really be asking this question based on the first gear ratio, with secondary consideration of the OD ratio.
The .68 OD TKO is the TKO-500 with a first gear ratio of 3.27
The .64 OD TKO is the TKO-600 with a first gear ratio of 2.87
The big difference between the two is in first gear, with a small difference in OD
The best all around rear end ratio for the TKO-500 is 3.07 and for the TKO-600 it's 3.55

[68jjf]

thanks for the help... i actually dont know about rear tire heigth .. i knew that would be a part of it.. all i know is that im either puting 17 or 18 inch rims on the back (prolly 17"X 8" torq thrust II's) and i would like to know about the rubber i could stick on those.. i would get the 2.87 first so consider that.. soo 4.11's? as for the tires.. how tall would i want them , and how fat can i get out of an 8 inch rim and still stick them in the stock wells, or even a deepend wheel well? i hear you i have an '83 scottsdale 20 with a stick, not sure about the tranny but its a 4 speed with a granny, and it is a grain truck.. and i always start out in second... let me know thanks

[68jjf]

oh yea by the way.. i want to drive this baby to shows.. so a pro touring/ cruiser..

[TMessick]

OK, if you're looking at the 2.87 1st gear TKO, that's the TKO600 (2.87 1st, 0.64 5th)
3.42's to 4.10's are "good" ratios for that trans in general with the 3.42 giving better highway manners and the 4.10's giving better off-the-line performance.

There's a lot of personal opinion involved w/ tire selection, but a "stock"-ish tire is ~26" in diameter. If you're looking for that drag-type look (or you're actually going to drag race the car) you may want a bit taller rear tire. "How tall can I fit" will depend on the rear suspension setup.

Search the wheels & tires forum, but on a 17x8" rim, 255/45R17s are a good choice for the rear. Fronts would likely need to be narrower to keep from rubbing (235/45R17?)

[Steiner]

What is your motor setup? That'll help with deciding your rear gearing.

The wheel and tire section will have all you want to know about fitment if you'll search it. On the rear you can do a 17x9.5 with 5.5" backspacing and fit a 275/40 tire. It looks like this with non-lowered springs:

[69SS 350 5 Speed]

If you intend to drive your car more than a few miles at a time, do not go with anything over 3.73.

I have 3.08's in the wife's Camaro with the TKO 500. Plenty of torque out of the hole and you can cruise the interstate and get over 24 MPG. We drove over 1,800 miles on the Hot Rod Power Tour last year and even after doing a lot of idleing and making a few passes at Great Lakes Dragway and Thunder Valley in Bristol we got 18 MPG overall for the trip.

The only thing you will have to adapt to is the slight lag when you shift to second because of the large gap in the ratio.

[Hurst - Jeff]

Assuming a close to "typical" height rear tire, 3.08-3.36's seem to be the best bet when using a TKO-500.
Most popular choice for TKO-600 w/.64 5th seems to be 3.55, 3.73 or 4.10's.
Your intended use, motor type, and personal preference will help fine tune your decision.