rear end options
Thread Starter
5th Gear
Joined: Dec 2024
Posts: 5
Likes: 1
rear end options
I have a 69 BB and am going to install a Tremec TKX WR. 1st gear is 3.27 and 5th is .72. I currently have a 3.08 rear end and was contemplating changing it to a 3.55 or maybe 3.70. Recommendations?
Melting Slicks
Joined: Nov 2006
Posts: 3,409
Likes: 1,821
From: Apple Valley, MN
The 3:70 (or 3:73) is the most popular choice when installing a TK. Problem today is finding good replacement gears. A friend of mine recently told me he saw a NOS set of US Gear 3:73s at a swap meet and the seller was asking $1000 for them.
Melting Slicks
Joined: Dec 2009
Posts: 3,232
Likes: 656
From: Thunder Bay
I have the .64 overdrive in mine and if I had to do it again I would go with a lower gear. I had the choice of .64 or .82 and the .82 would probably have been better. Your .72 with the 3.08 rear is about the same as my final ratio. It should be fine since my complaint is just with the drop from 4th to 5th, not with the overall ratio.
BTW I have a 3.55 rear.
Tech Contributor
Joined: Aug 1999
Posts: 15,173
Likes: 3,982
From: Connecticut, USA
Just do the math
1st x final for your first gear or launch ratio
Examples:
Muncie 2.52 WR and 3.36 gears = 8.46 used with the base SB and BB
Your 3.27 x 3.08 = 10.07 which is stout, no go to 3.70= 12.09 Very short.
When the TKO were the deal they came with 2.87 so 2.87 x 3.73= 10.70 and many liked that combo, OD dropped the cruise to about 2200-2400 with plenty of torque.
3.27 x 3.36 = 10.98 which is close to the TKO, you have to see what the OD drop is and make sure the engine won't be lugging in that range.
1st x final for your first gear or launch ratio
Examples:
Muncie 2.52 WR and 3.36 gears = 8.46 used with the base SB and BB
Your 3.27 x 3.08 = 10.07 which is stout, no go to 3.70= 12.09 Very short.
When the TKO were the deal they came with 2.87 so 2.87 x 3.73= 10.70 and many liked that combo, OD dropped the cruise to about 2200-2400 with plenty of torque.
3.27 x 3.36 = 10.98 which is close to the TKO, you have to see what the OD drop is and make sure the engine won't be lugging in that range.
Thread Starter
5th Gear
Joined: Dec 2024
Posts: 5
Likes: 1
After 11 miserable hours, we got the TKX installed. What a PITA, but, side pipes knocked an hour off of install time since exhaust was a non issue. It is a nice upgrade. Still on the fence on changing the rear end. At 70 MPH, 5th gear drops RPM to 1800. At 60 MPH it drops it to 1500. I found a rebuilt 3.36 on GearPartsCenter for $217 and free shipping. Seems too good to be true. Has anyone dealt with this website? Is it legit? Other thoughts?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Race Director
Joined: Mar 2016
Posts: 14,399
Likes: 8,204
From: Napa Valley California
Is your big block mostly stock or have you made any performance upgrades to it.
I would leave your rear end gearing as it is and maybe look at a new camshaft that will produce more torque in the lower to mid rpm ranges.
You don’t want a high lift aggressive cam, because they can kill low end and mid range torque.
Find one that makes torque from off idle through 5000 rpm.
That way you’ll get more pulling power at 70 when cruising at 1800 rpm.
There are many hydraulic roller or hydraulic flat tappet cams that are easy to install.
There is no need to swap heads, intakes or carbs to install a better performing cam, but you can while you’re in there.
I would leave your rear end gearing as it is and maybe look at a new camshaft that will produce more torque in the lower to mid rpm ranges.
You don’t want a high lift aggressive cam, because they can kill low end and mid range torque.
Find one that makes torque from off idle through 5000 rpm.
That way you’ll get more pulling power at 70 when cruising at 1800 rpm.
There are many hydraulic roller or hydraulic flat tappet cams that are easy to install.
There is no need to swap heads, intakes or carbs to install a better performing cam, but you can while you’re in there.
Thread Starter
5th Gear
Joined: Dec 2024
Posts: 5
Likes: 1
I have not done any mods, and don't know of any. From the block tag, it's 2003 ZZ454 from GM Performance. The car was an original 427 400HP tri power, and whoever swapped engines, kept the tri power on it. Those 3 Holleys are a PITA, but I dig them, in a nostalgic kinda way. This car is my childhood dream car. It's a big block, tri power, side pipe, 4 speed (well, now5 speed) coupe. The only box that isn't checked is that it's Monaco Orange, and my dream car is black. I'm really leaning towards leaving the rear end alone. For now, I plan on driving it this summer and deciding later. Cam does sound like a better option. This is my first big block car, so I'm still learning. I'm also recently retired, and have a very good friend who is been a car guy his whole life and is rapidly turning me into one. I'm learning fast, that once you go down the rabbit hole, there's no escape. 
I want to do the Borgeson steering upgrade and Wildwood brakes. And,and,and.......
I want to do the Borgeson steering upgrade and Wildwood brakes. And,and,and.......