changing 3:08 to 3:70...
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
The richmond, th200R4, and th700R4 have the same tail shaft mounting point. so if you are not a fabricator or welder it is as simple as purchasing a bowtie overdrives or a G-force cross member.
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
With 3.70 gears, you will definitely be looking for an overdrive!!! Unless you intend to cruise on the two lane back roads all the time! I put 3.55 in a 4 speed camaro. Cruising on the interstate in the slow lane sucks after the first 5 minutes and cranking it up to cruise in the fast lane sucks even worse without an overdrive! IMHO 
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
Doing it yourself all depends on your mechanical competency. There are good videos on the web on how to do it. If you have any doubt about your ability, don't do it. They are not that difficult to do, but require a few special tools, time, and patients. You want to aim for perfection, not just good enough.
I built a Super 10 with Richmond 4.11 gears last summer. It required much more time and some machine work for the 12 bolt size cross pin and larger stub axles. I have built differentials since I was a teen (a long time ago), but this one was a springless posi, a first for me. I watched and read everything Gary and Tom (Tom's Differentials) had on the web. Even old dogs need to learn new tricks sometimes. I have a machine shop too. You would have to outsource the machine work if you don't have a mill and lathe.
Gary and Mike mentioned in a previous post have excellent reputations and one of them would be who I would send mine to if I couldn't do it myself. Whoever you send it to, tell them your power level and if you plan on upping the power later so they know how beefy the diff should be built.
And yes, you will definitely feel the difference in gearing.
I built a Super 10 with Richmond 4.11 gears last summer. It required much more time and some machine work for the 12 bolt size cross pin and larger stub axles. I have built differentials since I was a teen (a long time ago), but this one was a springless posi, a first for me. I watched and read everything Gary and Tom (Tom's Differentials) had on the web. Even old dogs need to learn new tricks sometimes. I have a machine shop too. You would have to outsource the machine work if you don't have a mill and lathe.
Gary and Mike mentioned in a previous post have excellent reputations and one of them would be who I would send mine to if I couldn't do it myself. Whoever you send it to, tell them your power level and if you plan on upping the power later so they know how beefy the diff should be built.
And yes, you will definitely feel the difference in gearing.
Thread Starter
Le Mans Master
Joined: Jul 2003
Posts: 7,501
Likes: 1
From: Maine
hmmm I didn't realize changing the trans might give me the same end result... I just wanna be able to realllllllly smoke the tires off the line... I never drive on the hiway.. maybe a few times a year and I have sidepipes so its loud anyways...
Le Mans Master
Joined: May 2002
Posts: 5,086
Likes: 787
From: Lebanon Township New Jersey
Since hi way driving is not an issue, there is no downside to changing rear gears. Have the 3.70s put in for half the cost of a trans, or less. Use the money you save for tires.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
If you have 308 flywheel HP now.
The trans change makes first gear feel like 456 hp.
The differential change will make it feel like 370 hp.
Safety Car
Joined: Nov 2008
Posts: 3,726
Likes: 558
From: Seattle Washington
I would like to go the other way with my gear ratio. When I bought my 1969 427 390 hp the owner said that the rear ratio was changed to 4.11. I would like to return my car to the original ratio. I was thinking 3.36? Not really sure. The owner gave me a set of gears and a posi unit. I have no idea what ratio they are or if any of it is worth keeping.
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Instructor
Joined: Oct 2006
Posts: 127
Likes: 0
From: Monroe Washington
Rebuild the Diff
J
Here is an article Stinger 12 wrote Check it out.
http://forums.corvetteforum.com/c3-t...ild-paper.html
Ron
Here is an article Stinger 12 wrote Check it out.
http://forums.corvetteforum.com/c3-t...ild-paper.html
Ron
Team Owner
Joined: Jul 2004
Posts: 40,420
Likes: 792
From: Redondo Beach, California
My 68 with a stock Muncie and a 3.73:1 would spin about 3000 rpm at 60 mph ....just really hated the engine speed at such low freeway speeds...the engine was just wearing itself out.
I installed a TKO 600 5 speed overdrive tranny...now I turn 2000 rpm at 70 mph and have a tremendous first gear. Can light up the wheels in first gear and still cruise with a very economical, quiet, engine non-wearing speed.
.............
If you have a 3.08:1 diff, you need to buy a Richmond 5 speed. They have a 1:1 in fifth gear, with a sort of bull dog 1st gear. The TKO won't work with a 3.08:1 diff.
I installed a TKO 600 5 speed overdrive tranny...now I turn 2000 rpm at 70 mph and have a tremendous first gear. Can light up the wheels in first gear and still cruise with a very economical, quiet, engine non-wearing speed.
.............
If you have a 3.08:1 diff, you need to buy a Richmond 5 speed. They have a 1:1 in fifth gear, with a sort of bull dog 1st gear. The TKO won't work with a 3.08:1 diff.
