1968 Rear End Work

[NosAvrenim]

Hope everyone had a very merry Christmas and is enjoying the last days of 2011. Just got back from a trip to a cabin in the woods of western VA where we don't have any cell or internet access. Felt so good to completely disconnect for a while, though I am now having to catch up on emails and forum posts. Will send pics of the cabin/views when I can.

As I get ready for 2012, I'm about ready to pull the tirgger on a (Eaton) Detroit TrueTrac differential for the rear end and am considering changing the rear gears at the same time. Figure, we'll be in there putting in the diff, so might as well do the gears while we're in there.

So I have two questions for the experts:

1. Has anyone had experience with Richmond gears? I've heard good things about them, but wanted to check here first. If anyone has other recommendations, please let me know.
2. I'm considering either 3.5, 3.7, 3.89 or 4.11 gears. Currently, I have 2.75s in and while puts out solid torque, I'd love to have a bit more.:thumb: I'm leaning to either the 3.5s or 3.7s since I do drive her as a daily driver and I don't want to spend a fortune on gas (I'm already getting only 10-15mpg in a X code 390 converted to 4bbl). Any suggestions/thoughts? Would the 3.89s or 4.11s just be overkill? I know that this is always a hot topic - particularly when it comes to mpgs, engine size and overall "experience/feel" - and that there are lots of threads all over the internet on the topic. Just curious what the good folks here think.

With this done, the last big project will be finally installing an A/C system. I just can't do another summer without it! :tongue: Well, let's just say the last big project for which I'm currently saving $$.

 

[di81977]

What tranny do you have in the car, assuming C6, and how tall are your wheels and tires? Also, you planning on doing any highway driving, or just around town with an occassional romp over 65MPH?

Personally, I would not go any higher than 3:55's (unless your tires are pretty tall). That is what I had in my old HCS and it was pushing the RPM's, but still acceptable at 65+ MPH. I was probably less concerned with the amount of RPM's and more annoyed with the noise of the engine/exhaust when driving on the highway.

I am guessing, but might be wrong, that with a stock big block, you probably don't want to be turning too many RPM's for an extended time.

You will get different results with a manual vs an automatic. My 4spd Corvette has 3:73's and the RPM's are about 50% of the MPH (i.e. 70 MPH turns about 3500 RPM's). My current 68 Mustang has 3:73's but I have an AOD.

What ever you do, you will see a signifcant performance increase from your current set up.

Have fun
David

 

[JohnnyQuest515]

Hey Nate! Funny I was going to do almost the same thing with that car. I wouldn't go beyond 3.50, my Shelby has it and appears just right.

There is a guy on ebay that can make whatever you want, turnkey for under 2 grand. Not sure if they are richmond setup. Unless you change to a AOD, driving any highway speeds would not be good unless you doing drag strip all the time. That car has so much torque, going too high will be impressive for the kiddies watching burnouts but not much use around town.

Randy

 

[franklinair]

3.50 would be my choice. Rob would probably choose a 4.11, but he can't be trusted:icon_lol:
For the A/C: Are you looking for a used factory setup, or going with a new aftermarket system? Classic Air in Tampa, FL sells a good system. I'm converting my old one lung compressor to a new rotary & R-134 freon.

Neil

Alexandria? My daughter & family live there. Next time I make a trek up there, I'll give you a heads-up, and we can finally meet.

 

[robert campbell]

Actually for this setup and driving purpose........ Gasp... 3.50 would be my choice. With a big block, I might even consider 3.25 cogs.

Tire diameter, as David said, can make a big difference. If I had stock diameter tires, 3.5. And if you are using a lower profile, 3.25.

Rob

 

[CougarCJ]

The company that supplies our rebuilt traction locks uses new Richmond gears for 8 and 9 inch rear ends. He has tried others, and Richmond has the highest quality, and is the quietest.

 

[NosAvrenim]

@ David/Rob -- I have the original C6 tranny still in the gal but had it rebuilt and a shift kit put in (it sure makes a difference! :thumb. Current tires are 225/60R15 radials. Since I do drive her quite a bit (when I'm not traveling and am actually in town and not carting the wife/kids around), I will be doing a mix of highway/city driving. Still thinking 3.50/3.55s or would 3.25s be a better choice?

@ Randy -- You're dead on about the torque right now. I may regret it later when I have to keep filling her up, but I did swap out the stock gas tank for a 22gal one ('70 model) which should reduce the frequency of fill-ups a bit. We do have a strip across the Potomac in MD (same one that was used during the MCA GN) that several friends have been asking me to head to, so some very occasional strip use might be in the future -- but highway/city driving will be more typical.

@ Neil -- I have been looking at Custom Auto Air's Perfect Fit system for a while and it'll likely be the route I take. Since I'm not wedded to a strictly concours restoration, I'd prefer the performance of a modern system. Likely, I'll also swap out to an electric fan and improved radiator at the same time to reduce overall load on the engine. If you do make it up to NoVA, please do let me know. Would love to meet and learn just a few of the tricks that are making your Highland Green CS restoration so top-notch!


Just out of curiosity (because I really haven't heard of anyone recommending it), does anyone suggest just sticking with the 2.75 gears?

Thanks all!

~Nate

 

[robert campbell]

2.75..... gag.... puke... Well ok, if you live in Germany and want to compete on the Autobahn.....

Rob

 

[NosAvrenim]

2.75..... gag.... puke... Well ok, if you live in Germany and want to compete on the Autobahn.....

Rob

Yep, that's pretty much the response I was expecting to get back. :icon_lol:

 

[davidathans]

The company that supplies our rebuilt traction locks uses new Richmond gears for 8 and 9 inch rear ends. He has tried others, and Richmond has the highest quality, and is the quietest.

that is the opposite of what i've heard about Richmond gears LoL

 

[NosAvrenim]

Wow...just checked in on this thread and it's been a while since I first considered regearing.

Well, like many things this project was postponed by a new job in 2012 and a new home in 2013. I did, however, manage to squeeze in the A/C project in 2012 (just couldn't take the scorching summers anymore). Here we are in 2014 and I'm finally getting around to completing the rear end project.

Just ordered the Eaton TrueTrac, Motive 3.50 gears, Timken bearings, etc. and they should arrive by week's end. By mid next week they should all be in the gal and by the 17th I'll enjoy getting thrown deep into the seats by all the new torque :grin: (certainly not by a heavier wallet! ).

Thanks, again, for all the input on this project. I'll definitely provide an update once I get a sense of the performance and mpg impacts.

 

[NosAvrenim]

Picked up the CS last night and from what little I drove her, the rear end is running great. Haven't put her through the paces just yet. I'll certainly know more after the break-in period and when I swap out the gear oil.

One thing that I noticed was just how off the speedometer was. I was expecting it to be off, but not by that much.

To correct the issue, I'll need a 21 tooth RH gear (based on my calculations). Trouble is there are Type 3 & Type 3a gears (both 21 tooth & RH). The only difference seems to be the length of the pilot shaft. Any thoughts on which to use in a C6 tranny? At present, I'm planning to order one of each and figure it out. That said, I know someone on the forum has gone through this before and can spare me the trial & effort.

Thoughts?