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Discussion Starter #1
Hey guys,
I have a question and im just looking for advice before I make a decision

I have 67 with a mildly built 302. AFR 185 heads, Air Gap intake, headerss, SoT strut rods and a Edelbrock Performer Cam.

The purpose of the car is to cruise around in and have fun, but also to smoke any rice burners that pull up next to me.Im new to the hobby this is the first classic car I have restored oor even ridden in for that matter ( other than a buddies 58 chevy)

My next upgrade is my rear end gearing I currently have 2.79 stock gears. I bought some Accel Richmond gears (3.55) and I have an opportunity to get a complete 3rd member with posi already installed and 3.8gears
I had never heard of 3.8 gears before I thought it was 3.55 to 3.73
I have a C4 tranny with a 2800 stall torque converter and I heard dthat 3.55 is a great gear for quick acceleration off the light but I would hate life on the freeway. And if thas true then 3.8 I assume would run about 400 RPM higher ( even though I dont plan on doing much freeway driving)
So my question is Should I stick with the 3.55 gears or go ahead and go for the posi unit with 3.80 gears.
I dont want to install the 3.55 gears and wonder down the line if I should have installed the 3.80.
I know what Posi is but tI dont know if I will even notice its presence or absence
Eventually I may upgrade to a AOD, and a 408 stroker ( but thats way down the line)
BTW. I was told by an installer that these Accel gears are junk and make noise, has anyone ever heard that or had that experience.
 

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Posi is a Cheby term, Trac Lock is what Ford used. If you really are going AOD the 3.80 would be better. I had an 89 with 3.73 gears and the AOD, great take off and freeway was good. With a C4 I think the 3.55 are better suited but if you really are doing no freeway driving then the 3.80 should be fine. A 408 is a torque monster and you would don't need as much gear, a 408 would be fine with a 3.25 since so much torque. You might also want to verify what Spline the carrier has as our stock ones are 28 spline and you don't want to get a 3rd member that has 31 spline which means you would have to replace your axles. Definitely wants a trac lock to spin both tires, don't want to be doing a 1 legged peel out especially since you are starting from scratch. I guess the question is being realistic how long do you plan on staying on your current combo to see which gears would be best, since 2 totally different combinations?
 

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Discussion Starter #5
IMO you will quickly become unhappy with a 3-spd auto & anything >3.50 gears.
Why do you say that, is it because of the higher RPM's.
I guess my justification would be its mostly street driven and if i get annoyed, I will be forced to get the AOD sooner rather than later. DARN.... I have to buy more parts for more car >:)>:)>:)
 

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I second the thought that 3.55 is probably the best with a C4.
When you upgrade to a better gearbox, go for a 4R70W. The wide ratio gearset will make the 3.55 act like 4.11s in first and second.
 

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I see you live in LA. I'm south of you. You say you won't do much freeway driving...that's kinda hard to do in LA. I would not go with anything greater than 3.55s with a trans that doesn't have overdrive. Going from 2.79s to 3.55 will make a huge difference.



I have a T5z and changed from 3.50s to 3.89s a while ago and i'm still debating whether i should return to the 3.50s. Haven't drivin the car a lot yet since I got the 3.89s so maybe I just need to get used to it. With 3.50s, it had a real nice sweet spot that it liked to cruise at 70-75.
 

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Discussion Starter #10
I have 17 inch tires 235/45/17 not sure if thtats like 25 or 26 inches.
I do Live in LA but im not part of any car club or cruise night.

So the general consensus is stick with the 3.55's

It just seemed like a sweet deal its
$300 to get the 3.55's installed in the pumpkin
or
$600 to buy a rebuilt pumpkin with posi and 3.8 gears
 

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When my mustang was my daily driver it had a C4 and 3.70 gears.
I didn’t mind it at all. Even at highway speeds over long distances.
75mph was about 3700 rpm.
 

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I have both a 3:55 and a 3:80 trutrac, have run both with a 2500 stall C4. Street wise, the 3:55 is much more driver friendly around town. The 3:80 is roughly a 400rpm increase. At 65 with a 235/45/17 I'm at 3200rpm w the 3:80. The engine is happier with the 3:80 but knowing LA (Huntington beach) the 3:55 will suit your needs better. Over course on a separate note, LA freeways don't move anywhere fast...so it doesn't matter what gear you use.
 

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I have 3.89 gears with a Truetrac and a T5z 5-speed sitting behind a 347 stroker. I absolutely love this combo. It runs about 2200 rpm at 70mph.

That being said, if I didn't have an overdrive gear, I'd probably go for the 3.55 gears.

-Shannon
 

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Seems most are running a 25" tire so... If it's a driver and it doesn't have over drive I would stick to 3.42 range and lower (numerically) if you have over drive then going up is OK.

If it's a weekend fun car and rarely sees the freeway then go with whatever you want.... Personally I don't like a V8 spinning nearly 4K just to cruise down the freeway. But it also depends on your freeway speeds. Here you figure freeway speed at 75-80.... So high 3.XX or 4.XX gears will spin the crap out of an engine at 75. Course if you are used to driving something like a 90s Miata that spins over 3K at 60..... (that car was a horrible driving experience that no one should have to endure)
 

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Discussion Starter #16
I have both a 3:55 and a 3:80 trutrac, have run both with a 2500 stall C4. Street wise, the 3:55 is much more driver friendly around town. The 3:80 is roughly a 400rpm increase. At 65 with a 235/45/17 I'm at 3200rpm w the 3:80. The engine is happier with the 3:80 but knowing LA (Huntington beach) the 3:55 will suit your needs better. Over course on a separate note, LA freeways don't move anywhere fast...so it doesn't matter what gear you use.

Well this is a new one,,,, why do you say the engine is happier with the 3.80
 

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With regard to the differential type, with your engine setup a 3.55 open rear end is going to be a real tire spinner. You most certainly would notice the difference between an open rear end and T-lok type rear end with regard to off the line traction.
 

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I certainly wouldn't be happy with open 3.50 gears. Get the 3.80's and enjoy spinning it till you get the OD tranny.
 

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If you don’t end up going with the 3.80/limited-slip, I’d be interested in buying it from the seller. $600 seems like a fair price. Let me know, please. Thanks!
 

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Discussion Starter #20
20 posts and I am still no closer to a decision. Even the people who say go with the 3.55's say the 3.8 is also is a good choice lol.
 
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