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Discussion Starter · #1 ·
Well I've been holding off on changing the gears on my Impala but now with the 22's and a 3200 stall I would like for my car to feel torquey again and I'm thinking about going this route but am unsure wether I will need a new drive shaft or not. I have called two places here in the Chicago land area. One being Speed Inc and the the other one being Finish Line Performance. I have heard great things from FLP so I'm thinking about going to them, they are a littlte bit pricey but I'd rather pay for a great service. FLP told me that I will not need a new drive shaft however I have heard from some members that I will need a new drive shaft Is this a hit or miss type thing? Any luck from my Chicago Brothers with their gear install?
 

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It can be hit or miss. Buffmans car didn't have any vibes with 3.73's and a 26/27" tire. I think he had it up to 120mph. On the other hand, my 96 Caprice would vibe like crazy at 70mph with 4.10's, and a 29" tire. The overall RPM at 70mph, was virtually the same, so it wasn't the gear difference. The 9C1 driveshaft was just rusted to hell. I have heard of guys fixing a vibe issue, by buffing all the rust off. Would be worth doing before the gear swap.

I would keep in your head, that you NEED to do a driveshaft. If it turns out you don't have vibes, consider yourself lucky, and save that money.

The lower gears make a big difference with a high stall. My 3400 felt spongy with 2.93's in my Roadmaster. Put it in the Caprice with 4.10's, and it felt MUCH better.
 

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I had my ds rebalanced. Also, if you're looking for a reputable shop that could save you a coin, give Mike @ Transpro in Lansing a call 708-895-0003. I had them rebuild my 4l60e, install an Auburn unit and 373's. He's a great guy to deal with and very knowledgeable. I'm not too sure about Speedinc, but right now what I feel about FLP aint too good.... But thats for another topic. Just be sure to get the correct reluctor for the 373's or else the abs wont play nice.
 

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the guys who luck out and have no issues with vibration when going to lower gears are very rare. count on needing a 3-3.5 inch driveshaft with 3.73's.

don't even waste your money re-balancing your existing one.
 

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I had no issues/vibrations using my stock drive shaft when I went to a 3.73 gear ratio. I'd try it first before spending the coin on a new D.S.
 

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I had some vibration with my 3.73's, not terrible and not until about 70 actual mph (100 on the speedo).
The driveshaft shop replaced my joints, straightend and balanced the shaft... now it is smooth.
The shop owner did recommend a custom driveshaft in the future.
 

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Discussion Starter · #8 ·
ok heres my question now, lets say I do get vibrations from my driveshaft, where could I turn for a new driveshaft? Or who re-balances driveshafts? I took of my driveshaft when I did my trans and I don't see how you could balance it, I mean it has four bolts to the diff and then it slides on to the trans. What am I missing out on?

thanks for the replys
 

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Count me in for the lucky bunch. I've got 3.73's no vibrating since putting em in couple years ago.
 

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I think the vibe issue is a 50/50 thing. I have yet to hear anyone explain why...all you hear is that the DS is spinning faster....BUT they can't explain why the vibe comes in at a LOWER RPM...If I can run 140+mph with no vibe, and go thru the gears up to almost 6k RPM in 1st, 2nd, & 3rd with no vibe, then it makes no sense that you would have a vibe at MUCH lower speed even if the DS is spinning a little faster...I believe it is the gear install/ set-up &/or pinion angle that causes most vibe issues.
 

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Just plan on a new driveshaft and put the gears in. Any small vibration will eventually affect something in the drivetrain which will cost you down the long run.

Basically. If you can justify the cash for a new driveshaft. You'd better wait.
 

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Just try a google search in your area for "driveline repair", that should start you in the right direction. cwm1

ok heres my question now, lets say I do get vibrations from my driveshaft, where could I turn for a new driveshaft? Or who re-balances driveshafts? I took of my driveshaft when I did my trans and I don't see how you could balance it, I mean it has four bolts to the diff and then it slides on to the trans. What am I missing out on?

thanks for the replys
 

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I had no issues/vibrations using my stock drive shaft when I went to a 3.73 gear ratio. I'd try it first before spending the coin on a new D.S.
Same here,but I will still be going with a dennys aluminum when $$$ permits..
 

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I didn't experience any vibration when I upgraded the 9C1 rear to 3.73s with the OEM driveshaft.

I bought a new Dynoshaft just to be on the safe side. Like others wrote it's a 50/50 chance.

As far as driveshaft rebuilding & balancing I'd look for a 'Drivetrain' shop. They're usually businesses that do nothing but driveshaft, axle, spindle, CV joint repair. The one I used in Austin was just 'Austin drivetrain'.
 

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I was skeptical too as I posted a number of times but 3.73 is really the least offensive gear you can get, in fact you need to throw lots of torque at that heavy beast. Especially if you have it loaded, or you tow something. The MPG difference is pretty minor, probably 2mpg between 3.08 and 3.73. And none in the city and a mountain terrain.

No vibration in mine. No idea if the PO replaced the driveshaft or not.

Also keep in mind your tire size will change your gear ratio. For example I run 3.73 but with a 28" tire (255/55/17) meaning that I get a slightly lower ratio, closer to 3.60.

Bottom line, 3.73 is likely the best choice for you.
 

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I recently went with 3.73's and I don't have any vibration at all at any speed. My car had 37k miles at the time of the install, so all of the markings on my car are real clear. There was a factory painted line (looked like a white grease pen) on my DS and the pinion shaft. I just made sure that the the lines matched back up so I wasn't 180* off. I have since put about 1500 miles on the gears and no problems.

It wouldn't hurt to try your stock DS before dishing out $400.00 - $500.00
 

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I personally added it in to the budget.

I researched around and ended up buying a new one from Dennys.

I also opted for the driveshaft saftey loop to keep it purdy if something breaks :)
 

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ok heres my question now, lets say I do get vibrations from my driveshaft, where could I turn for a new driveshaft? Or who re-balances driveshafts? I took of my driveshaft when I did my trans and I don't see how you could balance it, I mean it has four bolts to the diff and then it slides on to the trans. What am I missing out on?

thanks for the replys
Dennys is where most get their driveshafts

"rotational mass" is part of the equation when going to lower gears as a wider diameter DS helps eliminate those at the new higher RPM's the DS is spining

a good driveline shop can balance a DS....but very few have the machinery to do it at the RPM's needed. Denny's has one of those machines.

do the gear swap...you will find out in very short order if you need to address the DS...most do.
 

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Discussion Starter · #20 ·
Wow putting these gears in is going to be quote expensive! So far just in diff parts I am
Lookin at $850 plus install and if I have to buy a driveshaft then it adds another $400 ish! I am running 22" inch wheels on tbe car but i might end up going back to stickers. I'm not liking the additional weight of te big wheels.

Thanks for the responses
 
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