rear end ???

83Jason · Posted: Sat May 31, 2008 1:49 am Post subject: rear end ???

Well I am going to look at a rear end out of a 1987 Buick tomorrow. I know it is a 8.5 in and he says it has 3.42 gears. would this be good for my application? I am going to be running a 350 motor with a 700R4 trans. With this ration would the gas millage be good? I am getting it for only $600 so it sounds like a good deal. since I have called every junk yard in so cal and non of them have seen one is about 2-15 years, so they said good luck finding it!! I am looking sometime tomorrow so hopefully I will get some responses before I go to look at it.

Steve81OR · Posted: Sat May 31, 2008 3:54 am Post subject:

Jason,

The higher the gear ratio (larger numbered) in the rear axle the higher your engine's RPM's will need to rev at driving speed. My '81 EC came with 2.73 gears which is a nice highway gear, but doesn't help at the track AT ALL. I can cruise at 60 MPH at 2300 - 2500 RPM's (TH350 trans).

Most guys that set their cars up for racing start with a MINIMUM 4.10 gears. 60 MPH may make the engine run closer to 3200 - 3500 RPM's (TH350 trans). If gas milage is an issue, this would not be your best choice.

I've always thought of 3.43 - 3.73 gears to be a nice middle ground of power and economy (maybe tilting a bit to the power side). You should expect to cruise at around 2800 - 3200 RPM's at 60 MPH (TH350 trans). With a 700R4 (4 speed) trans it will reduce the RPM's even more at cruising speed.

I would also check to see if this is a posi rear end (both tires will spin the same direction with the rear axle off the ground). If so, that will be quite a find.
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464elky · Posted: Sat May 31, 2008 7:26 am Post subject:

I'm running 3:42's and in overdrive at 75 I'm turning 2250 rpm HTH. It is a pretty nice setup with the 700r4 and the 3:42.
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83Jason · Posted: Mon Jun 02, 2008 10:20 pm Post subject:

So I went and looked at the rear end. We pulled it out of his Grand National and loaded in my truck and I gave him the $600 and he told me that it is $900 so I didnt buy it because I didnt have the money. So now I have the money do you guys think that $900 is a good price. I think it is. The rear end is out of a 1987 Buick Grand National and it is a original posi with 3.43 gears and when we spun it it was very smooth. so it is what I need. just wanted to see what you guys think about the price?

CoyoteOn2 · Posted: Mon Jun 02, 2008 10:55 pm Post subject:

The price is good if that's what you want to pay. Only YOU can answer that. And your the one that "needs it".

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Ebbsspeed · Posted: Mon Jul 21, 2008 4:47 pm Post subject:

I bought one at a swap meet here in Kansas City this spring for $400, so to me that $900 number is WAY high.........

I think $700 is more like the going rate, but if you gotta have one now, then you'll have to pay the price. If you can wait, chances are a better deal will come along.

Redster · Posted: Wed Jul 23, 2008 8:29 pm Post subject: Build Option

OK there is another route. Don't go looking for a rear end w/ the gears you want etc. Just look for a rear housing (preferably 10-12 bolt) 8.5". Then buy the gears (ring and pinion) and have someone set it up for you. admittedly I know a guy who messes w/G-bodies and got a rear for $100. Gears $130 - 180 all day. Pay someone at a shop to set it up for you (pays to have friends there too). clean and paint yourself. Posi is extra. Mine came out with new gears, bearings and seals for <$600 (w/o posi)
As for the ratios, do a search on google for 'rear gear calculations'
and plug in your numbers. You will have to know your tire height.
Good luck and hope I haven't confused you. Texas Flag

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elcamino74guy · Posted: Wed Jul 23, 2008 10:48 pm Post subject:

The other thing to be aware of with GM limited slip rear ends is that they use a cone system instead of gears (like a locker or full posi) After awhile that wears out (especially if you race it) and you end up with a peg leg rear end. You can fix it but most people just go out and get another rear end setup.

Anyway, be aware of that.

Happy

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