Thread: Rear End question

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I have just purchased a new differential off a place that was closing for 300 bucks...CHEAP. It is a 4.10`s, posi. Now, i have a 91 chevy caprice with a 305 TBI, and was wondering how bad it's going to be on gas, and how bad is it going to affect my top speed. I have a 700R4 as a tranny, and don't know if it's going to put up with it. Now from my knowledge, this car will probably go down the highway @ 100km'h, revving up to 3500-4500 RPMs. I did't install the diff yet, but i know that the one i have now is a 2.56 granny ratio, one wheel burnin' diff. It will probably make a world of difference at low speeds, but at top ed, it will probably be a drag on gas. Any suggestions or comments would be appreciated. Thanks

Seems you should have asked those questions before you bought it. The 4/10 will probably cut your milage by at least a third.

Thing is, i knew they were cheap, and that it was a posi and that it would fit my car, so i said, why not. Even if i don't use them, i could probably sell them for 600. Its a brand new auburn!! I have never had new gears on my car, so that's why i'm asking all these questions. I don't know what experiences i'll run into. Is there a chance that it would go past 120 on the highway, because i have a buddy that runs a 3.55 posi, on a 93 dodge dakota with a 5.2 and no major mods, and goes past 180km/h no problem.

you say you have the 700r4, so it want be all that bad with the overdrive. my truck 700r4,4:10 gear@60 mph tunes about 2600 rpm's. i get 20 mpg. hard to have a lot of power and gas mileage. low gears and hi speed dont mix, unless you have a good motor.

You mean, how soon i'm planing on overhauling it or cracking the block? I want to have a lot of fun, even though the car weighs 2.8 tons, it hauls its own weight pretty good. It's the original 305, with 327000kms on it, never been overhauled. Lifters tick, a/c clutch squeals like a bitch, and it's not the nicest caprice out there, but it makes me happy. I plan to getting the body work done by september.

That S10 of yours has the LT1 tho. It probably would work at higher rpm's anyway. As for the 700r4, i was thinking the same thing, but my block originally had 180hp, and i pumped it to about 250, with the air intake, exhaust, fuel pump, and a few other things. I'm planning on dropping a hot cam in it, but, i don't know how well that's going to work with my computer.

Originally Posted by vdorobantu

That S10 of yours has the LT1 tho. It probably would work at higher rpm's anyway. As for the 700r4, i was thinking the same thing, but my block originally had 180hp, and i pumped it to about 250, with the air intake, exhaust, fuel pump, and a few other things. I'm planning on dropping a hot cam in it, but, i don't know how well that's going to work with my computer.

hi mileage 305,4:10 gear,120mph=

yeah, i thought you might say that, but hey, you know what, i am planning on another engine(350) and maybe a shift kit and an overhaul for the 700r4. I am only 20 yrs old and am an apprentice, so if it blows, let it blow, i'll get a camaro or something and swap engines, because i just love the caprice!!! Domestics all the way!!!

Originally Posted by vdorobantu

yeah, i thought you might say that, but hey, you know what, i am planning on another engine(350) and maybe a shift kit and an overhaul for the 700r4. I am only 20 yrs old and am an apprentice, so if it blows, let it blow, i'll get a camaro or something and swap engines, because i just love the caprice!!!

Domestics all the way!!!

i'm with you there.!!!

93 caprice here. i do lots of highway, but getting it to launch from the stoplight with the granny gear and 3700# takes some pedal.

if you change the rear to 4:11 and don't like it, you can always add 20" rims to drop it back, just have fun trying to stop

What do you guys think i should do about that lifter tick that i get?
get a new cam, or just readjust my rockers? And if i need to readjust my rockers, some info on how u guys would do it would be appreciated!!

I finally got to install it today, and it's amazing!!!! Well, of course, a couple of issues. My tranny goes through gears like a knofe through butter, and my speedo is gone crazy. My old pinion shaft, had a sprocket on it, that the new one didn't have. That was for the ABS sensor, but the new pinion is so much smaller than the old one. Anyway, i don't know how to recalibrate the speedo. Does anybody have any ideas?

Do we have an electrical section for questions on how to install a tach???

You don't have one and you want it installed or what? It's really easy to install. U have the negative wire from the coil, and the rest is mix and match.

The 700/R4 has a 4th gear overall drive ratio of .70. This means that your 4:10 gears are equivalent to 2.88s in high gear. The 700/R4 gives you punch on the low end, and a decent cruise on the high end. The tricky thing about this trans in a specialize application is proper calibration of the TV cable.

With those gears, you DO not want to switch to a TH350. It doesn't have overdrive. Don't switch transmissions. The 700/R4 is a pretty darn good performance transmission. They came stock in a lot of Corvettes.

If your transmission is dragging the engine down when you let off the gas, then the converter isn't unlocking. That's not good.

It feels like my transmission isn't strong enough to spin my gears at high speeds.

I have NO idea what that means.