MONTE CARLO GEAR RATIOS... Huh?!?!

[The Last Don]

Hello. The previous owner I bought my car from tells me the car has a rebuilt 350 with a rebuilt turbo TH400 transmission and a limited slip rear end. I want to get a posi rear end installed - I want to do it myself - I need to understand how the gear ratios work. Can someone break it down for me?

 

[Mike Geepers]

Hello. The previous owner I bought my car from tells me the car has a rebuilt 350 with a rebuilt turbo TH400 transmission and a limited slip rear end. I want to get a posi rear end installed - I want to do it myself - I need to understand how the gear ratios work. Can someone break it down for me?

Higher the gear ratio, more torque produced, higher rpms. Lower gears, more for mileage. I got all into it when i wanted to posi up my mc. Check this out, mite help https://gbodyforum.com/threads/10-bolt-3-series-posi-unit-will-it-fit.35075/

 

[Qdub24]

"Posi" was GM's marketing term for a limited-slip differential way back when.

www.ringpinion.com/TechnicalHelp/contentframe.aspx?filepath=~%2fcontent%2fparts%2fgeneralinfo%2f%2fstandard_carriers%2c_positraction_and_limited_slips%2c_locking_differentials%2c_spools_and_mini-spools.inc

 

[fleming442]

Not a beginner project..... if you do tackle it, do as much research as possible on setup first. Then, get a shim kit and the special tools.

 

[ham1974]

I am contemplating doing the same thing as far as learning how to set up a rear end. I have two parts rears in my garage going to us as practice.

 

[fleming442]

I fancy myself a pretty fair amateur wrench, but that was definitely a frustrating experience. 2 things to note: reuse the pinion shim, and if using aftermarket gears, you will probably have to swap sides with the carrier shims. I never got to really reading the pattern- I had to call my buddy in to bail me out.

 

[Bonnewagon]

First- identify what you have. Limited slip- posi-traction- same thing. Open the cover and take a peek. Verify what kind of carrier it is and if it really is a posi then there are several kinds. Count the teeth on the pinion and ring gear to verify the ratio. If they are GM gears then the count will be stamped on the face of the pinion gear as well as the edge of the ring gear. You may have an optimum setup already. Anyone who put a rebuilt 350/400 in there may have done the right thing all around. If it is not- then you have 3 options. Get a whole rear and swap it in- easiest. Get a shop to build it up- costliest. Get a GM shop manual and read the part on rear end gears- buy the tools- get greasy- smartest. Be warned though- this is no job for amateurs. Read, read, read. Ask questions. Be prepared to fail miserably. We will help all we can.

 

[pontiacgp]

If you want to do it to say you did it then go for it. But for the tools you need for that job to set up the rear and to crush the sleeve and the amount of time to learn how to do it isn't really worth it unless you plan to do a few of them.

 

[The Last Don]

This sounds like a big job... I may need to re-think this one... I will find out more info on everything the previous owner did first.

When I was on the freeway this last weekend I put my foot into it and it didnt kick down. I am getting ready to start researching what the problem may be... Hopefully something not to difficult... Here is some of the feedback I got from the previous owner.

 

[UNGN]

Put a floor jack under the center of the axle. Block the front tires. Jack it up. With the emergency brake off and the car in park and both tires in the air, try to spin one of the tires by hand.

If it doesn't spin freely, you have a posi.

Turbo 400's don't use the same kickdown process as the factory trans (200-4R, TH350's, 700R4's use a TV cable). TH400's use a switch. You need a TH400 kickdown kit. Check summitracing.