The 4.56 rear gear gives some really nice acceleration, but highway speeds for any length of time are really impossible, so it's gotta go. This evening I did the first steps of putting the car on jack stands and pulling the cover off the differential. I need to identify the carrier as a 4-series before I order the new 3.73 gears from Big-Gear-Head Freddie. How do I identify a 4-series carrier from a 3-series? The rear axle tube is stamped "BW" and the gears inside are GM, so it all may be original stuff, which would most likely be the 4-series.

This is my first time changing out rear gears so it could get interesting. One thing that I am really concerned about is the 300 lb of torque necessary to crush the new crush-bearing from under the car with the two Flowmasters on either side of the yoke. I personally cannot even lift 300 lbs, heck I don't even weigh much more than half of the 300 lbs. Perhaps some of you can share your experiences.

By the way, I do plan to keep the 4.56 gearing and spacers so that it can be reassembled as original at a later date.

Thanks,
Andrew

The carriers have different casting numbers.
A 3-series will be EDB 30140 and a 4-series will be EDB 30174.

IMHO, I would leave the "BW" rear complete and set it aside, and build a different 3.73 rear from scratch. The BW coded rears are fairly hard to find.

Additionally there is nothing wrong with a 4.56 gear on the street I have been running that ratio for years. The difference of course is I have an overdrive transmission that knocks the 4.56 down to a 3.21 rear gear in OD. That way I have the best of both worlds (what little economy that can be had from a 582 BBC and steep gears for acceleration: or tire smoke which is more common).

Larger Dave

[QUOTE=L72/RS;814195]4-series will be EDB 30174.

IMHO, I would leave the "BW" rear complete and set it aside =QUOTE]

4-series it is, and the ring gear is stamped "GM". Maybe you are right, it really is a shame to take this thing apart. I think I am going to put the change out on hold for now. Since I have removed the cover, should I change to a synthetic oil or something different than the GM mix when I fill it back up?
Also, I ofter hear of a differential vent, but I cannot find one or a place for one. Where should it be?

Thanks,
Andrew

Also, I ofter hear of a differential vent, but I cannot find one or a place for one. Where should it be?


Yes, the vent is located on top of the axle housing however I can't remember what side.....The vent has a cap on top of it.....Your cap is probably missing which would explain why you can't find it!:thumbsup:

The vent is on the right (pass) side. It is in the cast iron part of the housing just up from the right axle tube. It is about 1 inch tall and will be made of plastic with a cap on it. Be sure that it is clean. You can pull it out of the housing and clean it, but be sure that the dirt around it is cleaned off before you remove it.

If you are not going to rebuild the rear end then I'd go back with the same oil that was in it. I don't know if changing would be the right thing to do.

The vent is there, I just wasn't looking at the right place. I'll give it a good cleaning before replacing the cover and refilling it with the fresh GM lubricants that I picked up yesterday. Does it just pull straight out?

Thanks again Freddy.