Finally, I got my Z back with new gears installed after breaking the original gears. I have a 9-bolt rear that had 3.45's until they broke. Now, I got the same rear, but with 3.73's. My question to you guys is: How do I properly break in the new gears?? I was only told to "take it easy with the car for the first 200 miles or so". I was also told that the rear may emit a whining sound until they break in. Is this correct? I haven't drove the car very far since I got it back, but it definately makes some noise back there. Any input would be appreciated.

 

Anybody???

 

What kind of gears did you get? Most aftermarket gears use a steeper pitch for more strength, which causes whining as a side effect. If you got GM Motive gears they shouldn't whine at all once they break in. I'd say give them 200 or 250 miles and if they don't stop whining go back to the shop and tell them to fix what they broke.

 

I have no idea what kind of gears they are, I just know the mechanic had a hell of a time finding gears for a 9-bolt rear. I guess I'll baby the hell outta the gears for a few hundred miles and see what happens.

 

My technique: run easy for 5 minutes, then park and let cool completely. I do that again a couple more times, then run normally for a couple hundred, and consider them broken in. I've never had any problems doing it like this.

 

9-bolt parts are easy to find if you know where to look. http://www.9bolt.com kind of expensive though, $305 for new 3.73s.

 

yeah, I knew about 9bolt.com but didnt know how their rep was so I was kinda skeptical. Anyhow, I just figured I'd get some input from you guys cuz I've always gotten great feedback whenever I've had a question about my Z. I asked about the whinin sound cuz the rear is whining and it seems to get slightly louder when I disengage the clutch when slowin down, etc. I guess I'll just take it easy and hope for the best. The mechanic I took it to came highly recommended so maybe I'm just worryin too much. Thanks for the input guys.

 

I have a 87 IROC-Z with a 9 bolt also, I have 372 in my rearend and it still whines. I was told that there are 2 pins that go into the rearend that can't get as close as it did when they were stock. I beat the hell out of my rearend at least twice a week at the track and have had no problem with the rearend. I was worried about it at first too but all is ok. I guess that all aftermarket gears are going to whine because everybody that I know that has aftermarket gears whine. I don't thimk that it is a big thing. Hope not or i'm going to be replacing some rearend parts. No worries.

 

Glad I'm not the only one with noisy gears. I just hope that after a few hundred miles, I'll be able to have a little fun with her again. I'll probably be a little scared at first cuz, the night I blew the stock rear, I was just cruisin home and decided to have a little fun on a nice stretch of road. I downshifted from 4th to 2nd and as soon as I let the clutch out, I heard a pop sound and then the rear started hummin like a **** and clunkin. I did a little cruisin today, although I was drivin it like a grandma but I did notice an acceleration improvement from the 3.45's I had previously. I wonder how much quicker the car will be (hopefully it isnt slower ). I've been told by some that my car would actually be slightly slower with 3.73's instead of the stock 3.45's. I know I won't have as much top end but I really don't care to go 140+ anyhow.

 

Any other input?

 

Some mechanics from backhome spray water on the cement in front of their shop like a water box and spin the tires after they do gear installs. I always found it quite funny, because everyone always says to break in gears. They have been doing that for years and have never had any come back problems. They also have a low 11 second '69 Chevelle, but spend most of there racing on a dirt track so they no what they are doing.

I guess my recomendation would be to take it easy on them for a while, but I don't know if you would have trouble doing the opposite.

Martin