Gear break in period

[rcdice]

I'm looking to replace my stock rear gear this spring with something a little shorter. 3.45 or 3.55's. I read on this site some time ago that you need to give the new gear a "break in period" of 500 miles or so after the swap before you give it WOT. Is that true?

If so, why? It's a gear, what's to break in? I understand breaking a new engine in, but a gear? Thanks in advance.

 

[FE 065]

When I did mine 7 years ago the local shop said 500 miles with normal gear lube, then change it to Mopar type gear lube and add a little bottle of Mopar friction reducer additive.

500 miles will come quickly don't just hit the freeway either; lots of accels and decels are best.

 

[Steve 00RT/10]

Here are the break-in instructions from Unitrax I got with my 3:45s last year.

"Drive your Viper easy (low RPM) for approximately 30 minutes or 20 miles in 5th or 6th gear. Avoid aggressive starts and hard stops. Avoid long distances at a steady speed. It is critical not to overheat the differential during the break-in period. Running in 5th or 6th will provide a low break-in RPM"

"Let the differential cool for at least 45 minutes"

"Repeat the above step"

"Change the differetial fluid between 1500 and 3000 miles."

I followed this procedure and have had no problems.(12K miles so far) I had also read somewhere that doing doing a few figure 8's in a parking lot (both directions) was beneficial.

Steve

 

[KenH]

I'm not too sure that changing engine RPM through gear selection would have any affect on the RPMs that the differential sees. Perhaps running in a higher gear reduces the amount of load that can be applied to the gear set or something.

 

[Steve 00RT/10]

I'm not too sure that changing engine RPM through gear selection would have any affect on the RPMs that the differential sees. Perhaps running in a higher gear reduces the amount of load that can be applied to the gear set or something.

I believe you're right about the RPMS to the rear end. Overdrive gears would definitely minimize the load to the gears. I'm sure anyone whose gotten a rear end from Unitrax got these same instructions. My rear end was broke in within hours of leaving the shop.

Steve

 

[Snakester]

I didn't do the break-in right with one set of gears and they were ruined in 600 miles (I had to buy a whole new set and try again). It could have been the installation tolerances from the guys who installed them, but for the second set of gears, I followed the break in instructions carefully and had no problems.

The new gears need to mesh properly, just like with new rings and cylinders in a new engine, it's excessive heat and wear than can wreck them if you push the car hard during break-in.

It's a long 500 miles to wait, but better than having to re-do it and have to start over. Still I've installed gears in 3 cars now and it's always been worth it.

 

[Johann]

Some gear makers recommend leaving the car on jackstands (lift) and running the gears at low speed for 5 minutes in both forward and reverse before hitting the road.

 

[CTViper]

I just drove mine normal for a few weeks. Nothing crazy. no problems so far!

 

[rcdice]

Ok. Thanks for the input. We'll break em in easy. Sounds like several cycles without too much load or heat is what's called for. I better get on this early this year as I only drive the car about 1k to 1,500 miles a year. If cycled correctly, sounds like you don't need to necessarily wait a full 500 miles to give them a good test.

Patience was never one of my strong points.

 

[Camfab]

I recently changed my rear end with the complete Mopar Perf. 3:55 Diff. Assembly. I did most of the above including running the car for about 5-10 minutes on jack stands. I went through the gears very slowly and carefully noting any potential vibrations etc.
I got out of the car to take a quick visual underneath the car. I am extremely meticulous about everything but I got caught with my pants down on this one. Mind you the install went perfect, gears work perfect, but get this.
When I carefully got out of the car with the engine running the door gently closed by itself as it always does. Here's the clincher the windows were up and my accelerating through the gears had auto locked my doors. The car thinks I'm driving and my spare remote does not work when the car thinks it's going down the road.
I opened the rear glass and put a clip on a paint pole and was able to shut the car down. Just goes to show you, anything can happen when you least expect it.
Anyway I don't have nearly the 500 mile break-in done and have jumped on it numerous times. No whines no problems that's not typical with aftermarket parts. I too will change the fluids at 500 miles.