Gear break-in period?
 

I am getting my 4.10's put in tomorrow, and ditching the 3.55's. I am supposed to go racing on Sunday, so I want to make sure I get these egars broke in first. Is there a "proper" way to break in new gears, or do they even need to be broken in? I will have most of the day friday, and all day saturday to break them in. Just thought I would see what needs to be done.

Thanks
Chris

Just go out and put a few miles on them ... don't go a constant speed ... accelerate some and deccelerate some. I wouldn't creep ... real slow high pressure movement is hard on new metal surfaces. Just go drive it.

Correct break-in as listed in the Ford mechanic manual is as follows. No hard throttle for 50 miles, No downshifting that could cause rearend to lock- up. Drive for 10 miles to get oil to temperature then allow oil to cool before driving additional miles. All of this is to allow the oil to help temper the gears. Now I have done this because I didn't want to take chances but 99% of everyone that I know it is never done and they have not had any failures with FMS gears.

I got 3:55 gears put in years ago and the shop (now out of business) never mentiooned a break in procedure for gears and thank fully I have not had any problems.

Chuck 88GT

This is a story from the flip side of the coin. We installed my gears then I drove the car for a quick test run. Everything seemed fine. I let the car sit for a few minutes then I drove the car back home to my house which was 60 miles away. I took it very easy on the car, but it was a non-stop trip. After a couple weeks I noticed a vibration coming from the rear. We pulled the cover to find that one of the teeth on the ring gear was chipped at the corner. It wasn't in the mesh pattern so it was ok, but the gear had been warped. We found 2 bolts right were the tooth had chipped that were no longer at 80lbs torque. I know for a fact we went through every bolt and torqued them exactly the same. We even made three passes around the gear. The only thing I can figure is that not breaking the gear in caused it to heat up and warp, causing the two bolts to back out. Do yourself a favor and break the gears in. Drive for 10 minutes then let it cool for 20 minutes. Drive for 20 minutes and let it cool for 30 minutes. Drive for a half hour then let it cool again. If it were me I would take the rear cover off and re-torque the bolts after the 3rd cool off period. That's just me though.

My break-in is far enough to get it onto the trailer, then off the trailer and to staging at the track!

For street gears, I always recommend about two heat cycles of coming up to full temperature, then cooling all theway down. After that, put 'er to the wood!

When I worked at Dana in the engineering lab, we'd do about a 20-minute break in on the dyno, change the fluid, then begin the endurance tests.

Ok, great thanks a lot guys. When I had my 3.55's installed, nobody said anything about a break-in period, and drove the car about 65 miles back to my house on the highway. They seem to be fine to this day which might be surprising. I just thought I would try and find out the "proper" way to do this. Thanks again for all the help.

Chris