New Gear Break-In. Why?

[Smokie]

A lot of our members have changed gears and I have heard mentioned many times that there is a break-in period, also a certain way you should drive them and stop and wait for them to cool down.

My question is why? What is the difference between the gears that came in my car with 11 miles on the clock and a new set of Ford gears. If the gears are correctly installed and backlash is correct and the differential is refilled with the proper amount and type of gear lube. What exactly happens to replacement gears, that does not happen to new car gears ???

[TAF]

I agree Smokie...I don't suscribe to that logic either. Drive the car like you're going to drive it, I say.

[03SILVERSTREAK]

A lot of our members have changed gears and I have heard mentioned many times that there is a break-in period, also a certain way you should drive them and stop and wait for them to cool down.

My question is why? What is the difference between the gears that came in my car with 11 miles on the clock and a new set of Ford gears. If the gears are correctly installed and backlash is correct and the differential is refilled with the proper amount and type of gear lube. What exactly happens to replacement gears, that does not happen to new car gears ???

The following is a quote from Bill Woboken in response to a similar question a while back on another board. Bill is a friend of Jerry and did work for Ford as a driveline engineer.
______________________________ ____________________

Today's Lesson: Self-Control.


BillW

There IS a break-in period for rear axles, or a new gear set.

Drive at varying moderate speeds (<60 mph) at moderate loads (NO WOT!!)for about 500 miles.

Change the fluid. If it looks like black metallic paint, you will understand why I suggest this.

If you do not follow this procedure, (aside from a crappy pattern emerging from brinelling/sfc checking on the tooth profile, and run high highway speeds and do hard shifts (big, short duration torque reversals) with either manual or automatics set up per Jerry's thesis,) a phenomena called "bump scoring" can occur. This is actually a breakthrough of the hardened surface to the soft, chewy center of the tooth, the part that provides strength but not wear resistance.

I have actually tested under extreme conditions (120F ambients, 80 mph cruise for 40 miles on a "green" axle) a Mustang Cobra 3.27 axle which actually got the axle lube to the smoke point (>400F)and very close to flashover. Now, subtract the appropriate amount from the 120F ambient to a typical summer day and you'll still find that the axle lube overtemps.

This overtemp condition results in a breakdown of the lube layer and can do great damage to the tooth finish and even close up allowances for expansion vs normal tooth mesh....GRRRRIIINNNNNNNNNDDDD! !!

Hope this helps.

BillWThis was posted by another member - any views on this ???

[TripleTransAm]

I don't think there should be any difference between the two, but then again I also practice the same 'break-in' technique on a brand new RWD car as well.

Either way, the gear teeth surfaces have to dig themselves a little bed on each others' surfaces. With varying torque applied on the whole assembly, the contact "patch" can shift so that's why it's important to vary load during the break-in period... to make as wide a 'bed' as possible. Otherwise, if the 'bed' ends up too narrow, the edges will end up causing accelerated wear down the road, and might generate some noise as well.

[CRUZTAKER]

Alright Mr. X!!!

We have covered this topic alot lately, and I know you were participating.;)

It's not a difficult theory to adopt, and even easier to perform. These steeper gears need the warm up cool down period to self seat. It's like a knee replacement, even though the doctor has you on your feet the very next day, you're not riding a bike for a week.:D

Just do it!

200 miles of varied driving passes in no time at all. I did it in 3 days. And drive a little in reverse damnit!:baaa:

[Smokie]

I understand about setting a wear pattern, and I am not even saying that there should be no break-in procedures. However having owned a fair share of new vehicles and always reading every page of every owners manual several times, I have never found any suggestion or mention of a specific way to drive vehicle to properly wear in gears. Auto makers have far more to lose in warranty claims than we as individuals do...so if it is important why don't they mention it in the owners manual ?

[CRUZTAKER]

I hear ya...but the gear swap won't be mentioned in the manual as I'm sure it's not manufacturer recommended.

However, every manual does mention a 'vehicle' break in period that is not item specific.

[Logan]

Bah! It's all poppy-****. Drive it like you stole it.

[CRUZTAKER]

....and hope it doesn't end up like a stolen one...blown engine / tranny:D

[Smokie]

Barry, you just hit the nail right on the head: gear swap. But there was a time when 3:55's were considered tall gears and 2:25's--2:80's were the norm. The owners manual for our cars is very casual and brief about break-in procedure, it really does not stress anything other than a very mild suggestion to drive at different speeds. Nothing highlighted or with great emphasis.:D

[BillyGman]

yes, I agree w/Barry. We have covered this a lot latley so I'm a bit surprised that you're bringing this up again Smokie. But I'll play along and repeat myself (again)........

you're overlooking the fact that 4.10 gears are called "4.10" simply because the driveshaft, and pinion gear will turn 4.10 revolutions to every one revolution of of the ring gear and axles. As opposed to the 3.55's only turning 3.55 times to every turn of the axles.

That might not sound like a big difference, but when you have the wheels and axles turning thousands of revolutions per minute while you're driving, then just think of how many more times that pinion gear is turning. Multiply that by four. The point being that w/a 4.10 gear ratio, that pinion gear will always be turning a considerable amount of more revolutions while you're driving than it will w/the 3.55 gear ratio. So it's turning a lot faster, and during break-in, while all the bearings (including the pinion bearings) are still very tight, they WILL have a trendency to heat up more.

I took apart the 4.10 rear end gears on my Marauder after only having put 1500 miles on them, in order to change to the 4.56 ratio, and let me tell you, those pinion bearings that I had just replaced w/the change to the 4.10 gears, were alreay a lot looser than they were when I installed them. I set the pre-load on the pinion bearings during the 4.10 installation to the factory spec of 25 in/lbs, and merely 1500 miles later when I went to remove the gear set from the rear end, out of curioisity, I checked the pre-load again on the pinion bearings BEFORE I loosened the pinion nut, and it was only 8 in/lbs which is the the minimum factory spec for used bearings. And that is normal. And they weren't making any noise at all beafore I opened it up again.

The bottom line is, before the bearings and the pinion gear breaks in,they will heat up because of friction, and w/a more extreme gear ratio, they will heat up more due to the higher speeds of the pinion gear rotation. And that's another reason why you need a break-in procedure w/lower gears( umerically higher).

It states right in the Richmond gear video, that the break-in procedure for rear end gears is as follows:

Drive the vehicle for 10 miles at moderate speeds not exeeding 50 or 60 MPH and avoiding any hard acceleration. Shut it down and let it cool for 30 minutes. Then repeat the procedure 2 or three times. That's it. It doesn't take long for the pinion bearings to loosen up a bit, and before they do, a lot of heat can be generated when they're still tight which can cause overheating and break-down of the rear end fluid. That wouldn't be good. When the fluid breaks down, it's ability to lubricate the gears is compromised, and that can spell trouble down the road for your ring & pinion gears.

With the stock gear ratios, that exessive heating during the break-in isn't as likely since the pinion gear as well as the pinion bearings aren't rotating as quickly as w/the more extreme gear ratios. So there's your answer.

Remember one thing. The Richmong gear company specializes in manufacturing gears unlike Ford. I have installed Ford racing gears in my MM because I like them better and they're easier to install if you're peforming the gear swap on a Ford rear end. But the only thing that Richmond does is the manufacture of gears and Transmissions. That's it. So if they recommend a break-in period, then that's good enough for me, because they should know what they're talking about.

So after this specific and detailed explanation, if there is anyone that still doesn't get it, then obviosly they never will. So it isn't even worth anymore debate.

[03SILVERSTREAK]

yes, I agree w/Barry. We have covered this a lot latley so I'm a bit surprised that you're bringing this up again Smokie. But I'll play along and repeat myself (again)........

you're overlooking the fact that 4.10 gears are called "4.10" simply because the driveshaft, and pinion gear will turn 4.10 revolutions to every one revolution of of the ring gear and axles. As opposed to the 3.55's only turning 3.55 times to every turn of the axles.

That might not sound like a big difference, but when you have the wheels and axles turning thousands of revolutions per minute while you're driving, then just think of how many more times that pinion gear is turning. Multiply that by four. The point being that w/a 4.10 gear ratio, that pinion gear will always be turning a considerable amount of more revolutions while you're driving than it will w/the 3.55 gear ratio. So it's turning a lot faster, and during break-in, while all the bearings (including the pinion bearings) are still very tight, they WILL have a trendency to heat up more.

I took apart the 4.10 rear end gears on my Marauder after only having put 1500 miles on them, in order to change to the 4.56 ratio, and let me tell you, those pinion bearings that I had just replaced w/the change to the 4.10 gears, were alreay a lot looser than they were when I installed them. I set the pre-load on the pinion bearings during the 4.10 installation to the factory spec of 25 in/lbs, and merely 1500 miles later when I went to remove the gear set from the rear end, out of curioisity, I checked the pre-load again on the pinion bearings BEFORE I loosened the pinion nut, and it was only 8 in/lbs which is the the minimum factory spec for used bearings. And that is normal. And they weren't making any noise at all beafore I opened it up again.

The bottom line is, before the bearings and the pinion gear breaks in,they will heat up because of friction, and w/a more extreme gear ratio, they will heat up more due to the higher speeds of the pinion gear rotation. And that's another reason why you need a break-in procedure w/lower gears( umerically higher).

It states right in the Richmond gear video, that the break-in procedure for rear end gears is as follows:

Drive the vehicle for 10 miles at moderate speeds not exeeding 50 or 60 MPH and avoiding any hard acceleration. Shut it down and let it cool for 30 minutes. Then repeat the procedure 2 or three times. That's it. It doesn't take long for the pinion bearings to loosen up a bit, and before they do, a lot of heat can be generated when they're still tight which can cause overheating and break-down of the rear end fluid. That wouldn't be good. When the fluid breaks down, it's ability to lubricate the gears is compromised, and that can spell trouble down the road for your ring & pinion gears.

With the stock gear ratios, that exessive heating during the break-in isn't as likely since the pinion gear as well as the pinion bearings aren't rotating as quickly as w/the more extreme gear ratios. So there's your answer.

Remember one thing. The Richmong gear company specializes in manufacturing gears unlike Ford. I have installed Ford racing gears in my MM because I like them better and they're easier to install if you're peforming the gear swap on a Ford rear end. But the only thing that Richmond does is the manufacture of gears and Transmissions. That's it. So if they recommend a break-in period, then that's good enough for me, because they should know what they're talking about.

So after this specific and detailed explanation, if there is anyone that still doesn't get it, then obviosly they never will. So it isn't even worth anymore debate.I brought this up because about a week ago I had the 4.10 installed by the dealer up by my way and as was said many times before , this was a vast improvement over the 3.55 gears . next step is to complete Stage-1,s install and move on to the DR Exhaust system... :rock:

[mjb711]

I brought this up because about a week ago I had the 4.10 installed by the dealer up by my way and as was said many times before , this was a vast improvement over the 3.55 gears . next step is to complete Stage-1,s install and move on to the DR Exhaust system... :rock:
I am thinking of the 4.10 route as well, how much rpm increase have you noticed at 65-80 mph ? How about the fuel consumption ? Lastly, what did you do computer wise with the shifting ?
Thx.
Mike.

[BillyGman]

It isn't just the shifting that you have to worry about. it's the spedometer being thrown off too by the new gear rastio. You really have to get a computer chip or an SCT handheld tuner that's for the 4.10 gear ratio. The gas milegage went down 2 MPG when I had the 4.10's. The RPM difference at 70 MPH will only be 350 higher. No biggie.

[rookie1]

So after this specific and detailed explanation, if there is anyone that still doesn't get it, then obviosly they never will. So it isn't even worth anymore debate.

How do you really feel about this BillyG?

[BillyGman]

How do you really feel about this BillyG?
I guess that really means that you don't get it........anyway, this thread is just too old for me to even give a rip about anymore. Hows that for true expression?