rmurad38

Hello all,

This weekend I'm getting 3.73's installed in my Mustang.

When I spoke to the shop, asking general questions, the topic of breaking them in came up. The shop said that for the first couple hundred miles, trips should be kept short (just a few miles at a time) to allow the gears to heat and cool, more or less hardening them. Going on a multiple hour road trip could be detrimental due to possibility of overheating them. After about 500 miles he also suggested the fluid be changed as the mating of the new gears will produce some metal shavings in the fluid, i'd believe that.

Now i'm sure he was just staying on the side of caution but it seems a bit extreme. (the very short trips part.) However, after the lengthy break in, drive it like you stole it.

For those of you who may of changed gears, what do you recommend?

rmurad38

a_guerrajr

makes sense, just like a new car. a little break in period.

Ltngdrvr

Never heard anyone say to stick with short trips but just like the new motor stay away from extended periods of one speed.

David Young

Rene, be sure to let us know how many r.p.m.'s your Mustang does at 60 m.p.h. I'm really happy for you on your new gears

jlmounce

He's a shop and erring on the side of caution. He doesn't know how you drive your car.

While a traditional "break-in" period doesn't really apply as the gear set is a non-wear item, there are steps that should be taken that can reduce the chance of noise and vibration.

As a best practice it is good to heat cycle the gears completely several times before you go messing around with them. Drive the car normally to get all the fluids hot, then park the car and let it completely cool down. Then do it again at least once.

I've had gears installed by two different shops and this was the only bit of information that was the same between the two different recommendations.

One shop said heat cycle then beat on them, another said heat cycle and give them a couple hundred miles run-in.

Neither set had issues with noise.

So, it's kind of at your discretion.

rmurad38

I posted this on another forum, here are the RPMs i got:

70mph-2250rpm
65mph-2000rpm
60mph-1750rpm

So yes, a bit of a change, but not too drastic, still very mellow if cruising on the freeway.

rmurad38

Ltngdrvr

What did you do for speedo correction, tune or speed cal?

Reason I ask is that those rpm for speed at 60 numbers are off quite a bit according to the gear/speed calculator.

Calculator shows 60 as being about 1900 for a 3.73 gear.

David Young

According to my ScanGaugeII (it has a digital tach feature) at 60 m.p.h. my engine with 3.31 gears is doing around 1,735 r.p.m.

rmurad38

My speedo was calibrated by the tune. I havent been checked by radar, but it seems to be accurate to me. It seems pretty close to Davids though which is slightly odd.. though they are higher, as would be expected. I do have the MCA wheels with 235/50 ZR 18 tires if that matters. BAMA does have a new tune for me though, which i hope ill get on tuesday (will fix my harsh 1-2 shift and torque converter bump on deceleration) maybe the speedo could change too.. I'll keep everyone posted

rmurad38

David Young

Keep us up-dated. I have 235/50-18 tires too. I have to agree with Ltngdrvr, at 60m.p.h. your engine should be turning around 1,900 r.p.m.

Ltngdrvr

You may need to manually change the tire revolution per mile setting in your SCT tuner.

08SGT1977

Congratulations! I am doing the same thing except 4.10 based on everything I could educate myself on here. My car should be done tomorrow. What the heck. I may have gone overboard but hopefully it will be fun fun fun. I have an automatic. It should be drastic going from 2.73.

edit - thanks for the feedback from the shop. Bye bye to 3 bottles of Royal Purple synthetic gear oil if I change it out after break in $$

Ltngdrvr

4.10's are just too much for a street car, going to make first gear basically useless.

3.55's would be pretty much optimum for a street car.

08SGT1977

My 08 has 3.55's but I remember driving a fleet F150 with 3.73s in Iraq right after coming back from vacation and driving my Shelby Mustang at home and thinking "holy crap", this thing jumps compared to my Mustang! Hopefully I won't regret the 4.10's in the Pony.

08SGT1977

Ok for everyone wanting to know about 4.10s on the automatic tranny I just got my car back this afternoon and have been driving around - initial feedback of potential interest

2500 rpm at 70 mph **(major edit)** 70 not 75
2200 rpm at 60 mph
2000 rpm at 57 mph

sorry didn't check 65 or 70 but confirmed those numbers several times

the car is comfortable and quiet at 75mph and ready to pounce at any speed

the car is not out of control at all when taking off from a dead stop even with a 93 octane race tune

I didn't get down on it because I am breaking it in but certainly went from 0-35, 0-40, 0-80 very rapidly with a much lighter foot than previously required

I suppose I expected to be accidentally burning rubber from what I had read - It does break loose without much effort, especially with the sand and salt on the roads around here - I just have to be much lighter on the pedal

so far I am very pleased with the very swift acceleration that is there at the ready, all the time

08SGT1977

sorry to change direction on the thread a little but hopefully the feedback is helpful for those trying to decide what kind of gears they want

Ltngdrvr

Where did you pull your speed/rpm numbers from, just the speedo and tach?

Because according to the calculator those numbers are off a little.

Calculator shows 75 at a little over 2600, 60 at 2100.

May need to adjust the tune a little to get them right on if you care.

If they are off then your fuel economy figures will be off too.

Like I say, if you care about any of that.

08SGT1977

those "calculations" are from my eyeballs on the factory gauges (haha!)

I used the SCT tuner to recalibrate the speedo - it was reading 80mph at 40 when I drove it home - totally wacko till I loaded the tune

I know it is probably not as accurate as more sophisticated methods but the mph was reading the same as my GPS

As long as I don't get any tickets it might be as close as other vehicles I have owned which were off by 2-3 mph from factory, not noticed until I saw the mph on the GPS

08SGT1977

Thanks and I like what you have done with your Mustang. Very Sharp. I have always liked those FR wheels.

David Young

08SGT1977, Thats not too bad on the r.p.m. My last car was a 4 cylinder Dodge and it did 2250 r.p.m. at 60 m.p.h.

I bet your Mustang feels alot faster now .