Swapping rear end gears on a PP?

[908ssp]

There are two options as I see it. Change the gears in the dif or change the transmission. It might be obvious to change the gears as they are cheaper but would you be sorry if shortly after that the gear box proves to be the weak link? Once SCer is done I have reason to believe I'll need a clutch at that point the transmission is out of the car. Putting the T56 magnum back in with a new clutch and scatter shield is real straight forward and only more expensive. Pulling the entire IRS to get at the dif might be the harder way to go.

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[D3adch1ld]

Now that I have the car, 1st gear is so short its scary, 2nd is a bit short too, with this in mind, I will NOT be changing the gearing, instead ill work on getting a bit more RPM out of the engine and possible enlarge the rear wheels. I would like to get the car similar to the ratio I had on my DSM (Which I loved) I was getting 50 MPH on 1st, 75 on 2nd, and 105 on 3rd. All my gears where changed and I was running 8.5k RPM. With the Mustang I feel comfortable with 7.5K RPM maybe even. Im not expecting anyone to agree, but for those interested on another development follow me.

 

[foghat]

So if first is so short with the 3.73s, I imagine starting in 2nd wouldn't be much of a problem? Just thinking about starting on an icy road with a bit of an incline.

 

[dwaleke]

There are two options as I see it. Change the gears in the dif or change the transmission. It might be obvious to change the gears as they are cheaper but would you be sorry if shortly after that the gear box proves to be the weak link? Once SCer is done I have reason to believe I'll need a clutch at that point the transmission is out of the car. Putting the T56 magnum back in with a new clutch and scatter shield is real straight forward and only more expensive. Pulling the entire IRS to get at the dif might be the harder way to go.

I know you mentioned it would be more expensive, but $5k+ for the T56 swap seems a lot more expensive than swapping out the rear gear.

A 3.15 would get you pretty close to what the 2.97 T56 trans would get you with the stock 3.73 rear gear. At least in the first 4 gears anyway.


EDIT: Now that I compare the '15 MT-82 /3.73 and the '14 GT500 TR6060 / 3.31 I may leave everything alone and treat 1st as a creeper gear. 2-6 are close enough to 1-5 in the GT500. I'm going to have a SC BTW.

 

[Mountain376]

Now that I have the car, 1st gear is so short its scary, 2nd is a bit short too, with this in mind, I will NOT be changing the gearing, instead ill work on getting a bit more RPM out of the engine and possible enlarge the rear wheels. I would like to get the car similar to the ratio I had on my DSM (Which I loved) I was getting 50 MPH on 1st, 75 on 2nd, and 105 on 3rd. All my gears where changed and I was running 8.5k RPM. With the Mustang I feel comfortable with 7.5K RPM maybe even. Im not expecting anyone to agree, but for those interested on another development follow me.

Swapping in a Tremec T-56 or TR-6060 will put you right there with the 3.73 gears.

 

[908ssp]

I know you mentioned it would be more expensive, but $5k+ for the T56 swap seems a lot more expensive than swapping out the rear gear.

A 3.15 would get you pretty close to what the 2.97 T56 trans would get you with the stock 3.73 rear gear. At least in the first 4 gears anyway.


EDIT: Now that I compare the '15 MT-82 /3.73 and the '14 GT500 TR6060 / 3.31 I may leave everything alone and treat 1st as a creeper gear. 2-6 are close enough to 1-5 in the GT500. I'm going to have a SC BTW.

That includes drive shaft, clutch assembly and transmission with a shifter that is better than any currently available. You can probably get it for less.

 

[analogman]

So, after living with my fabulous new GT PP for a couple of weeks, with its 3.73 rear, I wish it had a numerically lower rear, but I doubt I'll be spending the money to do it.

The gearing is short in the first 4 gears. In normal driving, I'm in 5th by 40-45 mph. 6th is a long gear and reasonable on the highway. The car isn't broken in yet, so I don't have a good feel for gas mileage. I suspect that reducing rpm's from 2100 to around 1850 in 6th might pick up 1-2 mpg, might not.

The rear end gear swap is more complicated than I thought. The gears themselves are not expensive, about $150 from Ford Racing. But, the dealer wants almost $1,000 to swap them out, and a local speed shop wants $650. Apparently, the ECU needs to be re-flashed as well to recognize the new rear end ratio. Any way you look at it, it's around $1,000 to get it done. I would have to drive a lot of miles to make an extra 1 mpg on the highway pay for it.

So, at this point, I really wish the PP could be had with a 3.31 (or maybe even 3.15) rear, but it just doesn't seem cost-effective to swap it out.

Does anyone else have any thoughts or experiences with this?

Thanks, and happy new year!

 

[steve1107]

The problem is that the sheeple will parrot the "more gear is better" thing without having any clue as to why things should be geared certain ways for certain things.

There have been two people to post in this thread that understand gearing, what impacts it has, what the pro's and con's are and have had a extremely wide range of experience setting up and gearing cars for a combined 70 odd years yet they have been ignored because then masses have been brainwashed with the "the shorter the gearing, the better".

There is only one situation where a gear shorter than a 3.31 is suited and that is at the drag strip with a car running tall drag radials/slicks.

How many people will be taking their car to the strip regularly? I'm guessing less than 1%.

The MT-82 3.73 combo is just plain stupid in 99% of situations. I find it amusing that PP buyers get the 3.73 and that is the last gear you want for going around corners. People are buying the PP to go around corners right?

So, what gear should the pp come with?

 

[Grintch]

3.31 for autocross and longer road courses, 3.55 for shorter road courses. The standard GT get an option. The performance variant should have at least the same 3.55 option.

 

[mikeyjobu]

One of the taller stock -after looking on tire rack - the standard 18" 235/50. The 19's on the PP are shorter. Going to a 20, there are options that get you over 28" tall. Look for the posts about the stock at gt with 20's running a 12.7 on dealer gas, and also look at the posts from gt PP owners unable to get to 60 under 5 seconds. It's all very confusing. I wouldn't be surprised to learn that some of the boggy feeling setups are faster than they feel - maybe faster than the 3.73s sometimes. I've been looking some at the gear ratio spreadsheet and considering how to save the 3-4 shift in the quarter - looks almost unavoidable. I also keep replaying in my mind the top gear segments with the stars driving the reasonably priced car - the stig's advice is to remain in 4th many times when you'd instinctively downshift. So it seems what's fastest isn't always what feels fastest... also, if you drive with a light foot around town, you could theoretically gain mileage with the 3.73s - probably not realistic, which is why I'm careful to point out its merely "theoretically" possible...

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