Hey guys,

Back in my early car days we used to change out the rear differential gear for better low in grunt. I know it does not give you anymore horsepower but it will give you that feeling of having a lot more torque. I figure if this car can go 150 mph I could stand to lose a lot on the top in but gain it all back on the bottom end. I will never need to go 150mph. So can you change the differential on the TL? I don't know crap about front wheel drive cars and there gearing. This would be a great mod if we can do it. Also how would we correct the speedo after the change? I know these cars probably don't have a speedo gear. Can we have the dealer re flash the ecu? I see all the people on the forums changing there wheel sizes(18,19,20) and wondering what there doing about there speedo. If you don't correct your speedo for tires or a gear change then your odometer will put more miles on your car then your actually doing. A gear change would be great for those people putting 20's on there car. It would make it feel normal again. I remember when I had my F-150 truck. I put 33 inch tires on it and it couldn't get out of its own way. So I put a .410 gear in it and it was back to normal. I don't want to change my wheel size for this reason alone. I will stick with my 17's. I would love to put a better gear in the car and correct the speedo. What do you thing guys? Can this happen?

 

Thats a good Question!!!
i've done that in the 89 Mustang GT 5spd i had and also the 95 Z28 6spd it does make a big difference!

 

that would be crazy, I bet it would be expensive though, especially if you cant do it yourself. I don't know much about this "gear change" thing, would it give better acceleration?

 

You may never need the 150MPH, but wouldn't your MPG suffer as well?
After three weeks would it be worth the expense and only getting 15 MPG?

 

You have it backwards, if you put smaller wheels on a car the odometer will read more that you have driven, but bigger wheels let the car show less miles on the odometer.

 

when you get bigger wheels, you get thinner tires, to offset the wheel size, overall diameter doesn't change, meaning speedo stays the same.

 

Your right.

 

well, that's what you try for anyways...I did that with my Honda and it was still off 1/10th of a mile every 30 miles...it all adds up, but who the hell REALLY cares anyway?

 

Changing the rear was (is) a simple and quick way to increase a car's rate of acceleration because of two factors: 1) it increases torque multiplication; 2) it increases the rapidity of RPM development (climb) thereby increasing horsepower delivery.

By going to a lower gear, you could improve quarter mile times by a significant amount for relatively little cost. When I ordered my 1988 Mustang LX 302CID, I specified the lowest gear offered which was a 3.08.. hardly low in my day. Later I installed the lower 3.55's.

I have not heard of front wheel street machines being offered a choice of lower gears.. probably too much of a hassle to change them out. Our TL's have a rather high gear at 3.29 as I recall.

 

Well damn, thats to bad. This car would realy "get after it" if we could do this.

 

There is a drawback to going with lower gears in today's cars.. at least the ones with smaller, lower torque engines like our TL's. The manual transmissions used in these cars are not close ratio. I know, the ads say the are, but they're not. A true close ratio box has a higher first gear than what we have, and all of the gears are closer in their ratio spread. This is important if you have a lower rear end (final drive in a FWD car) because a lower final drive with a low first gear means you'll exhaust first gear very soon after launch.

My 1988 Mustang LX 302 CID, also not a high-torque engine (300 lb/ft) had a T5 manual with a 3.35 first and the lowest gearset shipped - 3.08. I later installed 3.55's and while this was a super setup, I would have preferred 3.73's but with a 3.35 first, that was too short a gear.

Hope this helps y'all.

 

Most manufacturers match engine/tranny gear ratios quite well especially when the car is of "sport" design. Like you guys mentioned about your Mustangs (I'm a GM guy myself ) changing rear diff gears was relatively easy/cheap and you could truly effect your cars "quickness". Today with the 5sp At's and 6sp MT's they really are "tweaked" to the best of both worlds. Not that I have performed a swap recently, but my opinion would be that in order to achieve any "decent" results, you would end up significantly reducing your TL's everyday drivability etc. factor.

And yes, it would be expensive.
One would be much better off increasing "engine" power and torque to better use the existing gearing .

Using my old F body as an example, with 500hp(plus 250 more w/NOS), stock 3.23 gears, and a beefed up turbo 400 automatic trans,,, I could run low 12's on the track w/street tires and cruse all day long on the freeway at speeds up to 155 (rpm limited) if desired...

 

I've never heard of this being done with a front drive car.
Rear wheel is easy, but a front wheel drive at least the TL's diff. is inside the transmission.
You would have to seperate the trans case and install a new one.
Is it even possible?
Sounds like a lot of work and if the results are unsatisfactory then the tear down begins again.
I think engine mods are the way to go.

 

a few peopl on contour.org did it to there svt's... they went the other way though. with the contour svt you had to shift to 3rd gear before 60mph, (2nd was bouncing off the limiter at 57mph or so... ) the four cylinder contours were geared more toward fuel economy so they had slightly lower ratios then the 6 cylinder. a few guys swaped over to the four cylinder gear. it allowed faster 0-60 times as no shift... and with higher power engines the close ratios spun to much...

so it can be done to a fw car... now if we can do it, i dont know...

 

technically your odo will never be perfectly accurate... ever thought about tire wear? as your tires wear they will have to turn extra revolutions to go the same distance as new tires.... 1/10th of a mile is nothing... new tires compared to old probably have a bigger difference