I had 3.55's a few years ago and now have 3.73's... Not much difference. Ofcourse I have 25 1/2 inches of tire in the back now which makes a 4.00 roughly I think.
ok guys i was just wondering i have had 2.73's in the car and i took them out and put .373's and i cant launch my car with out spinnign the tires. and i put brand new falon tires z rated . I went ot the track and ran a 14.5 am i doin somthin wrong or what???
I have another gear question(s)- should I install these myself in my driveway or pay somebody to install them? If I do it myself what special tools will I need? What do I need to buy other than the ring&pinion to complete the install properly? If I pay somebody to put them in what is a reasonable amount of labor. I have quotes ranging from $300 to $700 for labor only to install 3.73 ring & pinion in my 91 GT AOD?
I have read the whole thread I still haven't made up my mind on either 3.55s or 3.73s for a stock AOD transmission. Most people are talking about Manuals at 3.55 and possibly 3.73, but saying 3.73 are the best for AOD... am I reading that wrong?
I like to drive top speed around 80 (think speedo is a little off, so it might be close to 90) tops on the freeways, but as traffic goes these days in southern california it is hard to reach those speeds. I am only mainly concerned about the RPMs at close to 80-90mph... I drive that speed around 15% of the time.. so high RPMs on my aging motor is my only concern, and not gas mileage (but that goes hand in hand with higher RPMs )
Think I did all of the Tech formulas and it looks like in overdrive (4th gear?) with 3.73s the RPMs would be close to 2700? Is that right? Anyone out there with 3.73 AOD? what are the RPMs at 80-90 mph? what about for the 3.55s?
Right now when I am at my 80-90 mph speed the RPMs are just slightly over 2000.
I will never take this car to the track, but do some "spirited" driving occasionally
dude i just put in my .373's and they are good and bad. if ur car has a lot of horse then do .355 and u hould be happy.But if u have under 300 horses then go with .373 the thing with the .373s is that at 2grand in 5th gear ur at 60mph instead of 80mph. once u get the gears ur car is not a highway car anymore .
Please dont listen to previous response. Different ball game with the AOD. As luck has it my 91 with 112k on the clock is at the shop today getting my 3.73 gears put in. I'll let you know how it works out in a few days after I get a good feel for the difference. My plan though with the AOD is the 3.73's then a performance valve body from performance automatics to firm up the shifts in the AOD- supposedly much better than just a kit. more to come....
When you get it back and take some test runs, see if you can record/write-down/remember your RPMs at various MPH from 65 to 90, I would be soo stoked to find out what the numbers are.
I am just waiting for some more feedback before getting either the 3.55s or 3.73s this week or next.
ps. I have a rebuilt AOD with a minor shift kit in it, and it shift great (fast and hard)for 1->2->3, but the 4th gear (Over Drive) still shifts very smoothly (bad in my mind )
Gonna be tough to record times, rpms at specific miles an hour cuz the speedo is way off. I have to get a 23 tooth speedo gear to get it back close. I think it is somewhere around 20mph off but not sure until I can get somebody with a good speedo to pace me.
Anyway, the 3.73 is very very different from the stock 2.73 gear. With the AOD it is WAY better around town- motor is running instead of just chugging along. Wide open throttle is very different too. A little annoying is that where the AOD used to kick down to first if yu were under 30, now it will only do that at like 10mph (i wonder if the speedo gear will impact that at all?). But anyway I plan on the performance automatic valve body in the next couple weeks that will let me manually grab first. Around 40 or so the car also feels very different- seems like the motor isnt working as hard, but with my basically stock motor it doesnt toss you back into the seat or anything.
Now, the good part. Pulls WAY harder right off the line from a standing stop, and if you can grab first, or hold first manually to wind it out a bit more, the car pulls very hard instead of feeling kinda snoozy like it did before. I would say that now when it drops to second, its pulling about as hard as it used ot in first, but less fun cuz its less noisy, and first is like first should be. Revs at higher speeds are higher but not annoyingly. THe whole power band feels different- actually feels like the motor is working LESS hard to pull the car, which makes sense I guess. Seems like the tranny gets the shifts over with a bit faster too.
I have only driven about 10 miles since getting the car back today, but once I discovered the difference in first gear I was smiling. Based on what I am hearing and feeling I think 4.10 would be too much. I'll be able to get out a little more tonight to feel it out, and once I get used to the new shift points, etc. will post again. Overall, HUGE difference in 1st gear torque and the car seems happier, but I think I am going to be doing more manual shifting in 1st & second when not just putting around town.
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91 GT AOD, Flowmasters, K&N FIPK, timing advanced, Ford Racing 3.73, BBK unequal length shotry headers, off road h pipe, FRP underdrive pulleys
Oh yeah one more thing on the initial impression- OD is used much more often on the highway, and when it goes in it goes in more smoothly- it feels like a normal automatic tranny now instead of (at least mine) the annoying thing that was constantly bogging the motor. So at least based on the first ten miles, it FEELS like although the motor is turning some more rpm it is actually healthier for the motor because it is actually running and breathing instead of constantly being bogged and loaded up.
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91 GT AOD, Flowmasters, K&N FIPK, timing advanced, Ford Racing 3.73, BBK unequal length shotry headers, off road h pipe, FRP underdrive pulleys
Thanks for the extensive feedback! Gives me a better feeling for the gear.
Well after what I hear from you... I almost want to lean back to a conservative 3.55s as I do a a lot of driving in the 40-60mph range and 75-90mph and it seem that 3.73 might be too much of an emphasis on the lower 1st and 2nd gears.
How do you think it would feel if you stepped back a noch to 3.55s? I know you haven't felt them before, but the shift points would be slightly higher, less quick, and you would probably have more to work with out of first when shifting down like you mentioned from 20-30mphs right?
Put some more miles now- still haven't had anybody to pace me for speed/rpm notes though. Not very much different on the highway- OD is used a lot more often under all conditions, but it sounds and feels like it should be in OD instead of chugging. If you do 80% highway you might want to consider the 3.55's although I dont think the difference is going to be more than like 100rpm between those and 3.73 at any given speed. If it was me I would get the 3.73 all over again no matter what. Overall, now that I am used to where the kickdowns are I am thrilled with the 3.73 but I live in NJ and even on the highway here its a rare treat to have enough open road to get to 80. I did get one chance to open her up a bit to I would guess a bit over 100 and was really pleased with the gear. That final choice is gonna have to be all you.
Be sure to post what you end up doing and your thoughts after its done.
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91 GT AOD, Flowmasters, K&N FIPK, timing advanced, Ford Racing 3.73, BBK unequal length shotry headers, off road h pipe, FRP underdrive pulleys
damnit dude, why do you have to keep tempting me with the 3.73s
I am still just a little worried about a long road trip with 3.73s and high RPMS... and after doing some calcs, I am assuming the diference between 3.55s and 3.73s will be around 130-150 RPMs so you are pretty close.
I will definitely post back with my thoughts after I do it, but damn my hesitation in choosing...
I have just spent the better part of an hour going over this thread and noticed that there are not alot of references to New Age Mustangs ('04 in particular). I have...well, look at my signature line....and I am giving myself some mods as a Christmas present and I was going to include gears on the list. I am guessing 3.73's judging from the info listed herein. Could someone please approve of or refute that assumption before I make a costly mistake. Thank you all in advance for your feedback and/or opinions.
i typed "gears" in the search engine and it gave me this thread and i did not realize it was centered around the 5.0L brethren. i will repost in the right forum.
and also, just throwin it out there, if my engine were to need to be rebuilt and instead I were to go with say a crate motor from CHP (350hp or something)... I heard 3.73 were good with moderate horsepower, but if you had 300+ rwhp then 3.55s are better (for an AOD)...
Does anyone have any feedback on that idea?
Thanks
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