What are my Stock rearend Gears?????
 

Hey guys i have a 86 gt 5.0 and im woudering what the stock rearend gear is, i looking to upgrade to 4:10 and im working what i have and also wondering how much of a difference will it make when going to the 4:10s, also i was told if i get ford racing gears that i can install them myself? thanks guys.
Ernie

Check the tag on the diff cover. It should say 2L73 or 3L08 if it hasn't been opened up. It is either a 2.73 or 3.08. Some years GTs with AODs also had optional 3.27 gears. For more info you can check http://www.mustanggt.org/

You can also check the AX code on the drivers side door tag.

M=2.73
Z=3.08
E=3.27

That would be the easier way, unless it has been painted over or removed. Mine has long been illegible.

The gear change will be significant. I haven't had mine to the track since switching from 2.73s to 3.73s, but it can be felt seat of the pants. If you have 2.73s and jump to 4.10s, it will be like removing your overdrive gear on the highway.

As far as putting them in yourself, if you have the right equiptment and know what you are doing, you could install them yourself. I would venture a guess that most people take theirs to a specialist. I had to upgrade my 7.5 diff so I just bought a Ford Motorsport 8.8 with 3.73s. That was before the price on them jumped considerably several years ago.

Ok, go here:

http://www.4x4cyberstore.com/website/rpmchart.html

Figure out your tire height and then hit the highway and calculate backwards.

For 25.5 inch tires and a t-5, go 3.55's. For 25.5's and an AOD, go 3.73's

For 26.6 nich tires and a t-5, go 3.73's (hell, I'd go 4.10). For 26.6 inch tires and an AOD, dude.....go 4.30's and nothing less.

I ran a 3.73 and 26.6 tires and a t-5 and got 23-24 mpg with a carb. I got 22-23 with the same and an AOD. I'll let you guys know what aod , 26.6's and 4.56's get soon =D

For FMS gears, you can reuse your existing side shims. You only need to worry about the crush sleeve and pinion depth. This you can do trial and error with grease and looking at the contact pattern on the gears. Install, grease and turn. Observe, tighten if necessary, turn. Reassemble, go for a drive and let off the gas. If it makes noise, tighten the pinion nut and go for another drive. Repeat until there is no noise.

You WILL need an aluminum driveshaft for the higher gear ratios.

Thanks Pete,
I had never been told that I needed an aluminum Driveshaft with my 3.73s. I have had a vibration from 70MPH up since changing rear-ends. It's not as bad since switching T-5s (input shaft was seriously worn).

Ok, lemme qualify that...

With 3.55's (I assume), you wont be feeling much vibration.

I feel a decent vibration with my 3.73's and it's pretty bad around 80. You can feel it in the gas pedal and the wheel. The whole car is shaking.

Now with anything higher than 4.10's , you'll end up with enough vibration to damage something or at least be really annoying.

Plus, any excuse to lighten up the car and reduce rotational mass is a good excuse to me! ;)

Why? I know tons of people with 3.55's, 3.73's, and 4.10's with the stock drive-shaft and no vibration problems.



-Josh, aka the tireburner

hey guys right now i have p225 60 15s and later down the road im going to go with the ntto 555 and they are 275 50 15s, so im thinking of going with the 4:10, it is a T5

eeh102582

What wheels are you running? Stock 15x7 10 holes? 275s might be too wide for those wheels. A lot of guys around here used to run 265/50/15s on them because they are close to the same diameter. I never did because it is recommended that they be used on 8" wheels.

i have the 8" weld draglites on those tires, i just really wondering how hard it is to put them in the reason i say is because i got a hot kit that came with the gears and the good install kit for 20 bucks, and i dont really have the extra money right now to get it done, the cheapest i can get it done around here is 400 and with me giving them the stuff.
thanks for all the help.

DO NOT even atempt to install the gears yourself unless you have the proper tools and technical knowledge to set proper pinion depth and correct gear mesh for both drive surfaces on the gears.

If you have vibrations in the driveline, the gears were not set up correctly or the driveshaft is out of balance and installed in a different position then it was removed.

I can go over proper rear end setup if anyone would like that. I have done many drag race and also some hybrid 8.8/9 inch road race rear ends.

RPM if i buy the ford motorsport gear do i still need the tools, i was told that if i get them gears that i i could take the old out and put the new in?
thanks again

You do need to set up FMS gears, regardless of what someone tells you.

Basically you must preload the pinion bearings by tightening the pinion nut so that it requires 12-22 inch-pounds of pressure to turn the pinion with out the ring gear and carrier in. If you tighten it to much you need to get a new crush sleeve. You then will need to check for a proper mesh pattern and that will tell you if the pinion shim is correct. You need to shim the carrier so you have between .012-.015 of backlash checked with a dial indicator. If you just install your new gears without setting up a good mesh pattern, you will hear some whine, feel vibrations, or destroy your new set of gears.

If you don't care about bad vibrations, loud whinning sounds, or longevity, then try to install it yourself. My advice is to take it to a proffesional.

I got lucky installing my 3.73 FMS gears myself. Sure beats paying $400. I'm going to add fuel to the rumor that FMS gears are easy to install since I did no measurement and set up the pinion depth by trial and error and used existing side shims. It can be done and it can be done right but it takes one or two tries before the gears dont whine. I used the contact pattern grease test after putting the gears together, took it for a drive, heard some grinding on decel, tighened the pinion nut till there was a tiny bit of drag on it, took it for another drive and viola! Not a peep. I've been driving around on these gears for 2 years now, long hauls to maine and everything. I even (GASP!) reused the crush sleeve (hell, it got crushed just the right amount the first time) since I didnt have any way of getting the new one started.

All I'm saying is it is possible. It is your choice, convenience vs saving money. I've had many horror stories of people taking their ride to a "shop" and ending up with whining gears and the like. Around my town, no one has any idea how to do gear swaps (at least around the belmont area). The closest I got was a place that sets up commercial vehicles (dump trucks!) : they wanted me to detach the axle and bring it in and they'd do it for $350! . Bunk that! So I did it myself and got lucky.

Try your own install. If you dont succeed, take it to the shop. If you got it even close, you wont tear your gears up (too much) . Plus, it will cost you a lot less for an adjustment than to have them do the whole procedure.