i installed 3.90s and have problems, need answeres

bullitt15 · Mar 30, 2007

i installed the gears along with a cobra lsd. the gears are motive 3.90s. i bought and installed: pinion bearings, crush sleeve, pinion nut, and reused the carrier bearings(they looked great). there was ZERO endplay in the carrier, .001 runout, .010 backlash(before using +3 and -3 side shims, moving ring towards pinion). i used the same pinion shim that came out(.030). there is a little play on the pinion, which causes clunking(not any louder than trans clunking). and yes there is gear whine, above 30 coast and drive. i didnt recheck backlash b/c it felt the same. i think i am going to tighten the pinion more b/c i torqued the pinion nut and probably buy new crush sleeves. ill recheck backlash and everything. i only drove 30 mi, will the gears have been worn in yet and have whine no matter what? should the bearing be good?

white-04 · Mar 30, 2007

My 3.90s make some noise, but my dad can't hear it. I gotta have the stereo off, windows closed to hear it. I'm sure the aftermarket shifter allows more noise than normal as well.

spederman · Mar 30, 2007

I had 3.90's installed 3 different times by 3 different professional shops. Each time trying to get rid of the whine thinking that it was a bad install. It never worked out. I had to get rid of them for FRPP 3.73's. Its just a really hard gear to setup perfectly and get no whine. I have heard of very very few that dont have problems with 3.90's from motive. From what shops would tell me is that if you drive for more than just a couple miles, the gears are already worn and they will whine forever. Hopefully yours work out, good luck. I loved the gear while i had them in. I think they were perfect. 4.10's to me were too much and 3.73's i have now arent enuf. I miss the 3.90's but couldnt handle the whine.

BennyBlown2v · Mar 30, 2007

bullitt15 said:
i installed the gears along with a cobra lsd. the gears are motive 3.90s. i bought and installed: pinion bearings, crush sleeve, pinion nut, and reused the carrier bearings(they looked great). there was ZERO endplay in the carrier, .001 runout, .010 backlash(before using +3 and -3 side shims, moving ring towards pinion). i used the same pinion shim that came out(.030). there is a little play on the pinion, which causes clunking(not any louder than trans clunking). and yes there is gear whine, above 30 coast and drive. i didnt recheck backlash b/c it felt the same. i think i am going to tighten the pinion more b/c i torqued the pinion nut and probably buy new crush sleeves. ill recheck backlash and everything. i only drove 30 mi, will the gears have been worn in yet and have whine no matter what? should the bearing be good?

You probably didn't even crush the crush sleeve and the bearings aren't pre-loaded correctly. Did you check the bearing pre-load with an accurate in/lb torque wrench (best to use a twin beam, dial, or digital type to get an accurate reading)? Open it back up and check it out... Motive also calls for a different pinion bearing depth than stock Ford gears, so re-using stock shim isn't exactly the best idea. Also, backlash should be between .012 and .015 for the quietest and coolest operation.

04DarkShadowGT · Mar 31, 2007

I had some 3.90s installed on my old GT, by a shop close to me and they where perfect. No whine at all.

droid#83853 · Mar 31, 2007

My 3.90's had no problem. They made zero noise. We set the backlash at 8. My uncle set up everything. At backlash of 14 it had a crappy pattern. He said to do it right it takes time, as changing one thing changes something else. So you can't just set endplay, then endplay, then just leave it. It took most of the day to put in my 3.90's. And that is at a full blown shop. I only go to him or 4x4 shops to get gears done.
I don't think 3.90's are optimized for a stock trans and engine. I ran faster with 3.73's in my car, and am going to get 4.10's. After driving a 4.10 GT, that is the only way to go. A 3.90 car drives like a 4.10 car, and the RPM ranges at cruise are close to each other. The 4.10 seems to be better matched to the wide ratio's of the 3650 trans though. 4th and 5th were a lot stronger. So why not get the 4.10's? If gas mileage is your concern, buy a Prius.

ADRENLN · Mar 31, 2007

dont feel bad, i have the 3.73 frpp and i get a loud wine in 4th gear on decel only!!! NO OTHER GEARS. its strange huh? we cant figure it out.

is gear whine only noise, can it mess anything up?

four six · Mar 31, 2007

ADRENLN said:
is gear whine only noise, can it mess anything up?

I believe it eventually ruins the gear.

MeZ · Mar 31, 2007

There should be no noise on a good install. I have noticed that more people have problems with non FRPP than anything else .. grab you a FRPP 4.10 and let a shop who does gears everyday do them... There are alot of things I do myself, but gear work is something better left to someone who does 10 -15 a day ...

fast97gt · Mar 31, 2007

my input is going to be you gotta pull it back down man, the reason is the same as mine when i HAD mine installed by so called professionals. i had mine installed at christmas and had to tear it down two weeks ago cause they were wineing the monute i picked it up, the guy said it might do it for a day or so and it should be better. not true i bought a install kit and redid every thing my self. when tightning the pinion nut it was odd to me then i thought about the 8 to 12in/lbs the drag on the pinion was suppost to be, so tear it down and recheck everything and good luck

i installed 3.90s and have problems, need answeres

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