Rear end gear help

JonezySN95 · Aug 12, 2011

So I finally got my mustang back up and running after my new heart transplant (motor swap). The problem I have now is that the guy I bought the car from swears the car is not geared, but the speedo reads 90mph when im only doing 75mph (gps confirmed). I also scored some 3.73's in a deal but im affraid it already has them... so how can I confirm this without pulling apart my whole rear end if I dont have to? Also the AODE has been acting a little funny. When I take off and it tries to shift to 2nd it falls on its face for a little bit (feels like forever) before it shifts real hard braking the wheels loose again in second. I figured the tranny was done but didnt really care cause im swapping to manual here soon anyways, but i was just looking through other threads and just read that if its geared and the comp hasn't been chipped or adjusted/tuned the shift points could be off by up to 20%. So is this the possible problem with my tranny?

Last5.0 · Aug 12, 2011

Put the rear up on stands, put in neutral and spin a tire and count the revolutions of the driveshaft. If you have 3.73 the driveshaft should turn 3 complete revolutions and 3/4 of another to each 1 revolution of the tire. 3.08's would be just over 3 revolutions, etc.

SableSal · Aug 12, 2011

I'd say easier, remove the cover, count the teeth. Unless you've changed that fluid recently then do the above stated.

toyman · Aug 12, 2011

SableSal said:
I'd say easier, remove the cover, count the teeth. Unless you've changed that fluid recently then do the above stated.

Easier??

Since you need to jack up the rear to do both, it seems to me putting a mark on the D/S and counting the number of revolutions for one wheel rotation has to be not only easier but cleaner and quicker. Maybe 10 minutes.

SableSal · Aug 13, 2011

toyman said:
Easier??

Since you need to jack up the rear to do both, it seems to me putting a mark on the D/S and counting the number of revolutions for one wheel rotation has to be not only easier but cleaner and quicker. Maybe 10 minutes.

Hah, yeah. Gear oil is stinky. But I would say it takes out the guessing.

99FiveOh · Aug 13, 2011

SableSal said:
Hah, yeah. Gear oil is stinky. But I would say it takes out the guessing.

Yeah it's always nice to count the teeth, or better yet look at the model number on the side of the ring gear and google it! Mine had 4.10 right in the model number so it was easy, but I was in there already to replace a leaky axle seal.

JonezySN95 · Aug 13, 2011

Eh I'll try spinning the tires first, but I have not changed the oil yet and god knows when the last time was since it was serviced so I will just go that route. If I already have 3.73's in it (which by the sound of it i believe i do) then I will prob have some nice used 3.73's for sale here soon.

toyman · Aug 13, 2011

Counting the rotations of the drive shaft is NOT an approximation or a guess. It is just as accurate as counting teeth on the ring and pinion gears. It has to be as that is the exact same ratio between the ring gear and pinion. It may be true that you can't precisely count 3.73 turns it doesn't matter as the 2 next closest sizes are 3.55 and 3.90 and they can be counted just as accurately.

JonezySN95 · Aug 13, 2011

Well at least I now found a quick answer to what gears I may have, but I still hope its my computer being confused that is throwing the shift points off on my tranny. I am doing a 5 speed swap soon, but I would like to do it on terms when im ready and not be forced to do it early due to a pos tranny.

Chythar · Aug 14, 2011

The computer knows what gears you have in the rear end. The vehicle speed sensor (VSS) checks how fast the output shaft of the tranny is moving (and thus, the driveshaft). It does the math with the rear end gear ratio it has stored and displays the speed. A computer chip or a Speedcal will correct your speedometer

99FiveOh · Aug 14, 2011

I dunno about that Matt. I've riden in cars with AODE's after a gear swap and the car just goes nuts when it's time to shift. Bucking and backfiring like mad. The AODE 94/95 Mustang 5.0 should have never happened period! They are almost as bad as the Mustang II!!!

toyman · Aug 14, 2011

I never had an issue with the 4:10 gears. Sure the shifts occurred earlier (at a slower speed) than before but that really didn't make any difference. With a recalibrator the speedo was reading true and knowing my actual speed was more important than the shift points. WOT shift can be problematic without a shift kit and running 4:10's. You may end up hitting the rev limit during the shift with an auto especially the 1-2 shift.At no time did I ever have a bucking or backfiring issue. Like Matt said the VSS signal isn't changed just the speedo reading.

JonezySN95 · Aug 18, 2011

Then maybe my tranny is going out then? Im not worried about my speed reading so much cause I have a gps for safe measures anyway. It doesnt matter if it is bad or not right now anyway cause I have more issues with the motor at the moment. I just installed the new cam (TF stage 1). Now when I start the car it runs fine, but when I drive it and it warmes up it wont idle when I come to a stop. Also with the old cam (it was a flat tappet F cam) my oil pressure was around 50. Now with the new cam its at 40 and when it warmes up it it droppes to 25 (15 trying to idle). It had 2 codes 172 and 327 which I beleive are MAF and EGR.

five0xpres · Aug 18, 2011

JonezySN95 said:
2 codes 172 and 327

A code 172 for the EEC-IV is "HEGO (Heated Exhaust Gas Oxygen) sensor - voltage signal indicated lean in Bank #1"

and a 327 is "EGR Valve Position (EVP) sensor, Pressure Feedback EGR (PFE) sensor or EGR Pressure Transducer (EPT) - signal voltage too low."

JonezySN95 · Aug 18, 2011

five0xpres said:
A code 172 for the EEC-IV is "HEGO (Heated Exhaust Gas Oxygen) sensor - voltage signal indicated lean in Bank #1"

and a 327 is "EGR Valve Position (EVP) sensor, Pressure Feedback EGR (PFE) sensor or EGR Pressure Transducer (EPT) - signal voltage too low."

Thanks man! Hmm thats wierd because I was running rich before... I took out all the smog stuff (to include the EGR) so could that have anything to do with the 172 code? Obviously thats why its popping the 327 code...

BIGDATOWN · Aug 18, 2011

If you have a flat tappet F cam, you can be a millionare. The 95 motor is only a roller and so is a F cam.

JonezySN95 · Aug 18, 2011

BIGDATOWN said:
If you have a flat tappet F cam, you can be a millionare. The 95 motor is only a roller and so is a F cam.

Ok so it may not be an "F" cam... The guy I got the motor from only told me it had a 512 lift. Only knowing that and it being the old straight 302 firing order I just assumed it was an f cam. Yes it was a flat tappet setup because I just switched it over to a roller setup with a stage 1 TF. After days of wondering why my car wouldnt start and idle I finally found out it was a straight 302 cam (it was supposed to be a carb setup for a project). It would run on the old firing order, but obviously the comp was spraying the injectors at the 5.0 HO timing so therefor I put a different cam in it.

Chythar · Aug 18, 2011

NotA4.6 said:
I dunno about that Matt. I've ridden in cars with AODE's after a gear swap and the car just goes nuts when it's time to shift. Bucking and backfiring like mad. The AODE 94/95 Mustang 5.0 should have never happened period! They are almost as bad as the Mustang II!!!

It's been a while since I've had to deal with the speedometer gear and the VSS, so I redid my research. I was wrong, the computer does not hold a value recording the rear end gears; that's all handled with the VSS and the drive & driven gears in the tranny. What I used the computer chip for was to change the tranny gear ratios; I had 4R70W gears put in my AODE, so to fix the shift points I needed a chip. Good catch, Mark.

The computer does use the VSS to calculate when it needs to shift. With the inaccurate speedometer, the computer miscalculates and shifts 1st-to-2nd late. To correctly fix the speedometer and the odd shifting, you need to change both the plastic gear on the VSS and the drive gear inside the transmission. You can get close if you use a white 23-tooth gear for the VSS, but it's a Chrysler part and it doesn't mesh very well with the Ford drive gear in the transmission. It will eventually tear itself apart. But if you're going to do the manual tranny swap soon, the white 23-tooth gear might not be a bad short-term solution.

JonezySN95 · Aug 18, 2011

Chythar said:
The computer does use the VSS to calculate when it needs to shift. With the inaccurate speedometer, the computer miscalculates and shifts 1st-to-2nd late. To correctly fix the speedometer and the odd shifting, you need to change both the plastic gear on the VSS and the drive gear inside the transmission. You can get close if you use a white 23-tooth gear for the VSS, but it's a Chrysler part and it doesn't mesh very well with the Ford drive gear in the transmission. It will eventually tear itself apart. But if you're going to do the manual tranny swap soon, the white 23-tooth gear might not be a bad short-term solution.

Ok thanks for the info. It sounds like a good temp fix to get me by... now just to find a decent priced tranny and hardware to do the swap. I slept on a couple offers already thinking I would get one at the local junk yard (they said they had 2 at a pick-n-pull) umm yeaa when I got there they were stripped so I lost out on multiple good deals

alleymad95GT · Aug 19, 2011

You can change it electronically as well I think...

Ford Racing Mustang Speedometer Recalibration Tool (94-10) at AmericanMuscle.com - Free Shipping!

Rear end gear help

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