Progress Thread Transmission Gear ?

[SF Lex]

I have a 92 Mustang GT with a 302, and a AOD transmission i recently had rebuild. When i got the car, the transmission was wasted, and it never read the spedometer correctly, its was off by about 25-20 miles on the freeway. As i rebuild the transmission, the mechanic told me he would fix it with the rebuild. Unfortunately it did not. He changed a gear underneath that had less teeth i think ? Or more, not sure what he changed it to, but it still did not fix it. Recenlty on the last try, he changed it one more time, and it was suppose to fix it. I will test it this weekend, but now my Stang does not feel as strong when pulling, seems like it has more play now.
Can you tell me what gear you guys use ? I am in need of information. At this point i am wondering if i have to sacrifice the speedo for power. Or can it all be fixed ? Unsure. I have aftermarket wheels which are 225/45/17, with low profile tires. Does that have something to do with the speedo being off ?

Thanks

 

[Mustang5L5]

The speedo drive gear inside the AOD is fixed on the output shaft. It cannot be changed.

The drive gear can be changed. What rear end gears does your car have?


Tires are a bit undersized. Should be 245/45/17. This would cause some of the difference, but not all

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[jrichker]

@SF Lex
And the answer is....

Performance issue:
Changing the speedometer gear should not have any effect on performance. Something may have gotten knocked loose while working on the car, or something else quit working properly. Dump the codes to find out what may have popped up.
Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/


Speedometer accuracy issue
https://lmr.com/products/Mustang-Speedometer-Gear-Calculator - calculate the best speedometer gear for your axle/tire and transmission type


https://lmr.com/products/79-93-Mustang-Transmission-Speed-Correction - purchase the gear you calculated to be the best match. The choice may say manual transmission, but the driven gear works with both manual and automatic transmissions

 

[mikestang63]

When guys change either/and their rear end gears and/or tires size, this requires a change in the speedo gear that is on the end of the speedo cable that goes into the trans. The problem is on an AOD if you go with 3.73 or lower and/or larger tires, their is no direct replacement speedo geat that will be 100% accuate. Some guys end up changing the gear on the output shaft. Some guys end up having their speedo calibrated. Most guys just live with it. MIne is off by about 10 mph at highway speed. Know that depending on what year you have, it is either a 7 or 8 tooth output shaft gear. 83-89 are 7 tooth and 90-98 are 8 tooth. The 23 tooth speep gear does not mesh with the gear on the output shaft well and are known to get chewed up in short notice, requiring it to be replaced often.


http://www.steeda.com/mustang-speedo-gears/?features_hash=V6489

 

[SF Lex]

Guys, thanks for the info, i will look into some of these options. I drove the car this weekend, since i had not since bringing it back from the shop 3 weeks ago. Seems to drive great, but i dont' know what size rear end is on my car. I will call my local transmission shop to find out what gear ratio they put on this time around. This was the third change to try to get the speedometer to match. I will repost when i have more details, as i am unsure. It did not take them long to change the gear, maybe 20 minutes or so.

 

[Mustang5L5]

Changing the gears is easy. On bolt holds the speedo cable into the trans. Yank it out, pull the clip off the gear and swap it. Then stick the cable back in and screw the bolt on and you are done.


Takes longer to jack up the car


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[89oem]

There are some good speedo apps for your phone too that are accurate, it'll help you dial it in or just not worry about it