Can anyone tell me how to determine exact year of my tranny? I have an 83 N/A that the PO had swaped the factory auto and the diff for a manual. I'm running 215-70-14's on factory wheels which should throw my speedo off slightly towards the low side of actual MPH, but it turns out the opposite. When running at 70-75 my GPS shows I'm going 5-8 MPH slower. I'm also running 3000-3200 at normal highway speeds for Texas. (we all drive 75-80 here) I forgot to check RPM when I put it up to 100 last weekend. So, I'm wondering if anyone knows how to tell the difference between early 5 speeds and the later ones. Could he have the wrong diff in it? He said he had to swap it after putting in the 5 speed cause the auto diff caused it to lug real bad. Don't know if they both came from the same car or not cause he bought them used at different times.
Bottom line is I'm running higher RPM's than I should be at a given speed and my speedo reads under actual MPH even though my tires are one size larger than factory specs. What gives here?
Thanks for any help ya'll can offer.

 

year of the tranny doesnt really matter. to get your speedo working you need to know your diff ratio. its on the ring gear. then there is a chart somewhere (cant remember where) that tells what color speedo gear you need to use to get the right ratio. colors include red, blue, white, and black. the tranny basics can be 3 types, early 5 speed (has 2 tangs on the tail shaft) late 5 speed with only one tang on the tail shaft and turbo 5 speed which has a different shifter tower. you can tell because the shifter is bolted on with a plate. hope that helps

 

Well, the speedo not being accurate doesn't really bother me as much as the high rpm's. I was just real curious about the whole thing wondering why the backward shift in speedo v. tire size. In truth, I don't mind running higher rpm's either. The car runs better in the higher rpm range anyway. Thanks for your help.

 

Yeah, that's why I love the autos... running 3k-4k rpms on the highway. Right above the boost threshold. Boost hits - BAM - smooth sailing.

 

I think you're the only one to ever say such a thing.

 

I love them too.I know you run 3500 4000 RPM but I can keep up with highway driving and quicker on take offs.
I sold all my Auto ZXT's and got me a manual's they are more fun and the auto for comfort.

 

I wouldn't be so fast to believe the PO actually swapped the diff also. Unless you know for certain. You might try doing your calculations with the auto diff ratio???

 

I genuinely love my auto. I just need to find a shift kit for it...

 

Well, I'm pretty sure he did the diff. He claimed the car wouldn't drive right... lugged real bad until he swaped the diff. Is the first gear ratio that much lower in an auto tranny? I wouldn't think so but that was his claim so who am I to argue. One day I'll pop the diff cover and check out the markings to find out exactly what I got there. Thanks!

 

Wont really help you too much, maybe a little. But at 3k in my 5 speed, I am at 70mph with my speedo app on my iPhone. And of course of all the years driving my Z's. I pretty much know how fast I am going just by the RPM's while in any gear. When I am just over 4k, I am about 100mph. Will have to check it sometime again. Don't really like going that fast too much, because of the fuel consumption being my bad compression ring in number 6 being at fault. 75-80 is my comfort speed. Which is mostly what I do on the freeways.