I'm sure this question has been asked, but a search didn't show me what I was looking for.
When I swapped in my 87 thunderbird engine and AOD tranny from the car, I left the stock rear end. It is a one leg, 3.08 rear end, which came mated to the 1988 thunderbird 3.8lv6.
I have a vss signal error message when I run codes, and I'm guessing I have the wrong speedometer gear, so either vss thinks the car is going faster or slower. Having a 3.08 rear as opposed to the 2.73 limited slip rear the v8 came with, I would assume the speedometer would read higher than my actual speed, correct? What gear would I need to put in the tranny to make it accurate for the 3.08 rear? Is it hard to change a speedo gear? Are they expensive?
Scroll down past the ring and pinion sets and there should be a chart that will be helpful for you. :D
Chart (http://"http://www.fordracingparts.com/download/charts/129.pdf")
this might also help if you have done gear and tire size change
http://www.accuautoparts.com/calculatorfin.jsp
if needed i have a set of 2 speedo gears im not using i could sell ya on the cheap. bought em for my 84 that had the v8 with the 3.08 rear end.
the far right part of the chart is for autos...... with you having the 87 AOD,
depends on what drive gear you have in your auto trans, a 7 tooth or 8 tooth
but from what it looks like to me.....
if you have the 7t drive gear you need the 18T Gray C7SZ-B <-- that is an obsole number
chances are this would be more of your set up
8t drive gear and you would need the 20T Orange C8SZ-B
If it's a T-bird/Cougar AOD then you have the 8 tooth drive gear.
I answered in the misc tech as well but for everyone, THE SPEED SENSOR COULD CARE LESS WHICH REAR END OR WHAT GEAR IS IN THE TRANSMISSION....
NOW since you have a '87, there is no wiring connection to the EEC from the speed sensor... Of course this assumes you've swapped a '87 harness...
I was wondering why the hell a different gear ratio would throw a code? I always learn something new though. LOL