How to correct speedo after changing to 3.73 on '88 Cougar

Topic: How to correct speedo after changing to 3.73 on '88 Cougar (Read 9231 times) previous topic - next topic

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #15 – March 28, 2016, 11:57:14 AM

Quote from: AT8 Cat;454392

I've heard conflicting stories about whether my '88 AOD is a 7 tooth or an 8 tooth drive. How do you know for certain, can you see the drive gear well enough through the VSS hole?

If you start with a known configuration (as you have), count the teeth on your current VSS, let the website do the math and back out if the drive gear is 7 or 8 tooth.
http://www.sccoa.com/faq/speedgr.html

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #16 – March 29, 2016, 10:50:38 AM

Quote from: ISTLCRUZ;454506

Following your thread as I need to order a new gear as well.( just swapped in a 3.55 TC rear axle) What did you decide on your AOD? 7 tooth or 8? I have an 87 5.0 Bird with AOD. TurboCoupe 50 said MOST came with 8 tooth so I may get mine tomorrow. Ray

Sounds 99% like it'll be an 8 tooth in there so I will need a 23 tooth driven gear. I've heard guys on here with '87's that had an 8 tooth, but no one with an '88 has told me what they've got. Right now the car is still tucked away for winter but it will be out in a few weeks as soon as the weather warms up some more. I'll let you know what happens when the job is done.

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #17 – March 29, 2016, 10:57:41 AM

Quote from: Moonmount;454511

Could you post some more pics of that car its gorgeous also where did you get those sc wheels and how well do they fit?

Thanks!! I'll have to get some more pics on here when I get a chance to, but the wheels and tires came from americanmuscle.com and I would recommend them as the prices are good, quality is good, and delivery was very timely. These are SC replicas. I ordered 17X8 for the front with 245/45/17 Mickey Thompson tires, and 17x9 with 275/45/17 in the back with zero fitment problems. Any wider in the rear would probably have to remove the quad shocks but I didn't want to do that. American muscle does have a 10' wide rim as well.

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #18 – March 29, 2016, 09:54:52 PM

275/40 rear maybe? Don't think anyone is making a 275/45R17. 275/40 would match the overall diameter of the 245/45 fronts.

cheers
Ed

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #19 – March 30, 2016, 01:55:57 PM

Quote from: AT8 Cat;454392

I've heard conflicting stories about whether my '88 AOD is a 7 tooth or an 8 tooth drive. How do you know for certain, can you see the drive gear well enough through the VSS hole?

Also, if the 23 tooth gear does suffer premature wear does it mess up the "drive" gear as well?

You have an 8 tooth drive gear. My 88 Thunderbird's AOD has an 8 tooth drive gear.

If the 23 tooth gear wears prematurely it will not damage the drive gear. The drive gear in the AOD is metal. The speedometer driven gear is plastic.

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #20 – March 30, 2016, 09:05:58 PM

Sparking my memory, I think I needed the 23 tooth, but went with the 21 tooth because it wasn't the aftermarket and would last longer. I'm about 5 mph off at around 60/65 MPH.

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #21 – March 31, 2016, 12:08:33 PM

Quote from: fast Ed;454549

275/40 rear maybe? Don't think anyone is making a 275/45R17. 275/40 would match the overall diameter of the 245/45 fronts.

cheers
Ed

My bad, you are correct sir! Thanks for the correction.

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #22 – March 31, 2016, 12:09:58 PM

Quote from: thunderjet302;454555

You have an 8 tooth drive gear. My 88 Thunderbird's AOD has an 8 tooth drive gear.

If the 23 tooth gear wears prematurely it will not damage the drive gear. The drive gear in the AOD is metal. The speedometer driven gear is plastic.

Awesome, that answers that. Thank you!

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #23 – April 23, 2016, 10:56:19 PM

How well do you like the staggered setup does it induce alot of understeer?

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #24 – April 25, 2016, 11:38:42 AM

Quote from: Moonmount;454990

How well do you like the staggered setup does it induce alot of understeer?

Seems good. I don't race it or anything but I have thrown it into some of the roundabouts here in town and it grips very good considering it's a mostly original 28 year old car. No understeer noted. These cars need the staggered set up to fill up the large rear wheel wells. I get a lot of compliments on these rims as they really finish off the look of the car nicely.

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #25 – April 25, 2016, 12:11:56 PM

**UPDATE** Finally got nice enough weather here to get the car out of hibernation and have the 3.73's installed. Job went well. Car now has a bit more "get up and go". On the highway, car used to rev around 2000 rpms at 115 kph, now it's 2000 rpms at about 100 kph.

I ordered a 23 tooth speedo gear from the local Jeep dealer as suggested by fast ed. It was an exact fit and since it's from another OEM dealer I'm hoping it's better quality than the aftermarket 23 tooth that was also available. However, according to my GPS with the 23 tooth gear I'm off by about 7 kph less than what the speedo reads. Do I need another gear or is that as good as it's going to get with the limited amount of gears available? I did the math, and like many suggested on this thread we come up with 23 tooth. How can we be off by 7 kph? This is my first gear swap so I'm a little stumped.

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #26 – April 25, 2016, 05:00:54 PM

What's size tires are you running? 7kph is only about 4mph off.

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #27 – April 26, 2016, 09:15:23 AM

Quote from: Haystack;455011

What's size tires are you running? 7kph is only about 4mph off.

Rear tires are 275/40R17.

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #28 – May 01, 2016, 10:55:20 AM

It's still reading too high? If so, that it as close as it gets, no higher tooth count than 23 on the speedo gears (that I'm aware of).

cheers
Ed

How to correct speedo after changing to 3.73 on '88 Cougar

Reply #29 – May 01, 2016, 08:13:36 PM

Pull the AOD and put a T-5 in there with a black 6 tooth drive gear and that will solve the problem. I am kidding but it sure sucks that you have to replace the whole shaft on the AOD's to change the drive gear.