Drivetrain Speedometer Correction

Vettn71 · Mar 14, 2015

I currently have a 95 GT with the 4R70W transmission. My speedometer is running about 5 mph slower than my actual speed. Shortly, I will be putting 3.55 gears in the rear, somy speedo will be really off. Anyone know what gear is needed, or do I have to change rear tire diameter, also.

TIA

Jim

addermk2 · Mar 14, 2015

Speedcal...done

toyman · Mar 14, 2015

The driven gear that you need is dependent on the tooth count of the drive gear. The 4R70W in a '95 is not stock. However, the wide ratio gear set is a drop-in for the stock AODE. The AODE will have a 7 tooth drive gear if the car came with the 3:27 gear option. If that's what you have you might want to reconsider the 3:55 and go with 3:73 gears.

90lxwhite · Mar 15, 2015

The white (23 tooth I beleieve) speedo gear is recommended for 3.55 and 3.73. It will get it close for a little while but it's not really a ford part (I think it's jeep) and it will eventually get chewed up and your speedo will be off again. I have the fore mentioned gear w a 3.73 rear end. It was probably about 5 or so mph after the install and now like 5 years later it's 10 mph off. To get it as close as possible you'll have to change the speedo gear and the drive gear. Changing the drive gear isn't so easy.

Vettn71 · Mar 15, 2015

Thanks for the replies. In late spring I hope to pull my engine and trans to do a H/C/I, replace some seals and gaskets and have the trans looked over.

I installed the 4R70W to replace a bad AODE, and have been pretty satisfied with it. I will count gear teeth, and if needed ill replace the drive gear inside the trans. I was hoping for a bit less cost, as the H/C/I is going to cost a bunch. I plan to replace the timing gear set, water pump, lifters, rockers, pushrods and have it tuned. It all adds up.

Jim

addermk2 · Mar 15, 2015

Vettn71 said:
I will count gear teeth, and if needed ill replace the drive gear inside the trans.

Not likely, since its part of the output shaft, It's not a removable gear, like on the manual transmission cars.

As I stated before. By a Speedcal, and be done with it.

Vettn71 · Mar 15, 2015

Not good news. I always thought the 7tooth and 8 tooth gears could be swapped. I'd hate to add the complexity of a speedcal. I don't think everyone is using a speedcal unit. What are other people doing?

Jim

addermk2 · Mar 15, 2015

They are either using the wrong speedo gear and suffering an incorrect reading.

OR they are installing the VERY simple to use... Speedcal

Vettn71 · Mar 15, 2015

Looks like the VERY simple to use Speed Cal has two issues for me. It's only for 96 and up Mustangs and it's only for fife speeds. I see AM no longer carries it, but Dallas Mustang does. FRPP does look like it might work, though

Jim

90lxwhite · Mar 15, 2015

Vettn71 said:
Looks like the VERY simple to use Speed Cal has two issues for me. It's only for 96 and up Mustangs and it's only for fife speeds. I see AM no longer carries it, but Dallas Mustang does. FRPP does look like it might work, though

Jim

Yeah once upon a time when I changed my rear gear from 2.73 to 3.73 (t5) I was in your shoes searching out how to correct the speedo and what not. Yeah I do believe you're right. The speedcal crap is for the obd II cars. I'm not sure if the frpp one will work on ours but I read a post on another forum where a guy had the speedcal for his '00 some odd and it wasn't accurate so he bought the ford racing one and it was. Most of us just suffer through by jamming the white speedo gear in. It'll be close enough for horseshoes for a little while before it gets eaten up. After that we just drive w the flow of traffic or haul azz.

90lxwhite · Mar 15, 2015

addermk2 said:
They are either using the wrong speedo gear and suffering an incorrect reading.

OR they are installing the VERY simple to use... Speedcal

The speedometer being inaccurate is on the lighter side for suffering. If one can deal w a lopey cam and a steep rear end they can probably survive the speedometer being off.

94GTCoupe · Mar 16, 2015

Sppedcal worked fine for me in my old 94 GT.
Easily handled my many tranny swaps (testing used parts to sell) and 3.73 rear gears, with a simple change to the dip switches.

Most problems I've read, are user error. poor wiring connections and wrong dip switch settings.

I hardwired mine directly to the tranny harness and mounted in the engine bay.

Much better then under the shifter boot, imho.

addermk2 · Mar 16, 2015

Vettn71 said:
Looks like the VERY simple to use Speed Cal has two issues for me. It's only for 96 and up Mustangs and it's only for fife speeds. I see AM no longer carries it, but Dallas Mustang does. FRPP does look like it might work, though

Jim

I wouldnt have recommended one, if I wasn't sure it would work. I happen to be running it in my 94 Cobra with a 4R70W...

Just sayin'

Vettn71 · Mar 16, 2015

I understand. It seems a couple others have used it, as well. I went and ordered the FRPP speed calibrator, as there are multiple posts from people having issues with the DM SpeedCal, and some of those stated the FRPP unit worked better in their 94 - 95s. It seems it depends on a lot of variables, most of which I am not aware of. I'm certain it works for you and the others who give it a thumbs up, but I think there must be some underlying issues as to why it is only recommended for 96 to 04s now, and only 5-speeds at that. Seriously, if the vendor says it won't work on my car, I'm not ballsy enough to roll the dice. That's just my take. I'll update when I get the FRPP unit installed and working. If it's crap, I'll let everyone know

Jim

addermk2 · Mar 16, 2015

Vettn71 said:
but I think there must be some underlying issues as to why it is only recommended for 96 to 04s now, and only 5-speeds at that.
Jim

The auto and manual both use the same VSS... so I fail to see how the type of transmission is even close to relevant.

Vettn71 · Mar 17, 2015

I really don't know. It seems odd to me, also. I don't usually understand everything I know, though

Jim

Vettn71 · Mar 21, 2015

Installed the Ford Speed-Cal today. I spliced into the harness in the engine compartment at the large 16-pin connector on the right side firewall. My issue was that even with stock tires my speedometer was off by about 5 mph at 60. The speed-Cal was easy to set, just turn 3 pots inside after driving 10 miles to see what the error was. Very good directions and no issues whatsoever. All in all I pretty pleased with it, both on the installation and it's operation

Jim

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