Digital speedometer off

Topic: Digital speedometer off (Read 2681 times) previous topic - next topic

Digital speedometer off

March 12, 2009, 02:03:28 PM

hey all, I've got an 88 Cougar and have discovered that the digital speedometer is off by about 30-40 mph. Is there any way to correct this? I've looked in my Haynes manual but have found nothing that addresses this issue. Thanks ahead of time.

Digital speedometer off

Reply #1 – March 12, 2009, 07:42:24 PM

Mine is off a little off too. This would be useful.

Digital speedometer off

Reply #2 – March 12, 2009, 07:54:19 PM

I dont see any way that it could be calibrated. It just uses and electronic input. Unless your speedo gear is way off.

Digital speedometer off

Reply #3 – March 12, 2009, 08:28:39 PM

Quote from: Haystack;261190

I dont see any way that it could be calibrated. It just uses and electronic input. Unless your speedo gear is way off.

could also be a malfunction in the speed sensor.

Digital speedometer off

Reply #4 – March 12, 2009, 10:05:18 PM

Quote from: 88turbo;261206

could also be a malfunction in the speed sensor.

I agree. I was talking to a friend of mine and he mentioned that the sensor may need replacing. According to him, its near the brake calipher but I'm still not sure.

I checked the Haynes again and did find the only reference to the speedometer in the trannie section and referred to as 'Speedometer pinion gear and seal-removal and installation'. This doesn't seem to address the issue and looking at my parts list, there isn't anything remotely listed involving the speedometer as a replacement part (unless you count the entire instrument panel priced at $566.17:wtf: ) but I'm not giving up..I will fix this one way or another.

Digital speedometer off

Reply #5 – March 12, 2009, 11:50:41 PM

shop manual

Chassis electrical part 1 of 2 volB
page 33-05-16

PINPOINT TEST INDEX

SPEEDOMETER DIAGONSIS GUIDE
#37-Speedometer constantly reads too high or too low ,,,, GO TO pinpoint test SG

be right back with troubleshooting steps.

;
;
;
;
OK,, everything points to speedo sensor / gear.
remove speed sensor on the trans tailshaft
inspect gear
replace gear (good luck)

Digital speedometer off

Reply #6 – March 13, 2009, 09:41:05 PM

Quote from: Haystack;261190

I dont see any way that it could be calibrated. It just uses and electronic input. Unless your speedo gear is way off.

I agree, swapping speedo gears in the transmission will only correct one a maximum of 12-15mph... All these cars have a gear in the transmission at the driver side rear... A brake caliper has zip to do with the speedo, no sensor anywhere near it...

Digital speedometer off

Reply #7 – March 13, 2009, 11:55:39 PM

Are you sure the speedo gear hasn't stripped any teeth? It's rare, but can happen.

What size tires?
What rear end ratio?

Digital speedometer off

Reply #8 – March 14, 2009, 01:31:22 AM

Yeah, usually only the 23 tooth gear strips easily, but you never know. I suppose the digital encoder (the thing the speedo gear is attached to) could have taken a . Worst case the dash forgot how to count because it's effed - seems unlikely to me.

Digital speedometer off

Reply #9 – March 14, 2009, 07:34:41 AM

I bow down to all you car savvy people..

as I'm just starting out fixing my car, don't know diddly, but I'm trying to learn.
I'd really like to do this work myself..well also as a learning tool for my 16y/o son who I want to understand that learning to drive and taking care of a car, takes more understanding than just getting behind the wheel and/or taking the car down for an oil change.

Thanks for all the responses! After reading them I went back to my manual and still wasn't satisfied as there really wasn't any description of the speedo cable or any real instructions other than the given 4 steps. So I let my fingers do the google and this is what I found...(I hope its alright to post this in conjunction with the link..if not..Oops).

Changing your Speedometer Gear

Improving the overall performance of your favorite ride by changing rear-end gears is common, but it's not the only gear change required. Inside the tail housing of your manual or automatic transmission is another gear, which controls your speedometer and odometer. When you change the rear-end ratio, it throws off the gear in the transmission, so the speedo will read faster or slower until you get the correct trans gear. The various transmission gears are usually plastic and are color-coded to the ratio they correspond to. There is a great physical difference, as show here, comparing the early Super Turbine 300 Powerglide gear with a Muncie four-speed gear. Both are for 3.55:1 rear-end ratios; the four speed's is maroon and the Powerglide's is tobacco brown in color, but the shape change is dramatic.

Most manufacturers still stock (or can special-order) whatever transmission gear you need, but it might take a few days to get it. If you're planning on changing rear gears, you might order the correct trans gear and do the change simultaneously. The installation is normally simple and no special tools are required. The gear resides inside the tail shaft where the speedo cable screws to the trans. Normally there is a plate holding the gear in place, and the square end of the cable slides into the end of the gear. Here's the basic change-out; yours might be slightly different, but the prinl is identical.

Removal
After unscrewing the speedo cable from the gear housing, remove the small bolt(s) holding the retaining plate in position. The housing containing the gear has an O-ring (shown here) to prevent transmission fluid from leaking out. It might take a little jiggling to pull the housing free, as the seal is tight. Be prepared for a little trans fluid to leak out when the plate is removed. Having a rag or drain pan under the tail housing will prevent a mess. This Super Turbine 300 only leaked about half a cup of fluid. Some transmissions might spit up a little more, so be prepared and work quickly.

Install
The original gear is removed after the housing is taken off. It simply is pulled out and the new gear inserted. Trans fluid lubricates the gear, so no additional lubrication is required. Observe the way the original gear is fitted into the trans housing. It meshes with another gear in trans housing, which spins it and the speedo cable, registering your speed at the dash. Pretty simple in a high-tech world. The procedure is the same for either manual or automatic transmissions that have an external speedometer cable. Someday these gears will no longer be available, so if you're planning on keeping your car for a long time, get an extra gear just to be safe. Also keep the original gear in case you ever switch back to your original rear-end ratio.

Digital speedometer off

Reply #10 – March 14, 2009, 10:03:08 AM

Note that the digital dash doesn't even have a cable, there are just some wires that come out of the "gear housing" (which is a "digital encoder" in this case). So, you just remove the small bolt & pull it off, then check out the condition of the gear. Also shine a light into the transmission to ensure the drive gear on the output shaft is in good shape - you can see it through the opening when at the right angle. Note that automatic and manual transmissions have different gears (in case you need to replace one). Go here -> http://crt-performance.com/speedometers.htm for a table listing all the possible gears (if you end up needing one).

Digital speedometer off

Reply #11 – March 14, 2009, 10:39:52 AM

Hey, glad to see we got one more new england member!!!! Were gonna have to see pics, just letting you know before the hounds come out of the woodwork!!!!! Or ill have to take a ride and check out your project myself!!!!

Digital speedometer off

Reply #12 – March 14, 2009, 07:08:56 PM

Quote from: massCougarxr7;261550

Hey, glad to see we got one more new england member!!!! Were gonna have to see pics, just letting you know before the hounds come out of the woodwork!!!!! Or ill have to take a ride and check out your project myself!!!!

Howdy neighbor..lol..will post some pics in the appropriate thread..unless I can post them on my profile..(hasn't fully checked it out yet).
***
For all the posters, many thanks for sharing your knowledge with me. As far as knowing if the speedo gear is missing teeth, I've not gotten that far, but will find out hopefully by next weekend. (I only get one day off a week.)

Digital speedometer off

Reply #13 – March 14, 2009, 09:27:46 PM

you shouldnt have to unplug the wiring to check the gear all you need is either a 10mm or 11mm its been alittle while since I have done one on a fox but I think it is a 10mm.

Digital speedometer off

Reply #14 – March 14, 2009, 10:26:54 PM

Quote from: 88turbo;261648

you shouldnt have to unplug the wiring to check the gear all you need is either a 10mm or 11mm its been alittle while since I have done one on a fox but I think it is a 10mm.

Yup! Just one bolt :D