Well as some of yall may know I installed a new instrument cluster to fix my bouncing speedo problem. Well the new speedo works great until I hit 45 then it varies around about 1 mph. At 60 it is about 5mph and if i'm at WOT going 45+ it just goes crazy. I replaced the sensor in the rear end but maybe I have a bad one???? or could something actually be wrong in the rear end. I didnt notice this because this was the first time I had gotten up to interstate speeds since the install but under 45 the speedo is great. Any thoughts will be great.

 

Could still be the cluster. I replaced mine on my 96 when I bought it and the dealer got me the wrong one the first time...

 

Not the cluster I tried it out on a buddies and it worked fine

 

is it the same problem you were having with the first cluster, or are these different symptoms?

 

the old cluster was crazy all the time this one is only crazy at higher speeds

 

Hrmm, this sucks. Its got to be from where ever the signal is coming from...fords, I don't know much about the trannys or where things are located. If it was me, I'd get down there and root around lookin for a loose connector/wire/sensor.

I think the "older" 5.0 mustangs have a gear (nylon?) near the end of the trans that the speedo sensor works off of. check it out, maybe the trucks are completely different.

 

I believe that the trucks register their speed fro mthe rear end sensor???? I could be wrong

 

You're right. the VSS (vehicle speed sensor) is located in the diff housing on a 95. It reads the teeth on the exciter ring which rides outside of the carrier next to the ring gear.

 

could one of these teeth be missing therefore at slow speeds the speedo will wiggle slightly but at higher speeds the missing toothe would be going around alot faster and cause it to be off by more than when im goin slow

 

Not likely. the exciter is pretty robust. Sounds like the VSS isn't set up correctly. The gap between the sensor head and the exciter is pretty critical for proper operation. It may be marginal as currently installed. I'm away from my shop manual at the moment, so I can't check the setup procedure. I'll try to post this evening unless someone else beats me to it.

 

thanks for the help I didnt know it needed to be gapped

 

OK, the shop manual lists 4 causes for erratic speedo operation:

1) Damaged, missing or bent teeth on the exciter ring
2) Metal chips on the magnetic speed sensor
3) Open or shorted sensor
4) Improper gap between sensor and ring.

To check the first, you need to pull the rear cover off the diff housing, rotate the driveshaft and inspect the exciter teeth. If there's a problem, it's a major job to replace the ring.

To check the second pull the sensor, clean the tip and the hole into which it goes and the mounting surface. Inspect the o-ring and replace if damaged. inspect the electrical connector and seal. Replace the seal if damaged. Put it all back together.

This will also cure the 4th cause, improper gap. There is no adjustment in the sensor itself, but crud on the mounting surface can affect the accuracy by changing the sensing distance.

A sensor problem would probably also give you a warning light for your rear anti-lock brakes since they are controlled by the same sensor.

There could also be a wiring harness problem but the manual describes these as "difficult to diagnose." No ****, Sherlock.

Hope all this helps.

 

thanks for the help im gonna pull the diff cover off this weekend

 

Clean and check the sensor first. It's by far the least work and eliminates 2 sources of error. If that doesn't work pull the cover. If the exciter is damaged, you're looking at a full teardown of the rear end just to get at it. It's only a $38 part but it's virtually the same amount of labor as changing the R&P. you might want to learn to live with a jumpy speedo.