180mph BBK Speedo and 3.73's calibration

[trinity1988]

Ok, so I have a new project car here that has some speedometer issues. The car is an 88', has 3.73 gears, 275/40/17's and a BBK 180mph Speedo overlay (I know, I'm never going to go that fast, EVER!). I need to know how to correct the speed, It's off roughly 15-20mph. Should I just track down a factory 85mph speedo or get the 21 tooth gear? I have never done this before, so I'm clueless when it comes to changing it out.

Thanks in advance for your help!

 

[Mustang5L5]

What speedo is under the overlay?

When you change actual speedo gauge ranges, the mechanical speedo needs to be changed. Changing the gear in the trans will not recalobrate a speedo. That only changes the output to compensate for rear end gear changes.

The proper speedo gear for 3.73s and a t5 is 21 tooth. Of the speedo os off, you need to recal the speedo to whatever the gauge face is

 

[2000xp8]

I had to have my 170 re done, i think i called brothers performance.

 

[trinity1988]

It's a BBK overlay unit I think. I tried peeling it off, but I've never done the white face gauges so i'm assuming its an overlay Am I better off just getting a 140 speedo somewhere? My mileage will bee off then too right?

 

[Mustang5L5]

What speedo is in the car now?

 

[trinity1988]

Right now it has the bbk on it. Like I said, I don't know if it's a complete speedo or an overlay.

 

[2000xp8]

It's probably an overlay, bbk didn't make complete speedometers as far as i know.
If you want a 140, buy one and drop it in, if you want the 180, you have to send it out to be calibrated.

 

[srtthis]

i have saleen 200's in mine and even they are a bit off...

 

[Mustang5L5]

Your speedogea is correct for your trans and gears.

Your best bet is to go out and do some testing by driving at 2000, 3000 and 4000 rpm in say 4th gear and noting your indicated mph and using a gear calculator chart to compare.

When you say you are 20mph off, what speed is that measured at? 20mph off when doing 35mph....or 20 off @ 150 mph?

 

[trinity1988]

The speed is off 15mph going 60mph per the gauge. I had my wife pace me one day at different speeds when I got it cuz I knew it was wrong. Going 90mph I am actually going about 65, so it gets worse the faster I go, which makes sense.

If its an overlay, can I just peel it off? Is there usually some kind of adhesive? How do I remove the needle without those little tools that come with the kits? Thanks.

 

[2000xp8]

You can pop the needle off many ways, comes straight off, use whatever you can as a lever.
But the real question is, what are you going to do with a gauge with no face?

 

[trinity1988]

That's what I was wondering. I don't know if they were overlays or if it was a whole other gauge face. I have never taken these off before.

 

[trinity1988]

Just checked, it's the gauge face. So, I am wondering, can I just get those 85 or 140mph white face gauge overlays to work? I don't mind the look of them, but I'm wondering if my speedo will still be off? Any opinions on the white face kits?

 

[sully88gt]

I'm still confused on how many parts there are and how they work together to make the speedometer work. My speedo bounces real bad until I hit about 40mph then it steadies out. The previous owner said he installed 3.73 gears, any ideas how I can fix this?

 

[Mustang5L5]

Bouncing speedos are usually the cable. Either lube, or replace the speedo cable.

 

[trinity1988]

Ok. So I have since replaced the instrument cluster with an original 85mph unit. Well, the speedo is still off. Not as bad, but still 10+ and climbing as I go faster. Do I now need to look at the speedo gear?