Hey guys/gals, I wanted to share with you a great project to do on your '79-'86 Mustang/Capri. I learned it from my twin brother Paul Slaney (306gt on this site), who's done it on his '85 Mustang GT and on his son's '86 Mustang GT.
If you've ever wanted to have a 140 mph speedometer in your Mustang/Capri but cannot find those elusive Ford Motorsport or Certified Calibrated SSP speedometers, you're in luck. How? You can now convert your current 85 mph speedometer into a 140 mph unit pretty easily. I just finished this project for my '79 Cobra and it's 100% accurate, as I compared it to my I-Phone's GPS based speedometer app called Speed Box.
To do this, you must find an '89 - '93 Mustang 140 mph speedometer. I was lucky, as I had one that I took out of my '89 LX 5.0/5-speed when I stripped it last year. It's now been re-purposed into my early foureye with great success!
Step by step instructions are listed below.
1. Remove cluster from dash and remove original 85 mph speedometer from cluster
2. Remove the speedometer needle by pulling up on it. Be careful or it will break (Pull it upwards from center section and not the needle pointer). Once done, drill out the four small rivets from the face of the speedometer that hold it to the frame and remove the face
3. Now that you're down to the frame that contains the "guts", remove the two small screws from the front of frame that hold the "guts" of the speedometer. You can then remove the "guts." Once removed, you will see a round "brake drum" type thingy with a needle that's still attached to the frame (this needle goes through the frame and is held in place by a small spring on the front of the frame). Pull this out from the backside. Once done, you can carefully remove the spring on the front by gently moving it aside and by loosening the nut that holds it to the frame. BE CAREFUL with this spring because if it breaks the speedometer will not work. Also, you MUST change this little spring or it will not be accurate.
4. Disassemble the 140 mph speedometer in the same exact fashion and reinstall everything from the 140mph unit onto the '79-'86 frame (the '87-'93 frames are different). Again, be careful with that spring! If you break it, you cannot use the spring from the 85 mph speedometer, because they're different. I know that because I tried to use it and the speedometer was only accurate up to 40 mph. At 80 mph it showed me doing 140! I then relented and made the swap to the correct spring and it became 100% accurate.
5. Now you can reinstall the 85mph speedometer face by using small screws in the previously drilled out rivet holes. Once done, install your 140 mph gauge overlay decal and reinstall the needle by pushing it into place with it pointing to zero.
6. Reinstall your "new" 140mph speedometer back into your cluster, reinstall the entire cluster back into the dash, and reinstall your dash bezel. You're now done!
Tom Clark (69clark on this site) made me this set of gauge decal overlays and they came out great! His decal kits are very reasonable as far as pricing is concerned and he can customize them as well. If anyone is interested, send him a private message.
Anyway, here's some pic's.
Stock '89 LX 5.0/5-speed 140 mph speedometer
Tom made me these overlays out of Carbon Fiber Paper and I asked him to make a few custom touches. First, he changed the "Redline from 4,800 - 5,800rpms to 6,000 - 7,000 rpms, as my 347 makes peak power at 6,000 rpms and I shift it at 6,500 rpms. Also, instead of the "Redline", he was able to change it to an "Orangeline" to match the colors on my Cobra door decals. He was also able to add the Cobra logo to the speedometer in the same font.
Now, my original tachometer was the Turbo 4-cylinder unit that showed 8,000 rpms. The problem is that it wouldn't work with the V8 and the original 6,000 rpm tachometer for the V8 cars would have been useless, as I shift at 6,500 rpms. For that reason, I installed an '83 Mustang GT 7,000 rpm tach and that will work for me. I also added the MSD tach adapter (MSD part # 8920) to my ignition in order to make it work with my MSD 6AL ignition box and that too works flawlessly and is accurate. Here they are with the overlays installed. I also painted the needles Fluorescent Orange to match.
Pic of them installed. I had to take it back out again and position the needle on zero. DOH!
Pic of them at night with lights lit. I chose to remove the Blue covers on my lightbulbs to get rid of that Green hue and it worked out well. These are the stock lights at full brightness but they can be dimmed like normal with the headlight switch.
I hope you all like this info!
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