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Car Dolly

In-Dash Tach

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In-Dash Aftermarket Tach

My car didn't have the factory tach, and I can't see driving a 4 speed car without one. I wasn't willing to pay the big bucks on Ebay for an original tach, so I needed to find some way to fit an aftermarket tach where the factory one would've gone - in the dash. I didn't want to mount one on the steering column, or under the dash.

After quite a bit of searching, I came to realize that none of the aftermarket tachs would fit the hole in the dash. Something would have to be fabricated. Here's a write up of what I did. As of this writing, I think it will work really well. The only unknown is how it will stand up to the test of time.

Shopping List

1) 2 5/8" pedestal mount tach
2) 1/2" thick foam weather stripping
3) can of foam sealant

Items 2) and 3) can be had at your local hardware store. The weather stripping comes in a roll, and is commonly used for insulating windows. The foam sealant comes in an aerosol can; the popular brand name is "Great Stuff". It comes out of the can in foam form, and then hardens. Commonly used for sealing cracks in structures.

The tach that I bought is an AutoMeter 2891. Its scale is 6000 RPM; if you want 8000 RPM, get the 2892. I bought mine for $80 at Jeg's or Summit Racing (I don't remember).

AutoGuage also has 2 5/8" tachs, but I don't know if they would fit as well as the AutoMeter one did. They are cheaper, though.

Instructions

note 1: click on any image for full size
note 2: these pix were taken after I was done, so some things may seem out of order, like the presence of foam sealant before I've mentioned using it

The basic idea is to use the tach-delete piece in the dash as a mounting device for the tach (thanks to Bob Reed for that idea). That piece of plastic will be inverted, and the tach is placed inside it. The problem is that the case (or cup) of the tach is 2 5/8" wide, while the inner diameter of the tach delete piece is 3". That's where the weather stripping/foam come in.

Step by Step:

1) Remove the tach delete from the dash. Invert it (flip front for back), and rotate it 180 degrees. Looking at the back of the instrument cluster, you want the mounting hole on the left hand side to be used by the same mounting tab on the delete piece as before you removed it.



2) Note that the 3 holes no longer line up perfectly, and that part of the flange on the delete piece will need to be trimmed in order for it to mount flush. As for the 3 holes, I positioned the tach delete so that the 2 on the right lined up, and I wallowed out the flang on the left so it would work.

3) Trim the flange and wallow out the hole so that you can mount the tach delete flush with the back of the instrument cluster. My trusty dremel tool made this quite easy. Mark the tach-delete so that you know where the bottom (6 o'clock) position is.



4) Either cut or drill the tach-delete so that the wires of the tach have a place to exit. Dremel tool comes in handy here again.



5) Place 3 short (like 1/2") pieces of weather stripping around the inside of the tach-delete. These will hold the tach in place while we secure it. The back of the tach cup is domed, so be careful and get the tach centered in the tach-delete.

6) Remove the mounting bracket from the tach cup, but leave the cup on the tach.

7) Place a little duct tape over the gap in the tach cup. It needs to be sealed up to prevent any foam from getting into the electronics.



8) Once you've got the tach positioned in the tach-delete, spray some foam into the space between the tach cup and the tach delete piece. This is what will hold the tach in place. Get some foam around the entire perimeter of the tach. A little goes a long way, and it will expand as it sets, so don't go crazy. Don't worry about excess foam; it can be trimmed with a utility knife afterward.



9) Let the foam set up. It should sit for at least a couple hours; over night would be even better.

10) Trim the excess foam from wherever it might've gotten, and mount the whole thing in the dash. It should look like this:





Conclusion

It seems to have worked quite well. The good and the bad:

Pros:

  • Through shear luck, the tach fits very well. With the rear of the cup inserted into the tach delete as far as it can go, the bezel just touches the back side of the glass in the dash. It's perfect.
  • It's cheap. The weather stripping and foam sealant will cost you $5.
  • The diameter of the dial and placement of the numbers are great.
  • It's pretty easy. The whole thing can be done in a couple hours.
  • It can be undone. While the foam is firm and holds the tach nicely, it could be removed if need be. And although the tach-delete is cut slightly, if returned to it's normal position, it would still look like it did originally.

Cons:

  • The dial is slightly recessed, and you look through 2 layers of glass to read the dial. Given that it's right in the middle of the dash, I don't consider this a problem, though.
  • Will it stand the test of time? I don't know if the foam sealant will degrade due to age or vibration.

If any of this is unclear, feel free to send me email.





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