New Speedometer Issues

[Russtypickle]

So I'm getting ready to put the dash back together and I just received my LMC speedo (79-80 part# 36-1862) and speedo cable. However, the speedo does not have screw hole in the back to secure the retainer for the cable (see photos). Has anyone come across this? I suspect I'm supposed to drill a hole or use a short self tapping screw but that doesn't seem right. The speedo came with the retainer but no screw for it and after taking off the gasket, there's no hole for one. Anyone have ideas or had this issue? I'm pointing to my old speedo in the photo - where the screw hole should be...

 

[Russtypickle]

okay so I drilled the back and it's pretty straight forward, just go slow. Here's what I did, and why....

First, pick the correct location. There's a gear on the top or bottom (both mine were different) (see photo), you'll want to drill on the other side where there's nothing behind. It's easier to see on the older units but you can see both "shaft" ends on the new units. I started with a 5/64 bit and went down to the depth of the screw. Then went up to a 3/32 bit to get to the correct diameter for the factory screw. Be careful not to go through if you can avoid it, I didn't on mine and I used tape around the sides to keep filings from getting into the unit. Once drilled the screw goes in nicely. Again, go slow and measure the depth lots.

 

[bucket]

I just wonder why the heck the new one didn't have a screw hole?

 

[Russtypickle]

Ya, that's what I wondered. Strange but I suspect I'm not the only one who's going to get one of these in the mail so at least there's a fix. You'd think they'd at least tell you how or where to drill the hole, if you don't do it the cable WILL NOT stay in, eventually it'll pull off so ya, strange.

 

[Russtypickle]

Just to follow up.. Just got back from a test drive, speedo works great!

 

[ali_c20]

So I'm getting ready to put the dash back together and I just received my LMC speedo (79-80 part# 36-1862) and speedo cable. However, the speedo does not have screw hole in the back to secure the retainer for the cable (see photos). Has anyone come across this? I suspect I'm supposed to drill a hole or use a short self tapping screw but that doesn't seem right. The speedo came with the retainer but no screw for it and after taking off the gasket, there's no hole for one. Anyone have ideas or had this issue? I'm pointing to my old speedo in the photo - where the screw hole should be...

The old speedometer from your cluster is a 81 up with the clip attached to the speedo with a screw on the bottom side of the cable input.
The clips for pre 81 speedos are attached to the cluster backing plate with a screw on the top of the cable input. That's the reason why the 79-80 speedo does not have hole for the screw.
There where different backing plates 73-75, 76-77, 78-80 and 81-87


81 up:

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78 - 80:

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73- 75:

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[Russtypickle]

Love this group, every time I think somethings stupid or doesn't make sense, someone chimes in with knowledge to share that reminds me how much I don't know, thanks Ali_C20, that's you this time! It is odd that they sent my speedo with an 81 or later retainer clip. Had they put the earlier clip in I might have understood the difference. In any event, now guys will know that you can put an older speedo in a newer cluster, you've just got to drill a hole

 

[Gander]

I just wonder why the heck the new one didn't have a screw hole?

Because the later style cluster back has the retainer screwed to the cluster back. I just went though all this building a tach cluster for my 1987 with factory parts.

Edit: I see someone already beat me to the answer, with pics!

I think that cluster back labeled 78-80 was used beyond 80 on trucks without
Cruise Control. The 85 tach cluster I got for parts to build my cluster had that back labeled 78-80. That cluster was out of a 1985 C20 with a manual transmission and no cruise so no VSS.

 

[bucket]

Because the later style cluster back has the retainer screwed to the cluster back. I just went though all this building a tach cluster for my 1987 with factory parts.

Edit: I see someone already beat me to the answer, with pics!

I think that cluster back labeled 78-80 was used beyond 80 on trucks without
Cruise Control. The 85 tach cluster I got for parts to build my cluster had that back labeled 78-80. That cluster was out of a 1985 C20 with a manual transmission and no cruise so no VSS.

Yeah, I had forgotten about the cluster differences and was too lazy to walk out to the garage and refresh my memory.

...But that new speedo still came with the wrong cable retainer, which added to the confusion.