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Quick question on gauge compatibility before pulling the trigger on tach

jtrux

jtrux

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So I've been wanting to install one of those tach conversions from LMC since I swapped to a manual in my '91 burb. I've only messed with the gauges in my '71 and this '91 so I don't know squat about the years between them. The tach conversion kit shows it to work with years up to '87 and I called the LMC tech line and the lady didn't really seem to be too knowledgeable other than repeating what the description says. I thought I had heard that the 90/91 gauge clusters were different than previous years but I have nothing to go buy other than what I think I remember about that. So, will the LMC tach kit work on a '91?
 
The 90/91 trucks have an electric speedo and this makes some of the cluster wiring different. The plastic shell that all of the are attached to is also different because of the speedo. I'd find someone knowledgeable / experienced before pulling the trigger.
 
I put an older tach into a newer electric speedo cluster. Some cutting and wiring was required to fit everything into the housing, but the mounting bosses were in place. It all looked stock when I was done. Just make sure you grab a newer style tach with the orange ring and lettering to match the newer speedometer.
 
I see the LMC tachs have a separate fuel gauge now vs. on the tach. Me likely!
 
Russell said:
I put an older tach into a newer electric speedo cluster. Some cutting and wiring was required to fit everything into the housing, but the mounting bosses were in place. It all looked stock when I was done. Just make sure you grab a newer style tach with the orange ring and lettering to match the newer speedometer.
Click to expand...

Yea, that's an idea. Just buy the individual parts and make it work. I have a spare cluster I can use as a guinea pig.
 
IMO the big trucks tach/fuel gauge is the best idea.

The cluster is different, but as far as I could tell, in this regard only significantly different where the small fuel gauge went in a factory application with tach. On the later cluster housing it isnt cast for the clock/fuel gauge....its setup for the required alternator/charge light.

It's just plastic, I'm sure it could be cut up, and I want to say someone on here cut two clusters (old and "new") in half then combined them to get the right cutout for the fuel gauge. Again, the available tach/fuel gauge would seem to be a LOT easier. I want to say those were available with the correct font for the '81+ gauges.
 
I called Brothers on this same issue a few days ago to see if they 1) had the correct speedo for a 91 (they are out of stock and no idea when they will be available....2) the tach upgrade with moving the fuel gauge WILL NOT WORK in a 91 Suburban. I asked why and was told it wouldn't fit.......Totally confused me as they are the same vehicle as the 87 dash wise except for the electric speedo. I didn't argue with him. The Tach conversion kits were not in stock either. No help there. Still don't know if they will fit or not but I have a feeling that they will. Wiring modifications to be sure and maybe their instructions just didn't cover the 91 wiring. I'd be interested to know. I'm looking for a speedo since mine is wrong most of the time and the odometer is total gone. I wanted a tach just because and my fuel gauge is iffy at best. I found a few used old stock but hate to spend good money on 29 year old parts.
 
Well, this is one reason it "will not work":
full


But it's plastic. Not like it can't be modified to work, except it looks like there may be at best one stanchion (what the screw threads into) to mount the gauge. I can see why someone would cut two clusters apart and splice them to get the earlier clock position.

You also have to do something with the charge light that is in that position, as the later alternator setup needs that bulb to work properly.

If their tach upgrade (I can't get to their site now to check) comes with the flexible circuit that goes on the back of the cluster, that would be another reason whatever they sell won't work. The printed circuit and wiring pinout for the instrument panel connector is significantly different on the '90-91 clusters compared to the previous.

Anything can be made to work, but there is no chance anything out there except something designed specifically for the '90-91 clusters will work as a bolt up kit. Or the tach/fuel gauge combo that was used in the larger trucks.
 
dyeager535 said:
Well, this is one reason it "will not work":
full


But it's plastic. Not like it can't be modified to work, except it looks like there may be at best one stanchion (what the screw threads into) to mount the gauge. I can see why someone would cut two clusters apart and splice them to get the earlier clock position.

You also have to do something with the charge light that is in that position, as the later alternator setup needs that bulb to work properly.

If their tach upgrade (I can't get to their site now to check) comes with the flexible circuit that goes on the back of the cluster, that would be another reason whatever they sell won't work. The printed circuit and wiring pinout for the instrument panel connector is significantly different on the '90-91 clusters compared to the previous.

Anything can be made to work, but there is no chance anything out there except something designed specifically for the '90-91 clusters will work as a bolt up kit. Or the tach/fuel gauge combo that was used in the larger trucks.
Click to expand...
I believe the tach conversion kits comes with a new plastic bucket pictured here but you are correct about the flexible circuit. Seems like they could use correct bucket and circuit for the 90-91 year but maybe they are not available. Anything is doable if it is in plastic. Maybe a 3D printer could build a new bucket. Way past my expertise. I am leaning toward a 6 piece gauge set from one of the aftermarket gauge companies but really don't like the look of the factory dash that much so may buil
 
I cant find reference to the tach being used any later than 1981 based on the parts manual. Regardless, having never seen one, I am as certain as I can be that there was no tach cluster factory for the 90-91 clusters. Cost cutting measure for GM, I'm sure.
 
I had two factory tachs in my possession at one time. Did a lot of physical comparing the two housings and printed circuits. The tach cluster was from a '78 and mine is a 91. Circuits are different for sure. The housing could be made to work with some careful Dremel action.

What stopped me was the fact that I couldn't do anything about the signal mismatch from my engine control module for the tach to work correctly. The late model ecms don't generate a tach signal in the same manner an hei ignition does. Typically you can switch an aftermarket tach to 4 cyl mode for it to read correctly. I'm not sure if you could do the same thing to a factory tach by changing the resistance leading into it. I didn't have the time or patience to screw around with it. So I used an aftermarket tach instead.
 
Were the coils still not 4 wire on the TBI trucks?

I ran a factory tach with my TPI before I realized I didn't need it, and before I converted to the 90-91 cluster, but the tach signal wasn't from the ECM, it was from the coil. Same as the pre-injection trucks.
 
Both my 5.3 and 8.1 get the tach signal directly from the ecm. A TPI would still work like any other HEI system.
 
Somewhat tough to find, but this is in my 91 cluster. Medium duty gas truck tach.
Trimmed up the housing and put some jumper wires right to the printed circuit. Tach has its own harness.20190614_103043.jpg
 
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