Hi!! I recently got a 79 L48 and have found some issues.

Speedometer does not work at all. I'm thinking it might be in the cruise control transducer. Does this make sense?

Tach does not work at all. No clue there, I think it's electric, right?

Most gauges in the center console do not work. Is it possible that the PC board in back of the gauges is broken affecting all of them?

I think there are more issues, mostly that I think there is a leak on the drivers side that is getting the carpet wet.

Thanks in advance!!

 

Here's what I would check:

Speedometer - Worm gear is probably bad and needs replaced

Tech - The tach plug in the distributor is disconnected or not working. If that's not the case, then the circuit board is probably bad and needs replaced.

Gauges - I'm assuming the gauges are not working at all, as opposed to giving incorrect information. It's probably either the flexible circuit behind the gauge console, the plug into the gauge console, or both. These cars are old and the wiring can be corroded.

Leak in the driver's side - It sounds like your windshield frame has rusted through, allowing water to run down the inside of the birdcage pillar and into the passenger compartment. These cars are notorious for that.

Hope that gets you started in the right direction. Good luck.

 

id bet the speedometer is bad if it does anything at all. the tach probably needs to be rebuilt too.

 

Interesting that you mentioned the leak AND the gauges not working. Look closely at the gauge fuse, not just for it being open (blown) but look for corroded contacts both on the fuse and fuse box. Today's blade fuses are made out of garbage. Start with a new fuse, clean up the contacts on the box with some contact cleaner and compressed air and put it together with some electrical anti-corrosive grease.

This won't help the speedometer unfortunately.

 

What about one of the cables being broke for the speedo? Very easy to check/replace, I got a universal cable at Auto Zone cheap.

 

The speedometer did not work on my 78 and it was the transducer for the cruise control. I found one at a u pull it wrecking yard in a late 70s camaro for 5 bucks. When I opened up the one originally in the Corvette it was badly gummed up probably from years of cable lube. Cleaned it out and have it as a back up.

 

Tach does not work at all. No clue there, I think it's electric, right?

Check the ground as well .. had a tacho in my 79 and both the board was cooked and the ground was bad


I think there are more issues, mostly that I think there is a leak on the drivers side that is getting the carpet wet.

I've been on this journey for a while, even tracked down a copy of "Corvette Water Leak and Wind Noise Solutions" by Michael j. Davis.

My first problem was that the drain holes on the inner guard and the doors were blocked, I then discovered that Bubba has cut down the slots at the bottom of the door at the front (so the water never made it to the door drain holes), the door seal had separated from the door near the bottom of the front of the door, and there was a gap between the door on pillar seal (and door seals were shot) and some leakage also occurred as I did not have the plastic liner behind the door panel (good idea to take the door panel off as well to trace drip lines)

re the leak from the bird cage, pull the kick panel and have a look at the body mount .. if its rusted then odds are you have a leak .. in my case it was not the bird cage but the factory had missed parts of the bonding line with the glue between the guard, firewall and bird cage so as the water built up (remember the drain holes in the inner guard were blocked) it would leak over the body mount (only found with a scope camera) .. a quick test on the bird cage being rusted out is seeing if the top of your guard near the bird cage is fixed solid or it moves when you press or pull it .. if it moves you know you have a problem. If it doesn't move you may still have a problem .. have a look at the gap between the mounting plate that the guard is bonded to and the bird cage ( you will have to take the rubber fender/windshield filler off to take a look) .. its all about patience with a hose and a friend crazy enough to lay upside down with their head under the dash and a torch. The book I referred to has a plan for a "shower" setup to test for leaks.

Not sure if all above makes sense, happy to clarify .. I'm leak free with a temporary fix on the door seal (I need to re-align my doors and then put in new seals, have a few other things going on but I will get to it)

Good luck

 

and also, check if there are any gaps around the bolts on the door hinges .. you may need to put some sealer to close the gaps

 

so in summary my experience was

leak over body mount - blocked inner guard drain and gap in bonding between inner guard and firewall
leak at front of door sill - gap between pillar seal and door seal, and door seal detached from door, door seals stuffed, bubba ground down front adjustment slot
leak at middle of door sill - door seal detached from door and seal on door inspection plate shot (replaced with 1mm rubber)
leak at rear of door sill - water deflectors stuffed

 

Thanks for the help!! This weekend should be a good fun time!