My tachometer is not working and my speedometer jumps around. What do I need to correct these problems? Thanks. Rick

 

Hi Rick, sounds like you have 2 separate problems. I understand that the 2 gauges are side by each. However, they operate in completely different ways.
lets start with your speedo, you say it's "Jumping around ". Should be bolted tightly in place. Perhaps you mean the needle is bouncing, and or jumping. First thing to address is the cable. You have a factory service manual I hope. If not get one straight away! A Factory Manual, nothing less. Best investment you will ever make in your car.
Moving on. The cable unclips from the back of the speedo. With practice you can push the clip with your thumb while pulling the cable away from the speedo with the rest of your hand. You will most likely need to remove the aircon duct that go's to the far left side to get a hand up there. It unscrews on the trans under your car. See why you need a manual? Get the inner cable out of the housing and clean it real good. Then lube and reinstall, or, buy a new cable , (which is what I did a few years back). And install new cable after lubing it. Tie a section of string to the cable on the speedo side before you pull it through the firewall. Then untie when you get the end through the firewall. Use the string to pull the new cable into place. Once cable has been lubed or replaced. Check speedo operation. If it still bounces. Pull the drive out at the trans and check the plastic gear. If chewed up. Replace. If all good. Problem is likely in the speedo itself.
Tach not working at all? Wire on HEI not connected? Tach filter burnt out? Tach board fryed? Start at the distributor, the outer wire on the left. Normally white. As you are looking in from the drivers side fender. Is it hooked to the distributor? Unplug it. Does the connection look good? Wire runs down to tach filter, mounted on intake manifold. Through the filter, another connector before the firewall, check that. If all is good. Time to pull that left dash assembly. Lots of threads on here about pulling that left hand dash assembly. That service Manual???

 

4-vettes offers some great guidance and where to start with both issues. In regards to the tach, 90% of the time the problem is the tach board. In your 76, that would call for removal of the dash...not easy task and why its important to troubleshoot as 4-vettes describes. One of the forum vendors, Willcox, has videos that describe how to replace the board in 76 and also the boards. The article below, still relevant, describes how new boards replaces that 40-year old board technology.

Hope this helps!

http://hunt4cleanair.net/Articles/tachboards.pdf

 

I've also seen some great guidance for dash removal and assembly for the novice. One just needs to look at vendors how-to article's and sometimes you tube video's, however the later are often shot by people that know more about making a video than they do about working on cars.

 

Thanks for all the great advice. Will let you know how it all works out. Thanks again!!!!!