speedometer and tach issues

[Robert K.]

I'm recently had a problem with my speedometer and tachometer on my 76'. The speedometer stays low until the engine is warmed up (in other words, it doesn't register the correct speed until after warmup on the road. Additionally, (didn't happen at the same time so am not usre if related or not), the tachometer only registers 3000 RPM and is not responsive to engine changes.

Any thought(s) out there as to what might be going on here?

[Edward J.]

Re: speedometer and tach issues

Robert, the speedo problem sounds like the grease they used to lube the assy. has hardened ,there was a recent post with same type of problem,it will require removing the speedo head and cleaning the around area where the cable attachs, thats generally the area that may need alittle wd40 at first, then a little grease on the tip after cleaning , while you there pull the cable out and clean it and grease.

the tach may be a circut board problem which will require sending out for repair. maybe someone else can enlighten you on that.

[Joe L.]

Re: speedometer and tach issues

I'm recently had a problem with my speedometer and tachometer on my 76'. The speedometer stays low until the engine is warmed up (in other words, it doesn't register the correct speed until after warmup on the road. Additionally, (didn't happen at the same time so am not usre if related or not), the tachometer only registers 3000 RPM and is not responsive to engine changes.

Any thought(s) out there as to what might be going on here?

Robert-----


Check the tach filter which is mounted near the intake manifold (it looks like a condenser). You'll find it in your AIM. If one of the wires to it is broken, as they often are, that's your tach problem. These are now available in reproduction.

[Edward J.]

Re: speedometer and tach issues

Joe, can't you just by-pass the filter for a check of operation, and if needed just order?

[Joe L.]

Re: speedometer and tach issues

Joe, can't you just by-pass the filter for a check of operation, and if needed just order?

Edward------


That I don't know. However, the usual failure mode for these is a broken wire on one end that's difficult, if not impossible, to repair. So, if it has that problem, one knows one needs a new filter.

[Duke W.]

Re: speedometer and tach issues

'76 is an electric tach, so the first order of businees is to check all the electrical connections.

My '76 Cosworth Vega tach is electric (as are all HEI system tachs I believe). The AIM shows a "filter", which I think is a series capacitor, but it was not on the car, which I bought new. Back some years the tach would sometimes "go crazy" boucing up to the high end at constant speed. I couldn't find a filter, either new or used, so I just cleaned all the connections and the problem went away.

Capacitors degrade with age, so it would probably be a good idea to replace it, if a decent repro is available.

I believe the filter is designed to block passage of high frequency noise, but, at least in the case of my CV, it didn't seem necessary as long as the terminals were squeaky clean and didn't add any resistance to the circuit.

Duke

[Robert K.]

Re: speedometer and tach issues

Thank you to everyone who replied. I will go after these items. Also I wanted to let everyone know that I did a search of the archieves and there was some good info. there (which was consistent with the responses here)..

Thanks again for your help!