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View Full Version : Why are the dash instruments in my Avanti dying...?



edpjr
09-04-2010, 02:09 AM
The clock never worked - no big deal to me. The tachometer has always worked erratically and imtermittently ever since I've owned the car. Now, it's completely dead. Registers 0 RPM. Next, the gas gauge gave it up. Was working fine - had tank cleaned out and new sender installed last year. Now the dial is just frozen in place at a little under 1/2 tank. The Tach and gas gauge wires and ground all appear to be connected properly. The alternator, battery, coil, distributor and voltage regulator have all been replaced with high quality products. The amp gauge reads fine. For today at least. Any ideas would be appreciated. I'm afraid what will go out next....

Bob Andrews
09-04-2010, 07:15 AM
Don't know about Avantis specifically, but my guess would be they're unrelated, just individually tiring out. Even the best design is unreliable after 47 or 48 years. Just goes with the territory.

Might be wiring, might be the gauges themselves, might be grounds. Could be anything after all these years.

Good luck with your ongoing quest.

barnlark
09-04-2010, 07:48 AM
Uhhh, they're old. They may need more than harsh words, now! Try maintenance like everything else you've replaced. The sending unit usually goes out on the tachs... if there even is one for Avantis. The clock is easily taken out, opened up and checked for the problem...usually it just needs Kroil or a wire soldered. 50 year old NOS clocks even need lubed, so a used one really will. The gas gauge is also easily removed and tested with 12 volts by grounding it to see if the needle moves. Grounds for each gauge lose their contacts on any car and should be cleaned and/or replaced, but with a fiberglass car, even more so. One day it has a good ground, the next it doesn't on any old car. I'd start with the good ground search and/or test method. Opening gauges, lubing and cleaning them, second.
There are businesses who specialize in gauge repair if you aren't comfortable with it. My guess is they are swamped in the winter months. Pull them early, ship them & wait.

DEEPNHOCK
09-04-2010, 07:50 AM
Jim Turner's favorite motto is "It's gonna ba a ground"

barnlark
09-04-2010, 08:15 AM
Jim Turner's favorite motto is "It's gonna ba a ground"

He has a lot of mottos, I've found!

comatus
09-04-2010, 08:59 AM
Modern electronics tech's all-purpose answer: "Has anyone ever smoked in that car?"

Ironically, my ammeter is the only gauge I have a problem with. I replaced the alternator with a big hunking Mopar-compatible 2-wire thing, and didn't have the guts to poke around for which wire was safe to hook up , so it registers discharge but doesn't balance it out with the charge rate. I more or less accept this as part of contemporary reality.

Tap wood, I'm mightily pleased with how well the rest of those obsolete, strictly mechanical contrivances have endured forty-seven years of neglect and abuse. So I'm with the Oswald-acted-alone crowd on this, but do appreciate your concern. It would bother me, too. Electrics, even batteries, always fail in threes, and it's been this way ever since the EPA banned [B]gremlin-out [TM].

Gunslinger
09-04-2010, 10:04 AM
As already said...the problems are likely all unrelated to one another and related in the sense the car is so old and things wear out, get corroded, lose ground, etc.

The clock...needs to be cleaned and oiled...probably all it needs.

The tach...tach sender is probably bad...very common on Avanti's. You can have your sender rebuilt or buy a reproduction sender. The tachs were never that accurate anyway according to contemporary magazine reviews of the Avanti. The tach sender is easy to access...it's the round can attached under the dash by the steering column.

Fuel gauge...the shop manual tells you how to check and see if you have a bad gauge or a bad sender (even new can be defective).

Just keep repeating to yourself..."I love my car, I love my car!"

edpjr
09-04-2010, 10:35 AM
You are correct. Followed the shop manual approach and it does not appear to be the sender. I wonder if floats, even relatively new ones, ever get stuck? When my Tach was just behaving erratically, Jon Myer advised it likely wasn't the sender because it would go kaput if that piece was bad. I guess the sender just gave up, cause the Tach's completely dead now. I was mainly wondering if there was likely any connection between the two recent failures of electrical gauges.


As already said...the problems are likely all unrelated to one another and related in the sense the car is so old and things wear out, get corroded, lose ground, etc.

The clock...needs to be cleaned and oiled...probably all it needs.

The tach...tach sender is probably bad...very common on Avanti's. You can have your sender rebuilt or buy a reproduction sender. The tachs were never that accurate anyway according to contemporary magazine reviews of the Avanti. The tach sender is easy to access...it's the round can attached under the dash by the steering column.

Fuel gauge...the shop manual tells you how to check and see if you have a bad gauge or a bad sender (even new can be defective).

Just keep repeating to yourself..."I love my car, I love my car!"

Gunslinger
09-04-2010, 11:13 AM
Anything can happen...and with Avanti's they certainly seem to. Of course a float can get stuck...I doubt if it's common, but it's within the realm of possibility.

The recent failure several gauges is most likely age and coincidence. All the gauges have separate senders they're connected to. The only common wiring between the gauges is the lights.

A lot on how to fix things can depend on what you plan on doing with your car...are you trying to make it as correct as possible or doing modern upgrades without care of authenticity? With my '70 Avanti I went for upgrades...I replaced all the gauges with Auto Meter units...no problems at all with installation and they all look and work fine. I replaced the original ammeter with a voltmeter. Looking back I could have eliminated the clock and put the voltmeter there and had an ammeter as well.

It's your car and your money...how you want it is your decision. There are options if authenticity isn't as important to you. I (as we all do) want you to have a car you're proud of and enjoy driving.

StudeRich
09-04-2010, 11:51 AM
In my experience, on the Alternator equipped Larks/Hawks it has always been OVER VOLTAGE that has killed all of the electrical components over time; Battery, Alternator, Temp. and Fuel Gauge, Fan Motor, Wiper Motor and sometimes bulbs.

None of these premature failures ever happened with the Stude. Generator systems, except of course the generator, which itself did not always have a long life.

The cheap single contact mechanical Chrysler/Prestolite Voltage regulator has always been the problem over the years, it would heat up and stick closed. We now have the cure: the "ELECTRONIC" Regulator. Now on an Avanti (a stock one) you have the much better large, THREE Points type Regulator which does not seem to stick like the single point Lark/Hawk type which many times has proved to me to be the culprit.

However we know your car has a huge replacement alternator and (had?) a Lark regulator, so I don't know what "expensive" replacement you have now but, the only way to know if it is any good, is probably to monitor the voltage looking for over about 13.5 Volts running voltage.

Also, the damage may have been done before the "upgrade".
Of course this is in ADDITION TO, not to replace the good info already given to you about the component AGE, it very well could be both.

gordr
09-04-2010, 12:25 PM
I'm willing to bet that the tach is sending unit failure; that's a known problem, and several vendors have replacement boards for the sending unit.

Gas gauge is most likely a bad ground, The dash in an Avanti is made of fiberglass, and ground problems are commonplace. That, at least, is easy to check. Attach a clip-type test lead to one of the gas gauge mounting studs, and the other end to a known good ground. There should be a ground wire linking the metal shells housing all the instruments, but sometimes it fails to make good contact.

A ground problem might be the cause of your tach's troubles, too, so be sure to make certain the grounds are good before condemning the sending unit.

WCP
09-04-2010, 01:10 PM
Check the ground wire at the fuel level sender, and also the contact of the feed wire at the sender. Not the easiest thing to do.

edpjr
09-04-2010, 02:17 PM
I've kept it original and stock except for the T-bow Mallory electronic distributor and dynaflow mufflers.


Anything can happen...and with Avanti's they certainly seem to. Of course a float can get stuck...I doubt if it's common, but it's within the realm of possibility.

The recent failure several gauges is most likely age and coincidence. All the gauges have separate senders they're connected to. The only common wiring between the gauges is the lights.

A lot on how to fix things can depend on what you plan on doing with your car...are you trying to make it as correct as possible or doing modern upgrades without care of authenticity? With my '70 Avanti I went for upgrades...I replaced all the gauges with Auto Meter units...no problems at all with installation and they all look and work fine. I replaced the original ammeter with a voltmeter. Looking back I could have eliminated the clock and put the voltmeter there and had an ammeter as well.

It's your car and your money...how you want it is your decision. There are options if authenticity isn't as important to you. I (as we all do) want you to have a car you're proud of and enjoy driving.

edpjr
09-04-2010, 02:21 PM
I got a 40A Prestolite Alt, a HD electronic voltage regulator (chrysler type), a $140 battery, an accel coil, a T-bow electronic distributor and much new wiring.



In my experience, on the Alternator equipped Larks/Hawks it has always been OVER VOLTAGE that has killed all of the electrical components over time; Battery, Alternator, Temp. and Fuel Gauge, Fan Motor, Wiper Motor and sometimes bulbs.

None of these premature failures ever happened with the Stude. Generator systems, except of course the generator, which itself did not always have a long life.

The cheap single contact mechanical Chrysler/Prestolite Voltage regulator has always been the problem over the years, it would heat up and stick closed. We now have the cure: the "ELECTRONIC" Regulator. Now on an Avanti (a stock one) you have the much better large, THREE Points type Regulator which does not seem to stick like the single point Lark/Hawk type which many times has proved to me to be the culprit.

However we know your car has a huge replacement alternator and (had?) a Lark regulator, so I don't know what "expensive" replacement you have now but, the only way to know if it is any good, is probably to monitor the voltage looking for over about 13.5 Volts running voltage.

Also, the damage may have been done before the "upgrade".
Of course this is in ADDITION TO, not to replace the good info already given to you about the component AGE, it very well could be both.

edpjr
09-04-2010, 02:22 PM
Thanks for the tips. I check it out before I buy.


I'm willing to bet that the tach is sending unit failure; that's a known problem, and several vendors have replacement boards for the sending unit.

Gas gauge is most likely a bad ground, The dash in an Avanti is made of fiberglass, and ground problems are commonplace. That, at least, is easy to check. Attach a clip-type test lead to one of the gas gauge mounting studs, and the other end to a known good ground. There should be a ground wire linking the metal shells housing all the instruments, but sometimes it fails to make good contact.

A ground problem might be the cause of your tach's troubles, too, so be sure to make certain the grounds are good before condemning the sending unit.

edpjr
09-04-2010, 02:28 PM
Thanks to everybody that has offered technical advice and suggestions. I actually have an entire '64 Lark Daytona dash that has a factory tach. I got it from a junker, and intended to sell the whole thing since it's a rarity.. Wonder if it's worth trying that sender on my Avanti?? My current electrical configuration typically charges between 13.8 and 14.2 amps on an external meter. And my car's amp gauge is mostly steady.

StudeRich
09-04-2010, 03:07 PM
That would be VOLTS, right?

It is a bit high.

edpjr
09-04-2010, 10:31 PM
Correct! Leave it to an engineer (non-electrical) to mix up flowrate versus pressure.


That would be VOLTS, right?

It is a bit high.

edpjr
09-04-2010, 11:02 PM
Just made another "startling" discovery. After searching a picture of an original Avanti gas gauge, I find that mine is NOT original. It must've been replaced somewhere along the line with an aftermarket type. I wondered why it had a white bulb and white needle. Yecch!

Gunslinger
09-04-2010, 11:19 PM
If you have an aftermarket gas gauge, it could have the impedance mismatched with the sending unit. In that case it will not operate properly.

JDP
09-05-2010, 01:18 AM
Just made another "startling" discovery. After searching a picture of an original Avanti gas gauge, I find that mine is NOT original. It must've been replaced somewhere along the line with an aftermarket type. I wondered why it had a white bulb and white needle. Yecch!

The Avanti I'm working in now has a after marker gauge too, but it works fine, and I painted the needle to match. I'd bet about half the Avanti's and GT's have at least one gauge replaced. (Gas,Temp or both) i.e. the GT Hawk on ebay has had both replaced over the years.

edpjr
09-05-2010, 07:47 PM
Yes, I suppose dash gauges have a perfect right to tire out after 47 1/2 years. And, as you alluded to earlier, I don't see how one can keep all water out of an Avanti short of hermetically sealing it. Fortunately, I have located and procured an original NOS Avanti gas gauge. Naturally, it wasn't cheap. Now I guess I'll be calling Mr. Myer up for a new Tach sender. Replacing that piece doesn't look too bad. But, it looks like the oil pressure gauge has to come out to access the gas gauge. Egad.



The Avanti I'm working in now has a after marker gauge too, but it works fine, and I painted the needle to match. I'd bet about half the Avanti's and GT's have at least one gauge replaced. (Gas,Temp or both) i.e. the GT Hawk on ebay has had both replaced over the years.

Gunslinger
09-05-2010, 08:35 PM
Just a thought...if you have to remove the oil pressure gauge anyway, take a good, hard look at the oil tube. Since it's a direct acting gauge, not electrical, if it fails due to age fatigue, rubbing up against something, etc., the least it will cause is a nice mess inside the car. If that tube is going bad, replace it now while it's already disconnected. Just a suggestion.

edpjr
09-05-2010, 09:21 PM
Good advice indeed. That would be great having 60 psi oil squirting into the car, or even spraying outside till the motor runs low of oil.



Just a thought...if you have to remove the oil pressure gauge anyway, take a good, hard look at the oil tube. Since it's a direct acting gauge, not electrical, if it fails due to age fatigue, rubbing up against something, etc., the least it will cause is a nice mess inside the car. If that tube is going bad, replace it now while it's already disconnected. Just a suggestion.

N8N
09-06-2010, 12:09 PM
Good advice indeed. That would be great having 60 psi oil squirting into the car, or even spraying outside till the motor runs low of oil.

The usual failure is the rubber hose between the pass side head and the copper tube; when that fails you know it because a good portion of the oil blows up onto the windshield :(

I consider that a "replace automatically" item on any Stude that I want to turn into a driver, unless it's clearly been recently replaced.

nate