Tachometer intermittently stops working

[dbrisotti]

On my 1992 Range Rover the tachometer intermittently stops working. There is a belt whining when this happens.

My garage has been unable to get this to happen to them but has replaced the alternator and belt twice (this is the third belt, I replaced the first one), the second time under warranty after the first repair. The whining stops and the tach is dead when the belt blows out, but obviously there is no more battery charging going on so I can't drive it that way.

Anyone have this problem?

[Disco Mike]

Are you saying that when the alt. goes, you can't drive on the battery reserve? You should be able to drive on an average battery for a little over an hour. If you can't I am wondering if you battery is trashing your alternator.
Mike J.

[dbrisotti]

I can drive just fine on the battery but I obviously can't leave the car without an alternator. The issue is that the whining comes and goes as does the tachometer (together), and each time the belt has then blown off. The car continues to run.

[hamrendan]

maybe its not the alternator, but the power steering pump, or what ever that belt is also hooked up to..I would think once you replaced the alternator and the belt, and you still have belts blowing off something is siezed, or intermittently siezing up.. maybe you have some crap in your power steering fluid..?? Assuming for the moment that the alternator is actually hooked up to the PS pump.. My mind is not all here right now

[dbrisotti]

I'm sure it's not the alternator. I can't find in the manual what drives the tachometer. The alternator is turned by the belt connected to the engine itself, but that will turn with or without the belt that keeps breaking. Does something in the alternator drive the tachometer?

[hamrendan]

There is a white with grey (or light blue stripe) wire that has a plastic shield around it. It plugs into the back of the Alternator. Most likely this is loose or corroded. My tach stopped working a week ago and i found that the wire had come loose off the back of the alt.. thats probably your tach problem but the Alt problem worries me.. let me ask you this.. when you hear the winning of the belt does it just come off the alt or does it burn off like when something gets stuck in a vacuum cleaner and the motor shaft burns through the plastic....

If the belt is NOT burned and broken then it may be as simple as a loose belt... alt belts are hard to get right, because you don't want them too tight or too loose.. Too loose and they whine.. too tight and they wear out your bearings fast!//

HTH good luck!

[dbrisotti]

it's not just coming loose and flying off... it's melting. Something is seizing but I can't imagine where. The Alternator is brand new and there is nothing else critical attached to it or the belt. Ugh...

[Disco Mike]

It can only be something being driven by that belt siezing up besides the alternator or a really bad dead short that is kicking in and out that then overloads the alternator.
Have you looked at the bearing in the alternator and for that matter the brushes to see what has been failing? This may give you a good indication of what is wrong.
Mike J.

[Disco]

Check the power steering pump. My guess is that the bearings are shot and the pump is intermittantly jamming. When it does so, you will hear usually the belt squealing, and, depending on the belt tension, causing it to break. This would cause your tacho to stop working.

[hamrendan]

www.car-part.com for a cheap used pump... there is a company in LA that does refubishing that is pretty good too..
http://cgi.ebay.com/ebaymotors/ws/eB...sPageName=WDVW

these guys did me right on my ABS pump

[Kevin88RRC]

Wouldn't a bad power steering pump effect the power steering belt and not the alt belt???

Are you sure the alt belt tension is correct? If it's loose it won't just fly off, it will squeal, get hot and snap. Could the alt be slipping after adjusting the tension?

[dbrisotti]

I have the third alternator in the engine in three weeks... the third on warranty. I agree that something is seizing but I can't figure out what and neither can my garage. Here are my thoughts:

If the pulley from the engine was seizing, the alternator would slow down with the tach and I would get a warning light. This does not happen.

If the alternator were bad it would have to be bad three times including two new alternators. HIGHLY unlikely.

If it were simply a sensor the belt wouldn't whine nor break.

Without the belt, the engine runs perfectly, no belt sounds so the power steering pump is unlikely as are the heating and other major systems in the engine proper.

I'm stumped and so is my garage. We are going to take the pulley off the engine to see if it is sticking for some reason... but that is a bit illogical too since the alternator is driven off that one pulley. Wouldn't I have a charging problem?

[troverman]

We had a similar problem on our 1992 RR: The tach would intermittently work, and especially at stop lights or when the car was in drive but stopped (Like at a light) When it stopped working, you would hear belt squeal. Giving the car gas (even with the car stopped in drive, foot on the brake) would cause the tach to work again, and the noise goes away. The tach is in fact driven by a signal from the alternator, one wire, correctly described in a previous post. On our RR, sometimes the squeal would become very bad and not go away even when driving away from a stoplight for some time. You also could notice a burnt rubber smell occasionally. Turning off electrical accessories usually alleviated the problem. A failing tach typically means a failing alternator. We had ours rebuilt for $50. Problem came back and it was one of the brushes. We put one of those Goodyear "Gatorback" quiet belts on with the sideways grooves (local auto stores) and tightened the tensioner, but not overtightened it. We also put a Wal-Mart battery in it (The yellow one (Maxx?) like 1,000 CA, the only Wal-Mart batt that isn't junk.) This solved the problem. The tensioning device is extremely annoying, and has to be just right. The book says like 4mm of belt deflection when pressing in the center of the belt. Since the a/c in the truck doesn't work, we also disconnected that belt. At night, do you ever see the alt. light come on, just very dimly glowing red? That's what ours did, never on bright, just very dim and it got a little brighter like when you hit the brakes which requires a lot of electricity.

The other thing you can do to temporarily help the problem is adjust the idle throttle up to like 1,000 RPM so it might not squeal as much.

Remember--the alt. belt CANNOT be TOO TIGHT! This will smoke your belt off just as much as a loose belt can.
Good Luck

[dbrisotti]

Okay... we took the alternator off as well as the mounting brackets and realigned everything (we had checked alignment already and it was fine, but what the heck). Tension on the belt is back to optimum and there are no problems... yet. I'll keep you posted if that changes!

Thanks for the help all.

[tracengrant]

hi there, problem can sum1 give me some advice please
when rev counter reaches approx 2000 revs, battery light comes on ,on dash also rev counter stops working.Reduce revs to below 2000 and alls fine,replaced altenator 4wks ago prob started 2 days ago any help or ideas would be appreciated thanx