71 Tach and Oil pressure guage issues...

vetteboy86 · 10-17-06, 10:33 AM

A friend of mine just purchased a 71 convertible and he has a few guage issues. The tach and the oil pressure guage currently do not function. I told him I would ask here first before we worked on it.

First question is about the guages being mechanical or electronic in nature? From there any suggestive fixes would greatly be appreciated.

Thanks,

muddywaters · 10-17-06, 10:52 AM

The tach. is mechanical, short speedo like cable goes to dist., I'm reaching back, but I think the drive gear in dist. is problematic, it's easy to trouble shoot. The oil guage is acually piped from a fitting on the engine off an oil passage. There is oil at the guage, if the line fails inside the car it's a mess.

vetteboy86 · 10-17-06, 12:04 PM

Thanks for the info. Can I disconnect the tack wire and spin the gear at the end to see if the needle tries to move to eliminate the guage bieng bad?

muddywaters · 10-17-06, 01:03 PM

Your not disconnecting a wire, it is a short speedo cable, has center core that does the spinning. Yes, you can spin the core and watch the gauge, you can also start engine and eyeball dist. connection. Sometimes just the core needs to be changed, ends round off. The gear is easy to remove, if thats chewed, the dist. shaft gear is also.

6880 Mike · 10-17-06, 02:03 PM

Quote:

Originally Posted by muddywaters

...The gear is easy to remove, if thats chewed, the dist. shaft gear is also.

I agree. If the drive gear is chewed up, the teeth on the distributor shaft are also almost certainly gone. The fix is to replace the distributor shaft and the drive gear. All the Corvette aftermarket providers carry the shafts and gears.

Consider: if you're going in far enough to replace the shaft and gear, why not rebuild the distributor as part of the process?

WhiteKnight · 10-17-06, 02:44 PM

Looks like most of the Tach related issues were covered. Except HEI conversions.. some owners will convert to the HEI distributor (with no mechanical tach drive). That was how mine was and I had to replace it with a different dist., and get a new cable.

On the oil pressure gauge first check if there is oil pressure by using a test gauge. The fitting is at the back of the engine near the dist.

If that is good usually a new gauge is needed. However, on mine (also had that same problem) I pulled the gauge and found the gear that moved the indicator was corroded and sticking. Cleaning with a little wd-40 got it free and the gauge has worked for a year now.

Jack · 10-17-06, 11:41 PM

Quote:

Originally Posted by vetteboy86

Thanks for the info. Can I disconnect the tack wire and spin the gear at the end to see if the needle tries to move to eliminate the guage bieng bad?

Disconnect cable at dist ... chuck cable (core) into a reversible drill motor ... spin it in reverse (CCW) & check for tach movement ... if drill turns 500rpm, the tach should read 1K. While cable disconnected, run engine & look at dist ... the tach drive turns clockwise.

BTW ... you have to disconnect cable from tach gage in order to remove core ... core slides out from gage end ... not out the firewall end.

thesurvivor · 10-19-06, 01:18 PM

What did it take to get to the oil pressure gauge? I think mine may be clogged up, too.

red70vette · 10-19-06, 05:12 PM

It is almost impossible to check the fitting and the oil guage without removing the center guage cluster. If you were a contortionist with very small and nimble hands you might be able to reach around behind the cluster and disconnect the oil pressure hose.

Removing the center guage cluster is no big deal. Once you have owned one of these Corvettes for a couple of years you can take one out in about 5 minutes. The hardest part are the 2 studs that hold the bottom of it to the center console. Once you figure that out it is a piece of cake.

cowboyra · 10-19-06, 05:58 PM

The Tack on my '75 is "stuck" at 1500 RPM - Would this be the same problem ?

WhiteKnight · 10-19-06, 06:00 PM

Red70vette is right.. the best way is to pull the console and cluster out of the car... I did that and fixed (or is that fiddled with) the gauge on the kitchen table.

JohnZ · 10-19-06, 07:01 PM

Quote:

Originally Posted by cowboyra

The Tack on my '75 is "stuck" at 1500 RPM - Would this be the same problem ?

Nope - '75-up tachs are electronic, not mechanical.