Very lucky Clock/Tach EBay purchase

[bigblockv6]

The big canister is the coolant recovery tank came with the 351E option. Again an improperly mounted Tach, makes mention that the vacuum gauge was a factory option though that particular one is a Stewart Warner gauge. The GMC vacuum gauge was completely different, if any one has seen the optional oil pressure gauge then you can visualize the vacuum gauge is the same size yet has the same block numerals like the Tach. Sun did offer a Vac-O-Meter that was the same dimensions as the Tach, I don't think GMC ever used it but it would be a nice fit for the cluster.

[Clarke]

Alright Gents,

I made it to the swap meet and the guy I've been trying to coordinate with for three years, finally came through for me. I am now a proud owner of Tach Model RC-5A, Tach Transmitter Model EB-7A and Bat-O-Meter Model RC-12V.

Problem is, I don't have any instructions on how to wire this stuff up... On top of that, the guy told me the tach transmitter requires an internal battery... He said you cannot get the Sun battery anymore, but he believes Duracell has a battery that is fairly close, but it may cause the tach to be a little off? He also said he believes there is a place that can modify the tach transmitter so it doesn't require a battery?

I opened up the tach transmitter and there is a sticker where the battery installs, noted MALLORY RM12R & SUN 1766-7.

Does anyone have information on the internal battery or mod to eliminate the internal battery, and wiring diagrams for hooking up the tach/tach transmitter/bat-o-meter? I'm much better at following instructions, than winging it.

Also, what color wire from the headlight switch do I use to splice in the gauge lights? I'm assuming I can ground the gauge lights to the fire wall?

I'm going to buy a 3-3/8" dia hole saw to cut the gauge blanks out of the instrument panel, cutting from the back side.

Thanks in advance,

Clarke

[jagarra]

Make it easy on yourself, there is a spade terminal on the side of the fuse block that has a gauge lights tap, use that. Up near the top, left side.

As far as the battery you need, do some Googling on that part number, not the first time solutions have been discussed on the internet.

AA will work, some guys say no difference. if you are concerned about having the just the right voltage, maybe using a lithium or a watch battery and a variable resistor to drop the voltage will work.


Found this adaptor to use a camera battery in there. Gets the voltage correct. Seems older cameras have same problem, you made need to get a battery holder.
http://www.amazon.com/Battery-Adapte.../dp/B00CTNZ9H0


gg

[Clarke]

Thanks for the feedback jagarra.

I'll post updates as I make progress.

[Clarke]

While looking for a tach transmitter battery solution, I found the following site (click on link below), which has a great deal of information... This gives me what I need to know to hook the items up.

One item I found really interesting... It also states the transmitter can indicate certain ignition system troubles by erratic or unstable operation. The cause of this condition is usually poor distributor point condition or improper dwell adjustment. So, I take that as a built in ignition gauge.

http://www.jalopyjournal.com/forum/t...ctions.467635/

In case something happens to the site link above, I uploaded a .pdf copy for our site copy (assuming I did it correct).

Speaking of transmitter battery, I called nearly a dozen different battery and electronic stores in hopes to find a recent solution. Of course, I struck out; however, several stores recommended using rechargable NiCAD batteries, as these are typically 1.2 - 1.5V, unlike alkaline batteries are typically 1.5 - 1.6V. The original MALLORY and SUN batteries were 1.35V.

I haven't given up on the camera battery holder yet. So far, I've been getting mixed feedback. I like the lithium suggestion, as I would think the voltage would be more stable, but none of the stores could match anything up that is comparible to the size of a AA and voltage both.

Since you guys informed me the tach transmitters are located in several different locations, I've decided to mount it on the inner fender on the driver's side (opposite to the battery regulator on the passenger side inner fender). That way it will be symnetrical and will be easier to access to change out the transmitter battery. It will also be close to all the existing wire harnesses above the steering column/linkage through the fire wall, so I can sneak my new wires along the same routes.

[jagarra]

Clark,

Looking at the schematic of the sending unit, looks like the batteries are used to pulse the tach head. The relay portion is switching the batteries back and forth as the contacts move following the points in the distributor. I really don't think an over voltage of .15 is going to make that much difference in it's operation. If you have a dwell meter, you could mock the whole thing up and compare the readings. If the Sun reads high with AA batteries in it, well then you may have to add some resistors in the leads going to the tach head to reduce the voltage.

After I posted this I did more research on the internet. Surprised how much this mercury battery is an issue. There are many sites out there with schematics of circuitry to build a board to regulate the voltage. Seems the problem with alkaline batteries is that they discharge at inconsistent rate, where the mercury discharged at a stable 1.35V rate. I did find mercury batteries in the UK, most were camera sized so they are a small package. There is a site called Tachman that does conversions to make the older Suns work. This seems like it is going to get involved and a bit convoluted. I have found where some posters on forums have said current AA batteries work OK, use the E series as they have more umph, just change them often. Found other sites where there are boards being assembled to address the voltage, current and to provide a stable discharge rate. Of course, you will need a new regulator to replace each battery, so 2 boards. If it were me I wouldn't make any holes yet and mock this baby up first as I suggested.

[Clarke]

Thanks for the feedback jagarra...

I've actually beein looking for a new dwell meter, but I cannot find one locally, so I have to order one. The one I have is a '70's model I used as a kid and when I used it a few weeks back, I noticed the RPM was 100 off (compared to my digital timing light) and the actual dwell seemed to match the 8 cyl scale instead of 6 cyl scale, eventhough I had the switch on 6 cyl. When I adjusted to the 6 cyl scale, the points barely opened, but when I adjusted the points with .016" feeler gauge, the dwell meter read 33 degrees on the 8 cyl scale and I think it was 40 degrees on the 6 cyl scale. Anyway, I'm going to order another one.

I called Tachman on Monday and he said it's $225-235 to do the conversion (eliminate battery). By the time I pay shipping both ways, plus the risk of damage during shipping; I'm not ready to invest in that yet.

I'm not thrilled about chaning the battery every 6-12 months either, but for me it's the lesser of two evils right now. It also depends how much the tach will be off too; appartenly, the error varies as the battery output varies. I'm not going to lose any sleep over it, I've driven it for five or six years without one. It's just I'm doing a lot more towing now and I would like to take advantage of my top end, without pushing it beyond the recommended RPM.

Yes, good advice. I will mock everything up before installing my usual half a roll of tape, dozens of zip ties, wire loom, silicone, etc in place. I hate undoing my own work. LOL!

Thanks again,

Clarke

[Clarke]

My 3-3/8" diameter hole saw came in today, so I cut the holes in the instrument panel for my new Bat-O-Meter and Tach. I'm happy with the results.

Because there was a pimple in the center of each gauge blank on the back side of the instrument panel, I drilled smaller pilot holes from the front side. I also attached an oak pilot block on the front side of each blank to keep the pilot bit in the hole saw from drifting off center line in the thin plastic.

With the hole saw, I drilled the blanks out from the back side, which left the front (exposed) edge clean.

I attached some pictures for reference. I still need to make some little clips or shims, so I can mount the gauges from the back side.

[bigblockv6]

Good job! You can use washers for hold down clips, that's what I use and they work just fine.

[Clarke]

Originally Posted by bigblockv6

Good job! You can use washers for hold down clips, that's what I use and they work just fine.

Thanks! Yes, that's my plan. I remember that from your photo you shared and I think that's a good idea. I just have to snoop around my garage to find something to fill the 1/4" gap for the washers to pinch.