Restoring Rusty

[motornut]

yup i used an extender too

[Gregski]

Originally Posted by enaberif

You need to get a 45 degree fitting with a 1/4 npt male to I think a 1/4 female of you have room behind the intake otherwise you will need a 1/4 nipple to 45 female/female.

you my friend are a gentleman and a scholar, I picked up just what you said, and ended up going with the 1/4 nipple (ie riser) to the 45 female/female elbow

problem = solved

thank you so much

[Gregski]

Originally Posted by motornut

yup i used an extender too

dang them is fancy, I like those risers, and thanks for the pic of your [ahem] unit... sender unit, sender unit

[Gregski]

time to compare the 1974 Mechanical Oil Gauge to the Electronic Oil Gauge circa 1978

note no wired plug into the mechanical one, just one hollow metal tube, on the other hand the electric one has three wires going to it

the take away here is that the electronic gauge is only half the battle, it's useless by itself, you cant just wire it up and get results, it is the sending unit behind the scenes feeding it all the pertinent information, ie doing all the heavy lifting

[Gregski]

next it was time to test the Electric Oil Pressure gauge

here's how I do it

I set it on the battery and connect the negative stud (bottom most) to the negative battery terminal directly with a black wire with aligator clips on either end

I connect the positive stud to the positive battery terminal directly with a red wire with aligator clips on either end

Then I connect the third stud to the oil pressure sending unit directly

I make these direct connections on purpose, this is to eliminate any wire harness problems such as shorts or broken connections, as well as any bad fuses, keep in mind this is a gauge test and a gauge test only, we are not testing the entire circuit here

the goal is to keep it simple

[Gregski]

I test the Tachometer in the same / similar way

put the Tach on the battery

the Tach's blade terminals on the back are labeled, thank god, we have a positive, negative, and coil

so we aligator clip positive to battery positive

aligator clip negative to battery negative

and [wait for it] connect the coil terminal to the left terminal on the HEI distributor I think it says Tach on it, the other one is Ignition or power something like that

But I think we might could have a problem, I used my trusty (I love the darn thing) digital timing light to stare and compare the Tachometer reading to its reading, and I think we is a bit off, LOL

[Gregski]

A Take Away Lesson Learned so far people, and we all may appreciate this, it appears that it don't matter where the needle rests on the gauge when it is unplugged, like for example on them eBay pictures you are staring at going is that Tach jacked why is the needle resting on 15, or why is that oil pressure gauge needle in the middle of that gauge on this guys table at the swap meet, what I noticed is as soon as I send juice to it, by connecting the gauge to the battery, both positive and negative, the gauges 0 zero themselves out

[enaberif]

Does that gun do 8 cylinders? I only see 2 and 4 on the panel? Could be why its reading weird?

[Gregski]

Originally Posted by enaberif

Does that gun do 8 cylinders? I only see 2 and 4 on the panel? Could be why its reading weird?

I think that's 2 stroke 4 stroke

[enaberif]

I thought 2 cycle and 2 stroke were the same thing.

[Gregski]

Originally Posted by enaberif

I thought 2 cycle and 2 stroke were the same thing.

You asked about cylinders, so I pointed out those numbers are not the total number of cylinders they are 2 stroke or 2 cycle and 4 stroke or 4 cycle there is no 8 cycle engine that I know of

[Chaplain]

Working on an 80 K5 back around 1998, I discovered the need for the offset extension to get the oil pressure sending unit to fit into the tight space.

Someone else must have become frustrated and installed the idiot light sending unit. I simply wanted the gauge to work so I bought what the local auto parts store said I needed...the big sending unit. After I could not get it to fit under the distributor I came up with the idea of using the elbow extension. It worked. I had no idea that's what was required. Again, I just wanted it to work.

I had forgotten about that until now. I'll have use that info once I start but this old 79 back together. I too will be going from idiot lights to gauges.

[hatzie]

Originally Posted by Gregski

ok, so far so good, but here's where it gets interesting, I noticed that three wires loop from one side to the other, so wrap your mind around that for a minute

looks like the pink wire, the tan wire, and the tan/black wire are playing both sides (politicians are they)

Pink is ignition power. You need add one more for the 78 cluster.
Tan should be the fuel sender. GM wired the harness for both large and small fuel gauge. You'll have to change terminal positions for the 78 cluster.

[hatzie]

Originally Posted by Gregski

ok, it appears the black mystery wire splices into another black wire that plugs in to Pin # 9 ie Ground, fair enuff, now we need to figure out where it was headed the other direction does it go to the fuse box, or screw into the dash somewhere?

1974 used a sheet metal ground for the main cluster ground wire. Sounds like the cluster Ground splice gave up the ghost.

[rusty76]

Good lord you been busy.....good grief.

[jeremybadeker]

Are you sure that's a v8 tach and not for a 6?

[hatzie]

Originally Posted by jeremybadeker

Are you sure that's a v8 tach and not for a 6?

If it were a 6cylinder tach it would read too high.

Freq_Hz=(RPM/60)*(CYL*0.5)

An 8cylilnder at 1500 RPM is generating a 100HZ signal
A 6cylinder at 2000 RPM is generating a 100HZ signal
A 4cylinder at 3000 RPM is generating a 100HZ signal

[greg64]

If the tach gets pulses inductively from the #1 cylinder, then it doesn't matter how many cylinders the engine has. #1 only fires once for every two revs.

If you can drive at a known speed (like using a GPS), and we know your tire size and rear gears, we can figure out what RPM the engine is actually turning.

[hatzie]

Originally Posted by greg64

If the tach gets pulses inductively from the #1 cylinder, then it doesn't matter how many cylinders the engine has. #1 only fires once for every two revs.

If you can drive at a known speed (like using a GPS), and we know your tire size and rear gears, we can figure out what RPM the engine is actually turning.

Yup. But the GM tach is reading the ignition impulse frequency from the coil and it's lower than the very accurate inductive pickup tach.

What I was explaining was why I know the GM tach is not a 6 cylinder unit... The needle would point to @2000 RPM on a 6cyl tach. @500 RPM too high at @1500 (1490) RPM on the inductive tach.
It's a calibration problem with the analog GM tach drive circuit and it can be repaired.

[greg64]

Originally Posted by hatzie

Yup. But the GM tach is reading the ignition impulse frequency from the coil and it's lower than the very accurate inductive pickup tach.

What I was explaining was why I know the GM tach is not a 6 cylinder unit... The needle would point to @2000 RPM on a 6cyl tach. @500 RPM too high at @1500 (1490) RPM on the inductive tach.
It's a calibration problem with the analog GM tach drive circuit and it can be repaired.

Shoot, I was talking about the Mac timing gun reading, not the GM tach.

Another reason you're right that it's not a six cylinder tach is that, all the six cyl trucks I've seen, including mine, are pretty basic, and are unlikely to have the full gauge package.

[Gregski]

OK fellas I was able to make it to the junk yards this morning to take advantage of the 50% off sale, although I did not find a radiator core support I did score some little things that I needed, some that are hard to find, so allow me to share

first off of a 1979 I pulled the Oil Pressure Sender Unit wire, that's right I could have made my own, but by pulling an original I get the right plug, the right color, and I get to see where it plugs into the bulk head connector

if you just take your time with some needle nose pliars you can actually push out one of them GM connectors, like so...

[Gregski]

still staying with the '79 I decided to see if I can find a similar black ground wire like the loose one in my truck and see where it bolts up to

I found a similar wire so I unscrewed the loop end and cut the other end where it splices into the wiring harness so I can graft it in properly to my own, score

[Gregski]

then I moved on to a 76 manual 4 speed like mine, the first manual I ever saw

this is where I found the Holly Grail... a part I have been looking for, for almost a year and knew the aftermarket one I bought wasn't even close to the original, I also got an answer to where these little two hole round brackets go and en explanation how this super tough spring can span such a huge distance

I give you the clutch pedal spring at last...

[Gregski]

here is my old broken spring with one mystery bracket, the used replacement one with both brackets which I paid $2.50 for, and the silly thing I bought somewhere online claiming to be the proper new replacement, shame on them

[Gregski]

also from the '76 picked up the Headlight Switch knob and rod for $1.50, LMC Truck wants $14.00 bucks for it and I doubt it would match my black knobs, score

my old one gave up the ghost, the insides crumble and it just slides right off

I like these small victories! How about you?