1975 Chevy SWB Fleetside

[RPOZ11]

Next on this is to start cleaning the cab areas exposed, weld up all of the holes created from the 81-up swap and use sealer there.

What is the best sealer to use here after welding up these holes so I dont get any rain or weather thru them?

Next, I took some images of my front frame ends.
Its been in an accident before I have owned it, as shown.
Can someone post an image of what the frame ends should correctly look like?
I am having them starightened out and need a reference image to go with.

[RPOZ11]

Picked up these NOS door hinges for $100.00

Is this a good price for these?

I got these as since I have the front end off, I can get to this area.

Plus, my passengers side door doesnt open/close properly.

[RPOZ11]

Merry XMAS to all.

Been a while since I've posted anything about this truck.
Been driving it sparingly.
A ton of power.
Looks like 12-15 mpg.
Tachs about 2-2200 @ 70-75 mph.

Been having issues with the brake system and fuel pumps.

Today I took it for a drive up PCH north of Malibu.
Started smelling brake pad smoke.
Pulled over to check it out then the motor quits running at idle.

We have already replaced a new after market fuel pump 2 weeks ago that failed.
I believe that the internal parts must be breaking down.

What it did two weeks ago happened again today.
Starts to surge like a vapor lock throw it to neutral and rev the motor to ensure fuel is being supplied to the carb.
Threw it back into gear and continued on.

Then the motor dies.
No fuel.
Once the engine stops running we think there is enough pressure to pull some gas to the fuel bowl but only enough for it to start then die.

Same issue again today.

Thoughts...

I am also thinking of running a performance fuel pump.
I just don't understand why these new aftermarket stock fuel pumps are failing.
I run a rebuilt 800cfm QJ.

[hatzie]

Sounds like you've been bitten by a chintzy Asian manufactured fuel pump. The diaphragm is probably gone because they made it from non fuel resistant rubber...

[RPOZ11]

Originally Posted by hatzie

Sounds like you've been bitten by a chintzy Asian manufactured fuel pump. The diaphragm is probably gone because they made it from non fuel resistant rubber...

Wouldn't that be nice if that was it.
I wouldn't be surprised if that was the case.
Supplier stated that they pulled that brand as their pumps were failing at a high rate
I'll ask if its the same aftermarket brand

[RPOZ11]

Well, here's a no where update.
We are running the factory metal gas line from the pump to the fuel inlet on the QJ.
Moved it over away from the water pump some so it's in the middle area there.
That area still generates a lot of heat there so even adding some hose around the metal gas line as an insulator, I'm still wanting to add maybe some heat deflecting wrap around it.

Today after some tweaking as above stated, my mechanic drove it and it again repeated the same failures.
This is our order of direction next :
Going to start with the fuel inlet filter.
Inspect for any debris as well as for being correctly installed before.
Next, install a brass conical style filter again in the correct direction.
Going to have to do this to every inline filter we installed all the way back to the tank.
Once each filter is checked, pulling off the gas cap, blow out the lines back to the tank.
Maybe we have a partially blocked line still having debris present.
I am running dual GM tanks.
With a new mechanical brass valve switch, new gas line hoses all the way thru.
Add :
We also are using the factory vapor canister.
May need to check the filter in that as well.
Going to have to check it all.

Lastly, we at going to have to isolate it to one tank; the factory main passenger tank.
Go thru the whole process then do the same for the auxiliary tank.

Kind of a mess and being picky but we have to locate this problem.

Will post our results.

[RPOZ11]

Update...
Fuel inlet filter at the QJ : Clean & clear.
Filters inline clean & clear.
The one we installed before the manual valve was loose on one end, but it didn't change our results.
Blew out the lines with the gas caps off.
All clear.

So, we thought about it.
Two suggestions came in being the same .
We decided to install an electric fuel pump on the frame rail between the mechanical fuel pump on the block and the mechanical valve.
Thought here is that the mechanical pump is forced to stay open through the delivery to the carb.
Hoping no issues occur on the mechanical pump.
We used a Mr Gasket 12S electric pump.
4-7 PSI, so not any huge change in line pressure.
Just constant pressure now.

The thought here is to keep full pressure in the gas lines throughout.

Its installed and working.
Now comes the test.

I will drive it tonite and Sunday and see what happens.

I hope I dont breakdown again.

[hatzie]

You can fill the crankcase with fuel by installing an electric pump and not bypassing the mechanical pump with the fuel lines...
Leaving the pump in place won't hurt a thing.

[RPOZ11]

Got 25 minutes in and still getting a drop off and stall.
Back to square 1.
However, after it stalls out, the electric pump is working and getting it to fire up and stay idling.
So, maybe once again that the mechanical fuel pump has failed again.
Going to look around and see what is available in a street performance fuel pump.
This is mind boggling.

[RPOZ11]

Progress...
We now have this traced back to the HEI.
We removed the coil and cap and replaced it with a stock GM coil & cap.
Seems to have made an immediate difference.
AT this time we left the Tach wire removed from the cap.
Drove it for 24 hours and no issues.
We reinstalled the Tach wire and it immediately shows issues.
So, with this, we think that either the tach is grounding out within the gauge itself, or the tab connectors may be loose.
At this pointe, I am unsure why the Tach is causing this, so removing the cluster is next.
I am electric challenged.
Going to have to find someone who can diagnose and repair it.

[RPOZ11]

I found some discussion on this on Steve's Nova site.

I may need to look into this more to determine if a pre 75 dash tach is incompatible with an HEI...
Well here is that discussion abbreviated...

"As I understand the pre-HEI tachs won't work with HEI unless you use a tach filter or tach adaptor. Here are 2 links to filter/adaptors. Can anyone tell me if either one is what I need to make this work? If not what do I need to to make this work?
IIRC it is the MSD system that does NOT play well with tachometers.

I just had another guy tell me he has used a 73 tach in his 77 with HEI without any filters and it has worked fine for 6 years. He said the ones that were the problems were the single transistor/capacitor ones from the sixties and early 70's.
GM did use inline filters on many factory tachs but I believe those were primarily to cut down on radio interference. The circuit inside is different, but they look like the capacitors (condensers) that are often used inline with the heater blower motor; also to reduce radio interference."

Food for thought.
Anyone have any input regarding this current issue I am experiencing?

[hatzie]

The early encapsulated 73-76 tach circuits could never be accused of extreme reliability. It's entirely possible that a bad tach could be intermittently or partially grounding the TACH signal line cutting into your spark voltage and/or affecting ignition timing.

A tach circuit has two basic sections. An amplifier driving a transistor to normalize the signal and reject noise and a charge pump to drive the air core meter movement. Look up LM2907 tach driver chips for more details on how a basic tachometer drive circuit works.

Automotive ignitions are a real world application of Faraday's law. "Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil." When the low voltage "Charge" side current is interrupted voltage is induced on the spark plug side of the coil.
The ground side of the ignition coil carries a low level impulse from the inductive field collapse inside the coil. The amplifier in the tach circuit "reads" this impulse. The points tach may have a more aggressive amplifier circuit that could be damaged by the slightly higher voltage impluses from the HEI but I doubt it.

Ray Macavoy's page on HEI conversion shows the tach hookup on Points ignition. I believe you'll find the HEI coil TACH connection is internally teed to the switched ground side of the coil in much the same way.
http://rmcavoy.freeshell.org/HEI.html

[RPOZ11]

Thanx
I'll start my research on this.

[hatzie]

I believe Wilcox Corvette makes a circuit board to repair the squarebody truck tachs.

[RPOZ11]

I looked around the site but haven't located it yet.
Will try again later

[RPOZ11]

Follow up on my Engine issues.

Add: I did install a new HEI cap, new Coil, new Module, new 8mm wires.

Well, after many issues, I finally decided to address this.
I decided to focus on the carb situation.

What I was using was the aluminum heat shield sandwiched between the carb base gasket and the intake manifold; additional sealing gaskets used with that plate.

I was using the open carb base gasket and the same under the aluminum heat shield plate.

So what I decided to do is to remove that aluminum plate.

Cleaned the intake surface and the carb base plate.

I then purchased and installed a QJ based Phenolic 1/2" insulator plate.

I used the 4 hole type; not the open type.

Moved to using the 4 hole gaskets to keep the primary venturies from dumping into the secondary venturies.

Just for safe measure, I used two 4 hole gaskets together, then the Phenolic plate, then two 4 hole gaskets between the top of the Phenolic plate and the base plate of the carb.

An IMMEDIATE improvement at idle as well as in gear & from a stop.
Acceleration is now vastly improved!

Even though this is a rebuilt QJ 800 cfm from a performance rebuilder, before and after these changes we checked for any vacuum leaks.
Before, when spraying some starting fluid around the base of the carb, the rpm's went up.
I feel that my changes addressed most of this.
However, even afterwards, doing the same starting fluid test for vacuum leaks, there still is a HINT of a vacuum leak.
My determination is is that the throttle plate shafts need to be bushed on the base plate.
I believe that will remove all the vacuum leaks forward at the carb.