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DarkMonohue
DarkMonohue Reader
2/11/21 2:05 a.m.

Last Sunday I managed to get out in the driveway and pick at a few scabs, so here are a couple of little chickenpoop updates.

First off, no pics of the new alternator belts, because I didn't bother to install them.  Turns out that, after breaking in, the one new belt I installed last month had about the same tension as the one that stayed on when the new one got installed.  But they were loose enough to make all kinds of racket.  So the alternator got a little tough love with a crowbar and everything seems happy again.

The cooling system had been leaking a little prior to the last round of work.  Never found an obvious culprit, but it was sometimes almost damp around the flushing tee, so during that last thrash I cleaned up the seams on the plastic and repositioned the hose clamps.  After adjusting the belts last Sunday I popped the radiator cap and it was full right to brim.  Very satisfying.  No pics.  We all know what coolant looks like.

Starting has been goofy in that the shift lever wanted to be pulled up just past the Park position before the starter motor would turn.  727s don't have an external neutral safety switch to adjust or replace, so the fix is to adjust the linkage such that the shift lever on the transmission is really in Park when the shifter on the column says it is.  Easy.  Now we have one-hand starting again, no gymnastics required.

There were a couple of extra leaf spring clamps on the left-front spring.  Not sure why they were there, but they got removed while I had the creeper out.

The last thing I messed with, primarily because it took forever to complete, was the heater control panel.  The problem is that there has been a hissing sound (i.e. a vacuum leak) from under the dash whenever the Off button was selected.  Heat and Defrost were fine.  So I pulled the instrument cluster out for a closer look.  It's an unpleasant task, but we do what has to be done.

Here's a look at the heater control unit from the left end prior to fully removing the instrument cluster.  There are three vacuum lines.  Here's how they were arranged when the unit came out of the truck.


And here is the unit on the healing bench, ready for diagnosis and disassembly.


The little gray unit is a disc valve of sorts that is rotated to one of three different positions according to which button is pushed.  Here it is disassembled.  Note that the flat spring shown on the spindle is shown installed incorrectly.  It should be installed so that the center presses against the back half of the vacuum disc valve.


To help eliminate the possibility of a vacuum leak due to bad surface prep, the mating surfaces got lapped on 1500 grit sandpaper.  They are smoother and flatter than they look in this photo.


Better verify the function of the heater control disc valve.  There are three ports on it, numbered 3, 4, and 1 in order from vehicle front to rear (left to right when looking at the disc valve).  There is also a vent in the center covered by a little round foam-like filter element so that parts of the system not in use can release their vacuum and return to their normal position.  With a Mityvac (vacuum pump) I put vacuum to each port with the controls in each position to see where the vacuum went.  Here's a table comparing control position to port communication.  In this table, "filter" means the purge filter in the center of the disc valve:


Now for the hard part.  Which one of these hoses goes where?  The one with the white stripe goes to manifold vacuum; the one with the red stripe opens the air inlet door to let air into the heating system; and the one with the green stripe redirects air from floor heat to the defroster vents.

Close your eyes and picture me kicking my own butt.  I had the hoses hooked up incorrectly.  The correct hookup is manifold vacuum (white stripe) to 3, heater inlet door (red stripe) to 4, and defrost door (green stripe) to 1.  I put it together connected in that order and it all works the way it should now.  It's been hissing at me for eight years because I borked the hose connections the last time I had the cluster out, and manifold vacuum had been sucking through that little filter in the center.  But it's fixed now.

And finally, here's a teaser for the next thrilling installment.


More when more is.

DarkMonohue
DarkMonohue Reader
2/13/21 5:35 p.m.

The heater control content in the last post has been cleaned up and fleshed out.  I realized there was an extra piece of information that might be useful.  It turns out the little foam pad in the center of the vacuum valve also functions as a filter, and it helps to fully understand what does what.   The table in that post has also been replaced with a better example to include that information.

 

11GTCS
11GTCS Dork
4/8/22 9:47 p.m.

It’s been a minute, any updates? laugh

DarkMonohue
DarkMonohue HalfDork
4/8/22 11:41 p.m.
11GTCS said:

It’s been a minute, any updates? laugh

Good grief, it's been more than a minute!  I didn't realize so much time had gone by.  Thanks for the reminder.

There's nothing really interesting to report on the old bucket.  It began cranking over slower and slower over a few months back.  I initially blamed that on cheap department store battery cables and their flimsy, stamped, integral terminals.  As they tend to do, they had become more green fuzz than metal.  A much better set of cables went on, along with marine-style brass terminals, and things were a little better until they definitely weren't.  The battery subsequently gave up completely at a particularly inconvenient time.  It was almost seven years old, and the truck gets used infrequently, so there's no point grousing about that.  The battery got replaced.  Now it's a truck again.  That's about the sum total of maintenance it has recieved since the last entry.  I guess I should probably check the oil sooner or later.

I don't know when I'll have an opportunity to work on it next.  Priorities (and thoughts, and budget) are elsewhere lately.  Realistically, there may not be a chance to tinker on it for a couple of months, at which point I will likely want to use it more than wrench on it.

I need a doppelganger.

DarkMonohue
DarkMonohue HalfDork
4/15/22 11:08 p.m.

There's most of a couch under all that mess. Truck stuff.

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