Studebaker Speedster and Hawk Tach
Some hand drawn notes that I scanned regarding the wiring of the tach
used on the '55 Speedster and some '56-61 Hawks, also known as the
Stewart Warner "Pulse Drive.".
Please note that the '56 Golden Hawk uses a different sending unit than
all the other models as the distributor is different. The wiring,
however, is the same.
The '55 Speedster uses a different tach head, with a different face
(the 56-61 unit is shown above) and is 6V unlike all other
Studebakers that use the SW tach. I honestly don't know if one
needs to reverse the wiring connections for the harness or not. I
do know that I haven't ever blown anything up by hooking it up
backwards, at least regarding these tachs. They just don't work
until you hook them up correctly.
If you have a later electronic tach, this page won't help you at
all. However, the December 1975 issue of Turning Wheels has a
reprint of the Stewart-Warner installation sheets for both types of
sending unit used for these tachs (the normal, rectangular one and the
Avanti-style round one.) Also, the January 1980 issue of Turning
Wheels has an excellent technical article on these units. You can
often find back issues for sale at Studebaker swap meets; there's some
real gems in there. There's an index available electronically at
the SDC web site that
can help you find topics of interest in the older issues.
I have found three problems that commonly cause these tachs not to
function.
1) Wiring harness brittle and shorted internally. I rewire all
tachs that come to my attention on principle, as I've spent way too
much time troubleshooting a piece at a time and then finding that all
three sections of wire were bad. If your tach doesn't work, just
rewire the whole mess. Trust me, it's worth it. However,
the 3-pin connectors are not available from any
source of which I am aware. Sorry to be the bearer of bad
news. Be careful when working with these connectors as if you
work the little tabs that hold them together too much, they will break
off. In a pinch, or if you're not a stickler for complete
accuracy, you could just hardwire everything together, although I would
suggest including at least one sort of quick disconnect so that you
could remove either the tach or the sender from the car for maintenance
down the road if required. I was told that these connectors were
originally used on stereo speakers (Magnavox?)
2) Tach needs to be lubed internally. The SW Pulse Drive
tach is basically a mechanical (cable drive type) tach, in other words
very similar to your speedometer. It has a synchronous electric
motor grafted onto the back of it so as to not actually require a
cable. If it gets dry, it will fail to work, or it may work at
low RPMs and then fall to zero when it can't keep up. Lubing is
easy, just remove the two nuts on the back of the tach and then remove
the rear housing. Remove the little nut holding the armature
piece on and pull off the armature. (this part is optional, but
will make it easier to get a straight shot at the bits that need to be
lubricated.) Get some lube on the shaft (I've used both
Sili-Kroil and 3-in-1, I'm not certain what the correct lube is) and
spin it with your fingers a few times. The tach needle should
register when you do so. If it does, and it doesn't make too much
noise or feel like it's dragging, you're probably good to go.
This should be SOP for any old tach, since you have to take the back
cover off anyway to rewire it.
3) Brushes in sending unit worn out. This is not as common as the
other two problems, but I've seen it. I have purchased some
brushes exactly the same size from a hardware store, but I've used up
all my stock and the store no longer sells Jandorf products. If
you can find a hardware store that sells brushes for small electric
motors (drills, vacuum cleaners, etc.) you will probably find something
that works. The ones I've used came with integral springs and the
lead came out the rear of the brush not the top as original. I
just cut off the integral spring and pulled the lead through the corner
of the brush holder, and then soldered a little extension onto the
lead, and it worked out just fine. If you replace the brushes, or
even purchase a NOS tach sender for your car, don't be surprised if it
takes a minute or two of running before the tach starts to work.
The brushes need to wear in a little before they send a good signal to
the tach.
I have never (knock on wood) come across a tach that I couldn't make
work by doing the three repairs I've listed above.
Dimensions taken from an original harness. This harness was too
brittle to use; the conductors in the cable were shorting out.
However, it was complete and unmolested. I use this as a pattern
for harnesses when all I have are the connectors and whatever incorrect
wire the previous owner used to make the harness work. Black 16/3
extension cord wire (available in bulk at any good hardware store) is a
direct replacement for the original wire and is indistinguishable from
it once you wipe off any lettering that may be printed on it. I'd
suggest using oil and temperature resistant wire if you can find
it. (SJTO? I think?) The black wire with a red spade
is cloth covered in the original harnesses, although I'm not enough of
a stickler for originality to actually make them that way. What I
usually do is cut a piece of cable about 4' long and then strip all
but the 25" that I need. Then I unwind the black wire for
the "pigtail" harness and then wind the second piece back in - that way
no splices. Not correct, but it's under the dash anyway (well,
usually, that is. I've seen some cars where the harness is hooked
up at the ballast resistor, not the ignition switch, and the owners
swear that the harness has never been out.)
Wiring of the sender and tach head.. I believe that the
green and white wires can be interchanged and the unit will still work;
it's only the position of the black wire in the connector that is
important. The wire from the tach to its male plug should be
16.5" from the tach case to the back of the plug shell. The wire
from the sender to its male plug should be 6" from the outside of the
tach sender to the back of the plug shell.
Overall view of tach. Note the fairly long cord on the tach; this
one is original, I have not done anything to it.
Note the wiring connections inside the tach head. As you can see
in the pic the wiring is becoming brittle on this one and I'll have to
rewire it eventually. If you can, at this point remove the nut in
the center of the tach and pull off the big gold colored armature piece
so you can get some lube down the shaft. Sometimes they are too
difficult to remove; in that case just use a spray lubricant with a
"straw" to get the lube where it needs to be. Also note right at
the edge of the picture there is a clip on the wire. This is for
strain relief and I'd try to save it if possible when rewiring so that
an ill-advised tug on the wire won't rip anything apart inside the tach.
This is the tach sender... it fits in between the distributor cap
and the distributor itself. It should come with special clips to
extend the distributor cap clips so that the whole mess will hold
together. I don't happen to have any originals to show you.
The tag is original as well, it has been reproduced and is available
from several vendors.
Disassembled tach sender. That's all there is to it! The
brush holder is shown upside down from its installed position so you
can see the wiring connections. Note again that even though this
sender is NOS the wiring is starting to become brittle. I can't
stress enough the importance of new wiring on any tach of this
vintage! Also note the sleeves on the screws that go through the
body; these often get lost or chewed up - a little heat shrink applied
to the screw will insulate the screws again. This is important as
it's possible for one of the brush leads to touch these screws.
A closer, yet blurry look at the tach wiring. Sorry about the
picture quality, but you should get the basic idea. If I can get
my hands on another NOS sender I'll try this exercise again.
Putting the sender back together.
This can be the most frustrating part of the job, as you're trying to
hold three brushes back while sticking the little rotating piece in
there. I've found that if you take some stiff paper, like a
business card, and roll it into a tube, you can hold the brushes back
while you position the plate, then insert the rotating piece and remove
the paper. At this point, assuming fresh wiring and good brushes,
just put the bottom (metal) cover on and you're ready to reinstall.
The sender that I've used for these pics is from a 1956 Golden Hawk
(Packard engine, Autolite distributor) but the Studebaker (Delco)
sending units believe are identical with the sole exception of
the big tan plastic housing.
Ray Fichthorn has another tach
repair page
up on the NCSDC website. The diagrams are somewhat more clear and
complete, however, he appears to be assuming that you have the original
wiring handy to copy which as we all know may not be the case. If
you're going to be rewiring from scratch, you may want to print out
both my scribbles and the pictures from his page to make everything
crystal clear.
If you're working on one of these tachs and find something on this page
unclear, drop me an email and
I'll try to help.
