Staghound Hydramatic Transmission Question

[Malcolm Towrie]

Rob, great info on the Honeywell switches. Just what i needed.

Regarding the two pressure taps on the one Hydramatic, I suspect the one you are seeing that's close to the engine, ie not between the two band adjustment screws, is not a pressure tap at all but the 1/8" NPT cover on an indicating pin that allows adjustment of the front band without removing the side or bottom pans. Check down the hole with a mirror. If you see the top of a 1/8" pin, that's what's it is. This is not a source of tranny pressure, so having a switch on there does nothing.

On the Chaffee, there is another pressure tap on the transfer case side of the two adjusting screws. I think it is unique to the Chaffee. It's an intake manifold vacuum source to the tranny, used as a source of engine load for modifying shift points. I think the M5 uses a linkage to the valve body from the carb throttle plate, same as the Staghound does.

Malcolm

[Malcolm Towrie]

Rereading your post, you have the extra port FORWARD of the adjusting screws on one tranny. That would match the vacuum port location on the Chaffee. Maybe you have a Chaffee transmission? In which case, you won't have a complicated linkage from the carb, just a tubing line to it from the intake manifold.

Malcolm

[rob love]

Malcolm: Of course it is on the transmission that is still hiding under the ammo bin/cover, but I will give it a look. The linkages appear to be the same as on the other transmission. I may put a gauge on each plug, and run up the engine and see what each shows. I'll try and get a decent shot of the transmission in question tomorrow and get your opinion.



Acklands Grainger carries the required hobbs switches, and if you get any kind of a corporate discount, the price is quite favourable. Unfortunately for me, the local Acklands Grainger was closed up a couple years back and now the nearest one is Winnipeg.



This thread turned out to be quite timely for me....sorry for the hijack.

[rob love]

Luckily for me it turned out to be the transmission that was accessible, so today I installed a 90° elbow and a 60 psi NC switch. I am now in the process of installing the second switch on the other transmission....it's a lot tighter working on that one.

For switches I used a pair of 60 psi switches from the MLVWs...they were rated for air or liquid, and have the bonus of even being adjustable if need be. NSN is 5930-00-434-5441. I modified this one for one wire, the other will remain 2 wire.

[marco]

Rob,

The "old position of sending unit" actually is the hole were the indicator rod is visible when adjusting the front band.
No oil pressure there...

Marco

[rob love]

Thanks for the confirmation Marco. I got sucked away to other projects the last day or two....hopefully tomorrow I can finish up this part and run up the vehicle to confirm the warning light operation. Then I can get back to buttoning up the panels below the turret and some items on the turret basket.

At that point, the vehicle should be able to move under it's own power to the other building, which will be all I am after at this point. I have 5 or 6 other vehicles/guns to prep for VE day. My preference is to drive them in as opposed to pushing them in....we'll see how it goes.

[Malcolm Towrie]

Your setup is the same as the Staghound, see photo. Nearest the engine is the cover for the front band adjusting indicator pin, as Marco says. The cover's missing in the photo. Then the front band adjuster, the pressure switch, the rear band adjuster, and the rear band adjusting pin.

GM had designed the Hydramatic just a few years before and, boy, did they modify it on the fly. First no band adjusting pins, which I think you said is like your other tranny. This requires removal of the tranny to adjust the bands, which was a routine task!
Then two pins to allow external adjustment of both bands.
Then they made the rear band self-adjusting, so only the front band had the pin. The Chaffee has this setup.

I don't know how far you are getting into the trannies on the M5, but the adjustment of the linkage between the carb and the tranny is critical. The tranny needs to know engine load so it can delay shifts, increase pump pressure, clamp bands and clutches tighter under load, etc.

Malcolm

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