Geoff Weeks

Sorry to hear that. I went through the prostate dance 2 years ago. Mine is in a jar somewhere. I thought if you were going we could finely meet. We have been conversing since the old ATHS days, when my town was going to seize my Dart.

Terry, are you going to the inspection day?

Mack rears have a smaller "bowl" that sticks below the axle housing (being a double reduction rear) which can be a real advantage when working off road in rough work sites. For fuel hauling,on road, there is no advantage to the design, more bearings and likely more heat when run down the road. I worked on some Macks, but I had IHC, Eaton and Rockwell (Meritor) and found that all were good, and all had something that could have been improved. The Rockwell's were the only ones that outright failed on me, but they were put though a lot, before they failed, sometimes hauling 168K GVW on 40 K rears. All will work and if cared for give good service, but I think single reduction for on highway service would be the best. If the interaxle driveshaft is designed properly it doesn't cause problems or vibrate, despite being at angles, that is what U joints are designed to do. You have to get the pinion angles correct, so the joint angles are correct.

It is a double edge sword. Easy to get in too deep.

I was alerted to this auction that is close to where I live. Some old Macks and other brands, dating back to the teens though more modern times. I have no connection to the auction. I will not be able to research any listed truck for anyone, but may make it to the inspection day if things work out and if I do could take some pictures for someone interested in something not shown. https://www.vanderbrinkauctions.com/auction/online-only-antique-tractors-vehicles-parts-more-the-dennis-bates-collection/ Again, I can't promise I will make it to the inspection day (I am on jury duty call in) but if I go, I would try and take some pictures if someone had a truck they were interested in.

Check the breather line (not the vacuum line) for a constant draw of air into the hydrovac. If the the control valve is faulty, there will be a constant air intake anytime the engine is running. Under no braking, both sides of the piston are under engine vacuum. If the piston is leaking, there will be no intake of air when the brakes are released, but continuous air intake when the brakes are pressed. In normal use when the brakes are pressed, an amount of air is allowed in but should stop if the pedal is held a some position between the floor and released. The hyd cylinder section can also leak brake fluid internally so even though the U cup moves it doesn't build pressure beyond what the master cyl already provides. Also don't overlook the brakes themselves. My Hy-Torque style brakes on the rear have siezed up requiring complete disassembly and cleaning + lubing of the pivot points. Once that was done, the brakes would plant your face on the windshield empty or loaded, if you jumped on the pedal hard. Needless to say, these units require a good vacuum source AND a good source of clean air. Some units have their own aircleaner (either dry or oil bath types, I've seen both). If the air intake is not filtered, all bets are off of how much dirt and dust has got inside a clogged passages, or even mud dubbers. Some installs have the air inlet plumbed to the clean side of the engine air cleaner. There should be two bleed screws on the Hydrovac itself. You start by bleeding to the screw by the control valve, then the one on the outlet, then the furthest brake from the master and working your way back to the closest brake. Another problem I see, is people don't use vacuum brake hose (which is required by law) but heater hose or hyd hose that is not rated for vacuum brake service. This can collapse, and prevent proper operation. I use as much "hard line" either steel or aluminum, and only use short sections of vacuum brake hose to make connections. If the truck already has steel vacuum tubing (1/2 or 5/8") make sure it doesn't have pin-hole rustouts in it.

this has a bunch of interchange numbers to track down: https://www.webbwheel.com/webbipad/pdf_files/102-(65511).pdf Take a bunch of measurements and see if another inboard spoke drum can be machined to fit that application. 16.5 x 5" drums still show on a catalog that is a few years old.

Original 3rd series could have a leather piston, so neetsfoot oil would be appropriate, but COULD have a rubber one, in which case jack-oil would suffice. On the hydraulic side, brake fluid should pass through from the master to the wheels. If it is leaking brake fluid into to vacuum line back to the engine, then you have to address the hyd side of the hydrovac. Again, I have 80+ year old unit that are still function. WHAT ARE THE SYMPTOMS???

Again, What are the symptoms? Oil will not solve a problem. It is PM. It can not cause no brakes, only no power assist.

That was the name I was looking for!

What are the symptoms? I have 80+ year old hydorvac's and they still work. You have to bleed them in the correct order, or they may not function properly as air gets trapped around the vacuum control valve if it isn't bled 1st. Also another "must" is a check valve in the vacuum supply between engine and hydrovac. It keeps combustible gases from being drawn into the hydrovac when the engine is shut down

https://powerbrakes.com/hydrovacs/bendix/ https://www.accupart.com/vacuum-brakes/bendix-type/hydrovac/?page=4

Not the way I read it. 4 six volts to make up 12volts so two sets in series the sets in parallel. Truck is 12 volt.

I drove from Gillette,WY to Illinois on the front with the interaxle driveshaft out. I was loaded but not to the max GVW.

From what I remember before deleted, he was driving in the local area where the previous owner had it. The latest from him before delete was he made the 3 hr trip with new batteries, so last posted it was not at his place of business.