Restoration of 1953 Mack 85LS

[mowerman]

I guess what I’m trying to say is they used to be separate on everything now it’s all one unit

[Geoff Weeks]

The frame mounted booster allowed for more boost an worked better with bigger trucks, larger M/C, and more overall flexibility in the whole brake system.

 They were used up and until air brakes took over the medium truck market.

 You can replace the hydrovac with an "airpac" that is the same booster but boosted with air pressure instead of vacuum, then you have a brake controlled pressure signal that can be used to operate a trailer with air brakes.  It was a popular conversion after the war when there were plenty of hydraulic braked surplus trucks and not enough  air braked tractors around for towing semi's.

throw an air compressor on, exchange the hydrovac for an air pack, a few air tanks and valves and you were set.

[Vladislav]

Wow! Greal truck and great project! And welcome to the group!

Also very nice to learn such a vehicle showed up in Poland. I keep my eye for different Mack trucks over Europe for more than a decade and doubtly remember any L-model firetrucks besides your example. And L-models are rare in Europe at all.

As you see both of your initial questions were answered immediately. This is an example of kindness of folks of here no doubt but also result of your approach putting questions in a correct manner and what was more important (as it seems to me) first representing your project and your needs with pictures and the story. People enjoy spending time on here communicating with persons of the same interests. And this goes better when info exchanges, not a one gate game.

Speaking a bit more about the rev governer I can say I have one Mack truck with similar 707 engine and similar (or nearly similar) governor. First when I found it taking place there I was surprized seeing such part on a gasoline engine. Since I used to see them on diesels. Probably the matter is huge size of a truck's engine and risk of collapsing it due to high revs which is not a common problem with cars. A governor in my diesel Mack provides two functions - limits maximum revs and keeps idle. But this gasolin unit only limits overevving if I'm not wrong. Better to refresh this point checking out a manual.

P.S. I very like your country and people. Used to drive there alot during many years, visited the most of big cities such as Warsaw, Krakow, Poznan, Gdansk etc. Unfortunately it's difficult or impossible for me to do that in the recent times, you know. Ok, let's hope for better times and better discuss Mack trucks.

Vlad

[Mack85LS]

7 hours ago, Geoff Weeks said:

 The brakes are hydraulic with vacuum assist (boost). The thing in blue is the master cylinder, just like a car has. It is bigger and only has a single line. Dual masters didn't come out until much later.

The master is connected to the foot pedal by a push rod. It make pressure in the hydraulic line which goes to the wheel cylinders in each brake.

Along the way it passes through the frame mounted "Hydrovac booster". If the engine is off and no vacuum, the pressure passes right through the unit and on to the brakes, un boosted.

 IF the engine is running and there is vacuum in the booster, the control valve closes off vacuum to one side (rear) of the big can and modulates how much atmospheric pressure is allowed to the back side, which moves the piston in the hydraulic portion, boosting the amount of foot pressure from the master. In this way it multiplies the pressure generated by the drivers foot but is always controlled by the drivers foot pressure. 

 So it is not true "vacuum brakes" which work like air brakes in reverse, but vacuum assisted hydraulic.

Well, today I managed to take out those two components to check if they are still usable. I must admit, you were right:

There are traces of oil inside, so they are indeed hydraulic with vacuum assist. However, there’s a piston (shaped like a cone) inside, which had gotten completely stuck for ages:

 

Since I’m Polish, this was no match for my 23-year-old hands, and voilà (don’t ask how I managed to do it...):

Here’s how the piston looks and a glimpse of the engineering inside:

So, yeah, it’s time to use a sandblaster for the external parts. I’ve already blasted one piece, so here’s a sneak peek of how beautiful it looks under all that rust:

Have a nice rest of the day!

[Geoff Weeks]

Looks like you threaded a bolt into the piston, this is NOT the way to get it apart. The push rod has to ride in the concave space.

 If you ever have to do it again, make up a fitting  and grease nipple and pump grease into the outlet of master forcing out the piston (after removing the lock ring).

Measure the bore, if it 1 3/4" then the rebuild kit I referenced should work.

 The real question is what shape the bore is in?

[Geoff Weeks]

Please post any casting numbers on the master cylinder casting.

[Mack85LS]

No worries, I didn’t thread the bolt directly into the piston. Since the piston is in decent shape, I wanted to avoid causing any additional damage. I only needed to twist it slightly to loosen the rust so I could push it out with grease.

The only visible letters/numbers are "Wagner Lockheed." I’ll double-check for any other markings tomorrow after cleaning off the external dirt for a closer inspection.

[mowerman]

It doesn’t look bad at all inside 

[Mack85LS]

Alright so after inspection here is what I found:

I believe one one side it says "Wagner Lockheed (9A?)" and on the other side "Made in U.S.A (AFE 800?). This is all I found on this part, and for you here is what inside parts look like. Surprisingly the gum seals are in marvelous shape:

Now it's time for hydrovac. Here are the letters/numbers i could find on this:

And inside of the hydrovac:

 

And that is all for now. I believe I found video explaining what this whole system does on YouTube called: Hydrovac Brake System uploaded by Daniel Lautenschlager.