Treadle-Vac

[Barry Wolk]

How long were the Continental sleeve-valve Treadle-Vacs used? I'm told that it wasn't much past the build of the Introductory Units, but I don't know for sure, because they are often swapped out.

The 1957 Mark II I'm working on should have the poppet-style booster, but it has the sleeve-valve type. I'm told the poppet-style are quite "grabby" because they are a more positive seal unlike the constant vacuum leak of the sleeve-valve.

Maybe someone can confirm this. Was the Lincoln T-V fitted with the refill tube the Continental had? If it didn't, I believe whoever rebuilt this last didn't know the difference and fitted the Continental lid to a Lincoln master cylinder. On the Lincoln unit the hole in the casting appears to be filled in with an epoxy where the Continental casting has a passage hole drilled through to the ring between the shaft seals.



Due to this hole being sealed flush the pipe nub on the slanted cover had no place to go, so every time Al topped off his fluid it all wept out. Speaking of the cover, why was it not flat, like the one shown in the service manual? Every single Mark II reserve I look at has too much fluid in it, which seeps out the lowest part of the imperfect cork gasket. The cover is the dipstick.



I don't think this is seal damage. I believe that drip came from the soaked cork gasket between the master and booster. The seals look new. I think the fluid came from the lid seal, but I could be wrong.



I found the check valve off-center and leaking. The spring had been install with two rubber nubs inside the spring and two outside. He had no reserve vacuum. Has anyone used Plastidip tool handle restorer to redo the surface of the plunger?

[Roger Zimmermann]

How is the shape of the sliding rod (or plunger)? Even with a single tiny rust spot, the wiper and spring-backed seal are quickly damaged and the brake fluid is seeping into the booster.

[Barry Wolk]

How is the shape of the sliding rod (or plunger)? Even with a single tiny rust spot, the wiper and spring-backed seal are quickly damaged and the brake fluid is seeping into the booster.

I believe you. I am on my way to the machine shop his morning. This rod has some minor pitting but too much to not heed your warning. I did test. This one is made of steel, chrome plated. I was pretty sure my spare is stainless steel, but you cast doubt on that. What grade SS would you recommend for the task? Would you polish the stainless or is a fine machine finish sufficient?

[Barry Wolk]

I found the shaft. It is stainless. Mad Scientist sent me a box of parts and a complete Treadle-Vac that his father acquired. I believe that they were all stainless, but many steel shafts got installed on many cars as these were usually repaired on an exchange, or core, basis.

I did a simple magnet test and one sticks and one doesn't. The machinist recommend 303 stainless for its machinability. Roger, do you agree?

Rob, the machinist has a very good touch for metals and that appears to be a smooth surface is covered in tiny razor-sharp shards of chrome surrounding the rust blossoms. He said the shaft would destroy the seal in no time. Rob said the original shaft could gave been centerless ground, plated and reground to size, but stainless is better. Anyone need a new stainless shaft?

[Roger Zimmermann]

This rod has some minor pitting but too much to not heed your warning. I did test. This one is made of steel, chrome plated. I was pretty sure my spare is stainless steel, but you cast doubt on that. What grade SS would you recommend for the task? Would you polish the stainless or is a fine machine finish sufficient?

On my '56 de Ville, there were maybe 2 or 3 pittings. Enough to destroy the seals rather quickly. At that time, no replacement was offered, I let hard chrome the rod.
For the good health of the seals, the rod should be polished. I just know that there are several SS grades, but I'm not a metallurgist; therefore I cannot help. You'll have to believe your machinist because if the chosen material is very difficult to machine, the end result will be deceiving.
On my '56 Biarritz, the brake system is Delco-Moraine (or the slider type). The rod was also regular steel. Had to let it hard chrome. It could be that the car manufacturer could choose and order, for costs reason, plain steel or SS.

[Barry Wolk]

I would think, in this case, that it would have been more cost-effective to make all the rods stainless steel for both warranty cost and manufacturing costs to not have to plate and centerless grind the chrome to a suitable finish. Of course, we have the lens of history to look through.

[Mark Norris]

303 and 304 stainless have superior corrosion resistance but the 303 has good machining qualities so if high stress is not an issue (eg. in the case of the booster piston) then go for 303. In cases where stress is an issue (eg. suspension bolts etc.) then use 410 stainless as it has superior mechanical properties though not as corrosion resistant ..but still a lot better that plated steel. For extreme corrosion resistance and stress go for 316 stainless especially where salt is involved (that's why yacht fittings are often made of this material) but it is a little more expensive.

[Barry Wolk]

Mark, I'm checking on this product to see if it's a match. I've asked about length and finish. Knowing what we know now, why would we keep doing the same thing, over and over, expecting different results. This is machined out pf 304.

http://www.cadillacpartsltd.com/19cavapirodb.html

[Mark Norris]

Agree Barry, I often renew in stainless on my cars ...its what the auto design engineers would have used if they'd had an option at the time although they were probably working to a service life of 10 years or so (ie. only the new car buyer). 304 is s good choice for this item if it already machined satisfactorily and hopefully its a fit.