News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

Bendix Treadle Vac rebuild?

Started by Alan Harris CLC#1513, January 21, 2021, 12:00:44 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Alan Harris CLC#1513

Has anybody here recently had a rebuild done on a Bendix Treadle Vac power brake unit? (1956 and 1958 Cadillac, numerous other GM, Packard, Hudson and Lincoln cars of the era)

Who did you use? How much did it cost? Were you pleased with the job?

Thanks in advance.

TonyZappone #2624

Mike Gadaleto did my '58 this summer.  Expensive, high core charge (the core you return must be rebuildable or 700 or 800 core charge),  good work, works well
Tony Zappone, #2624
1936 Pierce-Arrow conv sed
1947 Cadillac Conv cpe
1958 Cadillac conv
2016 Cadillac CT6 Platinum
2022 Chrysler Pacifica Pinnacle

Roger Zimmermann

Is that for your Continental Mark II?
1956 Sedan de Ville (sold)
1956 Eldorado Biarritz
1957 Eldorado Brougham (sold)
1972 Coupe de Ville
2011 DTS
CLCMRC benefactor #101

TJ Hopland

I assume you get these rebuilt as an assembly?   The booster and master cylinder?    I assume the booster involves having to make or have someone make the soft parts?   Then the piston and its bore must be a fairly tight fit since I don't recall it using any sort of rings so the tolerances have to be smaller than a molecule of brake fluid.   Must be a honing process like diesel injection pumps? 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Roger Zimmermann

Yes, both units are assembled as one unit.
The cylinder is a sheet metal part and the seal for the piston is leather. The result is good enough when a bit oil is used (don't remember which one).
The Bendix system is rather easy to work with; however, there are two vacuum valves which are usually not reproduced. Maybe Mike Gadaleto has them; I found years ago NOS ones by an American Motors dealer.
Delco Moraine booster is a bit more complicated with rubber parts which can go bad.
1956 Sedan de Ville (sold)
1956 Eldorado Biarritz
1957 Eldorado Brougham (sold)
1972 Coupe de Ville
2011 DTS
CLCMRC benefactor #101

TJ Hopland

I was more speaking of the piston and bore for the master cylinder part but knowing the booster is leather is interesting.

These hard to find valves I assume have to do with the function of the booster?   Isn't there also a valve before the vac reservoir tank too?

There is also a check ball that is basically what makes the master work that I assume must have some sort of seat cutting process I would be curious to see the tooling for.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Roger Zimmermann

The piston is indeed a plunger. The seal is attached firmly to the master cylinder. With that set-up, the piston must be perfect: if there are tiny rust pits, the rubber seal will be damaged by each plunger movement. Don't ask how I know it! The piston is reproduced for the Bendix unit, but not for the Moraine. If damaged, there is a sole alternative: hard chrome.
Yes, the hard to find parts are in the piston for the vacuum. There is also a valve just before the booster, with a rubber hose to the vacuum tank.
Unfortunately, I don't understand your last sentence. A special tool? for what? If I do remember well, the assembly can be restored without special tool. I did (long ago) both the Bendix and the Delco Moraine.
1956 Sedan de Ville (sold)
1956 Eldorado Biarritz
1957 Eldorado Brougham (sold)
1972 Coupe de Ville
2011 DTS
CLCMRC benefactor #101

TJ Hopland

I was kinda remembering a check ball in the brake fluid part of the system that had to seat to let the pressure build.  I was assuming that there was some tool to cut that seat if it was worn or pitted.  Since its a ball I would not think you could just lap it like you do valves.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

J. Gomez

Quote from: TJ Hopland on January 21, 2021, 06:30:01 PM
I was kinda remembering a check ball in the brake fluid part of the system that had to seat to let the pressure build.  I was assuming that there was some tool to cut that seat if it was worn or pitted.  Since its a ball I would not think you could just lap it like you do valves.

TJ,

The complicated side with the seals/valves/etc. in the booster is part of the vacuum control power piston, these are the hard to find pieces as Roger stated part of assembly A, B and D on the attach drawing.

These pieces controls and regulates the vacuum on the back of the power piston assembly G inside the canister the vacuum provide the brake assistance.
When you slightly press the brake pedal the valve opens pulling the vacuum on the rear of the power piston.  The large spring provides resistance when the brake pedal is pressed and also to return the power piston.

So the complete valve assembly provides a relief for the vacuum inside the canister when the brake pedal is release and to close the initial path for the vacuum when the pedal was pressed.

So as you see is a very complicated piece to detail.

The only special tool that is needed for the Moraine type is J-5794 to remove/install the M/C nut, the Bendix no special tools are require.

HTH
J. Gomez
CLC #23082

TJ Hopland

Yes I knew the booster portion of the system was somewhat complex but I was wondering about rebuilding the master cylinder part.   Or did Cadillac use a more typical master cylinder on theirs?   My experience with these was not Cadillac and those cars had a really unique master setup where a check ball sealed a chamber and then a piston basically displaced some fluid just by being extended into the chamber and that displacement then forced pressure down down the line.   This was quite different than what we typically think of where its more like an engine with a piston in a bore.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

TJ Hopland

There is a diagram of the bendix one I am thinking of in this thread but it doesn't have the list and names of the parts.   I don't see the check ball thing I am thinking of so maybe it was a different year or the different makes or I just can't make it out in that diagram.
http://forums.cadillaclasalleclub.org/index.php?topic=108494.0

The reason I am fascinated with that ball is both times I was exposed to these systems they had a problem where intermittently you just had no brakes and I eventually figured out it had to do with this ball and it didn't seem like it was a rare issue with them.  One was a really close call.   I just didn't like that it could just be nothing so easily,  at least the more typical system you usually had at least a slight amount of pressure. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

J. Gomez

TJ,

The M/C can be rebuild as long as the pieces inside are in good condition, the rebuild would have the “O” rings for the M/C nut and the three rubber seals. The first one inside the nut is for the vacuum seal, the second is for the brake fluid from the reservoir and the last one is to seal the fluid from back flush inside the reservoir when the M/C piston is apply pressure around the end cavity.

The M/C slides between all of these seals and applies pressure forcing the fluid out on the check valve on top of the M/C. The check valve opens with fluid pressure and closes when pressure is release so there would be a pressure on the main line to each of the wheel cylinders.

If there is a need to refill the cavity from the reservoir, fluid flows through the last seal once the M/C is retracted, there is valve (drawing #30) with groves which allows fluid to flow on either direction.

There is no ball inside the check valve for these units; I think you may be thinking of the Hydrovac which I believe those may have a check valve ball. 

HTH
J. Gomez
CLC #23082

Alan Harris CLC#1513

Yes, Mr. Zimmerman, this is for my Mark II. I felt justified in bringing it up here because it is also a multi-year Cadillac part.

The power booster and the hydraulic section are serviced as one unit. The check ball is called a compensating valve. When the brakes are not being applied, the valve is open and the system is not under pressure. There is no cylinder with a bore or cups as is usually seen. When the brakes are applied, the piston moves forward and allows the valve to close, which traps the pressure inside the system. The piston then moves forward through a seal into a chamber full of fluid. Pressure is created as the piston displaces the fluid trapped in the chamber.

It is quite different from anything that we see today. Because of that, you need to be very careful who you allow to work on one.


David King (kz78hy)

I have used Midwest Power Products for booster and master cylinder rebuilds.

http://www.midwestbooster.com

David
David King
CLC 22014  (life)
1958 Eldorado Brougham 615
1959 Eldorado Brougham 56- sold
1960 Eldorado Brougham 83- sold
1998 Deville d'Elegance
1955 Eldorado #277
1964 Studebaker Commander
2012 Volt
CLCMRC benefactor 197

Director and Founder, Eldorado Brougham Chapter
Past President, Motor City Region

Rare Parts brand suspension parts Retailer via Keep'em Running Automotive

Roger Zimmermann

David, the '56 and '58 master cylinder and booster are not the same as your '55 or the Brougham models. I will not say here that the company you used cannot overhaul the Treadle-Vac systems.
1956 Sedan de Ville (sold)
1956 Eldorado Biarritz
1957 Eldorado Brougham (sold)
1972 Coupe de Ville
2011 DTS
CLCMRC benefactor #101

David King (kz78hy)

Quote from: Roger Zimmermann on January 24, 2021, 01:29:53 PM
David, the '56 and '58 master cylinder and booster are not the same as your '55 or the Brougham models. I will not say here that the company you used cannot overhaul the Treadle-Vac systems.

I know they are different.  I had my '60 and '55 done there, they do all years and other brands.
David King
CLC 22014  (life)
1958 Eldorado Brougham 615
1959 Eldorado Brougham 56- sold
1960 Eldorado Brougham 83- sold
1998 Deville d'Elegance
1955 Eldorado #277
1964 Studebaker Commander
2012 Volt
CLCMRC benefactor 197

Director and Founder, Eldorado Brougham Chapter
Past President, Motor City Region

Rare Parts brand suspension parts Retailer via Keep'em Running Automotive