Half Track - Hydrovac overhaul

[BenM3A1]

Gents,

I'm currently doing a complete brake job on my White M3A1 Half Track.
At the moment I'm about to start with the overhaul of the Hydrovac.
so, any advice and all "tips & tricks " and /or " do & don't " are more than welcome

is there a story on the hydrovac overhaul "somewhere" available ?

thanks in advance

kind regards, out of Belgium,
Benny

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[Kevin Lockwood]

Opinions may vary. It has been my experience that the seal included in the NOS overhaul kit will fail within 10 hours of operation. Most have had success only by having a modern seal installed which has involved machining of the valve bore to match seal.

[Spec4Don]

I can cobergate Kevin’s post. I overhauled mine with an NOS kit, about 10 hours is about right. It took me about 3 different manuals to figure it out. Apparently there was a change and there was a clip that was no longer used. Personally I would think about getting done by a shop that has experience rebuilding them, (spend the bucks) or look into the modern replacement that is being used.

Don G.

[Big D]

Hi guys

I am interested in this as well. I am currently reconditioning the hydrovac on my M8, which is very similar to Benny's halftrack one.

Which is the seal that fails? The one in the main large cylinder or one of the two in the slave cylinder?

[BenM3A1]

Gents,

Thanks for your input.
The thing is : I allready have a rebuild kit available .(obtained with the halftrack )
So the plan is to use it, and see how it goes.
At the moment I'm disassembling the hydrovac .
First constat : a lot of brake fluid in the first compartment ...(+- 1liter !)
Next constat : internally on a valve, a bolt came off, I found it in the valve .
... To be continued ( if interested ... I can post pictures )
I think the 2 rubber seals in the large cylinder and the outlet seal towards the vacuum are source of all evel ...

Regards,
Benny

[mkoloc]

I too will be taking this project on and have one of those old Bendix rebuild kits. Kevin where did you source that modern seal from? Did you have to machine any other surfaces to get your rebuild done of were the other kit parts usable?

Pardon my jumping in with these questions Benny.

Mark

[jonsm114]

so how did the rebuild go? That is a twin piston Bendix..same one I have.....

Jon

[steve1973]

Instead of trying the rebuild myself I let the professionals do the work. I found a place some years ago that I took my hydrovac to and they rebuilt it. The place is Power Brake Exchange out of San Jose, California. I also supplied an NOS rebuild kit. The very first thing they did was open the rebuild kit, inspect all the parts and then, most importantly, rehydrate all the gaskets and seals. Once the kit was deemed usable the hydrovac was inspected to see if it was rebuildable. The hydrovac was then rebuilt and bench tested, yes, they have the capability to do this. Once satisfactory it was shipped back to me. I have yet to have a problem with it. Some things are better left to the professionals.

Steve A.

[BenM3A1]

Hi John,

Thanks for asking !
Well, the rebuilt/overhaul went pretty good !

Last winter I've done a complete overhaul : wheel cylinders - hooses - master cylinder - brakes and Hydrovac
and I used an available rebuild kit ( that was in outstanding condition )

The result is realy good. The brakes are operatings as they should.
I've used the halftrack this season without any brake issue
If interested, I can post a complete series of pictures that I took during the whole rebuild project.
Just let me know, I'm always willing to help and provide available info

kind regards, out of Belgium
Benny

[mkoloc]

Benny, post those pics please. We love pics!!!

[BenM3A1]

Wilco ... Will do ASAP ...

[BenM3A1]

hmmmm weird ... appatenty I cant post images anymore ?.
allthough I've already done this ( see this post )

... anyone an idea ?

regards
Benny

[BenM3A1]

OK here we go
( reading the FAQ sometimes helps ... when you tried everything, then read the manual ... R.T.F.M ... ... )

The first phase in the process is to dismount the hydrovac completely ( carefully )

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[BenM3A1]

Next step .... apply some cosmetics ... yep, I like it "like new " ...

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[BenM3A1]

THEN ... ready to start rebuilding the hydrovac

F.Y.I : ALL parts ( also seals and nembranes) have been given a (small) coating of silicon grease
later, when all has been overhauled and the brake ovehaul project is finished, I also used silicon brake fluid in the brake system ...

Don't hurry, take your time and be sure when assembling

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