Hydrovac

[1943ht]

Pulled my master cylinder and hydrovac as I'm finally getting to the brakes on my track. Both items are French made Bendix items, no surprise there as this was a recovered French halftrack. Am wondering if anyone has had one of these hydrovac units on their track and if the can provide a model number of the hydrovac or a rebuild kit number. Both MC and Hydrovac had brake fluid in them when I pulled them today.

 

[1943ht]

Research would indicate a Bendix Single Piston Hydrovac ... found a posting for tearing a similar one down and rebuilding ... trying to source parts next ...PIA!

 

[1943ht]

Lots of reading and peeling of the proverbial onion to get to bottom of my hydrovac question.

The model number for this hydrovac is 374750 (3rd series) and was used by the Army in the 50's as a brake upgrade. My HT was a BM M16 to M16A2 Conversion for Korea in 1952, number 315 of 413 A2 conversions. So the Hydrovac change to 3rd series is now making sense.

Now I just need to tear it down and find some parts.

 

[1943ht]

After doing a bit of reading and now having a clear understanding of the Hydrovac function I tore into mine this weekend. The outside was truly no indicator of my Hydrovac interior, which was increadible clean and beautifully preserved. Guess I shouldn't be surprised as everything else I'd opened up has been pristine. Those years of desert storage have been great for my preservation project.

The third generation vac seems much simpler than gen 1 and 2 regards moving parts and design (I purchased an original Bendix rebuild kit back when I 1st got my track not knowing that I had a 3rd generation Hydrovac....when I opened the kit a week ago ..I was surprised at all the pieces in the kit and assume that the original Hydrovac was quite a bit more complicated then the replacement put on my track in 1952. )

My leather diaphragm and the corded seal are still in excellent condition. The leather is supple and shows little to no wear. The cord seal is still white, pliable and in outstanding condition as is the blued retaining spring. Rubber cups and seals will need to be replaced, but the unit still had brake fluid in it when I pulled the brake lines and metal parts showed no corrosion. The biggest challenge was getting the big nuts loose on the valve body. The diaphragm body/shell is still shiny and there was a light layer of old dried lubricant on the leather boot.

I plant to reuse both the leather diaphram and original rope seal, they are just to nice to toss out and replace ....One interesting item I noted during my teardown, there was a cut washer hung up on the inside of the vacuum line where it bends coming into the vac. The check valve in the firewall is intact and the vacuum lines intact, so it's a strange bit of mystery that a cut washer made it's way down to the Hydrovac on the vacuum side. Maybe done by an errant mechanic back in the day? Pics attached:

 

[1943ht]

Just finished a very pleasant phone call with a gent at REMAN Inc, Atlanta GA. He is the resident expert regards all things Hydrovac and is sending a rebuild kit for my Hydrovac. He walked me thru the parts I need and clearly described each section of the hydrovac to include some tips on my assembly. Stated that he believes they may have some WWII hydrovacs still in cosmoline on the back room shelves. Sticking with what I have as it is original to my BM 1952 conversion.

$120 gets me all my parts for my rebuild . Happy camper!!! Will post pics of the kit when it arrives.