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Hydrovac Upgrade
#1364323 Wed Jun 10 2020 02:51 PM
Joined: Mar 2008
Posts: 1
Mark J Offline OP
Hi, I have a 1943 4400 series 1.5 ton truck. 216 all stock driveline and brakes. Regular manual brakes. I want to add a hydrovac, like the '46 6400S series had. They used a Bendix #374550 booster unit. I have one, but it looks like it came from the bottom of the ocean. I know I can use it as a core on a rebuilt one. My question is, can you use a better / newer / less obsolete / less expensive unit like a #51-8049, as seen on the Loadstar trucks in the 70s? Wondering if there would be any hydraulic pressure differences / issues, etc. My 216 has 22 in. of vacuum. So no issues there. I would rather use a newer unit if it will work ok. I am going to swap in a 235 splash intake manifold on my 216, that has the large vacuum threaded port in the side for the hydrovac vacuum supply. The brake lines I will just make up and put the hydrovac in line between the master cylinder and the 4 wheels, just like the 6400 truck was done. My truck has the stock 1 1/4" master cylinder, same as the 6400S had. Thanks!!

Attached Files
hydrovac 6400s.jpg (99.66 KB, 96 downloads)
hydrovac 6400S
hydrovac IH.jpg (60 KB, 99 downloads)
hydrovac IH
1943 Chevy at lumber yard.jpg (125.69 KB, 102 downloads)
1943 Chevy 4400
Re: Hydrovac Upgrade
Mark J #1364362 Wed Jun 10 2020 09:34 PM
Joined: May 2017
Posts: 344
Shop Shark
While I am no expert on Hydrovac interchange, your logic sounds good to me.

Have you checked with a commercial supplier or rebuilder of Hydrovacs to see what they say about your question?

Mac :{)

1962 K10 short step side, much modified for rally
1969 T50 fire truck, almost nos, needs a few things
Re: Hydrovac Upgrade
Mark J #1364530 Fri Jun 12 2020 01:47 AM
Joined: Mar 2004
Posts: 4,770
Shop Shark
Don't forget to add a vacuum system check valve and mount it on the firewall above the carburetor flood level. This prevents raw gas from finding it's way into the system and the check valve prevents an intake backfire from damaging the hydrovac.

You may also want to add a vacuum storage tank so you have stopping help if the engine stalls.

Mike B smile

Re: Hydrovac Upgrade
Mark J #1365535 Fri Jun 19 2020 10:14 AM
Joined: Feb 2012
Posts: 36
Wrench Fetcher
On my 1972 C50, I bought a rebuilt HydroVac unit from Reman,Inc worked great. I'm pretty sure your truck has an under floor master cylinder, if so it MAY NOT have enough volume to operate a HydroVac. I don't know what they require for volume. Also, if you don't have prior experience with bleeding HydroVacs, you should consult a manual for specific instructions. When properly done and bled, they will lock up all six tires if you want. Good luck!

Last edited by Shacklett; Fri Jun 19 2020 10:16 AM. Reason: correction

Moderated by  69Cuda, Grigg 

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