The Stovebolt Site Forums The Parking Lot Big Bolts How to adapt to dual reservoir cylinder?

The Bendix booster on my 2 ton is a 374000, the steel vacuum cylinder is about 7 inches O.D. and roughly 5 inches long, pretty sure it is the stock HydroVac since the mounting bracket and all of the plumbing lines fit in the factory holes.

Thanks much, Accupart just informed me that I must have read the tag wrong because Bendix never made a 574550 but they used a 374550 on that truck so I ordered a kit from them. Now I'm trying to figure out what to do for a MC. I may try boring it out and sleeving it. Kind of a challenge but I have other MC's that need replacing so I'd like to get it down. I looked all over on YouTube and could not find a video on boring a brake master cylinder out for a sleeve. If I ever do get it right I'll think about making a youtube vid on it

49TT - I did some digging through an old paper copy of a NAPA Brake Parts Catalog. It lists NAPA 9220 as the correct 1-1/4" bore master cylinder for your 6400. The current NAPA Part is listed as NMC M9220 and they want about $290 for one.

Some more web searching shows that the "9220" master cylinder has several providers, most being from Dorman, but all equivalent to the NAPA NMC 9220.

Here are a few "9220" master cylinders that you can order to fill your need, spending as little or as much as you want.

NAPA NMC M9220

ebay offered Dorman M9220

another ebay offered Dorman M9220

Jim Carter ME166

The Filling Station FS-241A

Hope this helps you get further along in your brake restoration.

Wow, thanks Dan, thats a big help. I called my local NAPA store a while ago and they said they had nothing but I'll give them this number now. I'd consider any of those options and will write them down in my files. AccuPart says they bore and sleeve them and also have some on the shelf that are "in tolerances" but I don't know what that means yet. They want a picture of mine, and say they can't go by the forged numbers on it. Will keep you posted. T have the rebuild kit for my hydrovac. Will get back in a few days.

After some measuring I'd say that if I ever did need to have the best safest brakes for this two ton and if I had the time to do it I would put
a hydro boost in it by making the pedal linkage offset so as to get the dual reservoir and hydroboost unit away (to the left) from the carb. The hard part would be adding a power steering pump. I guess if a guy were really determined he could even add power steering, which has been done before. I wouldn't worry too much about the size of the hydro boost as long as if was off of a 3/4 ton truck. If it didn't have enough power then it would be no big deal to swap it for a one ton. To offset the linkage I'd have a horizontal rod between two vertical rods. I'd weld the three together and when it was just right I'd replace it with a one piece with two bends. But I don't really know if that would be perfectly safe even if the offset rod was extremely thick. It's probably never been done

I've seen another fella on here put a Hydroboost and modern master cylinder under his '50s vintage truck, so it can be done.

I think a 3/4" offset linkage rod inside the cab with a one ton modern hydroboost would work well. The pedal doesn't need much pressure with the boost. But I'm going to stick with a rebuilt factory setup for now. BTW does anybody know how much torque to use on the four J bolts that hold the hydrovac tank together? The rubber O ring is so thin I'm afraid of ruining it. The one that was in it was so tight it disappeared completely but that doesn't seem right to me

I think the tie rod J-hooks are only 1/4-20 thread, just snug them down evenly until the can is seated squarely.

49TT - According to information in a 1947 GMC Maintenance Manual, which better details overhaul/repair of both the small 7" and large 9-1/2" diameter hydrovac units, it says to tighten the 4 cylinder shell securing hook bolt with nuts and lock washers. Then tighten hook bolts on the small 7" units to 24-28 inch-pounds. That is followed by "CAUTION: Do not over-tighten hook bolts." *

To the best of my knowledge, these hydrovacs where the same as the Chevrolet units, so the technical info should apply as well.

* Note - For the larger 9-1/2" diameter hydrovacs, the instructions indicate the hook bolts on those units are to be tightened to 5-6 foot-pounds.

Thank you Gdads51 for taking the time to look for the actual specs.

Thanks Gdads51, I appreciate that, I've been meaning to check in but I don't see a "follow" option that keeps me posted on new comments, which is not a big deal, just takes me longer to respond. I can torque them down now, used the same split lock washers that were on it. I'm going to get it back on in a few days, its taking a long time because I broke 15 ribs, 4 vertebra, in a rollover when I got rear ended by a much bigger truck going much faster than my little old Toyota when I was already going 70. No air bags or seat belts. (Hit and run) Wish I'd been driving my two ton that day. I may need a vacuum tank too, did most of them come with vacuum tanks? Also need to replace the line between the MC and hydrovac. And test the check valve and lines. should be in one piece in a few more months

49TT - Sorry to hear of your run in with the hit and run driver and the physical injuries. Glad though to hear you are still with us and on the mend!

On your topic of "follow" options, you need to look at and update your "Preferences" and "Follow Lists" (under your member name) so you can get notifications when folks reply to your threads or in a forum you are following. Send me a PM if you need more details.

I'll leave the answering of the "vacuum tanks?" question to other Big Bolters that are more familiar with that equipment.

Thanks, I should have looked at the preferences of course. I still haven't gotten around to looking for a tank underneath the truck, but will tomorrow

in Preferences I chose to get email notifications on threads i follow but now I dont see where to select a thread to follow. Thanks much

All vacuum brake system trucks came with the same 24" tank from 1946 well into the 60's and maybe beyond that...

Mike B