Just to add a little more info. I cannot find a line entering the back side of the booster diaphragm. In my feeble mind that makes it a simple vacuum assisted booster (being vented somehow on the pedal side) rather than a standard full vacuum booster? If this was true then why the cab filter other than to allow atmosphere in behind the VALVE (Image 4) for the two speed box?
I try and not use full retail places like NAPA because of the expense. I have used them in a pinch but for stuff like this I use these guys. They are re-builder's - at least one of them anyway - and I have been happy with them so far. They are usually backed up and you can wait 30 days or so but they normally have a core to rebuild and then you send them your core after the rebuild arrives. I have only purchased full under the bed 2 and 3 line boosters from them. No idea if they would have a firewall mounted unit but doesn't hurt to ask.
Have you checked with your local NAPA? They should be able to send it out or take it in as a core for a rebuilt unit.
I'm not sure if White Post does big truck boosters, make sure to inquire before sending it off...
Mike B
I talked to Whitepost about rebuilding the Bendix Hydro-Vac for my '57, they told me they have parts for everything and could do mine. After disassembling mine I chose to rebuild it myself.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
IDitit Seems like your NAPA store could help you find your local booster re-build company so you could ask them. We have one in Evansville Indiana,I talked to the guy about my '51 original booster,he said if it starts getting rid of brake fluid daily he knew how to fix that.Find those guys in Kansas and ask them.
Hy IDidIt, I have been meaning to get back to this for days, but life kept getting in my way. After checking a loose booster of the same type as your truck has, I find that the atmosphere air enters the booster through the back of the booster where the pedal shaft goes in. My conclusion is that the vacuum two speed control is somehow allowing the vacuum to escape. Possibly the vacuum shift diaphragm has a hole in it, hope that helps.
Just wanted to get back to you guys and let you know what I found and what I did to correct the problem. (See Images) Problem was actually in two places. #1 What I will call the UNDER CAB DIST BOX. This is a mechanical over diaphragm operated box that is controlled by the two speed button on the shifter. #2 The VACUUM OPERATED TWO SPEED CONTROLLER mounted at the rear axle.
Once I pulled the UNDER CAB BOX apart it was mostly gummed up. After cleaning it seemed to operate fine on a test bench so I re-installed it but still had a similar issue. Next I went to the rear TWO SPEED CONTROLLER and took it apart. Inside was also heavily gummed up plus a hole in the diaphragm. I finally found this diaphragm on ebay through Rebuilders Interprises. Part #GM#3847058 BENDIX#374451. About $30 Shipped.
PROBLEM HAS NOW BEEN CORRECTED.
Below I will just go ahead and do a copy and paste of the file I am building on this project. It may help others. Since I am not done with this project some of it may turn out to be invalid but here it is anyway. Thanks Guys - Much Appreciated!
******************************************************* 1967 Chevrolet C50 Grain Truck 327 Small Block V8 - 4 Speed Trans - 2 Speed Rear Axle - 14.5' Knapheid Bed - Anthony Lift - Original underhood items like Air Cleaner - Govenor'd Carb (Disconnected) Distributor - Firewall Mounted Vacuum Booster. VIN CE537J141691 - Mileage 58,173 (4/15/23) Engine: Fuel Pump M6624 - Dist Cap DR429T - Condenser DR70T - Points DR22780PT - Carb - Autoline C945 - OEM Part Numbers 7013353, 7015019, 7020109, R22G Rochester 2 Barrel;
Distributor Delco Remy 1112796
Paint Color: THECOATINGSTORE.com Habenero V-Belts Water Pump/Alternator 17560DR 56017DR x 2 Bendix 2501422 GM# 3959747 2 SPEED REAR AXLE DIAPHRAGM GM#3847058 BENDIX#374451 Eaton 47638 takes a GM 2398285. Bendix 374451 which takes a 3847058 GM Transmission - Muncie P21XC (M21) REMOVING THE GOVERNOR OFF CARB: On the passenger side of the carb is a diaphragm assembly. On the back side of diaphragm is a removable steel tube that goes into a T that enters the lower part of the distributor. Your distributor is mechanical advance so vacuum is not required. On the T you will find a wire attached to a spade terminal and solenoid. Additionally there is a small filter screwed in the side of the dist. These can be left in place if you want. This carb mounted diaphragm pulls constant (metered within distributor) vacuum. If you simply block that vacuum by removing the tube and plugging its entrance to the diaphragm then the motor will no longer rev up. Just forward of the diaphragm is a small flat plate held on by 4 screws. Remove this plate. Inside you will find a spring attached to a rod that goes up into the diaphragm. First remove the spring then the nut that holds on the "rotator". Now you can turn this by hand until you can line up the slots and remove it from the rod. Don't try to remove the rod from the diaphragm because the brass rod stays in place but it is now no longer affixed to the rotator plate. Put the small rotator plate back on and affix with the small nut and then re-attach the spring. Next make sure the rod is not binding up anywhere by hand throttling the carb. If everything looks free then go ahead and put the outer plate back on and you are done. For ease of removing the distributor or other wise working on it then it is advisable to remove the steel tube entirely and plug both the diaphragm and the Tee to prevent dirt from entering. Now you have accomplished two things: You have removed the governor and also removed what is mainly just a vacuum leak at the source.
IDidit, I'm curious why you want to disable the governor, it was intended to protect the engine from overspeeding. If the governor is in working condition it has a couple of adjustments to get it into spec. My '57 2 ton has the original drive train, 283 2 bbl, SM420 trans, single speed 7.20:1 rear end. The factory specs for my application and many other of our vintage trucks is a 'no-load' governed speed of 4000 RPM, I wouldn't want to run this engine any faster even though it is a 'modern' high speed V8 with a short stroke. Your 327 and my 283 are cut from the same cloth, same stroke, 3.875" bore on mine and 4.00" bore on yours. I would be cautious of too much RPM unless the engine has been rebuilt and balanced.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
78Buckshot. Born in 56 on a farm in SW Kansas. Was driving both tractors and vehicles by the time I was 7. Had to use both feet to engage the hand clutch on our Minneapolis. Depending on the vehicle it sometimes took my brother to run the gas/clutch/brake while I steered because couldn't reach both. Farmed about 900 acres and custom cut/chopped another 1,500 acres of customer alfalfa. 12 hour summer days - 7 days a week. During this era my brother drove the tractors and my job was driving the trucks. Did this for 9 years til my dad died.
To shorten this up. Would say I had a heavy foot as always needed to get back to the field before the next truck was full. Never blew a motor that I can remember. Never needed a Governor on our trucks. Same with this one I guess.
OK, just thought I might save someone a costly project. We turned the governor up on the "Sreamin' Jimmies" back in the '70's and '80's, loaded at 80,000 lbs every night coming out of the brew house in Columbus and back to Michigan. We could hit 3400-3600 RPM on those, took a little gettin' used to the slow turning Cummins but cubic inches and the long stroke way made up the difference. I made some repairs on the city route trucks, those were gas 366 and 427 with Holley 4 bbl and the same basic governor as yours. I didn't dare turn those up 'cus the city drivers would have scattered the engine.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
The 5th port on your vacuum selector switch (not labeled on your paper towel) goes to the speedometer to control its 2-speed reduction unit which keeps the speedometer reading correctly in both high and low range.
