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mdkelley #1437840 Wed Jan 19 2022 04:09 AM
Joined: Jan 2022
Posts: 23
M
'Bolter
Started it up again tonight. There is no vacuum, which is likely why the brakes were not working. Seems to run really well. A bit of a bog off idle probably timing but I am not seeing a regular timing indicator marks on the crank pulley (not sure there is even a balancer on this engine?). The air cleaner hooks into the brake booster vacuum line (it look like a 3/4 or 1" hose running to it!). Not sure how exactly to seal up the air cleaner to get vacuum to build. I think the vacuum canister is next to the carb but not sure really, and it doesn't appear to be connected to the "manifold" the brake booster unit is connected to. I think If I can get the vacuum issue sorted the brakes may actually work!

Dump seems to work pretty well. There are 3 cylinders, one that does most of the work to get the box up the first couple feet, then two others that lift it faster take over.

mdkelley #1437879 Wed Jan 19 2022 02:46 PM
Joined: Feb 2016
Posts: 689
7
'Bolter
If you have no vacuum the engine probably wouldn't run and idle, the engine is creating vacuum, but it might not be reaching the Hdyrovac booster. Even without the booster working, the system was designed to deliver manual brakes with more peddle pressure needed. If the peddle goes to the floor then you have an issue regardless of the booster. I would pull all of the drums first before you even put brake fluid in the master cylinder. If you have leaking wheel cylinders you might have a chance of saving the shoes if you don't pump more fluid into the drums. As far as tires, you could call Shrader and see if they have any 20".


1957 Chevrolet 5700 LCF 283 SM420 single speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
mdkelley #1438058 Thu Jan 20 2022 09:22 PM
Joined: Mar 2007
Posts: 164
A
'Bolter
Power King 7.50x20 highway tread are still available. About 10 years ago I was able to buy Denman Traction tires in that size but not anymore. I think the last traction tires I could find were 8.25x20. Tires, flaps and tubes are the easy part. Mounting them is another issue.

The tube connected to the air filter housing is atmosphere intake to the booster, you won't feel or notice anything there. Vacuum supply to the booster is on the intake manifold below the carb.

You'll have better luck getting a rebuild kit for the booster than buying one.

First, like noted above, get the hydraulic/manual side of the brakes in good working order. Then work on getting the booster working.

Last edited by asilverblazer; Thu Jan 20 2022 09:27 PM.
mdkelley #1438090 Fri Jan 21 2022 01:55 AM
Joined: Mar 2004
Posts: 5,536
M
'Bolter
The 6-lug 22.5" Budd wheels for the your truck were typically found in the 6", 6.75" and 7.5" widths for tires sizes ranging from 8.25 to 11.00 x 22.5". It seems like the 22.5's are easier to find than the smaller sized 20's. The 6-lug Budds were used on many trucks for decades and should be easy to find. You need to ask around at your local school bus garages and big truck repair shops...if you wait to find them on the internet you may be waiting a long time.

Make sure to replace ALL of the steel and rubber brake lines while your doing the brakes...these line may look good but will fail from the inside out.

Your Hydrovac should have a tag on it with it's model number...NAPA should be able to source a remanufactured unit or send your unit back for a rebuild.

Mike B smile

mdkelley #1438094 Fri Jan 21 2022 02:15 AM
Joined: Jan 2022
Posts: 23
M
'Bolter
Thanks guys, all good info and advice. I will start calling around local truck tire dealers and truck garages. There is a truck salvage yard in Saginaw, a little over an hour away. Lots of local schools that run buses and I would guess they still have on site bus garages but no idea really. I can call to see though.

I found a rebuild guide online for the brake booster unit and did see the vacuum comes from the base of the carb. Booster looks pretty straightforward to rebuild if I can get a rebuild kit.

I am busy this weekend but should be able to start tearing into the brakes next week, if the weather isn't too cold. I have a nice shop to work in the but section with overhead doors is not insulated or heated so I may have to get a big torpedo heater or wait for the temps to get at least into the double digits. Supposed to be -2 tonight I heard! Eventually I hope to section off and insulate and heat a portion but not there yet.

I will check the line size and buy some bulk steel tubing to bend up and flare some new lines.

Will NAPA have rebuild kits for the hydrovac and the wheel cylinders, or just rebuild services?

mdkelley #1438098 Fri Jan 21 2022 02:36 AM
Joined: Mar 2004
Posts: 5,536
M
'Bolter
Originally Posted by mdkelley
From what I had read in the 1957 Chevy truck info on gm heritage center I was expecting 22.5 wheels but maybe these were an option.

The 22.5" rims were "standard" issue tires...the 20" split rims were optional.

Your truck has the Firestone RH-5 "widow maker" rims...you probably won't find any tire shop willing to work on your rims as they were outlawed decades ago and the liability would be way to high.

Mike B smile

mdkelley #1438099 Fri Jan 21 2022 02:38 AM
Joined: Aug 2001
Posts: 5,120
2
Mixed Up
I talked to our local Napa store about a rebuild kit for a Hydrovac and they told me to take it off, bring it in and they would ship it off to be rebuilt.
It would be about a three week turn around. I don’t know if all the stores do that, but I will be watching this thread for advice.

Don


Of all the things I've lost in my life, I miss my mind the most!

1967 GMC 9500 Fire Ladder Truck
"The Flag Pole"
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'46 2-Ton grain truck
'48 3/4-ton grain truck
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'54 Pontiac Straight Eight
'70 American LaFrance pumper fire truck.
mdkelley #1438107 Fri Jan 21 2022 03:08 AM
Joined: Feb 2016
Posts: 689
7
'Bolter
My close small Napa only gave me info on sending it to Cardone, I think I'll send mine to White Post Restorations based on what I have read about both. Matt, all of the hard lines on mine are 1/4", I Used all of a 25 ft. roll to do it, Summit has copper/nickel at a good price. After you get the casting numbers from the wheel cylinders you can match a kit to each, don't order them till you have the numbers as I found different cylinders on the opposite side of the truck and had to get different kits.


1957 Chevrolet 5700 LCF 283 SM420 single speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
mdkelley #1438113 Fri Jan 21 2022 03:54 AM
Joined: Jan 2022
Posts: 23
M
'Bolter
Good point on the part numbers, never thought about there being ones in different locations.

I just read up on the RH5 wheels. Wow, I am kind of scared now to even take these off and really thankful they didn't come apart on me when I aired up the fronts the other day. I will wrap some chain around those and air them down and get them off, maybe turn them into tool stands or something.

Guess I am going to have more $$ into this truck than I was hoping but I am certain I will forget the cost when I am driving it around safely. Thanks for the heads up on those.

So, are the front wheel split in a way that the half bolted to the hub is solid and the back half is what would blow off (meaning if the rims are left bolted to the truck the piece that blows off would blow toward the frame/axle and not outward and the biggest risk is working on these off the truck)? Just want to understand my risk of airing these down while on the truck. I can chain them up regardless, but want to know what I am getting into. I am still reading about these trying to figure out how to approach safely getting these off.

EDIT: Just found a video about them, my assumption was correct. The fronts would blow off toward the inside of the truck. Makes me feel slightly better... Means the rear outer is oriented in a way to cause problems though.

Last edited by mdkelley; Fri Jan 21 2022 04:22 AM.
mdkelley #1438139 Fri Jan 21 2022 02:38 PM
Joined: Jun 2011
Posts: 4,519
E
'Bolter
One can get clip on air hose nozzles that can be unconnected to deflate suspect wheels by clipping one on and walk off ‘til all the air is out.

Ed


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
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