Hydrovac brake booster
Printed From: Unofficial Allis
Category: Other Topics
Forum Name: Shops, Barns, Varmints, and Trucks
Forum Description: anything you want to talk about except politics
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=206021
Printed Date: 30 Mar 2025 at 7:54pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: Hydrovac brake booster
Posted By: darrel in ND
Subject: Hydrovac brake booster
Date Posted: 24 Mar 2025 at 8:13pm
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I'm thinking about buying a 74 chevy truck that I found for sale. Just seen pictures of it, haven't looked at it in person, or even talked to the seller. But one of the items in the description states that it needs a new hydrovac brake booster. Where is a good source for a new one of them, and what would a person expect to pay for one. Thanks, Darrel
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Replies:
Posted By: Gary
Date Posted: 24 Mar 2025 at 8:20pm
This link might help you some:
https://www.youtube.com/results" rel="nofollow - https://www.youtube.com/results ?
search_query=1974+chevy+hydro+vac+brake+booster+replacement
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Posted By: wjohn
Date Posted: 24 Mar 2025 at 8:37pm
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I just bought a '62 C60 and you have to pump the pedal a lot, and the engine revs way up, so I suspect the booster is about toast. Might not be the exact same part number but I think both trucks are in the same boat as far as parts availability.
Looking around online, I had found one place that would rebuild them, and another place that would sell you a kit to convert to something like an F-550 brake booster and master cylinder that mounted on the firewall. Both paths were $5-700 as I recall.
Knowing what I know now I would definitely factor that into any offer I made on the truck.
EDIT: I stand corrected - looks like these are able to be ordered through most auto parts stores, but you may need a guy behind the counter that knows what he's doing. The model/year lookup doesn't work for many of these older medium-duty truck parts.
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1939 B, 1940 B, 1941 WC, 1951 WD, 1952 CA, 1956 WD-45
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Posted By: HudCo
Date Posted: 24 Mar 2025 at 9:26pm
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must be 454 is it leaking ?
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Posted By: DMiller
Date Posted: 25 Mar 2025 at 3:00am
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Friend of mine has a failed Hydrovac, is on his Dad’s old IH Farm truck, bought new in 63. He has gone every route of phone calls and in person contacts found nothing. Thought should be some New old Stock laying around for diaphragms and seals, nothing. Last known rebuilder near to here closed shop several years ago.
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Posted By: 8070nc
Date Posted: 25 Mar 2025 at 4:53am
I just got one from carquest. I would think napa would have one.
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1984 80780
1957 D14
DES 300 with 25000 engine
616 tractor
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Posted By: 8070nc
Date Posted: 25 Mar 2025 at 4:56am
It was for a 87 ton truck. Yor 74 is the same basic body style
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1984 80780
1957 D14
DES 300 with 25000 engine
616 tractor
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Posted By: darrel in ND
Date Posted: 25 Mar 2025 at 6:34am
I think that I have one located. Thanks for the replies.
Darrel
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Posted By: DaveKamp
Date Posted: 25 Mar 2025 at 6:05pm
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So... Just for those who don't know... in power brakes, there's Hydrovac, and Hydrobooster. Two different systems, commonly confusing to those who don't realize...
The Hydrobooster is a brake booster that, instead of using manifold vacuum to assist the brake pedal's actuation of master cylinder, it uses hydraulic pressure from the power steering pump, or a secondary equivalent. My '84 Grumman (Chevy P30) step-van uses a hydrobooster, because the firewall shape doesn't have space for a conventional vacuum booster AND.. it's original engine was a 6.2L diesel... then a 3.9L Cummins 4BT, now a Buick 455...
The HydroVac was pretty common on Chrysler/Dodge medium trucks and RVs... they're essentially same as a vacuum power brake system, but the common vacuum-power brake system integrates the master cylinder WITH the booster diaphragm/chamber. A HydroVac is actually separate from the master cylinder... it works exactly the same way, but the physical link between the foot pedal/master cylinder doesn't exist, it's all result of the master cylinder's outlet pressure triggering the HydroVac.
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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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Posted By: DMiller
Date Posted: 25 Mar 2025 at 6:11pm
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Most mounted behind the Left Cab Step(Extended below cab), many were crud traps and damage occurred when not kept clean. Best laugh I got from a Brake system, I had Changed a Hydrovac on a Old IH as noted above, old guy was tickled got it back(Decades ago) as needed it to run grain harvest to elevator. Came strolling in, "It's Brake AGAIN" and beet red, walked out to truck stepped on brake sure enough little boost, but Also Muffled Sound of Vacuum relieving. Folded bench seat forward, removed the Coveralls sucked up tight to the Vacuum Vent in the floor behind the seat. All Was again Right in the World, Ed turned Beet Red of Embarrassment at that point. NO Charge!!
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Posted By: LouSWPA
Date Posted: 25 Mar 2025 at 6:42pm
fwiw, MY experience with those Hydro boost systems was with fleet cars. The company vehicles we had when new were problematic. Just antidotal to be sure but we had higher than normal failures as compared to the older cars w/o
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I am still confident of this;
I will see the goodness of the Lord in the land of the living.
Wait for the Lord;
be strong and take heart and wait for the Lord. Ps 27
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Posted By: SteveM C/IL
Date Posted: 25 Mar 2025 at 8:16pm
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73 C60. Mine was rebuilt by Cardone. None in stock for exchange....send it in.
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Posted By: KJCHRIS
Date Posted: 25 Mar 2025 at 11:49pm
Haven't replaced a hydro-vac brake unit in 20+ years. BUT see if you can locate an older truck shop that has a "pressurized brake bleeder" that attaches to your brake master cylinder. It'll make getting air pushed out of the system lots easier. Might want to try pressure bleeding existing unit before replacing it, may have an airlock from sitting. IF can't find 1, follow directions that come with the replacement unit. NAPA, O'Rielly, Inland Truck Parts, MidWest Wheel Co., Vander Haag's, are some places to check for a rebuilt unit.
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AC 200, CAH, AC185D bareback, AC 180D bareback, D17 III, WF. D17 Blackbar grill, NF. D15 SFW. Case 1175 CAH, Bobcat 543B,
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Posted By: Codger
Date Posted: 26 Mar 2025 at 8:44pm
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Not a hard thing to rebuild at all. Just another type of hydraulic master cylinder, and a lot simpler than most believe. I've rebuilt several over the years.
Just another thing my wife loves seeing at the kitchen table, or next to the toaster on the counter. Not really but she doesn't get irate till the carburetor cleaner comes out.....
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That's All Folks!
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Posted By: desertjoe
Date Posted: 27 Mar 2025 at 12:19am
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I have a 1988 Chevy 1 ton with the 454 that needed the power steering replaced and wound up having to send back the unit they sent three times as the PS required had to have an extra pressure line for the power brake booster. the first item they sent me was A BIG POWER BRAKE BOOSTER unit THAT HAD THE EXTRA piece of the power brake booster ,which we sent back. this was from Oreilly's,,,SO,,it is still available,,,,Good Luck Darrell.
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Posted By: darrel in ND
Date Posted: 27 Mar 2025 at 6:23am
Hey Joe! Good to hear from you. Been a while. Hope all is well for you.
Darrel
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