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| | | | Joined: Apr 2009 Posts: 181 'Bolter | | 'Bolter Joined: Apr 2009 Posts: 181 | Hello, I'm a new member here - am working on a 58 chevy 8700 series w/ a 283/5 spd/2 spd., which has air over hydraulic brakes. Have any of you forum members rebuilt this brake system? I would like to hear your experiences. The air pump works fine, but I would just as soon not get into a rebuild of the booster. I would prefer at this stage to bypass this system and go w/ a straight hydraulic system. This truck will never be loaded and I am speculating that such a system would suffice, of course using all new/rebuilt lines, hoses and cylinders.
1955 GMC 630, 1959 GMC W660, 1958 Chevy Spartan 80
| | | | | Joined: Nov 2005 Posts: 6,100 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,100 | Hy jaycoop, if the booster is not malfunctioning, why not just leave it in the system? | | | | | Joined: Mar 2004 Posts: 6,214 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,214 | Jaycoop, I can't find the info on the Air Over Hydraulic Brake (AOHB)system, but did find it on the Hydrovac. The Hydrovac provides 88% of the braking effort while your foot through the pedal produces 12%. I did see that the AOHB has a 36% increase over the Hydrovac, so your giving up a lot of power. I think by eliminating the the booster you will have a hard time stopping the truck even if it is empty. I'd see how much of the system works before bypassing it... My 2 cents! Mike B  | | | | | Joined: Feb 2008 Posts: 207 Wrench Fetcher | | Wrench Fetcher Joined: Feb 2008 Posts: 207 | Don't air over hydraulic brakes have air chambers on the axles just like semis so you would have to find a set of hydraulic brake axles? Or am i thinking backwards? | | | | | Joined: Nov 2005 Posts: 6,100 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,100 | Hy 47chevy6400, air over hydraulic brakes simply replace the Hydrovac with an Airpack unit, which uses compressed air rather than vacuum to achieve the boost feature. Other than that, both systems are standard hydraulic brake setups, hope that helps. | | | | | Joined: Jul 2007 Posts: 461 Shop Shark | | Shop Shark Joined: Jul 2007 Posts: 461 | I have a '58 Chev truck shop manual. I'll see what I can find there. But I would agree with the others to leave the system as it is if the air system is working.
Harvester | | | | | Joined: Apr 2009 Posts: 181 'Bolter | | 'Bolter Joined: Apr 2009 Posts: 181 | Thanks guys for all the good replies - I simply haven't had a chance to get back to the computer since posting the questions. The compressor works good, but the air booster seems frozen. 3B, you're right, the air booster looks to be just a 'replacement' for the vacuum booster and the brakes are basically hydraulic. After reviewing all of your comments, I guess I might be convinced to try to rebuild the booster. My main concern is finding the right parts/services to get it done without sinking large amounts of time and money into this single aspect of the truck. None of the fellow enthusiasts that I happen to know have any idea of exactly what it would entail and none of them for that matter have any real knowledge about the air booster. Most seem to be much more familiar with the vacuum boosters. Any thoughts on the booster rebuild would be greatly appreciated.....
1955 GMC 630, 1959 GMC W660, 1958 Chevy Spartan 80
| | | | | Joined: Mar 2004 Posts: 6,214 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,214 | Jaycoop, Check NAPA, they may have your booster. Or try Precision Rebuilders at http://www.precisionrebuilders.com/about_us.html. I would guess the cost to rebuild an air vs vacuum booster would be about the same $200-250 range. Don't forget to replace ALL of the hydraluic parts while you're at it (steel and rubber lines, reline shoes if needed, wheel cylinders and master cylinder). The lines will fail from the inside out. The entire project might set you back about $800-900, but being safe is worth WAY more than that! Mike B | | | | | Joined: Apr 2009 Posts: 181 'Bolter | | 'Bolter Joined: Apr 2009 Posts: 181 | Many thanks, Mike, for taking the time to respond - I'll follow both leads....jaycoop
1955 GMC 630, 1959 GMC W660, 1958 Chevy Spartan 80
| | | | | Joined: Nov 2005 Posts: 6,100 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,100 | Hy jaycoop, the airpack unit GM p/n is 2279787 = Bendix p/n 375756 = Napa p/n MBIRV2500690X =$485.00 + $184.00 core, hope that helps. Would you like the overhaul kit numbers if I can find them? | | | | | Joined: Apr 2009 Posts: 181 'Bolter | | 'Bolter Joined: Apr 2009 Posts: 181 | Yes 3B if you don't mind, I would like the info on the rebuild kit. I realize the convenience of a completely rebuilt unit but, considering the price and that I have done a fair amt. of general rebuilding, I would try it. I'm impressed that you came up w/ the specific part numbers.....MANY thanx for your time and effort..............jaycoop 
1955 GMC 630, 1959 GMC W660, 1958 Chevy Spartan 80
| | | | | Joined: Nov 2005 Posts: 6,100 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,100 | Hy jaycoop, the repair kit is GM p/n 2297689, Bendix 376037, unfortunately neither of these numbers crossed for me at Napa or Rock Auto, good luck | | | | | Joined: Apr 2009 Posts: 181 'Bolter | | 'Bolter Joined: Apr 2009 Posts: 181 | Thanx Shark I truly appreciate you getting me these numbers - I'll follow thru, starting w/ GM......jaycoop
1955 GMC 630, 1959 GMC W660, 1958 Chevy Spartan 80
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