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Tractor Talk Discussion Forum

O/T IH Truck Hydrovac System

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DRL

03-20-2007 16:55:38




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Not totally off topic, as this pertains to my tractor hauler. Have a '81 IH S Series truck, diesel engine, with vacuum assisted hydraulic brakes. When I push on the brake pedal, it now goes to the floor, on second pump, I have good solid pedal, but I can apply all my weight on the pedal and have very little braking action. I have bled the slave cylinder on the hydrovac and wheel cylinders and have found no air. The fluid level remains at the top of the master cylinder, and there are no visual leaks.

I have come to the conclusion that the hydrovac has gone south. Is there any aftermarket places that supply these units? I won't say how much Navastar wanted for one, but even with a generous discount, it was almost as much as I gave for the truck. Navastar only sells the units and no rebuild kits for the slave cylinder.I thought about used, but with the truck being that old, if I did find one it may be as bad or worse than what I already had. Any constructive and helpful advice on this subject would be appreciated.

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the tractor vet

03-21-2007 07:54:26




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 Re: O/T IH Truck Hydrovac System in reply to DRL, 03-20-2007 16:55:38  
Well the first place i go to on truck brakes is ADJUST THEM , as truck brakes are NOT self adjusting . There will be two adjuster per wheel on the rear and some time on the ft. Also install a vac. gauge to monator your vac. I think what is happening here is that you are reahing the end of the stroke of the brake pistons . When adjuting truck brakes if you are not experanced at it then get someone that knows what he is doing . Now you may and proably find that the adjusters are frozen and if you try and force them if they are the STAR wheel you will either strip the tab off the wheel or one of the outer stars , if they do move then tighten one at a time up till it locks the wheel then back off till the wheel turns with light drag then go to the next one and do the same .

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DRL

03-21-2007 12:55:04




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 Re: O/T IH Truck Hydrovac System in reply to the tractor vet, 03-21-2007 07:54:26  
Forgot to mention in my original post that I did adjust the brakes. Was the first thing I tried. Adjusted both brake shoes at all four corners as you stated. Been there and done that several times on other vehicles, so not my first dance. FWIW, the fronts have adjusting cams that you turn a bolt one way or another to adjust the shoes. According to the book they are supposed to be self adjusting, but wouldn't rely on that. From some other replies on other forums, I may have air in the lines, although I did bleed the system once. If it is air in the lines, will still have to figure out how the air got there in the first place. Thanks for all replies so far.

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Ben There

03-20-2007 20:04:26




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 Re: O/T IH Truck Hydrovac System in reply to DRL, 03-20-2007 16:55:38  
FWIW. Brought a used IH 2 ton truck from a dealer. gas engine, brakes didn't work, pedal would be real solid. Worked a little engine was at idle. Tore everything apart, replaced Hydrovac, same problem. Found prior owner name on old registration in glove box, called him, he said he could never get them fixed, replaced darn near everything. He got rid of truck because of problem.
Everything looked good. I found another IH truck, got to looking and the 2 steel lines to the vacumn tank were opposite mine. Lookedat mine some more - looked like a logical routing 'cause that's the way the tubes were bent - looked like they hadn't been tampered with. So, I switched them around and low and behold it had brakes.

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melh

03-20-2007 19:13:40




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 Re: O/T IH Truck Hydrovac System in reply to DRL, 03-20-2007 16:55:38  
You stated that your truck is a diesel. Diesels don't make vacuum without a seperate pump. I had a GMC with a 6-71 and hydravac boosted brakes. It had a seperate belt driven vaccum pump just for the hvdravac and the trailer.



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DRL

03-20-2007 19:29:56




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 Re: O/T IH Truck Hydrovac System in reply to melh, 03-20-2007 19:13:40  
That's exactly correct. Has a vacuum pump for the brakes. Gauge shows excellent vacuum and moves down some when brakes are applied and then comes right back up. I'm pretty sure the pump is working correctly, but will have to check to be sure it is getting all the way to the hydrovac unit. Since the gauge is moving when the brakes are applied, I would assume that it is getting there OK.



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marlowe

03-20-2007 18:22:43




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 Re: O/T IH Truck Hydrovac System in reply to DRL, 03-20-2007 16:55:38  
most of the time it's just a matter of setting up the shoes. on your first pump your shoes are going to the drum and on the second pump you hydrovac runs out of travel for assist set your shows up first before you change your hydrovac. had lots of old binders and they are kind of funney on brake set up



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DRL

03-20-2007 18:30:13




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 Re: O/T IH Truck Hydrovac System in reply to marlowe, 03-20-2007 18:22:43  
Forgot to mention that I went through and adjusted the brake shoes also. Was the first thing I thought of. Yes, I adjusted both shoes as each one has its own adjuster. The shoes are in good shape also. Someone along the line cut small peep holes in the back plate so the shoes could be inspected without pulling the hub. Thanks for the thought, though.



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Dave in Tx

03-20-2007 17:56:08




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 Re: O/T IH Truck Hydrovac System in reply to DRL, 03-20-2007 16:55:38  
Napa should be able to get them....check to be sure you are getting vacuum to the unit.



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DRL

03-20-2007 18:05:33




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 Re: O/T IH Truck Hydrovac System in reply to Dave in Tx, 03-20-2007 17:56:08  
I'll try NAPA if I can find a store. Pretty scarce around here for some reason. Used to be one about 30 miles away. Will have to see if they are still there. I haven't removed any vacuum lines yet, but the vacuum gauge does go down when the brakes are applied, so something is using the vacuum. Will make sure, though before spending $$$$. Thanks



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730virgil

03-20-2007 17:55:21




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 Re: O/T IH Truck Hydrovac System in reply to DRL, 03-20-2007 16:55:38  
i have a phone number for a guy in Wa or Or. 509-483-9062. in-to-deep this is the guy i told you about. i have got parts for my old truck. i hope this is still a good phone number.



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in-too-deep

03-21-2007 08:38:42




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 Re: O/T IH Truck Hydrovac System in reply to 730virgil, 03-20-2007 17:55:21  
Thanks Virgil. Oh, I keep forgetting to call you, I'd like to buy your trailer, but I can't come get it until the cabinets my parents ordered are ready. I'm going to get the trailer from you, go to Rockford and pick up the cabinets all in one trip. I'll call you as soon as they're in.



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730virgil

03-21-2007 18:40:39




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 Re: O/T IH Truck Hydrovac System in reply to in-too-deep, 03-21-2007 08:38:42  
that's great in. keep me posted as to what is happening. virgil



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jack-iowa

03-20-2007 17:53:57




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 Re: O/T IH Truck Hydrovac System in reply to DRL, 03-20-2007 16:55:38  
might have luck with the salvage yards as they seem to offer a warranty of sorts.
went thru it with a chevy hydroboost six plus from chevy or used.
went used.



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Ozarker

03-20-2007 17:46:48




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 Re: O/T IH Truck Hydrovac System in reply to DRL, 03-20-2007 16:55:38  
I encountered a booster problem about 3 years ago on a 1966 Loadstar 1600. Found a reman unit at Springfield Brake, Springfield MO 417-862-9233. They are a brake service co for medium and heavy duty trucks and a Bendix dealer. If memory serves, it was $279 exchange. The banjo brass fitting to make it work however, was available only from the Navistar $40. Ouch!



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DRL

03-20-2007 17:56:21




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 Re: O/T IH Truck Hydrovac System in reply to Ozarker, 03-20-2007 17:46:48  
That's just the kind of info I was looking for! Don' know why I didn't think of Spfld Brake before. Lived there for almost 10 years and drove by the place quite often. Thanks. Keep the tips and leads coming!



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in-too-deep

03-20-2007 17:28:56




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 Re: O/T IH Truck Hydrovac System in reply to DRL, 03-20-2007 16:55:38  
You might try heading over to the Classic Trucks forum on this website, or perhaps oldihc(dot)org and post a message there. I wish I could help more, but I've never dealt with that system.



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