Power brake boost loss

[Dave Burden]

When I autocross the '82 Series 75 with a '76 500 under the hood, the boost for the brakes just goes away. It's fairly consistent so I get used to it, but it takes a bit of pressure on the pedal to slow it down. Obviously I'm on the gas a bunch which does not create vacuum, but the two 90's Impalas (5.7) there didn't have a problem.

Under normal driving conditions this doesn't happen, but is there anything I should check?

I checked out a '75 Lincoln Mark IV, that was for sale locally, and saw it uses the power steering pump for the brake boost. Did GM ever use a setup like that?

Dave

[Nashalac]

Hydro boost was used on 70's Eldos. Don't know what else. Somebody will post with more knowldge

[Schurkey]

1. Verify that the brake booster check valve still works.

2. A bigass vacuum tank--with it's own check valve--will cost a LOT less than a hydroboost system.

3. Hydroboost was extremely common on Diesel pickups. (Diesels don't have any manifold vacuum--although some may have had accessory vacuum pumps.)

[thecad]

My 84 GMC 1500 with the 6.2 diesel had hydroboost as well as a step van I had but forget what year it was. The 74 eldo I got my 500 from also had it.

[STDog]

1. Verify that the brake booster check valve still works.

2. A bigass vacuum tank--with it's own check valve--will cost a LOT less than a hydroboost system.


I second both those option, in that order.

If the check valve is bad the booster isn't storing vacuum like it should. It should store enough for 3 or 4 applications of the brakes.

Cadillac used storage tanks for the AC system, so the the air control doors didn't move under heavy acceleration/long hills. Without then the active vents/temperature would change under acceleration. My '70 has a send tank that I've never figured out what it was for as well.

So you should be able to find something on a patrs car really cheap. You might even have something already?

[Ted in Olympia WA]

I checked out a '75 Lincoln Mark IV, that was for sale locally, and saw it uses the power steering pump for the brake boost. Did GM ever use a setup like that?

Dave

76-78 Eldorados had the hydro boost system. If you need one I can get one for you, $175 plus shipping for the complete unit. Hydro-boost, lines, power steering pump, even brake pedal if you would like and pump cooler.

But it does make me wonder if there's something wrong with your power brake unit now. Maybe a vacuum tank would work for you.

TED
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[Dave Burden]

Thanks for all the information. I plan to dig under the hood this week since I have another autocross on Sunday. Right now I'll look at the check valve and see what happens.

Dave

[Nashalac]

That's a hell of a deal Ted - wish I needed a system

[Ted in Olympia WA]

Maybe I'm selling them too cheap?

If it was me I would go to manual brakes. But maybe he needs power brakes for his kind of hobby?

TED