Air Brake system

ScottG wrote:

CharlesinGA wrote:

ScottG wrote:

moisheh wrote:
There are diesel vehicles with hydraulic brakes and a VACUUM pump.
I thought that huge full moon was the other day. Maybe the OP is pulling our legs.

Moisheh

ALL diesel LT's have hydraulic brakes. None of them use vacuum.
Many of them have vacuum pumps but they have nothing to do with the brakes.

Without getting this thread too far sidetracked (after all, it is about air brake systems, not hydraulic systems) I gotta ask, what do you think the vacuum pump is for if its not for the brakes????? Did 'ja ever notice that big old round Bendix vacuum brake booster on all of those diesel light trucks? Something has gotta operate them. Yes, some do use a hydraulic driven booster (the Duramax had a vacuum pump but it was eventually eliminated in favor of a different boost system) My '06 Sprinter chassis for my View MH has a vacuum pump connected directly to the Bendix booster. Lots of trucks do.

Different manufacturers do use different thinking in designing their braking systems, but yes, if there is a vacuum pump, its there mostly to provide "power" for the brake booster, and possibly to provide vacuum for the enviromental system damper actuators (though most are electric nowdays).

Charles

I'm sorry Charles but your mistaken. There is no Bendix (or any other make) vacuum booster on diesel trucks.
Vacuum pumps are not strong enough to provide enough volume for brakes on trucks. The pumps are purely to provide vacuum for accessories like HVAC and operating cruise control or in some cases, exh. brakes.
They all use hydroboost systems - which are MUCH stronger than vacuum systems.
Even the light duty GM diesels from the 80's had HB systems (and they worked great).

Best regards,
Scott

Gee, that is very strange.
My 1994 Dodge Ram CTD 3500 dually had a vacuum pump between the front gearcase and the power steering pump. Mounted between the brake master cylinder and the firewall was this big can that looked an awful lot like a Bendix power brake vacuum can. the vacuum also operated the heater/defroster/air conditioning controls, and the exhaust brake. When I stepped on the brake, I could see the needle on the vacuum gauge bobble. It moved less than it did when the exhaust brake actuated or disengaged, but it moved.
Many medium duty diesel trucks had what was known as a Hydro-vac unit mounted on the frame. It was a piston type vacuum brake booster. Some motorhomes had an identical unit.
Years ago, I even worked on 15K capacity fork lifts that had a DD 4-53 engine, with vacuum pump, Hydro-vac brake unit, S-cam brakes, and the slack adjusters were actuated by hydraulic cylinders!
Yes, some light and medium duty diesel trucks and other equipment DID have vacuum boosted hydraulic brakes!