Do I have Air Brakes?

[Skip]

I have a 72 passenger 1989 GMC Thomas with a 366, and I thought it had air brakes untill my cousin (who drives fire trucks for a living) took a look and told me I don't have air brakes, but the next day I drove it over to his house and when I shut off the engine in went "pssshhh" and he then said it might actually have air brakes.

What is the tell tale sign whether I have air brakes or not?

[bansil]

okay do you have a air pressure gage on dash with a buzzer that goes off with low pressure?



do you have a yellow push/pull knob to control park springs/brake?



look on the axles near ends for air chambers and adjusters...like these:



or



I am trying to be nice with this, you need to find out what kind of brakes you have so they can be safely used

I really hope you don't have air brakes, because if so you have been very lucky bus hasn't rolled away yet

It may have hydraulic brakes similar to an older car/truck

[bansil]

look on firewall (under hood) and see if the bus has a brake master cylinder mounted similar to this:



it will steel lines coming from it like your car/truck

This is typical for hydraulic brakes, you may have a pump for vacuum for power assist or it may run off the PS pump setup

(edited for extra info)

[Skip]

No, no, no, no, and no I don't have any of these things..

Thanks for not calling me a dumbass Bansil, I didn't realize it was that obvious.

[bansil]

Okay so we now know you have hydraulic brakes, so next nice day trace all the metal brake lines from the master cyclinder to each wheel cylinder/caliper

You want to check for rust and kinked lines (they can break) and look at rubber parts for cracks and dry rot issues

We will get you hooked up and others can use the pics for learning...plus your Avatar is Kool

[bansil]

Originally Posted by Skip

No, no, no, no, and no I don't have any of these things..

Thanks for not calling me a dumbass Bansil, I didn't realize it was that obvious.

Your welcome...heck you now have the knowledge to call your buddy one

[Redbear]

No five times? Four for no air brake parts plus one for no hydraulic master cylinder?

I would guess that four out of five means no air brakes, especially with no air canisters behind the rear wheels. But then again, I have no clue what the "dreaded Lucas-Girling air-over-hydraulic brake system" that other members talk about is. They are usually talking about Fords, I think, not GMs.

I have seen vehicles with two air pressure gauges instead of one with dual needles as in the first picture, but I don't think you can make an air brake vehicle without any pressure gauges. Some hydraulic brake commercial vehicles have an optional vacuum gauge so you can be sure that you have enough vacuum for power assist, usually with a big red light for low vacuum. But that gauge is not a requirement.

Regarding the second photo, I have seen some older vehicles with air brakes whose emergency/parking brake is not a yellow diamond like all newer trucks, but I can't remember which ones. Maybe '80s-'90s Prevost coaches had round knobs? Some older buses have a black plastic diamond knob with a round yellow metal insert instead of the yellow plastic diamond. I don't think an '89 would have an older knob, but I don't know for sure.

If the bus has hydraulic brakes, there has to be a master cylinder somewhere, perhaps below the floor instead of on the firewall? You should locate it, because you have to be able to check the fluid level as a preventative maintenance item.

[juliol]

Hello, I'm changing my oil for the first time, not being familiar with Diesels makes me paranoid, I've read somewhere in the net that you have to fill the new oil filters with oil before installing them so the oil is prime is this correct? I know you have to do that when replacing fuel filter but oil?