Bad '78 brake booster after 38.5 yrs (1 Viewer)

[algeeba]

So, it looks like my '78 brake booster is finally giving up the ghost.

This morning I found some fluid leak under the 40 and it turned out to be brake fluid. The leak is between the master cylinder and the booster. Order the master and will come next week. I start the engine, let it idle awhile, turn the engine off and after about 30 seconds I hear a noise like boiling fuel or a vacuum leak.

I open up the hood and the sound sounds like it is coming from inside the booster with a "crumpling" sound at the same time. I put a mechanic's stethescope to the booster, intake manifold and carb and I can't hear anything through it. But it does sound like it is in the area between the booster and master cylinder.

What do you all think, booster?

 

[luvdamud]

Tough to diagnose. I know that I made odd noises when I turned 38.5 as well, and it was tough to find out where they were coming from.

 

[GA Architect]

^^ ^^

 

[thebigredrocker]

Not sure on your symptoms, but you should test you booster...

Easiest way...

Run the motor with your foot off the brake... turn off the cruiser, and allow it it sit for a few minutes... you should be able to then push the pedal a couple times before the vacuum is gone... if the pedal feels firm, you may have a vacuum leak (which can be very horrible for your motor)

Hope that helps...

If the booster is in further decline, you might be able to duplicate the hissing with the motor running by very slowly moving the pedal thru a full cycle. Kurt's method is better for finding marginal leaks.

Do you have a vacuum guage? If so you can also run a vacuum check with the booster connected and then without.

Then with the booster connected and engaging the brake pedal. Vacuum should only drop momentarily.

Leaking out the rear will most certainly take out the brake booster with it. Get the booster off the truck NOW, pull the grommet out that seals the check valve, and lay the booster down on it's face to drain the fluid out.

And start saving your $$ for another booster. IT's no longer a question of if, just when.

Mark

 

[bikersmurf]

Racer sells boosters... as well as 40,45,55,60,70,80 series boosters also fit... not to mention 4Runner & others.

 

[sggoat]

I had the same symptoms--It was just the master leaking by. Fortunately, the booster seal was intact, and nothing got in there. Before you go to the expense and labor on the booster, install a new master(or rebuild the old), then see if that doesn't fix the prob.
The gurgling/bubbling sound could easily be coming from the fuel boiling in the carb float bowl------

 

[algeeba]

O.k., thanks for the info (oh, and the laughs also) guys. Will read, try some testing and look into ordering from Racer. If it is bad, does it make sense to eliminate the vacuum assist for now so that it won't, potentially, burn any exhaust valves? It's my daily driver and my parts wouldn't come in until next week.

 

[algeeba]

Sggoat, didn't see your post earlier. I'm pretty sure it's not fuel boiling at this time because I was just idling for about a minute or two and then turning it off. The engine was basically still really cold. If the booster is leaking, how long would it take to burn exhaust valves driving every day to work?

 

[Coastline]

So, it looks like my '78 brake booster is finally giving up the ghost.

This morning I found some fluid leak under the 40 and it turned out to be brake fluid. The leak is between the master cylinder and the booster. Order the master and will come next week. I start the engine, let it idle awhile, turn the engine off and after about 30 seconds I hear a noise like boiling fuel or a vacuum leak.

I open up the hood and the sound sounds like it is coming from inside the booster with a "crumpling" sound at the same time. I put a mechanic's stethescope to the booster, intake manifold and carb and I can't hear anything through it. But it does sound like it is in the area between the booster and master cylinder.

What do you all think, booster?

I think you should demand a refund. Edit: Scuze me. It's a Toyota, not a Cheby. 38 years young, eh?. Duct tape might work for another road trip or two.

 

[davespider]

If you think you need to swap out your booster...it's really pretty easy. I did it a few years ago and posted my experiences on here. There are a lot of doner vehicles to choose from - so the price shouldn't be too bad, either.

Let us know what you end up doing.

 

[tls3601]

Been thru this before replace both master and booster, excellent brakes and modulation now. Not seeing how this could burn up exhaust valves though??

 

[tls3601]

Racer 65 has a nice booster, running one of his units.

 

[Landpimp]

You don't want to bypass the booster, it will be a very hard pedal. disc brakes need a booster, drums can get away without.

Check the vacuum line and check valve for leaks

 

[LAMBCRUSHER]

if you disconnect the vac line, you will have zero assist. which is ok if your master is shot, because you shouldn't be driving it...

 

[3_puppies]

Not seeing how this could burn up exhaust valves though??

if it is sucking vacumn much more than it should it will lean out cylinders 5 and 6, thus causing exhaust valve issues

 

[tls3601]

Ah ok makes sense.....

 

[algeeba]

So, today I received my master cylinder from RockAuto. Was expecting it Wednesday so I'm happy to get a head start on it. Will finish it tomorrow.

Now, I was thinking of removing the booster to see if any fluid got in and draining it as Mark had suggested in another thread. But, the check valve seems a little to difficult to remove at this time and was afraid of breaking it and I don't have a spare.

1. Removing the old master cylinder I did see some fluid in the recess of the booster but not much. There was white grease around the booster rod
2. Started the motor, let vacuum develop in the booster and turned the engine off. Didn't hear a vacuum leak at all even after a minute. I moved the booster rod sideways with my finger then that is when the vacuum went bye bye. Tried it twice with the same results.
3. I blew through the check valve with my mouth and could not blow through. Sucking on it did create a vacuum and was holding. That was the extent of checking the valve at this time
   
4. Put some silicone grease around the booster rod, mounted the new master cylinder and will go from there once I get it going again. Will check by using the methods suggested in the above links.

Hope the booster is still good!

 

[LAMBCRUSHER]

don't forget to check and adjust if necessary the booster to master push rod length...measure the old master from tip of housing bore to bottom of piston in the bore and compare with the new ones dimensions. adjust the booster push rod to maintain the same clearance as the old one had...