Brake booster vacuum leak

[Tofudebeest]

with perhaps a 10% loss in braking power, if that, the brake dash light does not come on unless I use the hand brake. If I pump the brakes repeatedly, it'll come on for a split second. I hear the vacuum leak after the engine has been shut off if the bonnet is open. It takes a good 60 seconds+ for the leak to become inaudible. Below the gasket between the brake master and booster, the booster is corroded/rusted, no idea if the master leak was ever resolved, but I imagine the booster was damaged to some extent with this apparently old master leak.

Front brakes recently serviced, rear drums, cylinders, etc. inspected and no failure or advanced wear is present.

Protocol? Diagnosis? Replace booster? Replace master?

 

[canucksafari]

If you are sure the leak is in the booster, then JB weld it or buy a new one. I know on the BJ40s the vacuum canisters can also get rusted out and leak. I've got a leak on my clutch power assist circuit that i can't figure out. Most of the time I have no power assist. However, it will come back on maybe once every two months for a bit and then go again. Clutch still works fine but it is just heavy. When I get to it, i will pull the check valve for that vacuum circuit. I got the feeling that it may be plugged. Good luck.

 

[rchalmers3]

I recommend you make sure its the booster by pulling a vacuum on the booster and isolate it to be sure it's the culprit.
A failed check valve could allow vacuum out of the booster.
A marginal vacuum pump will decrease boost.
Leaky hoses or resivoirs can cause vacuum loss and noise from under the hood.
My recommendation is to isolate and test!

SOR had my replacement booster.

Rick

 

[Tofudebeest]

thanks fellas.

 

[Tapage]

I thought IIRC Toyota sells a repair kit for those 60 series boosters .. not a easy task much more with the main spring but doable ..

 

[rchalmers3]

I thought IIRC Toyota sells a repair kit for those 60 series boosters .. not a easy task much more with the main spring but doable ..

The boosters on my trucks are sealed units, requiring a special tool for joining the housing. It may be possible to source and change the seals on the input and output rods if he wants to go that route.

Rick

 

[Tapage]

The boosters on my trucks are sealed units, requiring a special tool for joining the housing. It may be possible to source and change the seals on the input and output rods if he wants to go that route.

Rick

I source a kit that include new diaphragm, spring, seals and other mist stuf .. my booster have some tabs that are securing it ..

My special tool ( a chisel and hammer ) do tha job .. years ago.

 

[Big Blue 84BJ60]

go to the wrekers, the break booster off a 90-95 4 runner is the same as my old bj60's booster the truck now has one from a 92 4 runner going on 2 years works great no problems

 

[Tapage]

go to the wrekers, the break booster off a 90-95 4 runner is the same as my old bj60's booster the truck now has one from a 92 4 runner going on 2 years works great no problems

great info mate .. thanks .. !

 

[Jan-78FJ40]

First, a loss of vacuum will not make the dash light go on. the light is strictly for the brake fluid level, it has nothing to do with the booster. If your light comes on you have a fluid problem, not a vacuum problem.
Then, the 60 series boosters can be disassembled easily, but it is very difficult to reassemble them on the truck, as it is impossible to align everything when the booster is not on flat ground, front facing straight up.
Third, rebuild kits are available, but they are very VERY expensive.

The brake boosters for the different 60 series have different sizes (HJ60 largest diameter, but least thick, FJ60 intermediate, FJ62 smallest diameter, but thickest). The good thing is that they all have the same bolt pattern to the firewall, and they all accept the same master cylinder. So in fact they are all interchangeable, with a little wiggling of the brake lines.

Tofu, to test the booster turn the engine off, wait a few minutes, then depress the brake pedal and turn the engine on. the pedal should sink about an inch. then turn the engine is off, you should lose brake travel after about 3 pumps.
How do you measure a '10% loss in braking power' anyway???
have you checked the vacuum canister and lines?
The original HJ60 booster does not have a check valve (at least not till 8/84, not sure about later).

 

[Tapage]

First, a loss of vacuum will not make the dash light go on. the light is strictly for the brake fluid level, it has nothing to do with the booster. If your light comes on you have a fluid problem, not a vacuum problem.

Not at least not on Tencha .. when I go out of vacc I got the e-brake light inmediately and until the vacc reservoir it's full again ..

 

[canucksafari]

First, a loss of vacuum will not make the dash light go on. the light is strictly for the brake fluid level, it has nothing to do with the booster.

On my truck (different make and model but a diesel) draining the brake vacuum by repeated pumping can be done on low idle. And yes, low brake vacuum does trigger the brake warning light. If I stop pumping the brake and allow vacuum to build then the dummy light goes out right away.

 

[Jan-78FJ40]

On my truck (different make and model but a diesel) draining the brake vacuum by repeated pumping can be done on low idle. And yes, low brake vacuum does trigger the brake warning light. If I stop pumping the brake and allow vacuum to build then the dummy light goes out right away.

Not at least not on Tencha .. when I go out of vacc I got the e-brake light inmediately and until the vacc reservoir it's full again ..

Wow, thank you for that info, I did not know that. My truck does not do that (84 HJ60, originally from central america). Does anyone know where the sensor for the vacuum is? I have no electrics at all on either the vac pump, the vac reservoir, lines or the booster.
thanks again and apologies for trying to spread wrong information.
Jan

 

[lostmarbles]

... a loss of vacuum will not make the dash light go on. the light is strictly for the brake fluid level, it has nothing to do with the booster. If your light comes on you have a fluid problem, not a vacuum problem.....

......apologies for trying to spread wrong information.......Jan

No need for apologies here Jan. Your info was no doubt correct for your vehicle.

Actually it would be very interesting (to me) to run a thread to expose the variations in just the BJ40, BJ41, BJ42, BJ43 and BJ44 models alone. --- Despite the similarities between these models, the colours and wording on those two rectangular warning lights seem to vary quite a bit (even within the same model too depending on which market it was destined for), as also do the conditions that trigger those lights to illuminate.

On my BJ40 I even have a factory-fitted audible alarm that comes on (in addition to the light) should I loose vacuum boost.

And I have a bulb-check relay that turns on my brake warning light whenever I crank my engine just to prove to me that the bulb is working.

Cheers
Tom

 

[Tofudebeest]

First, a loss of vacuum will not make the dash light go on. the light is strictly for the brake fluid level, it has nothing to do with the booster. If your light comes on you have a fluid problem, not a vacuum problem.
Then, the 60 series boosters can be disassembled easily, but it is very difficult to reassemble them on the truck, as it is impossible to align everything when the booster is not on flat ground, front facing straight up.
Third, rebuild kits are available, but they are very VERY expensive.

The brake boosters for the different 60 series have different sizes (HJ60 largest diameter, but least thick, FJ60 intermediate, FJ62 smallest diameter, but thickest). The good thing is that they all have the same bolt pattern to the firewall, and they all accept the same master cylinder. So in fact they are all interchangeable, with a little wiggling of the brake lines.

Tofu, to test the booster turn the engine off, wait a few minutes, then depress the brake pedal and turn the engine on. the pedal should sink about an inch. then turn the engine is off, you should lose brake travel after about 3 pumps.
How do you measure a '10% loss in braking power' anyway???
have you checked the vacuum canister and lines?
The original HJ60 booster does not have a check valve (at least not till 8/84, not sure about later).

10% loss, is a very rough guesstimate. I am going by feel alone. It's just a smidge less powerful than I expect and recall.

On my truck (different make and model but a diesel) draining the brake vacuum by repeated pumping can be done on low idle. And yes, low brake vacuum does trigger the brake warning light. If I stop pumping the brake and allow vacuum to build then the dummy light goes out right away.

This is precisely what I experience, and I doubled checked the phenomenon to make sure what I postedf was accurate. well, it is, but the light stays on for about one second, not "a split second".

Also, I am not using the HJ60's booster (I gave it to Mel Lowe who painted it and installed it on his BJ(t)62), just the vacuum canister and lines. The booster and master are native to the FJ62.

Lastly, I have a replacement, from Mel Lowe, from either an FJ60 or 62. If it is my vac canister, this booster will not help, so we will do the soap test on the lines and canister. My fluid levels MAY drop, but if they do, they return to normal after vac rebuilds.

Place your bets:

vacuum lines, vacuum canister (reservoir) or booster. I guess it still could be a check valve too, huh?

 

[Tapage]

Wow, thank you for that info, I did not know that. My truck does not do that (84 HJ60, originally from central america). Does anyone know where the sensor for the vacuum is? I have no electrics at all on either the vac pump, the vac reservoir, lines or the booster.
thanks again and apologies for trying to spread wrong information.
Jan

my vacc sensor it's at the vacc canister ..

 

[lostmarbles]

.....so we will do the soap test on the lines and canister. My fluid levels MAY drop, but if they do, they return to normal after vac rebuilds. ...

So you're going to pressurise your vacuum system to check for leaks?

And how are fluid levels connected to vacuum levels?

 

[Jan-78FJ40]

So you're going to pressurise your vacuum system to check for leaks?

And how are fluid levels connected to vacuum levels?

second. how do you connect the fluid levels to the problem? if your fluid levels drop there is a second problem.

regarding your bet, I say connection of vac canister to lines. don't forget to check the lines where they exit the vac pump.

cheers,
J

 

[canucksafari]

A vacuum gauge might be the better way to check each item than soap. If the hose looks brittle and old, just replace it with new clamps.

 

[Tofudebeest]

Ok, so here's where I have to make it clear, as if it were not already, that I am dealing with a novel situation for me. In fact, a good 85% of the working mechanicals on this truck are foreign to me at this point in my wrenching career.

I do not know if my fluid levels drop at all as I suggest, the reservoir levels are not droping over time (no fluid loss, thus I must presume no leak between master and booster--no leak into booster or to anywhere). But, as I stated, there was definitely a brake fluid leak between the booster and master at some point in the past, based on the corrosion on the lower half of the booster's shell, but apparently repaired.

After shutting down, I attempt to locate the hissing sound (the vacuum leak) and to the best of my ability, with me crawling up into the engine bay (hey, I am small enough to do that), it sounds like the leak is inside the booster. Presumably a torn diaphragm, right?


My plan of action, and Mel Lowe agrees, is just replace the booster and see if that stops the leak. If so, great, done. If not, no harm other than loss of maybe 30 minutes or so.