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Brake Servo / Parking Brake Issue


NeilAvensisT
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Morning all. For a few days, intermittently, I have heard a bit of a 'hissing' type noise which goes when I press the brake pedal. Last night I was out for a drive and the brake pedal became 'hard' a few times with the 'hissing' worse. When I pulled up home on my drive the engine management light came on and a warning message on the dash (see picture). The message says 'check parking brake system'. The handbrake works fine, but when I have stuck my head under the footwell, the noise is (I think) servo pressure coming out of the rubber seal on the brake rod (pictured). When I clamp that rubber seal with my hand the noise stops/gets less. I have used a code reader but it is not a sophisticated one and no codes come up.  Any pointers?

 

 

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I think the brake booster/servo has torn membrane internally, so needs replacing. The bit you squeezed is probably the dust boot. It will be a matter of sourcing one and cost.  

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7 minutes ago, Konrad C said:

I think the brake booster/servo has torn membrane internally, so needs replacing. The bit you squeezed is probably the dust boot. It will be a matter of sourcing one and cost.  

Thanks. That sounds in line with my thinking, its a servo issue. Not having done one before, have you? what sort of job is it on an Avensis?

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17 minutes ago, NeilAvensisT said:

Thanks. That sounds in line with my thinking, its a servo issue. Not having done one before, have you? what sort of job is it on an Avensis?

I have done a servo swap many decades ago, so not on the Avensis. You can see the bolts on the inside, but you need to remove some of the scuttle cover in the engine compartment, to separate the master cylinder from the servo and the servo pipe. Do this first before working on the inside. I think the hard bit is setting the pedal adjustment. Use the old servo to match the new, and take measurements before starting the work. It is a case of working in awkward positions and having the right sockets and spanners.
 

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OK, I don't think my mechanical skills are quite up to this job, but I do have an excellent local garage for the jobs beyond me. Interestingly, I had real difficulty tracking a replacement unit down. My local motor factors could not source one for love nor money. Out of curiosity, I spoke to my local Toyota dealer to see if there was any known faults/recalls etc. They say no, but wanted (wait for it) £762 + VAT for a replacement. Wow. I tried a few specialist brake companies online, but no good. Getting slightly despondent,  I looked on eBay and found a good looking used item which matches up exactly to my parts references (Bosch 0204054175  47200-05280). If anyone knows however of a contingency supplier for me though, please feel free to let me know (in case the used part also leaks/doesn't hold a vacuum, unlikely I know). Thanks.

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Going off the info in your sig, Toyota part No. 44610-09520 Substituted by 44610-09521

A quick look shows Aisin make an equivalent

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On 8/19/2022 at 3:59 PM, flash22 said:

Going off the info in your sig, Toyota part No. 44610-09520 Substituted by 44610-09521

A quick look shows Aisin make an equivalent

Sorry to be a pain, but I can't seem to locate this; have you a link? Thanks.

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21 hours ago, flash22 said:

Sorry, the aftermarket sucks some times for messing up part numbers - the Aisin part doesn't exist

No worries, yes, its a right pain to track down a new part. As I mentioned I have managed to get one from a breakers which looks in very good condition. It matches up with original part numbers and has all the correct connecting ports for the ASC etc. I am having it fitted on Monday. The vacuum will be checked before the process commences but surely, I can't be unlucky enough to have another one leaking 🙂 I will continue however to search for a new, replacement, to have a Plan B in place.

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Remember I said I replaced a servo on a car (Maestro) many decades ago, I also had another servo fault on another car (Simca) years before that. The non return valve failed where the cap fell apart. This meant no servo assistance and a hard brake pedal, needing a lot of force to stop the car. The non return valve was attached to the servo drum as part of a hose. I manage to get one off a scrapped car in a breakers yard the next day. Once in place everything returned to normal. 

I would check the other vacuum components for leaks. The vacuum pump should be effective within a few seconds of starting the engine. 

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20 hours ago, Konrad C said:

Remember I said I replaced a servo on a car (Maestro) many decades ago, I also had another servo fault on another car (Simca) years before that. The non return valve failed where the cap fell apart. This meant no servo assistance and a hard brake pedal, needing a lot of force to stop the car. The non return valve was attached to the servo drum as part of a hose. I manage to get one off a scrapped car in a breakers yard the next day. Once in place everything returned to normal. 

I would check the other vacuum components for leaks. The vacuum pump should be effective within a few seconds of starting the engine. 

Thanks, I have tried listening to see if I can find the actual source of the 'hissing', to no avail at the moment. I am pretty sure it is not one of the hoses as they all look in excellent condition, but the main plastic valve that comes off the front of the unit, where I guess the pressure from the inlet manifold comes up to it via a hose is still a suspect. Would the seal where it goes into the servo unit fail?

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Just as a quick update, I have made a bit of extra progress. 'Fiddling' around under the dash, by the pedals, I 'pushed' slightly the boot (see picture) and something internally moved. The hissing stopped completely. A few hard pressing of the pedal and the hissing started again, although to a lesser extent. I therefore feel that the fault is on the inside of the car, servo mechanism, rather than the unit in the engine bay side? I had bought a second hand unit, which is the one in the photo (less than £30 delivered), so I can clearly see the area where there maybe an internal collar or similar. Has anyone ever delved that far into the system to give me some pointers?

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5 hours ago, NeilAvensisT said:

Thanks, I have tried listening to see if I can find the actual source of the 'hissing', to no avail at the moment. I am pretty sure it is not one of the hoses as they all look in excellent condition, but the main plastic valve that comes off the front of the unit, where I guess the pressure from the inlet manifold comes up to it via a hose is still a suspect. Would the seal where it goes into the servo unit fail?

The plastic valve was what I was describing on my old Simca. If you had some putty like substance, you you put it on the suspect components. I don't think you will hear hissing as such, depending on the size of the leak and how much vacuum is being created. If you can find a way to test individual components, to isolate the leak.

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1 hour ago, Konrad C said:

The plastic valve was what I was describing on my old Simca. If you had some putty like substance, you you put it on the suspect components. I don't think you will hear hissing as such, depending on the size of the leak and how much vacuum is being created. If you can find a way to test individual components, to isolate the leak.

Thanks. I will have a good look on the weekend under there, but I feel I am making progress; it may be just that the boot is 'sticking' and pulling off its mounting point? I will update further once I have more facts to hand.

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So I had a play around with the rubber 'boot' which covers the end of the rod connecting to the brake pedal (see photo above) and the part of the servo that is inside the car/bulkhead. By manipulating this the noise has completely stopped. There are 'breather' holes on the end of the boot which are there, I suspect, to draw air inward to counteract / balance the vacuum air pressure in the servo. I used a Silicone Spray which is specifically for lubricating and protecting rubber parts (the rubber boot and shaft seals) which seems to have done the trick.  If I am honest I don't completely understand why; it is likely that the boot was getting a bit 'stuck' when the pedal pressure was applied and, over time, was 'rising up' and not functioning correctly, releasing air pressure. Just a theory. Whatever, it has (for me moment) completely cured the problem. Just posting this to hopefully help other members who may come across this unusual fault avoiding the need for a servo change (which looked a swine of a job).

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