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ABS / Brake Problem

denjil

New Member
Joined
Oct 18, 2014
Messages
24
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malta
Hi all,

I have a problem with my front right caliper which only happens when the ABS functions.

The ABS light only lights up for a few seconds on start up and goes off which I guess its normal.

When the ABS kicks in, it works as it should and does not let the wheels lock up.. the problem is when I release the brake 1 caliper (right front) does not release the pressure and the caliper locks, vehicle will not be able to move... It will release the pressure if I pump the pedal for some time but i'm sure its not normal.

Could this be a problem from old brake lines? or maybe oil fluid? For now i disabled the ABS my removing the fuse.

Thanks.
 
Hi,
I would expect that it is caused by a sticking valve in the ABS unit. If it was a hose I would expect the issue to still occur on a hard brake with the ABS disabled. I am more familiar with VAG group cars and have only been a Toyota owner for less than a year but I know that on the VAG cars the regular brake fluid change is considered important not just from the moisture contamination causing boiling point reduction issue but also because of the need to keep the ABS valves clean and free from potential problems. My guess would be that the ABS unit is where the problem lies but especially if this is a recent occurrence and the fluid is old and/or there has been potential other fluid contamination then a good flush through might help sort it. On some units (don't know about ours) there can be problems with bleeding if the ABS unit is drained causing odd operation. I had a Rover 75 for a while and although I did not have the issue myself there were some owners who had ABS unit bleeding problems and there was a purging routine that could be activated via the diagnostics system but like I say I have no idea if this applies to the Toyota. In the light of these possibilities though I would suggest it may be safer to not drain out the system then refill but instead ensure it is kept full and just pumped through with fresh fluid. I normally use an eazibleed which uses tyre pressure to pump it through but have not had to do any bleeding yet on the Toyota. It would seem useful if you could ensure activation of the ABS in doing the bleeding if you can figure a safe way to do so. If it is the ABS unit and you can't sort it then used units are not too steep in the UK (30 to 90 quid).
 
Hi,
I would expect that it is caused by a sticking valve in the ABS unit. If it was a hose I would expect the issue to still occur on a hard brake with the ABS disabled. I am more familiar with VAG group cars and have only been a Toyota owner for less than a year but I know that on the VAG cars the regular brake fluid change is considered important not just from the moisture contamination causing boiling point reduction issue but also because of the need to keep the ABS valves clean and free from potential problems. My guess would be that the ABS unit is where the problem lies but especially if this is a recent occurrence and the fluid is old and/or there has been potential other fluid contamination then a good flush through might help sort it. On some units (don't know about ours) there can be problems with bleeding if the ABS unit is drained causing odd operation. I had a Rover 75 for a while and although I did not have the issue myself there were some owners who had ABS unit bleeding problems and there was a purging routine that could be activated via the diagnostics system but like I say I have no idea if this applies to the Toyota. In the light of these possibilities though I would suggest it may be safer to not drain out the system then refill but instead ensure it is kept full and just pumped through with fresh fluid. I normally use an eazibleed which uses tyre pressure to pump it through but have not had to do any bleeding yet on the Toyota. It would seem useful if you could ensure activation of the ABS in doing the bleeding if you can figure a safe way to do so. If it is the ABS unit and you can't sort it then used units are not too steep in the UK (30 to 90 quid).

Thanks for the info ren. I also think that the ABS unit is faulty now.

I replaced the flexible brake hoses and oil and the still have the exact problem. Oil was drained completely.

Is it too complicated to change the ABS unit when it comes to bleeding?
 
I would overhaul the caliper before i started spending on ABS components .

When you bleed brakes on a 90 series the rear axle needs to be carrying weight and not hanging ?
 
Shayne may have a point as although the problem does not occur with ABS disabled, if the caliper has a bit of friction working against piston or pad return then the addition of extra resistance from the ABS circuitry might be just enough to stop the pad and piston returning at all. I would have thought that this sort of problem would be more likely on a sliding caliper rather than the fixed types we have though. Also ABS activation does add the ABS pump pressure to that of your foot which also may push things into a more rougher/sticky area.

Been reading up on the issues with the Rover 75 as well as reading up on ABS modulator types to try and get an idea if it is a common problem or not. It seems that the issue is the secondary circuits used used can get air in which only comes out if ABS is actuated and the diagnostic tool does this activation. The symptoms if improperly bled are that when ABS activated the air gets into the main circuit causing a sinking of the pedal. Obviously the more air the more the sink and then there will be a spongy insufficiently bled feeling in the brakes. Looking at the different modulator types (4 main variants and not sure which 90s use but guessing 3 position ) there does seem like the potential to have this sort of issue on other types. One R75 forum suggestion was to brake on loose gravel to active ABS and then bleed again.
 
Interesting but all too technical for my way of thinking ren , who's to say the caliper isn't failing to engage with any great force unless ABS is activated ?

To pull it clean the pistons and sensor to test again costs nothing but time .

I thought the brakes on my 90 were pretty good , despite hearing the abs more often than i would like but i put that down to my having a big lift and heavy wheels and tyres , until i had the calipers refurbished and replaced all 4 disks , stop means stop now so apply with caution if you only want to slow down .
 
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I’d be checking the calipers as well. I thought mine were ok until I found only half of the pistons were free
 
Go with what Shayne suggests and pull the caliper. He is right that it is nothing but time. As he suggests the force should be more when the ABS activates as it's the foot AND the ABS pump pushing the fluid. Maybe denjil has an idea of whether braking performance has deteriorated over ownership or compared to a good brake test result at MOT or whatever similar thing there may be in Malta. This would reinforce Shayne & Mark's diagnosis. Hope yo get it all sorted OK.
 
check voltage both at batteries and at ABS pump at idle. When you brake foot is off Acc pedal so unless ABS unit is getting correct voltage/ amperage it will play up. I hade a bad earth and it was causing an issue with mine. Dangervis that it activates but doesnt pump properly so brakes never engage if you are on ice or gravel. You may notice things like slow windows or wipers at idle or even the battery indicator sitting low. Maybe just pull and clean the ABS multi plug connector
 
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