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Discussion Starter #1
Hi all,

hoping someone on here can help me as I'm at my wits end with my t4s brakes. It's a 2.5tdi with ABS and for a long while now has had a soft brake. In normal driving it seems ok but if you slam on the pedal goes straight to the floor, it stops, but slowly. It seems solid when the vans not running but once the vacuum pressure's built up I can sink it straight to the floor, pump it a few times and it firms up. I know about diesel creep and it's way beyond that (and several mechanics who have seen it agree, the current one even owns a t4 although with no ABS). It's been bled repeatedly both the traditional method and pressure bled and the ABS pump bled, I've replaced the master cylinder, the flexi hoses, the vacuum servo, the vacuum pipe with the check/no return valve. I've sent the ABS pump off to be tested which came back as fine, still couldn't find the fault so replaced that still no joy. The only hint is when the front left flexi hose was clamped off there was somewhat of an improvement but when the mechanic put the caliper from his own van on it went back to normal. We then replaced the right rear (that being on the same circuit) still the same. There are no leaks, the fluid level has never dropped. I'm at a loss as to what to even check next, any ideas out there?
 

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Hi all,

hoping someone on here can help me as I'm at my wits end with my t4s brakes. It's a 2.5tdi with ABS and for a long while now has had a soft brake. In normal driving it seems ok but if you slam on the pedal goes straight to the floor, it stops, but slowly. It seems solid when the vans not running but once the vacuum pressure's built up I can sink it straight to the floor, pump it a few times and it firms up. I know about diesel creep and it's way beyond that (and several mechanics who have seen it agree, the current one even owns a t4 although with no ABS). It's been bled repeatedly both the traditional method and pressure bled and the ABS pump bled, I've replaced the master cylinder, the flexi hoses, the vacuum servo, the vacuum pipe with the check/no return valve. I've sent the ABS pump off to be tested which came back as fine, still couldn't find the fault so replaced that still no joy. The only hint is when the front left flexi hose was clamped off there was somewhat of an improvement but when the mechanic put the caliper from his own van on it went back to normal. We then replaced the right rear (that being on the same circuit) still the same. There are no leaks, the fluid level has never dropped. I'm at a loss as to what to even check next, any ideas out there?
Which ABS have you got, with EDS or ESP? Obviously those pumps are different when being changed or tested, did you also test the used replacement unit that you fitted.

I have experienced this situation in the past, but normally all the checks you appear to have done and a complete fluid 'flush' has cured it. I assume your servo is also OK?

Whilst the system is a little more complex and with extra plumbing, you seem to have touched all bases; and anything obvious should have come to light :*
 

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Discussion Starter #3
To be honest I didn't think it had either, only late t4s even had ABS and then it was an option I believe? I replaced the ABS pump based on the VW part number, didn't have the new one tested but it made no difference so very unlikely to be the culprit I reckon? If it makes any difference it did have an engine change at one point (an ACV for another ACV) but all the same ancillaries original ECU etc.
 

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To be honest I didn't think it had either, only late t4s even had ABS and then it was an option I believe? I replaced the ABS pump based on the VW part number, didn't have the new one tested but it made no difference so very unlikely to be the culprit I reckon? If it makes any difference it did have an engine change at one point (an ACV for another ACV) but all the same ancillaries original ECU etc.
Not so, mine will be 20 this year, has ABS with EDS, later were ESP. ABS has been an option since day one!

It just sounds like you are loosing vac assistance somehow; and or still have air in the system, which unlike brake fluid of course does compress :confused:
 

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Discussion Starter #5
Not so, mine will be 20 this year, has ABS with EDS, later were ESP. ABS has been an option since day one!

It just sounds like you are loosing vac assistance somehow; and or still have air in the system, which unlike brake fluid of course does compress :confused:
I did not know that! It really feels like there's air in the system but if there is I have no idea how or where? It's been bled repeatedly by myself and by mechanics including bleeding the ABS pump. The vacuum servo was replaced with a brand new on as was the hose with the check valve.
 
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