I have noticed on my van and similar Alko TAG chassis's when you put your foot on the brakes although you always stop even in a emergancy, the brake pedal does slowly sink to the floor giving the effect of a spongy system.
I and many others have had this since new. My van has just passed its MOT with not even a mention of a problem.
One Fiat expert in Germany said its because the fiat braking equipment was designed for the smaller Ducato and not for a 6 wheeler. I have tried bleeding the system conventionally, back bleeding, pressure bleeding even changed all the seals in the system. tested pressure hold on the master & slave cylinders, no faults anywhere, but still there is this sinking feeling in the pedal.
I can't find any other forum relating to this phenomena.
Has any body out there experienced similar problems? And have you any suggestions, other than trashing the van
As you probably know Richard, (but for those who don't) a spongy feel to the brake pedal is usually caused by air in the system. A descending pedal (critical) is caused by either a leak, which is easily ascertained, or by fluid seeping back past the master cylinder seals. This is usually caused by perished seals but if you have changed them then I can only suggest that the master cylinder and piston are not compatible.
I was once told years ago that old master cylinders can wear to a slightly larger bore where the seals rub.
When you put in a new seal and bleed the brakes by pumping the pedal you will move the new seal over this slight step where the wear is, as the piston during bleeding moves past its normal travel distance. This can damage the edge of the new seals.
I remember when I was an apprentice, that on a few occasions changing the seals did not work as after you had bled the brakes, when you pushed the pedal down to check the seals the pedal would slowly go to the floor.
My mate had the same problem with his tag axle euramobil. I think he (partially?) resolved this by changing the flexible hoses to the braided stainless steel type. Apparently the rubber hoses were expanding. PM AWR and ask him.
I was told by someone in the know, that brake problems on tags are largely down to the fact that the original master cylinder is used which was designed for a single set of rear brakes, they were having lots of complaints about low pedal ect,They kept fitting new rear pads which effectively minimised piston movement, which in turn resulted in a higher ,harder pedal.
Thank you all for the replies so far. With regards to wear as the van is only just 3 years old and has 31400Kms on the clock I did discount the wear point. As many others with brand new TAGs have the same problem, I feel there must be something inherently wrong in the system. I spoke to Alko Uk at shows they never had a issue with this,mind you they would say that.
I never gave the flex pipes a though, my only concern is if that is the case at some point I would have thought the spongy feel would increasingly get harder.
No matter what method I used to bleed the system there was never one bubble that showed in the disposed fluid.
Thanks David I will Pm your friend and see what the results of his change had.
To eliminate brake hose expansion clamp all hoses at the nearest fixing point to the body work and see how much brake creep you have. If none master cylinder is ok. To eliminate the tag axle clamp the rear most hoses and see what the pedal is like with the 4 wheels.
We have a tag axle Auto trail and on braking I have to apply the brakes twice quickly in sucsession this improves the pedal. I intend to replace all the brake hoses with the stainless steel braided type made by Goodrich.
Hope this helps Rich
Hi Rich nd Lin
Thank you for your post on the BF Goodridge pipes, have you a part number for them? I take it there is 6, or is it a case of measuring whats on the van and having them made up, or are they stock items?
Hi Richard Try contacting Goodridge, if you tell them the vehicle you have they will probably have your question answered. Their web site address is below, I also noticed on their web site they have an ebay shop for clearence items
hi can anyone help me?
I have a 1993 fiat ducato humor motorhome
1 of the rear brake pipes was leaking so I changed the pipe
its a copper pipe we tried to bleed that pipe but now the brake pedal has to be pumped to get any brakes at all
have I got to bleed all the brake lines as we only done the one we changed
pedal now goes to the floor and have to press the peddle a couple of times to get them to work