Hi
Has anyone had a problem with the rear axle brakes on a DAF XF running hot? its a 3 axle unit and this can happen wether empty or loaded. I changed the airdrier a few weeks ago hoping this would solve it but it hasn’t. I don’t think it is a sticky caliper as it is on both sides. Have also looked at the brake exhaust valve and that seems to be working normally and the brakes appear to be releasing fine. Any thoughts would be appreciated.
Thanks
Graham
it could be the footvalve not releasing the brakes fully causing the caliper to get hot
Hi shuttlespanker,
thanks for that. I’ll have to try and sort this out during the next few weeks. It has to be something like a sticky valve holding the brakes on a little. It can’t be doing the back discs alot of good. I had to change the front discs last week, ( got a prohibition for 1 crack 
) Its not a job I would want to do to many times.
Graham
I wouldnt want to do the brakes too many times either! Useless setup. Really need to check the brake pressures, these can be checked on the rear chamber test points or through the Davie diagnostic computer, You might find that the rear axle brake modulator has an issue, this controls the rear axle as a whole.
Hope this helps.
Most likely calipers sticking I would say. Is it one side or both?
renaultman:
Most likely calipers sticking I would say. Is it one side or both?
grahamrfd:
…I don’t think it is a sticky caliper as it is on both sides…
bullitt:
renaultman:
Most likely calipers sticking I would say. Is it one side or both?
grahamrfd:
…I don’t think it is a sticky caliper as it is on both sides…
Ooops should read the whole post 
My Money’s still on the calipers like, specially if it’s loaded or empty.
Just a thought, are the brake lights stuck on?
May sound silly
But we have had it before on a xf in our workshop
“Rubber footmat slipped forward and jammed under the bottom of the pedel ,and not allowing the brakes to properly release”
Geoff
GBtransp, thats exactly what I was getting at in my previous post, I have personally had 4 breakdowns for this, plus numerous workshop jobs (I am a DAF master tech.) Any pressure at all on the pedal presses a microswitch and puts 0.5 bar to the callipers, doesnt sound much but if you do 300-400kms with the pads rubbing the discs, theyll get hotter than you might think.
[quoteGBtransp, thats exactly what I was getting at in my previous post, I have personally had 4 breakdowns for this, plus numerous workshop jobs (I am a DAF master tech.) Any pressure at all on the pedal presses a microswitch and puts 0.5 bar to the callipers, doesnt sound much but if you do 300-400kms with the pads rubbing the discs, theyll get hotter than you might think.]
[/quote]
we have evreything jammed under the pedel, Biro´s , boiled sweets ,stones , When a driver phones us up stuck somewhere with jammed brakes the first thing we tell them todo is to check under the pedel, and the most dont ring back 
grahamrfd:
Has anyone had a problem with the rear axle brakes on a DAF XF running hot? its a 3 axle unit and this can happen wether empty or loaded. I changed the airdrier a few weeks ago hoping this would solve it but it hasn’t. I don’t think it is a sticky caliper as it is on both sides. Have also looked at the brake exhaust valve and that seems to be working normally and the brakes appear to be releasing fine. Any thoughts would be appreciated.
Correct me if I’m wrong, from my experience on DAFs (albeit not trucks), the handbrake circuit is on the rear axle. It may be that you have a sticking valve somewhere - Try draining the (braking system) air tanks to see if there is any moisture and oil carryover in the tanks as gunk in the tanks can cause valves to become partially seized in the open or closed position. An earlier post alluded to the modulator; this is usually a four-way valve as part of the braking circuit.
In my experience, it is often the pistons on the brake calipers that tend to sieze, although if you have checked these for operation and freedom of travel then there should be no problems here.
The_DAF_Man:
Any pressure at all on the pedal presses a microswitch and puts 0.5 bar to the callipers, doesnt sound much but if you do 300-400kms with the pads rubbing the discs, theyll get hotter than you might think.
IIRC, the brake light switch on the footbrake valve is activated at approx 0.5 bar.
i would say possible rear axle modulator fault if something was getting stuck under floor mat and operating micro switch in foot valve puttting 0.4 bar to front and rear brakes and 0.6 bar to trailer .you would have all brakes getting hot also this normally puts ebs warning on dash because ecu notes vehicle is in constant motion with footbrake applied and no deacelartaion. has this had any work previous to this happening such as a multi circut valve fitted or brake pads ect. also check pipe work for kinked or crused pipes causing air to trap when it sould have exausted out of system and check exaust silence on bottom of modulator valve incase it has got blocked
Hi all,
Thanks for your replies. Mattaid the rear axle had new pads fitted before this fault seemed to start, i took it back to where it was done to ask them to check everything had been done correctly and it was given the all clear. The problem is still there but only causes trouble when driving on non motorway roads. I can hear a relay clicking in and out as i apply/ release the brakes. Its booked in again in 2 weeks time ( when i have a holiday) so will suggest this rear axle modulator. What exactly does this do ?
With this WTD being introduced it might all become irrelevant as i will probably have to sell it anyway, its hard enough making a living on 5 1/2 days a week so being reduced to 4 will be a problem.
Thanks again
Graham
the modulator controls brake pressures to rear axle and rear axle abs through electronic the network . sounds like may be sticking pads if caliper carriers not been cleaned fully and on country rds braking a bit more causing heat expansion and pads to stick and bind .you find when they are in workshop everything is cooled down and free just a possibility