andyfreelandy

andyfreelandy

Well-Known Member
So a hot brake last week. A pair of new calipers and pins and all bled and tested. Cool with no brake application. Even warmth with gentle brake application. What could possibly go wrong ??

Went to the coast today, not sure why!! On way back brake smell. Both front brakes hot. Pumped pedal a few times and drove slowly. Brakes cool. Drove faster brakes cool.
It appears that about 1 in 10 brake applications and the front brakes stay on!!!

So got me thinking about how he piston returns after braking. If all seals don't allow reverse fluid travel where does the fluid go to allow pad clearance??

I'm thinking sticking ABS valve or valves and or master cylinder.

Anyone had such a weird fault?? Or wish to comment on the pad release dilemma!??!

Thanks....

This is the 2003 TD4 Sport playing me about.
 
I know this is silly but my grandmother had a similar problem with her car a while back and we couldn't figure it out for ages. Turned out the floor mat was slipping behind the pedals and causing the brake pedal to stay slightly "stuck" after braking.

You've probably already ruled that out but just incase 🤔

(Also hers isn't a land rover)
 
Yes John. I serviced all the caliper mech and renewed one pin as it was a bit bent. All slides nicely. New calipers.

The thing that is making me think it is not caliper related is that all is fine for several hundred miles, then one brake application seems to lock them partially on and brakes heat up. Further use seems to release it again.

Going to be tricky. Shall I replace hoses or master cylinder first?!?!?

Hose collapse is not something I have ever experienced but 21 yrs old and a lazy last few years ?
 
andyfreelandy said:
Yes John. I serviced all the caliper mech and renewed one pin as it was a bit bent. All slides nicely. New calipers.

The thing that is making me think it is not caliper related is that all is fine for several hundred miles, then one brake application seems to lock them partially on and brakes heat up. Further use seems to release it again.

Going to be tricky. Shall I replace hoses or master cylinder first?!?!?

Hose collapse is not something I have ever experienced but 21 yrs old and a lazy last few years ?
Click to expand...
I'd go for hoses first, as they can break down inside and make a sort of non-return valve.
If it was the master cylinder I'd expect worse problems and more consistent ones. I know there is a split braking system but even so, might it not then occur on both axles? I don't think it can possbly be caliper related as that would have to be the identical fault in both of them, which is unlikely.
I did once ages ago have a problem with a piston not returning properly, until it went over a bump or something. It turned out to be down to a tiny bit of air in the caliper. But I say this out of interest as the symptoms are not the same. (And is was not on a LR.)
Does the problem go away if you pump the brakes when coming off them? Counter-intuitive I admit. But if it was me, I'd try it.
 
andyfreelandy said:
So got me thinking about how he piston returns after braking.
Click to expand...
Pistons return because the seals in the calipers are designed to distort slighty when braking pressure is applied, when pressure is released the distorted seals go back to their normal shape and pull the pistons just a fraction back with them.
So if they are sticking on it implies pressure remains applied when you don't want it to be, if all else is clear, as it would be with new calipers.
 
OK. This is going to be impossible to diagnose logically as I did 400 miles yesterday with no fault. Did plenty of roadside checks and also rolling tests to see if the brakes were still off.

So, please comment if you see a flaw in my argument but I am going to eliminate all possible causes:

Replace front hoses although would they both be bad? Possible and I can check condition by cutting one up.

If nothing found replace master cylinder and then flush all fluid through. Also a complete bleed with ABS power bleed with PScan.

Servo is a remote possibility but not convinced it is a likely cause.

Will also investigate pedal assembly to ensure nothing is catching although pedal returns to full height.

There is no other possible causes that I can think of ?

Anyone add to list or suggest alternative approach?

Thanks
 
If it's just the front brakes getting hot then I would forget master cylinder / pedal fault
 
I thought that but because it is so infrequent and because discs get hot and drums do less braking and therefore less hot, I can't say if all 4 brakes are staying on intermittently or just fronts. Obvs if it happens again I will be doing more comprehensive checks. In my experience drums rarely get hot unless the brakes is seized on hard

So hoses and maybe bleed and new fluid first. Easier !!
 
Perhaps it's had moisture in the fluid in its past life, and corroded the pipework somewhere ?

I know it'sa pain, but consider a full fluid flush through with a pressure bleeder ? Should help shift any crud getting stuck in pipe fittings ?
 
Yes will do. Needs a fluid change anyway.

Just looked at the pedal, servo and master cylinder mechanical arrangement. The pedal and servo push rod connect all the way through. The master cylinder however does not connect to the servo push rod directly. Only by pressing. So the pedal and servo could retract fully and the master could stay pressed in undetected.

Master is becoming a higher likely cause I think.

Also, for a 50k vehicle the old discs were very worn. Makes sense now, problem could have been there for some time. Had a look at old discs. Some blueish tinge too. Ho-hum not well for a while me thinks.
 
So, checked ABS fault codes and have C1154 and C1148.

Haven't had a chance to check them out yet but could ABS have a fault that is putting brakes ON ?? Presumably it can.

Is the ABS ECU part of the modulator ?

Maybe electronics and not anything mechanical. That would certainly fit with the intermittent nature of the fault.
 
Can't definitively identify the 2 fault codes above.
ABS ECU is bolted onto the ABS Modulator and the block contains the solenoids for the valves too. 3 x Torx bolts hold it on and it looks like it can be changed in the vehicle without loss of fluid. On the TD4 the air intake hose will have to come off.

Will continue to look for the codes but as the few time the fault has occurred it has cleared after the car has been switched off and on again - I'm focussed on the electrickery...

Anyone know any Teves MK25 experts ?
 
Those two fault codes are listed in this thread. (was a google search, not forum search !! )

C1154 Historical CAN Signal engine speed error
C1148 Historical No Can message from engine ECU

But also found these descriptions on another forum, so not sure which would be correct:

C1148 - Right front wheel speed sensor coherency fault.
C1154 - Right front wheel speed sensor air gap fault.
 
Thanks. I did see that but had hoped to find the ABS related symptom. As written there they appear to relate to loss of CANBUS.

I have messaged a company that refurb Teves MK25 units and claim to know the codes and effects on the ABS.

Watch this space! Thanks for the research.
 
Wheel sensors all show same speed when driving so don't think it is wheel sensor. Wouldn't put brakes on.
I'm suspecting the ECU for the ABS.
 
Have you tried getting the ABS to come in? I'm wondering if one of the shuttle valves is sticking through old fluid and lack of use. Maybe flexing the ABS modulator's muscles will get things moving internally.
 
Would a power bleed exercise all the valves ?
There are loads (12 in fact)!! I thought there would be 4 !
 
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