Reply With QuoteSeized caliper?
Regards PhilipA
YarnMaster
Supporter
Two Brake callipers not bleeding the entire brake pedal stroke - faulty ABS units?
Experiencing a strange fault with the brakes on my D2a. I've replaced the front drivers side (right) flexible brake hose as the hose was pulling out of the crimped end to the caliper causing a slow leak. Fitted the new hose and while bleeding all the brake callipers I've found that the front drivers side (right) and rear passenger side (left) only push brake fluid out for the first half of the brake pedals travel before the brake pedal becomes firm and doesn't push down any further (same thing with the engine running or off) - I assume that this isn't right?
In comparison, the front passenger side (left) and rear drivers side (right) callipers push brake fluid out the bleeder nipple the entire brake pedal stroke and the pedal is able to be pushed down to the firewall. Ran the power bleed cycle on the Nanocom a number of times but this continued. Despite this finished bleeding them all to ensure no air in the lines and refitted wheels. The brakes work but don't feel right - feel that they are lacking braking power. I've run it for a few days now and activated the hill descent control for a 2km of downhill to activate the ABS module etc. No SLABS faults on the Nanocom.
This afternoon I tried bleeding all the callipers again - same issue with the same calipers. Removed the bleed nipples from the front drivers side (right) and rear passenger side (left) brake callipers. Checked that there was no blockage in the brake nipples holes and pushed brake fluid out of the callipers with the nipples not fitted. Tested and the callipers are holding strong stopping me from being able to turn the hubs with an extension bar.
I find this strange as the issue is diagonally across the vehicle effecting one front and one rear caliper. The master cylinder looks to have the two front callipers and two rear paired up for the combined outlets, after this the ABS module looks to have four individual outlets for each caliper. Could the issue therefore be with the ABS module and some sort of internal blockage?
Swaggie
SubscriberSeized caliper?
Regards PhilipA
YarnMaster
SupporterI assume by that you mean seized piston in the caliper? I don't think so as 1. the calipers were all rebuilt a few years ago, 2. no noticeable excess heat on those two wheels when driven, 3. hub turns freely easily when brakes aren't working and are unable to be turned with a bar when brakes are applied which indicates that the pistons must be moving.Originally Posted by PhilipA
If the piston was seized I still would have thought the brake fluid would push out of the bleed nipple.
But I'll lift the caliper up and see if the pistons push back to confirm.
YarnMaster
SupporterTurns out I was wrong. Thanks to sierrafery for pointing out that the D2's brake hydraulics are diagonal in the output from the master cylinder. I'm betting my current master cylinder is failing. According to my records it was replaced in 2013 with a pattern aftermarket unit (buy cheap, buy twice).
The hydraulic circuits are diagonal and it's a straight line which splits through the modulator for that so might be a problem with the master cylinder secondary circuit on your's or there's a blockage in the modulator on that line
YarnMaster
If you change the master cylinder you'll need power bleed with tester cos air will get into the modulator unless you keep the pipes full and bleed the cylinder alone before you connect the pipes to it
Discovery Td5 (2000), manual, tuned
ChatterBox
SubscriberIt's a tandem master cylinder so normal behaviour.
If all brake calipers are bleeding up , working and giving you a firm pedal, I'd be looking at the vacuum side if the braking performance is reduced.
The vacuum pumps definitely lose performance over time
RoverLord
the cheats way....
pull the pads out of the front or rears. carefully put the brakes on to put a heap of fluid down in the caliper.
change out the MC, bleed it using the blanking plugs it should come fitted with.
depress the brake pedal about half way and hold it there ( I use an extension bar off the seat base to the pedal
attach the lines but dont lock them up fully (have someone watch for the air bubbles to stop when the air is all gone from the MC/ABS module ine)
use a spreader to push the pistons back into the caliper
close up the lines
then bleed by normal means to change out the fluid.
Dave
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YarnMaster
SupporterAre you sure? I've had the vehicle for 9 years now and replaced the brake fluid every two years during that period. I don't recall ever previously having noticed that the brake pedal stops half way through it's travel for two of the brake calipers when bleeding - from a braking balance perspective doesn't it also seems strange that two calipers would stop pushing further pressure while the other two would keep applying further pressure?
I replaced the alternator only a year or two ago with a genuine Denso unit. Pretty sure it came complete with a brand new vacuum pump on it.
I believe the Nanocom did this for me back in 2013.
Your cheats way sounds very practical but can you explain this part to me please? How does one bleed with blanking plugs - isn't a bleed nipple required for the air and fluid to push through?
ChatterBox
SubscriberBlknight is talking about bleeding the master cyl before fitting.
The ABS master cylinders have no secondary compensation port unlike pre ABS.
The modulator valves are probably closed on one circuit.
Is it possible you are doing a different bleeding sequence to what you have done in the past ?.
After bleeding , do you have a firm pedal?, if so , did you notice the braking performance getting worse before you noticed the bad brake line, if so , how old is the vacuum pump / alternator ?
YarnMaster
SupporterYep, I understand that. It's his 'cheats' way for changing Over the master cylinder without using an electronic device to bleed the system.
Possible, but I don't believe so. I bleed the furthest away first and then work closer - so rear right, rear left, front right, front left. Check the fluid level between each. I use a hose with a one way valve on it and recruit a second person to assist with the pedal pushing. Afterwards the bleed nipples are torqued to 10Nm.
The brake pedal feels fairly normal. Car drives ok and brakes fairly normally. But push the brakes hard and it feels like it's lacking biting power.
Maybe I need to go and take it on a dirt road out the back and hit it hard to see what happens and what locks.
Hadn't noticed a brake issue before I noticed that the area on the inner side of the front drivers side wheel was wet. When I investigated I found the brake hose failing at the fitting crimp.
A year or two old. Replaced the alternator with a new genuine Denso unit and pretty certain they include a new vacuum pump fitted on the front of them.
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