Soft brake pedal

[nielsc]

I really did not want to open another spongy brakes thread, but after reading so many threads on here and Mud and not finding an answer I am a bit out of options.
My 80 has had the low spongt brake pedal for years, and for some reason I figuered it was just an 80 thing, untill a drove a couple of other 80s that all have a nice and firm brake pedal and have much more stopping power then mine.

Parts replaced are:

Front and rear brake calipers rebuilt + new pads
I've replaced the master cylinder with an aftermarket unit (OEM unavailable here)
Replaced the LSPV since it was totally rusted and could not open the bleeder without snapping it. Since brake lines at LSPV were in the same condition, I've made those out of copper brake line with double flared ends.
All flexi hoses have been replaced with braided steel hoses aswell. (So I cannot clamp of the rubber lines to see if things improve)

I've bled and bled and bled for a lot of times with a pressure bleeder at 25PSI , whilst bleeding with the pressure bleeder I pumped the brake pedal several times with the bleeder open.
I tried all possible sequences bleeding the calipers and LSPV, I've activated the ABS a dozen of times on a stretch of unpaved road, and bled some more.
I still have the same spongy pedal I had before.

2 things I have noticed:
-When I moved the LSPV arm completly up and moved LSPV down on the bracket, and even with the ABS fuse removed, I am unable to lock up the rear wheels when braking hard, even on wet grass!
This make me think there still is air somewhere in the system.

-When pumping the brake pedal with the engine off it gets quite hard, pumping with the engine on makes it spongy, and when pressing hard enough will always sink to the floor slowly, even after pumping it up several times.

The only thing I can think of that is causing me these issues is the ABS actuator.
Is it possible these units are impossible to bleed, or leak internally.
One thing I'm going to try is put the car on 4 jack stands and run it so I can activate the ABS while pressure bleeding it, see if it makes difference.
Other than that I'm thinking of either removing the ABS pump or buy another used one to try it, but might be a waste of money.

Any opinions or help is greatly appreciated!

 

[whereisgibson]

On the off chance this is useful as a troubleshooting step, my 80's ABS doesn't try to work when the vehicle is moving backwards - and if I recall it's regardless of being in reverse gear or not, implying the sensor/unit can't do the negative maths.

 

[frank rabbets]

Sometimes there is dirt and corrosion on the caliper piston shims ? Have you tried getting the brakes very hot by left foot braking and driving a few miles with the brakes on ?

If you have the old OEM cylinder you could replace the seals and try that. Chapel Gate used to have some.

 

[flint]

Did you bleed the new master cylinder ? If not it might be worth a try (plenty of rags handy !).

 

[nielsc]

All calipers have been rebuilt and move free.
Rebuilding the old master is an option indeed.
I’ve bled the master by cracking the unions while my pressure bleeder is on it. I think it will be the same result?

 

[Highlander]

New callipers all round fixed mine, I also changed the LSPV arm/lever which was seized. Might be worth looking at if you haven't changed it. Pedal still a bit mushy, but doesn't sink to the floor any more and stops good.

If the ABS "brain" has air in it, you will need to actuate ABS while pressure bleeding. I fully expected to have to do this and collected the necessary kit, but like I said, my truck stops well now so not actually done the procedure.

I think I got this from Ih8mud:

 

[nielsc]

LSPV and arm have been replaced. Literally everything except ABS pump and the booster.
Brakes have been bled with the 80 on jackstands, the wheels spinning, and applying the brakes while bleeding each wheel and LSPV, in different orders aswell.
This way ABS actuates whilst bleeding.
Changed nothing.

I’ve now discovered that when I press the brakepedal, that brake fluid level in the reservoir rises a bit, and drops again when letting go.
To me this looks like a faulty new master, but i’m keen to hear some opinions, or if anyone wants to check with his ABS equiped 80?

 

[Highlander]

I tried your technique but wasn't terribly impressed by the results. I recommend triggering it electrically

If the MC is the only thing you haven't changed, then it seems sensible to swap that as well

 

[nielsc]

With me it worked really good! The ABS pump went crazy.
The MC has been changed for an aftermarket one.

 

[frank rabbets]

If the level in the reservoir rises then I think you have a faulty cylinder. Probably incorrect/bad seals.
I changed my MC seals for OEM ones as a precaution and brakes bled with no trouble at all.

 

[nielsc]

I have plugged the outlets of the master and pedal is rock hard, same with the engine running. So I think it checks ok?

I removed the ABS pump and temporarily bypassed it with some custom made copper lines, resulting in the same spongy pedal.

Because I have braided steel flexible lines that I cannot clamp I tried the following:

I plugged the rear output of the master, same result.
Then I reconnected it, and plugged the line to the front left caliper, nice and firm pedal!
Reconnected, and disconnected the front right pedal, and also a firm pedal!
Reconnected everything and bled the system for the 100th time, again spongy low pedal that drops to the floor when keep pressing it.

This is getting confusing!

Any ideas as to why I have a firm pedal with only 1 left or right front caliper, but not with both connected?

 

[SeaJay]

Have you tried this?

Bleeding the LSPV.
1. Disconnect the LSPV control arm from the diff mount.
2. Gently lift the control arm to fully up position and hold it there. This will ensure maximum fluid flow to rear brakes.
3. Now bleed the rear brakes. If your brakes have recently been bled then only the left rear needs to be bled.
4. Lower the control arm to full down position and hold. This forces the fluid to the front brakes.
5. Now bleed the front Left brake. There is a “Y” joint near the front left wheel (RHD) so you are bleeding from the front brake and rear brake lines. Allow plenty of fluid to pass to ensure you have flushed the by-pass line fully.
6. Temporarily refit the control arm and test brake.
7. Repeat above if necessary to get good peddle.

 

[frank rabbets]

I have not re read or remembered your post in total but if the pedal goes all the way to the floor I would have thought you have a faulty master. If the pedal is slowly going to the floor the fluid is going back in to the reservoir. As to the spongy pedal you might have faulty/dirty shims on the back of the pads.
I know the frustration. I bought a brand new Land Rover with slightly spongy pedal in 1972. 5 years after buying it one of the slave cylinders on the rear started to leak so I stripped all of them to replace seals as a precaution. Some idiot in the factory had put 2 seals in the cylinder so there was air trapped in between them! Sabotage, carelessness, who knows.

 

[Jon Wildsmith]

I have plugged the outlets of the master and pedal is rock hard, same with the engine running. So I think it checks ok?

Only really checks as ok in that plunger position, and for some of your other tests with a single calliper connected, a limited depth of travel. Perhaps further into the bore it starts leaking and you only reach that point when there is more movement e.g. all the pistons on all the callipers being moved.

 

[nielsc]

I have done this exactly like you described, but I think the line from the Y joint of the front circuit is not connected to the rear circuit. It is only a “signal” line so the LSPV, but fluid cannot go to the rear circuit I think.

Have you tried this?

Bleeding the LSPV.
1. Disconnect the LSPV control arm from the diff mount.
2. Gently lift the control arm to fully up position and hold it there. This will ensure maximum fluid flow to rear brakes.
3. Now bleed the rear brakes. If your brakes have recently been bled then only the left rear needs to be bled.
4. Lower the control arm to full down position and hold. This forces the fluid to the front brakes.
5. Now bleed the front Left brake. There is a “Y” joint near the front left wheel (RHD) so you are bleeding from the front brake and rear brake lines. Allow plenty of fluid to pass to ensure you have flushed the by-pass line fully.
6. Temporarily refit the control arm and test brake.
7. Repeat above if necessary to get good peddle.

 

[nielsc]

I have not re read or remembered your post in total but if the pedal goes all the way to the floor I would have thought you have a faulty master. If the pedal is slowly going to the floor the fluid is going back in to the reservoir. As to the spongy pedal you might have faulty/dirty shims on the back of the pads.
I know the frustration. I bought a brand new Land Rover with slightly spongy pedal in 1972. 5 years after buying it one of the slave cylinders on the rear started to leak so I stripped all of them to replace seals as a precaution. Some idiot in the factory had put 2 seals in the cylinder so there was air trapped in between them! Sabotage, carelessness, who knows.

No shims behind the pads.

Faulty master keeps coming up in my mind aswell. I’ve ordered a rebuilt kit, and might just get another new one aswell.
The old one that came off was faulty, as the rear part of rear brake piston was broken off and jammed crooked inside the bore, impossible to remove it, it might have been jammed while bleeding.

 

[nielsc]

Only really checks as ok in that plunger position, and for some of your other tests with a single calliper connected, a limited depth of travel. Perhaps further into the bore it starts leaking and you only reach that point when there is more movement e.g. all the pistons on all the callipers being moved.

This is what came up my mind aswell.
With only 3 calipers the pistons might not move far enough to leak internally. With 4 calipers the pistons need to push more fluid and thus perhaps move along an imperfection in the bore wich creates an internal leak.

 

[Towpack]

I'd also go with it being a fault with the MC of some sort. I drained the reservoir completely when fitting all new flexi hoses, 2 new rear callipers, rebuilt front callipers and a bit of copper pipework last year. I then bled the system with a pressure bleeder and it was a doddle compared to the 2 man peddle pumping/nipple opening method. If you've used the same pressure bleeding method I can't see how there'd be any air in the system.

 

[frank rabbets]

Faulty master cylinder = the mechanical equivalent of electrical gremlins.

 

[Highlander]

LSPV and arm have been replaced. Literally everything except ABS pump and the booster.

80 series brake boosters do go bad, and have been implicated in soft pedal issues. I considered it might have been my issue. OEM is pretty much impossible to find.

There's an Australian unit made by PDI: PDI Dual Diaphragm Brake Booster Landcruiser 80 series (Late 2 bolt master) - [Leaving Land Cruiser Club]

Heard good things about it, will lock up all 4 wheels while running 35's. It's substantially bigger than the stock unit, so you might have to reroute the throttle assembly slightly and possibly the air box