Excessive brake pedal travel

[Bat21]

Went to use the 80 today to give it a run, it would have been its second outing since returning from this years Morocco trip in September.

It's an auto so I put my foot on the brake to select D and it went to the floor

After a few pumps the pedal came back but as I pulled her down the drive and went to stop, then pedal went to the floor again

Before the Morocco trip I did a break fluid flush plus I replaced a weeping load sensing valve. The 80 did about 6,000 miles after the work with no brake problems.

There are no leaks or fluid loss anywhere so I'm guessing it's the master cylinder?

I know there are sometimes problems with the master cylinder seals following excessive pedal travel that comes with the 'old style' bleed but, how come it was fine for 6,000 miles following this?

 

[joinerman]

Just lucky i would say but agree it's the master cylinder

 

[frank rabbets]

If faulty m/c seals let air into the system I don't know how the pedal would recover unless you do rapid pumping but then the pedal would have full travel again very quickly. Have you had a look under the dashboard brake pedal to see if fluid is leaking out? There is a bleed nipple on the load sensing valve. Perhaps there is trapped air in there which sometimes gets compressed giving you a feeling of no air in the pedal.

 

[frank rabbets]

Ah just thought. With a tandem cylinder you can get seal failure with no air getting into the system which would explain why you sometimes have full pressure.

 

[Bat21]

Thanks for the replies, looks like I will be giving RoughTrax a bell tomorrow to order a new master cylinder.

I have a vacuum bleeder but find it prefers to 'suck' air from around the threads of the bleed nipple rather than draw fluid through..... anyone else have this problem?

 

[Towpack]

Yes, I had a similar problem trying to "suck" bleed a front motorcycle brake a while back using a large plastic syringe. It pulled the fluid through eventually but couldn't get a completely bubble free stream which I assumed was coming from round the nipple threads. Virtually no chance of this air getting into the brake line of course but it can be misleading. I have a pressure bleeder that pushes fluid through from the reservoir. This wouldn't fit the bike but I used it for a complete fluid flush/change on the LC back in the Summer and it was easy peasy. JMO

 

[Chris]

No, my Sealy vac bleeder is a miracle of modern workshop equipment. I use it quite a bit and its performance is quite astonishing. Just done a lot recently on the brakes - new hoses, LSV refirb, full brake refirb and that's on two trucks. Tried a pressure bleeder once and it was a complete failure. Couldn't get the lid to fit and it was such a pain to take off to top the fluid up. Oh and also put new nipples in from Mr T. It seems to waste far less fluid than bleeding with the pedal. Sounds daft but it sort of only seems to suck the air out and very little fluid.

 

[Towpack]

Mine is the Gunsons bleeder (I think). There's a clamp on type lid thats fits reservoirs (round neck only) that are not screw type and it seals OK. A large plastic bottle holds the fluid and this is pressurised, feeding fluid through to the reservoir via a tube so the reservoir doesn't run out. I guess you use whatever system you're happy with.

 

[frank rabbets]

I've just emptied my brake hydraulics completely and reconditioned the callipers. No rust on the pistons so very pleased. Fitted 4 new discs and pads. Bled the brakes which took 8 minutes with wife pressing the pedal completely to the floor. Even got air and very dirty fluid out of the loading valve which I had never opened before. Bled each calliper twice until there was no air. Very easy with the car on 4 axle stands.

 

[Dave2000]

Don't forget the wheel bearings can cause identical problems you describe.

regards

Dave

 

[Bat21]

I know what you mean Dave, I had a wheel bearing go on an old Rover SD1 (it was actually a Volvo 260 that I grafted an SD1 front subframe with V8 motor onto). It was only a few miles from home so I drove it home, it was an interesting couple of miles with the wobbling wheel/disc pushing the brake pistons back in.

This is different, it is losing the pedal while just sitting there. You can pump the pedal to 'get' a brake, but then a few seconds later you can press it again and it has gone.

 

[Mblinko]

I'm considering looking into my M. Cyl. so I checked pricing. Genuine ones are more than 300 quid. Anyone got experience of Roughtrax or Milners ones, or even a m/c seal kit ?

 

[chapel gate]

I would also say master cylinder, ive had a couple go on cars over the years, that little bit of brake you get back by pumping the pedal will soon vanish. I replaced the seals with good results. Not had to touch the one on the cruiser yet.

 

[Bat21]

The plot thickens.

Today I was about to order a replacement master cylinder from RoughTrax but thought I would give all the calipers etc a once over for leaks. I noticed a couple of drips right below the load sensing valve (LSV).

It appears the LSV that was replaced with a RoughTrax one less than 6 months ago is weeping. Is this just unlucky or is RoughTrax parts that bad?

Has anyone else removed the LSV? If so we're the results noticeable?

I'm still going to replace the master cylinder but are now worried about the quality of the RoughTrax ones. Amayama want £188 + £51 shipping, plus whatever UK PLC will shaft me for once it arrives on these here shores.

 

[Chris]

Replacing the LSV is dead easy unless like me you snap the studs. Then you have to take the bloomin fuel tank out. Arrrrrrrgggggggghhhhhhhhh and breathe.

I think that RT parts in general are a cut above. You need to determine where the LSV is leaking before casting nasturtiums I guess.

 

[Bat21]

Yes Chris, replacing the LSV is simple, sounds like I was lucky with mine as everything unbolted just fine.

The new one is leaking into the rubber boot down through the plunger, which is exactly what the original one was doing.

 

[Chris]

Dang. The difficult bit was easy and the easy bit was errrm. Crap. That's a bit rubbish really. I am surprised at just how well these 20 year old devices actually keep going. So for a new one to fail so early is very disappointing.

 

[Bat21]

.... Has anyone else removed the LSV? If so we're the results noticeable?....

What I meant was, has anyone done away with the LSV and just linked the 3 pipes?

The brakes on my none ABS 92 80 are so archaic am I really going to notice the difference?

 

[frank rabbets]

I don't know if that load sensing valve is a bit of over thinking or necessary. The theory is that it is a no no to have the rear brakes lock up because then you spin the car. The load sensing valve safely increases pressure to the rear wheels if you put more weight over the rear wheels. In by passing the valve it could be that all pressure goes to the back which would be dangerous.

Could it be that air is getting in through the load sensing valve? It is working even when there is no pressure in the hydraulics so it's possible that the leak is acting like a pump and sucking air in.

Toyota do a reconditioning kit for the master cylinder. Many a time I've saved an obsolete corroded cylinder by polishing the bores. Yours may not even be corroded.

I cannot see a recon kit for the load sensing valve. Years ago I used to get any hydraulic seals straight from the specialist but I don't know if there are those type of places left any more.

Some Toyota prices are reasonable at the moment. The LSV looks quite simple so may not be that expensive.

 

[Chris]

The LSV is very simple. I took mine to bits. It's amazing to see it still working after all these years actually. It most certainly has a noticeable effect that's for sure but quite where it'd sit if you removed it, I can't say. It would be easy to do, so just by pass it and go for a spin. I considered putting one of those three position rally car ones in so I could bias the brakes a bit at least.