Excessive brake pedal travel

[Chas]

Is there anyway of knowing if air in the system is evenly distributed or gathered in one, or a few, places.

 

[frank rabbets]

No.

When my dad used to bleed the brakes he used to stamp on the brake pedal to flush trapped air through, close nipple, then SLOWLY up on the brake pedal so as not to draw air in through a possibly weak master cylinder. Also if fluid level is low it is possible to suck in air through the depth of the fluid a bit like a plug hole. In fact I've had cars where even with 1 cm of fluid in the reservoir where the suction of the MC can suck air from the surface. Really annoying noise lol.

 

[Bat21]

I think I've almost got it BAT. If there was a hole in the bottom of the tube atmos' pressure would be acting on both ends so it would just be the weight of the fluid causing it to come out. There would be more pressure at the bottom of the hole if the height of the column was higher though.

Yes to both statements.

Is there anyway of knowing if air in the system is evenly distributed or gathered in one, or a few, places.

Yes, but only if all the components in the braking system were made of a transparent material, then you would be able to see where the elusive air was hiding.

 

[Dave2000]

Good point on the bore size Towpack, I have witnessed many times on my pressure bleeding system fluid passing under the bubble that will invariably be in the pipe leading to the MC, I based my theory on the assumption the same would be happening in the brake pipes, I guess the bubbles would have to be very small indeed for the fluid to pass under them.

The key IMO is speed of fluid movement, if you can carry the bubbles along with a good shove of the pedal it does seem to work better.

Regards

Dave

 

[Chas]

Yes to both statements.



Yes, but only if all the components in the braking system were made of a transparent material, then you would be able to see where the elusive air was hiding.

I was just wondering if there were obvious places where air would collect.

 

[Bat21]

Just a quick update on this one.

Using the pressure bleeder I can get all the air out of the system but....

After 2/3 weeks the pedal goes spongy again and I have to bleed them again.

There is no fluid loss during this time but air is 'getting in' somehow

In the last 12 months both front calipers and the master cylinder have been replaced with RoughTrax items.

Even when the pedal is good, if you keep your foot on it it slowly descends to the floor. A mate of mine had this happening and ended up getting rid of his 80 after replacing all the braking system and still not resolving the creeping pedal problem.

 

[Dave2000]

A mate of mine had this happening and ended up getting rid of his 80 after replacing all the braking system and still not resolving the creeping pedal problem.

That's a bit excessive.

Even if there is no air it is possible the fluid is passing the master cylinder rubbers? IIRC the master is dual chambered, if one part of the system fails you have some effort from the other. This in itself is extra odd, unless you have two separate problems? Despite pressure bleeding my entire system I am sure the pedal is not as good as it was prior to the brake overhaul.

Without wishing to cast aspersions is it possible there are problems with the new parts?

regards

Dave

 

[frank rabbets]

Are you losing fluid level ? As in going into the vacuum system. Is it a diesel engine ?

 

[frank rabbets]

I hav'nt experienced your problem at first hand obviously but I would google "diesel brake creep" and see if anything there adds up.

 

[Towpack]

I would say this has to be a MC issue. There's only 2 reasons the pedal should go to the floor. Either, fluid is being ejected from the system due to a leak or it's creeping back past the MC seals into the reservoir. If you are 100% certain there are no leaks then it must be the latter IMO.

 

[frank rabbets]

MC was my first reaction TP and having now read up on "diesel brake creep" it's not that. I would there fore change the MC with a new Toyota one and forget about it.

It may be possible to get a seal kit from Toyota and polish the bore of the old one.

 

[Dave2000]

I think I would just have to go for a new MC Frank, if the problem still exists then the polish and new seals may or may not have been successful, you end up chasing your tail.

regards

Dave

 

[Bat21]

Thanks for the feed back so far. This one has me perplexed because everything points to the master cylinder.

The Master cylinder was replaced 2 months ago. I replaced it because of this spongy pedal problem. I guess I could be unlucky and the new one is faulty giving the same symptoms.

Having Googled 'diesel brake creep' I guess it may just be a common trait with the early 80. Anyone else out there with a 92 none ABS 80 care to try theirs and let me know.

Just to clarify, there is no fluid loss and once the brakes are bled they are fine but once my truck has stood for a couple of weeks the pedal goes spongy. I'm not sure if it would still suffer this problem if I used it daily, but I can't see how that would make a difference.

 

[frank rabbets]

When I used to restore cars in 60's there were not any alternative parts apart from the breakers. Then slowly you could buy pattern parts and they were generally crap. I don't think much has changed. I remember in 1977 taking some LR leaf springs back to a shop because the bushes were loose. The owner told me to f... off and I could not have a refund. I'm not sure if trading standards were operating at the time but I complained to someone who wrote back to me saying to go back to the shop for my money. On collecting my money all hell broke loose but I was strong in those days. His shop looked rather empty lol. No springs in sight. He told me I was a B.....d for reporting him. WTF? I suppose he was born in wedlock.

 

[clivehorridge]

I think it's the master and I'd have a word with Karl to see if he can let you gave a s/h mc at a reasonable price.

On the same theme, moons ago I had fluid leaking into the vacuum diaphragm chamber of the servo. It was a petrol car, so the servo was vacated by a hose to the inlet manifold. I must have been topping up the master with fresh fluid quite regularly (it wasn't an uncommon thing to do in the old days) to he extent that the servo had filled right up to the vacuum hose, with fluid.

I only found out when stopping sharp at lights or a zebra, and I'd be overtaken by a cloud of white smoke big enough to block out the whole street!

I'm not suggesting you have the same problem, but there were no external leaks, and there was creep.

 

[frank rabbets]

I had the same thing Clive that's why I asked about loss of fluid with no obvious leaks. Seals in 50's 60's didn't seem to last very long at all. There were only 2 manufacturers in this country i.e. Dunlop and Lockheed. You could buy kits from both.

 

[frank rabbets]

P.S. Girling as well.

 

[Bat21]

Thanks once again guys.

To eliminate the master cylinder once and for all, I am in the process of ordering a genuine Toyota one from Amayama. It looks like it is going to be about £300 by the time it arrives to my door.

I'm not too bothered about the pedal creep as that seems to be a common occurrence with early 80's, it will just be nice to have brakes once again that last more than 3 weeks before having to bleed them again.

 

[Dave2000]

IIRC Frank it became Lockheed Girling?

regards

Dave

 

[frank rabbets]

I don't remember that Dave. Lockheed had stopped making the GIANT servos I was reconditioning. I telephoned them and they sent me 2 recon kits which they made up for me free of charge. There must have been 16 pieces in each box. Diaphragms, seals, gaskets, springs etc.