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Brake problem help or suggestions please

Julian T

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Recently my truck had developed a worrying habit, the rear axle was doing more braking than the front axle so having diagnosed front callipers requiring a rebuild I got my hands on a pair of seal kits and stripped and rebuilt the front callipers both callipers had partially seized pistons, I also replaced the pistons and seals in the brake master cylinder, I was not overly concerned about the rear callipers as I rebuilt those a couple of years ago when the o/s/r seized.

However after reassembly and bleeding the brake system I have discovered that should you apply the brakes and hold pressure as if doing a crash stop the pedal will drop (fade) after initial resistance, engine on, with engine off it does not and is hard as rock, engine on and first application brakes feel like they have air in the fluid, second application they feel right and after approximately 2 seconds the pedal starts to drop, also the brake warning lamp (not handbrake) is now staying on after the engine is started.
The sensor for the brake warning lamp is I assume the one in the bottom of the reservoir.

Brakes were bled initially at the master and then at the callipers starting at furtherest from the master cylinder.
At this stage I am wondering what I have missed, any suggestions will be appreciated.

Thanks Julian
 
Well as likely as not you have scuffed the seals in the master cylinder. It's very common and there are threads about this. Your seals move up and down in the same old bit of the cylinder for 20 years. When you bleed them, you push the seals right down the tube. Now when you brake, fluid is being pushed past the seals in the MC giving you this soft pedal. This is why on my current truck I only bleed with a vacuum bleeder and never by pedal.
 
Appreciate that Chris, I did visually inspect the bore and give it a very gentle hone with some very fine water paper, there was no ridge to speak of in the bore but I think I will probably be stripping the master again tomorrow, I certainly hope the seals are alight.
 
I'm not sure that there will be a ridge as such. Brake fluid turns a filthy colour and bits drop in there through the lid, scrunge builds up in the cylinder etc and you push the seals into all of that. It's not that the walls have worn away, I don't think. It's just muck and dirt. The seals have given a lifetime of service and this might simply be their end. I picked up a clutch slave yesterday. I just figured that it must have done like a million gear changes so whilst I didn't detect any issues, I wasn't going to chance it. Maybe you can just put new seals in yours
 
Thanks Chris, I put new seals in this morning, front callipers and brake master, I kept the old ones so at the moment it looks like I will have to strip and check the master, ........
I checked for fluid leaks, double guessed myself, well live and learn I suppose ;)
Working with brake fluid and hydraulic brakes has reminded me why I like HGV trucks and pneumatic (air) brakes lol.
 
Mine's always done this from when I first had it in 1998 with 30,000 miles on the clock. I've worked on dozens of different braking systems. It has not got any worse and I assume it is part of the normal ABS operation. I have to press the pedal very hard with the engine running and it slowly sinks. Nothing wrong.
 
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Hmmm interesting, thanks frank, I don't have ABS (thank goodness) and I don't recall mine doing this before but then again, its the first time I have had to bleed the front brakes, did not notice this when I did the rear callipers.
 
It does do it with the engine running. That's normal. It's called diesel creep or something. But it's not supposed to do it with the engine off of course.

See what it's like with the new seals. Bleed through all over again including the LSV and MC. I have to say that this Sealey vacuum bleeder is the mutts. It seems to pull very little fluid through, just the air. I keep thinking, well that can't be done and the brakes are superb. Pulling the fluid through just seems better than pushing it through for some reason. It's quite a low vacuum pressure so I guess it's easier to pull air than fluid
 
Just a quick update, master cylinder seals all ok, re bled the brakes and the sinking pedal is slightly improved, took a quick test drive and the rear axle still does more braking than the front axle, so for my next trick I will probably have to look at the load sensing valve.
 
I noted the warning light comment, this may indicate an imbalance in the fluid lines. normally bleeding again sorts this problem out. The pedal sinking is in fact you slowly compressing air in the lines with the assistance of the servo when the engine is running. The other reason this happens is as per Chris's comment, the fluid slowly passing the new seals in the old cylinder.

The rear compensator arm can seize in the loaded position and cause the issue you describe, of note has the vehicle been modified suspension wise, if so the compensator should be set up with a set of pressure gauges, having said that there are many that simply bolt a new one on and call it good.

regards

Dave
 
LSV, simple and bolt on are not necessarily words that you'll find in the same sentence Dave. I swapped mine recently. The old one was toast inside. Not letting fluid through at all. But I had one on the shelf. So I tried to unbolt the old one from the bracket. Nope. I tried to unbolt the spare one from its bracket. Ha ha ha. I tried to unbolt the bracket from the car. Ho ho ho, heee hee ha ha. Not a fnurking chance. In the end I bent the bracket back and forth until it snapped off, bolted the new one on with one bolt to get me going and then last week I dropped the fuel tank to get at the other bolts. What a job. If the LSV slides off the pins then super. Easy job. But even on the bench I couldn't get it off the bracket.

All good now though. New cals on the back and rebuilt on the front. Slotted discs all round
 
LSV, simple and bolt on are not necessarily words that you'll find in the same sentence Dave.

LOL, I agree Chris but you know what I meant. I still feel they should be set up with the gauge though, I have heard of them being removed completely, then rely on the ABS to release the wheel if it locks, not the right way though as heat and wear end up on the wrong end of the vehicle during normal use. Drifting a little off thread how do you find the slotted discs?

I had considered them along with the cross drilling, was not going to do the mod for braking power just the pub talk point of view, I am thinking mud (rare here) but wet sand with little stones (plenty here) getting caught in the grooves/holes making lots of noise/wear? Those beach parties are hell! :dance:

regards

Dave
 
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ABS? What's that?

Hard to say how I find the slotted discs. They stop the vehicle which weighs a lot. Are they better than std, hard to say as I swapped so many things all at once. They are not worse, that I can say. The slots are pretty shallow you know, it's not like a cheese grater. I think I have genuine pads in at the second and having played around with pads in the past the best ones I have had were.... yes....wait for it....... drum roll please ...... the Milner ceramic ones. By a long way. They stopped the off roader better than anything I'd had in there for sure. That beast took some stopping.
 
I'm a bit lost here. If the standard brakes are inadequate isn't the vehicle loaded over it's manufacturers limits ?

Ceramic discs we're talking Ultima territory and I never needed ceramics on mine.

A very quick brake setup will wear out relatively quickly whereas a long life one will take warm up laps which you won't have in an emergency.
 
Hey Frank, ceramic discs, wow, who mentioned ceramic discs? Maybe I could get some to go with the ceramic PADS that I mentioned. Eh?

SHGTSS maybe
 
BTW way I've seen plenty of Typos on your posts but being older than you didn't mention them.:icon-biggrin:. At least I think I'm older than you.
 
Plenty of typos? Hmm I doubt that. But to say ceramic disc when you meant ceramic pad isn't a typo Frank. It's called a mistake. Ceramic pdas would be a typo.

I'm not going to answer the first question because it's pointless and dull. Who says that upgrading something is only done because the original is no good? Enhancing is not an admission of failure Frank.
 
Yes Chris I made a mistake by typing the wrong word. What drew my attention to your ceramic pads was that I had never heard of ceramic pads before, only ceramic discs, and had to google it to make sure you did not mean disc. I was amazed that they even make ceramic pads.
 
Well I never said they WERE ceramic in fairness Frank, so I can't tell you more than that. They are CALLED ceramic pads. It's what it says on the box. Hence me calling them ceramic pads as opposed to the old ones they sold that weren't called that. They don't look very different but as I maintain, they are the best stopping pads I have fitted to a Cruiser.
 
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