Serious safety issue! -Master cylinder mods (1 Viewer)

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Lostmarbles, I've read as many post on this thread (and the previous thread) as I have time to read (not many), and it appears that there is alot of "the blind leading the blind" on this subject matter.
Put simply, drum brakes need approx. 10 lbs. residual pressure to hold the brake shoes up to the brake drum, and disc brakes need only 2 lbs residual pressure to hold the pads up to the rotors. If you left the OE 6 lbs residual valve in the master cylinder after a rear disc brake conversion, the rear brakes would always be applied, and probably burn up or wear out prematurely.

This subject matter really does not have to get more complicated than that!!!!!
 
You're ignoring pbgbottle's contribution to this post Pin_Head. He tells us it is not just a "New Zealand thing". The same valve thingies are fitted to vehicles originally sent to your country.

Don't make the mistake of thinking that Canada is in the US. I don't really mind, but it generally pisses off Canadians. He is in Canada and they don't get the same vehicles as the US.
 
This subject matter really does not have to get more complicated than that!!!!!
Thanks Downey.

"Blind leading the blind" is an entirely appropriate comment. I'm not offended by it because that is what a lot of us use MUD for. We usually lead ourselves eventually to the right conclusion by this method, don't we? (Provided we each think hard about what we say and don't automatically take anyone else's preaching as "gospel".)

When a thread gets as long as this, I can understand posting without reading it all. I do that myself (and often regret it). But I think you should see my problem if you were to read it all.

How can you classify my valve as a "residual valve" when it has a hole right through it that stops it from leaving "residual pressure"?

For me - it IS a lot more complicated than what you say!!!!! Perhaps that's just me though.

Yes I'm somewhat humiliated but I'm going to persist!

We're hardy bastards in this part of the world!
 
Don't make the mistake of thinking that Canada is in the US. I don't really mind, but it generally pisses off Canadians. He is in Canada and they don't get the same vehicles as the US.

Hey. For God's sake. It's all "America".

I can't even distinguish your different accents.

Accept it "you're all one people".
 
F'n Brits...
 
F'n Brits...

Be quiet you!

You're too scared to even show where you're from in your "profile".

(And I'm too scared to click on your MySpace link for fear of what I might be confronted with.)
 
This is getting good!
 
the masters will be the same .other than our canadian spec 76-80 fj45 -different , we didn't get the same vehicles we received the cooler ones :doh::grinpimp: but we do get the same ones now as the U.S. there for no new toyota diesel's anymore .thanks to Cali emmisions standards

Don't make the mistake of thinking that Canada is in the US. I don't really mind, but it generally pisses off Canadians. He is in Canada and they don't get the same vehicles as the US.
 
i just got an e-mail notification that someone revived this old thread ,i guess it got deleted :doh:

anyways i had taken some pics of the plastic thingy in the later disc brake master ,i thought Tom (Lostmarbles) might want to see them

plastic part has 4 holes in it and the metal disc has one hole in it .:grinpimp:

any more ideas ?????
2 (Medium).JPG
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6 (Medium).JPG
 
i just got an e-mail notification that someone revived this old thread ,i guess it got deleted :doh: ..

That's weird Jake....... Appearances are that you revived it? (Yours being the only post since Nov 07.)

....anyways i had taken some pics of the plastic thingy in the later disc brake master ,i thought Tom (Lostmarbles) might want to see them

plastic part has 4 holes in it and the metal disc has one hole in it .:grinpimp:

any more ideas ?????

Thanks very much for posting these pics. (And thanks to the mysterious person who revived the thread to prompt you to do so too;))


At the time this thread was running, I felt a bit guilty about raising alarm (concerning the practice of throwing away these "residual valves") because I began to doubt my theory (as to the REAL reason behind Toyota fitting them).

I found that the valves on my cruiser have a "permanently open bleed hole" that prevents them from leaving any residual pressure in my brake lines.

So now I'd like to know -- Does that bleed hole you've photographed in the metal disc do the same with that older design of valve too? (IE. - Prevent that type of valve from leaving residual pressure as well?)

:cheers:

PS. In answer to your question - I have no new ideas. I still think those "thingies" serve some purpose other than - "straight forward LEAVING RESIDUAL PRESSURE". But I remain unsure as to exactly "what-that-purpose-is" or "how-they-operate". So of course I also remain unsure about whether there is a safety issue associated with discarding them.
 
this was the e-mail i got :grinpimp: :cheers: Tom your welcome for reviving this thread ;) i am still very curious myself how these things exactly work and there exact function , these where pulled from a 78 master front disc rear drum.if they where residual valves . the parts catalog would show a different part # for the front curcuit and the rear curcuit. but it doesn't
both the front and rear use the same plastic disc thinging for both curcuits. where as one is suppose to be 10lbs and the other 2 lbs. if so there would be two different part numbers ?
hope that makes sense :grinpimp:



Gumby has just replied to a thread you have subscribed to entitled - Serious safety issue! -Master cylinder mods - in the 40- & 55-Series Tech forum of IH8MUD Forums.

As in every disc brake system the return force for the calipers is the square seal in the caliper. It distorts when the piston is pushed out and returns to it's normal state when there is no pressure. When the piston needs to push further than the seal will distort because of wear, the piston will only return the distance the seal pulls it back allowing for constant and automatic adjustment of the caliper.


It has nothing to do with residual valves. 2lb residual valves keep pressure on the system to make sure the brakes leak out and not in. The drum brake ones also help to overcome spring pressure.
***************





This is such a fun looking discussion I thought that I'd have a go at it. :grinpimp:

Just curious where everyone thinks the returning force is coming from for the calipers? I can think of only one main force that would apply to our 40's.

The rotor run-out will push the pads/pistons back till they just touch at the high points. I don't know of any significant springs in the system trying to push the pistons back beyond this point. Now some may argue that there's a small vacuum created in hydraulic system as the master cylinder piston returns, or there is some small thermal expansion in the hydraulic system. I could see those as being a reason for using the 2psi residual valves.

So there we go, my personal opinion. What do you guys think?

Jeff :popcorn:
 
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this was the e-mail i got :grinpimp: :cheers: .....

Ah... I get it now. Sorry I'm a bit slooooooooww today Jake :eek:.


..... The drum brake ones also help to overcome spring pressure.
***************

and you're preaching to the converted really. Except I don't think I need "residual pressure" to counteract any return-spring pressure on my drum brakes. I believe it is my "adjusters" (and not "residual pressure") that counteract the springs and thereby keep my shoes close to my drums (so that I don't need much pedal-travel in order to apply my brakes).

:cheers:
 
On the return stroke, spring pressure against the piston forces the piston to move back into its cylinder. Fluid now flows from the wheel cylinder towards the master cylinder. The tension of the brake shoe springs pull the brake shoes away from the brake drum and this forces the the wheel cylinder pistons inwards .Fluid is therefore returned to the master cylinder.
however, some fluid is healed in the lines by the check valve at the end of the master cylinder. This pressure, knowen as residual pressure, keeps the wheel cylinder cups expanded to prevent them from leaking, and also reduces the chances of air leaking into the system.
CHECK VALVES
The pourpose of a check valve is to provide resudual pressure in the system to keep wheel cylinder cups expanded. Residual pressure is not necessary with the design of of seals used in wheel cylinders of disk brakes and, in fact, is undesirable. Pressure remaining in the system would prevent the pads from releasing fully.
Where drum brakes are fitted to a system as well as disk brakes, a residual check valve is not always used. Expanders fitted to the wheel cylinder cups of the drum brakes, and the design of the cups which fit into the groove in the piston, have reduced the need for residual pressure.
METERING VALVE
A metering valve is used to meter the pressure to the disk brakes and so balance the operation of the front disk brakes withe the rear drums brakes, particualarly during light brake applications.
The metering valve prevents the disk brakes from being applied untill a low pressure has built up in the system. This alows the shoes of the rear drum brakes to be expanded against the tension of their springs, and ready for application befor the disk brakes are applied.
DISK BRAKE CYLINDER
The cylinder of a disk brake is part of the caliper assembly. The caliper straddles the the disk and carries the disk pads as well the cylinder and piston.
When the brakes are applied, fluid pressure behind the piston forces it against the brake pad and the pad is forced against the disk.
The pads have no return springs. The piston is returned in its bore, and drag between the pad and the disk is prevented by the spring action of the piston seal.

hope this helps:)
 
Hmm weird, I always thought that type of master cylinder was fitted to disk brake 40's, now I'm really confused!
Here's a pic of a disk brake master/booster, tiny bit different to yours Tom, but looks like the same setup.
 
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I was doing a search on master cylider differences in hopes of finding the differences between the three types I have on the shelf at the shop. I had written a response to the debate that was going on, but saw that it had been pretty well resolved later in the thread so I deleted it.


Someone had posted that the residual valve helps the piston to return or some such. The square seal in the caliper returns the piston. It has nothing to do with the residual valve. As was posted above, the residual valve helps retain a little pressure in the lines so they tend to leak out rather than in. Much like the air pressure in an operating room being higher than the outside air pressure.

They are important on a drum brake system. Their effectiveness on a disc brake system is debateable.
 
.....some fluid is healed in the lines by the check valve at the end of the master cylinder. This pressure, knowen as residual pressure, keeps the wheel cylinder cups expanded to prevent them from leaking, and also reduces the chances of air leaking into the system...........

..... As was posted above, the residual valve helps retain a little pressure in the lines so they tend to leak out rather than in. ....

Thanks Guys.

Well ya know what.................I think I may have finally got it.

This thread was started on the basis of my finding that my "residual valves" are completely incapable of leaving any "residual pressure" (for any length of time) because of the "permanently open porthole" (shown in post #18) that MUST automatically equalise pressures (rather than leave "residual pressure"). And from this finding, I suspected then that those "thingies" may actually have a different safety-related purpose than the "text-book explanations". (As you can see - I felt very sure of myself at the start. But then I lost confidence in my theory. :eek:)

But now this latest talk of "seal behaviour" has made me see things from a different perspective.

So now.......Let's see...... I have always known that the return-springs in my drums briefly push my pistons back into my wheel-cylinders when I take my foot off my brake pedal. And of course I still need the seal lips to be held against the cylinder walls DURING THIS BRIEF PERIOD OF REVERSE PISTON MOVEMENT (to stop fluid leakage). So my "residual valves" achieve this by restricting the reverse-fluid-flow through that "permanently open orifice" and thereby maintain some fluid pressure within my wheel cylinders during this reverse movement (and thereby keep the seal lips held tight against the cylinder walls while the pistons move).

Sound right? Has the penny finally dropped for me here????? Whoooopeeeee. Please do tell me I've finally got it after all these YYEEAARRSS! (This could represent my "slowest ever uptake" of knowledge!)

:cheers: :beer::beer::beer:

PS. The key to my understanding of all this is my realisation (assuming I'm finally right) that the residual pressure is designed to be present ONLY BRIEFLY DURING THE PERIOD WHEN THE WHEEL-CYLINDER PISTONS ARE MOVING IN THE "BRAKE-RELEASE DIRECTION".

PPS. And finally understanding this - opens the door (for me at least) to understanding when to discard these residual valves and when not to (if fitting discs for instance)!!!!!!!!
 
Hmm weird, I always thought that type of master cylinder was fitted to disk brake 40's, now I'm really confused!
Here's a pic of a disk brake master/booster, tiny bit different to yours Tom, but looks like the same setup.

Hi Alex.

I assume that is off your BJ40 which has been converted to "discs on the front" by your PO.

I wouldn't be surprised if your PO used the original master (meant for drums all round) and simply discarded the "residual valve assy" for the front circuit.

I have no comment on whether this is acceptable practice or not. (I can now see that discarding the residual valve is wise but I haven't a clue what the brake-proportioning would end up being .... front versus rear.)

My present brake master cylinder is the OEM one meant for drums-all-round and I'm sticking with drums-all-round because I've no complaints about them in 30 years' service.

:cheers:
 
Sorry should have made this clearer, that setup was on ebay and stated it was of a 40 series with factory disks (not sure what model exactly). Here's a pic of my MC. I have drums at the front but am going to be converting to disks. The fitting of a later series bigger booster with a spacer isn't going to be an option to me from what I can see as there's not much clearance between the MC and the air filter, ok for an FJ but not a BJ.
 
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