Brake problems, 4runner calipers and standard master problems?

[ntsqd]

Finally got some time to plug the numbers into my spreadsheet, overall system leverage ratio as reported is 70:1. The booster throws me a curve as I'm more used to non-boosted brakes, but going bigger on the m/c bore is the wrong direction. The booster may allow going to 1", but bigger than that is very questionable. The change in line pressure btwn the 7/8" bore and a 1" bore at the same pedal effort is 23% lower. Big change from seemingly not all that big of a bore size change.

Old rubber hoses can expand under pressure, wouldn't take much to make the pedal feel mushy. Replacing the rubber hoses would be high on my list, but I'm leaning towards entrained air somewhere. Volume of fluid pumped thru the system is no guaranty that you got all of the air out. That the brakes get better by pumping them is a classic indicator of air in the system. The most ideal flush/bleed method is to pump fluid in from each bleed nipple. That is how aircraft are done. Next best is probably a professional power bleeder, and then after that something like the peanut butter jar power bleeder.

 

[dbleon]

Finally got some time to plug the numbers into my spreadsheet, overall system leverage ratio as reported is 70:1. The booster throws me a curve as I'm more used to non-boosted brakes, but going bigger on the m/c bore is the wrong direction. The booster may allow going to 1", but bigger than that is very questionable. The change in line pressure btwn the 7/8" bore and a 1" bore at the same pedal effort is 23% lower.

I may be reading this wrong...and im a dummy, but are you saying that a SMALLER than stock MC with 4 runner calipers would provide the same line pressure and peddle effort as stock?

I wonder how 4 runner calipers, booster, and master would feel?

Our just remain all stock and forget about upgrades?

 

[dbleon]

Btw thanks for taking the time to work on this NTSQ.

 

[Slow Left]

Yes, I'd be interested in seeing the calculation - not that I don't trust your numbers, rather I'd like to understand the principle and if, in the future, I had to build a system that required such a calculation, it would be nice to have an understanding.

Just thinking out loud, though, if the surface area of the 4 runner calipers (and therefor brake pad to rotor contact area) is greater than stock, then in order to maintain the same force/unit area, the amount of pressure (force) built up in the lines will have to increase, so the cross section ID of the brake lines will have to be decreased...

 

[Christian]

somehow my last reply got eaten by a bad internet connetction, and I have been trying to get on for a few hours...

Elbert, you're right, I should..

ntsqd, thanks for your calculations, so your vote is that it's NOT because my master is too small, thanks!

I've bled the system again, no air, and not any any better, but i have also been driving it some more, and might be able to describe the symptoms better AND come up with another theory of my own (which might be a Dooh-moment...)

Ok, so the brakes don't work as they should, but it's not like it does the same every time?!? I thought I could pump them like there was air in the system, but it's not quite like that, and there's no springyness in the pedal feel. I just tried to stomp the brakes hard, and she stopped like an oiltanker with engine failure, NOT GOOD, the pedal felt fine, linear and then it reached a point (not the bottom) where it got hard, like I reached the end of movement for one piston, and the next was considerably harder to move?!?
Then I tried applying moderate pressure, and she stopped fine! Actually while stopping, the brakes gripped harder and harder!?! But this is not how it goes every time... Whats up with that? if they behaved consequently it would make more sense to me...

So here's my new idea, it's the booster that's at fault!
I know that a conventional diagnosis of a faulty booster is hard brakes, but having looked in to how boosters actually work, it might just be that that's at fault here. A booster has two valves, that are actuated almost simultaniously; the first one closes the passage between the two sides of the diagfragm, the next opens the rear side of the diagfragm to ambient air pressure, but these two valves are not necessary linked, although actiivated by the same pushrod, in one video I looked at, they were kind of rubber bellows acting like springs closing or opening a cylindrical hole in which the pushrod acts (I'm getting longwinded now, sorry).

Well, a malfunction that means bad brakes when I stomp the pedal, and ok when I apply moderate pressure sounds like something not right in the booster, what do you guys say?

 

[ntsqd]

Disconnect the booster downstream of the vacuum check valve (booster side) and cap it off. That should render the booster null. If the check valve is still connected to the booster you'll have made the brakes firmer feeling than they really are because you'll be working against the booster too. Then try the brakes.

The calc is a simple one, total system leverage = pedal ratio * hydraulic ratio. Where people go astray is in calculating the caliper piston area. You're only interested in the area of one side of the caliper. You'll to either trust me on this or figure out why on your own. I'm not sure that I full understand the physics of it well enough to explain it, but that is how everyone in the industry does it.
Total ratio (TR) = (pedal pivot to center of foot pad dist./pedal pivot to push-pin dist.) * (one side piston(s) area/m-c bore area)
From this equation I hope that it can be seen that if you increase the caliper piston area and increase the m-c bore area by the same percentage of change that you've made no difference to the TR or how the pedal will feel.

The curve-ball is the booster. In a manual, unboosted brake system you want a TR somewhere above 93:1 and below 100:1 though some folks can tolerate or even like slightly more than 100:1 (well into mushy). Very, very few will like the actual stopping of below 93:1 even though the pedal feel is nice and firm and really inspires confidence in the brakes*. Ideal that most everyone will at least not complain about seems to hover very close to 95:1.
With a booster in the mix the TR can drop well into the 70's and maybe below that, I don't know. Boosters are too much of a wildcard to approach system design like this. Takes a more sophisticated approach and one that I'm not familiar with. The reason is that the valves in the booster can vary the boost. That's like having a variable ratio pedal. Two identical appearing boosters can have pedal feels that are totally different due to the 'tune' on the valve or valves. The venting valve isn't an all or nothing kind of valve, it vents a percentage based on how far the push-rod is moved. Move movement = more boost. My brakes education was more about race car systems and didn't deal with boosters at all so what I know about boosters is from what I can find (truthfully haven't looked very hard) online and in James Walker Jr.'s book on brakes about booster design.

Pad surface area doesn't matter. That's no easy for most to accept, but it is the truth. I know that I covered this somewhere here: https://forum.ih8mud.com/threads/comments-on-brakes.256361/

*All too often on forums a good feeling pedal is equated to be good brakes. Those folks don't understand why the vehicle stops so poorly when the pedal feels so good. A good firm pedal that doesn't stop in a reasonable distance means that the TR is too low (or wrong/bad booster) so it doesn't generate enough line pressure. This is the devil in monkeying with brakes, a firm pedal is confidence inspiring, but the line btwn good and firm that stops well and good and firm that doesn't stop well can be very thin.

 

[Christian]

Thanks ntsqd, your explanations are highly appriciated!
I did disconnect the booster after my last post yesterday, and the pedal (and clutch) went very firm. I have just dismantled both sides on the front axle, just to check that the calipers moved ok, I managed to change the two short hoses, and ground the surface of the pads on the suspicion that the hanging master had caused them to glaze. Scientificly I should have done these things independently and test driven in between, but I didn't... Now I will go and test if these steps have made a difference...

 

[Christian]

Well that didn't make any difference...

 

[ntsqd]

That both sides of the diaphragm(s) be vented to the atmosphere is crucial to the testing that the booster is not the problem. Your comment about "very firm" leads me to suspect that it wasn't vented on both sides. Without a vacuum on the one side of the diaphragm you have to compress the air trapped in that volume in order to apply the brakes.

 

[Christian]

Heureka! I'm an idiot!!!

First of all, I hope you all will accept my depest appologies for wasting your time.
Secondly, I got brakes!!!

After having taken master, calipers etc. apart several times, without finding any faults, I did what I should have done days ago... I decided to go back to basics, and check the entire system and routing to check everything was connected correctly, and lo and behold, what did I find?
The two input lines on the LSPV was attached opposite of what they should be, meaning that the front cirquit had to act on all four wheels, and the rear cirquit only went to the safety cirquit on the LSPV.
NO WONDER IT FELT LIKE THERE WASN'T THE NEEDED HYDRALIC CAPACITY

I will not deny my stupidity, but the reason for this fault is the following: The LSPV was bad, and I had to put another one on. But the lines where so corroded I could not get them off, without damaging the pipes, so I had to put new nuts(?) on the pipes thereby shortening and bending them. When I wanted to install the LSPV, I attached it as I thought it should go, but the brakes felt wrong, so I traced the pipes as best I could in all the grime underneath. This was done late one evening after having battled with the brakes for more than 10 hours... I was sure the pipes where crossed along the frame, and switched the pipes, this was last weekend...
I pressure washed the frame yesterday, and traced the pipes today - three times over - and they weren't crossed!?! so I switched them back, and although I might need to bleed it once more, after having had the LSPV off, suddently my brakes are alot better!

Thanks alot for all your help and patience, this is what makes this forum great!

 

[Christian]

That both sides of the diaphragm(s) be vented to the atmosphere is crucial to the testing that the booster is not the problem. Your comment about "very firm" leads me to suspect that it wasn't vented on both sides. Without a vacuum on the one side of the diaphragm you have to compress the air trapped in that volume in order to apply the brakes.

Thanks for all your help, I hope you don't hold it against me, that I messedup the way I have... On the diesels, the check valve is in the vacuum canister, not in the booster. The second I disconnected the hose, the pedal went firm. btw. damn I love my clutch booster!

 

[60Works]

I'm glad you got it figured out, Christian. We've all made silly mistakes. I know I've made some expenive, bone head moves more often than I care to admit.

We look forward to pictures as you build up your Cruiser.

 

[Slow Left]

Hey man, it's happened to us all, as Juggernaught points out. Glad you got it all sorted out. Your persistence is commendable and it paid off since you solved the problem. And the upside to your persistence is that I also got to learn, because if you didn't keep at it, @ntsqd would have never jumped in and I would have missed out on his knowledge!

 

[dbleon]

So does the 4 runner caliper + 1" master = stock TR?

Glad you got it fixed Christian.

 

[FJ60Seth]

Good for you persevering and figuring it out. I might be the stupidest person I know.

 

[Christian]

Thanks guys! I updated the first post, so others in the future, who might have problems too, can get the most relevant information in the first post, a summary if you will, and the most important information, the combination works!

I have learned a lot more about brakes from this, and that's not a bad thing!

I will make a proper build thread, when I dig in to the full resto of this old beast, this time I intent to finish it!!!

 

[ntsqd]

So does the 4 runner caliper + 1" master = stock TR?

No idea. The eqn is there, my advice is to use a spreadsheet program and have each cell do only one step. Work out the errors against something known and then you can copy the formulas down or across to try different combos and see what the results are.

Glad you got it fixed Christian.

Me too!

 

[Christian]

Thanks!

Regarding stock feel, leverage etc. If (like a lot does) you take the T100 booster and master, and pick them from the same year and model as the calipers, IMOP you end up with T100 stock feel (on the pedal), EXCEPT the pedal leverage, and only on the front cirquit. I don't know what brakes the T100 has in the rear...
From center pedal pad to pivot pin is 407mm, 16.023622", and from center pushrod pin to pivot pin is 95mm, 3.74015748", if the numbers on the T100 pedal gives the same leverage, it should give the same feel in my book

 

[TLC Norway]

Am i correct, you did swap in a t100 master? what year?
And now, months later, are you happy with the brakes?

Good thread!!

 

[Christian]

Thanks!
I did put a new master in, but original.
The brakes are perfectly driveable and just passed the official inspection, but I'm not totally satisfied, the feel is not perfect, but there's still some old components in the system and it might be a good idea the bleed it again.
All in all I have full confidence in stock master + S13WB calipers, but the combination might be more unforgiving in regards to old worn parts, tolerances etc...
But I'm sure the T100 master + booster will work too.