......what kinda cost "we" looking at here?

 

Well, I guess I’m not the only one that had this thought. Pads are the same but not sure about the piston bore. The obvious difference is the 13” which gives you a bigger “arm, leverage or moment” for the pads to operate on. I know they might be stronger but I don’t think that is any real factor. Its hydraulic related I feel.

Never needed to rebuild my J55 calipers yet since they came overhauled already. If someone knows the 12” bore vs. 13” bore, please chime in. Info would be interesting.

It seems if something is undersize, any change in calipers or master will make a difference. But what is the design correct answer. I think the replacement master will be an interesting test for ski_dwn_it. Please share results.

I am willing to meet anyone in Orlando with a 12” system who thinks they have good brakes for a demonstration. Show me how fast U can stop and activate ABS. U can check me out to.

This thread is like the de mail man’s brakes, it just won’t stop.

 

......like i said, a larger caliper and rotor always does help but, still, the difference with leaving the factory with good brakes and brakes of the very same car in the future?...has to be a common denominator......did/could anything change like hydralic pressure entering the calipers from the lines or the pressure from the calipers against the rotors because of the rotors?...not talking rotor or caliper size here at the moment..

 

Sounds like the larger master would be an upgrade as it would have more "push to the caliper". It would seem without that upgrade larger brakes may make things worse. Im no engineer though.

 

I know, I feel like a proud papa! I started a thread that went 6 pages and over 100 posts! I am finally impotent. Me so Happy...
Roy

 

.....????....HUH?....

 

Your car's no good anymore if you use a Harbor Freight wrench

So I'm guessing you had air in the master? How come you removed the warning switch when you bench bled the master, any special reason?

RE: making another vacuum tank - You can buy a new one for about $15. Probably not even worth the effort to try and make one at that price.

All that and no "happy ending"!

 

Just removed the wire so I didnt break the switch with with the wrench.

Fwiw my front line going in was already partially rounded by someone who had worked on it at one time so I used vise grips on that one. Luckily the solid line on mine is a short piece that connects to braided and can easily be replaced.

AIr in the master....Yes.

 

Good idea on the switch, I didn't know if there was some other special reason.

I just replaced every metal & rubber hydraulic brake line on my truck. If it wasn't for vise grips, I wouldn't have gotten some of them off!

 

Sorry it took so long to get the answer but did not have a vacuum gauge at hand.

This is what I found out:
At Idle (<1000 RPM's) it had 14 inches of vacuum
2000 RPM's it was 15.5 inches
3000 to redline 15 inches.

When letting go the accelerator pedal the vacum would climb all the way to 19 - 20 inches and settle back rapidly to 14 at idle.
Do you think that I would benefit from the "home made" vacuum resovoir to compensate low vacuum, maybe.

How much vacuum is normal?

 

.....it would not do ya any good and you could not benefit from it......your vac sounds normal.....

 

Thanks

 

....pm and explanation sent....

 

I couldn’t help chiming in after looking at your data, it just seemed low to me. Just made these checks on my 94.

My idle vacuum is 19”

My 2000 RPM is 22”

And when I let the throttle go it spikes to about 25 and quickly settles back to the 18”-19” range.

My gauge is new and I had 2 at one time and they both agreed. To the best of my knowledge they are accurate even though not the most expensive unit.

Either your gauge is not accurate or you might have low vacuum. I would either get or borrow another vacuum gauge or do a test on another few cars and see what the numbers are.

I don't think an additional vacuum tank would help you. I think you might need a higher vacuum pressure if indeed your gauge is accurate.

 

I just read that a vacuum of 19 is ok.

But how could I increase this vacuum?

Maybe it would not be a bad idea to have a vacuum reservoir just in case. I guess that it would not do any harm.

I will get another gauge to redo the test. It seems low to me too.

Almost forgot to tell that I live at very high altitude, 2200 meters above sea level. I do not know if that has something to do with it. But I do know that power is down a lot. It has to do with less air density or something like that.

Maybe someone with airplane pilot background could explain this a little.

Thanks Pcolt for the comment.

 

Some real interesting questions and thought.

2200 meters is about 6000 feet. At sea level there is 30” of pressure and you loose 1 inch for every thousand feet. So at 6000 feet you can only pull 30-6 or 24 inches of pressure. This will reduce the amount of power (HP) that the engine can produce at WOT.

As for the brakes, the booster sees a difference of pressure of 30-19 = 11 at sea level. If you start out at 24 inches at 6000 feet you would have 24-19=5 inches of differential pressure that the blatter in the booster will see.

Never thought about elevation and braking before but if this is true, you have about half the boost to work with. I don’t know any simple way to increase the vacuum of the engine.

I would also think the idle vacuum might be lower due to the altitude but not sure. But if it is true, the differential pressure would go up.

Does any of this make sense or is it

 

Guys your starting to cut straws with your analysis of altitudes.

The vacuum your booster sees is generated through your motor. Basically what happens is when you are at anything other than wide open throttle, you are STARVING the motor of air. More specifically you are limiting the amount of air the motor wants to digest (suck in). Hence the reason there is a vacuum generated. At WOT you are allowing the motor to digest everything it wants (or removing the restriction) and therefore your vacuum decreases as you go to WOT or vanishes (if it doesn't than you have a restriction - like a dirty air cleaner or something physically that is limitiing the amount of air the motor can pull in.).

The above reason is why you see your vacuum gage move when you rev up the motor. When you initially hit the throttle you will see the vacuum gage descrease (as you are removing the restriction or some degree of it), but when you let off you are closing the throttle body and putting that restriction back in place. At that time the motor is spinning quicker than it was at idle - therefore you pull more of a vacuum.

That is why your brakes work so good when you are decelerating from a 60mph roll, especially if you have a manual and you are using the gears to slow you down. You are creating a TON of vacuum, and essentually trying to pull the pistons off the rods when there is that much vacuum. Hence the reason you will hear of guys throwing their cars into neutral as they cross the finish line while drag racing or shut off their cars all together and coast. (neither is advisable for other reasons).

More specific to this topic, I just placed a 300 dollar order with summit and some of the items are brake related. Just got a new aftermarket master cylinder ordered and will try it on my car very soon - probably get it installed this weekend.

My thoughts are there is design flaw or undersized mastercylinder on these cars not allowing for the proper flow or pressures to be generated. I have removed/replaced everything else - so this has to be the last piece of the puzzle. If this does not make it better I will be a little aggrivated- and look into aeromotive aftermarket brakes - but have questions if they will fit 15" wheels??

Also as a side note I rebuilt the calipers last year with no improvement

 

...i disagree (in part) with the vacuum of 15 reading...while it is not very high, it is not nesessarily low to make much of a difference..imo.

 

.....still don't think the resovoir well help...

 

I was reading that electric cars use electric vacuum pumps as the source of vacuum for their brakes. That sounds interesting.
But i was also thinking that if low vacuum was the problem, then it should be at all times, since engine startup.

But it is worth giving some consideration.