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  #1 (permalink)  
Old 02-26-2009, 04:32 PM
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another brake question

just put in a new master cyl and all new brake lines with all new calipers, I bench bled the m/c installed it and got me one of the hand held vaccum bleeders. I vaccum bled each line for about 30 min each and still no stiff pedal, checked all the fitings and no leaks, Is 30 min vaccum bleeding enough for each line? or does it need to be more?I cant even get the rear caliper pistons to move. also the m/c is under the floor so i cant gravity bleed the

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Old 02-26-2009, 04:38 PM
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Quote:
Originally Posted by alle4901

also the m/c is under the floor so i cant gravity bleed the
Do you have your 2# Residual Valves installed?
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Old 02-26-2009, 04:40 PM
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Did you install the calipers on the proper sides. The bleeders need to be at the top. If they are at the bottom you will never get the air out. I have seen this mistake many times
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Old 02-26-2009, 05:09 PM
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yes , i do have #2 bleeders, but i believe that if i didnt, it shouldnt affect bleeding them it will just affect how much pressure the pistons apply pressure for stopping so the wont lock up as easy, And the bleeding valve is almost at the top , I guess you can say they are at the 2 o'clock position
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Old 02-26-2009, 08:12 PM
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I've never had very good luck with a vacuum bleeder, it may be operator error, I just do it the old fashion way and yell for the wife to help.
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Old 02-26-2009, 11:08 PM
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Or a better bet, call a friend. I replaced the wheel cylinders in my daily driver, and called the wife to help me bleed em. Couldn't figure out why I wasn't getting any pressure when she stepped on the pedal. Kept trying for about a 1/2 hour, and the she say's dinners ready. Over dinner I racked my brain. Went back out and looked, and thought. Lot's of fluid in the master, nothing coming out of the w.c. Dinggg! An idea! Called the wife out, climbed back under the car, asked her to push down on the pedal, climbed back out, looked at what she was doing. She was pushing the clutch pedal down!!!! And she's not even blonde! She's a great wife, but mechanically and technically challenged.
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Old 02-27-2009, 12:16 AM
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Quote:
Originally Posted by alle4901

yes , i do have #2 bleeders, but i believe that if i didnt, it shouldnt affect bleeding them it will just affect how much pressure the pistons apply pressure for stopping so the wont lock up as easy, And the bleeding valve is almost at the top , I guess you can say they are at the 2 o'clock position
It would effect bleeding as the fluid would keep returning to the MC as a result of gravity. That is their design.

The bleeders have to be pointing @ 12:00. Loosen and rotate to bleed if neccesary.
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Old 02-27-2009, 08:17 AM
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Are you starting the bleed process first at the furthest caliper from the MC?

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Old 02-27-2009, 09:43 AM
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My reply is incorrect. Ignore...

The most difficult part of vacuum bleeding is that the bleeders are NPT. As you turn them out, air will be drawn around the threads.

Last edited by KULTULZ; 02-27-2009 at 02:09 PM. Reason: Not Thinking Before Answering
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Old 02-27-2009, 10:47 AM
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Quote:
Originally Posted by KULTULZ
The most difficult part of vacuum bleeding is that the bleeders are NPT. As you turn them out, air will be drawn around the threads.
I don't know what bleeders you're using, but every one I've ever used is a straight thread with a tapered surface on the bottom for sealing. Having said that, you are correct that air will still leak in around the threads. I use a dab of grease around the threads to seal them when using a vacuum bleeder.
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Old 02-27-2009, 01:40 PM
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brakes

Is it a dual portion master cyl? Is it mounted level? If it is not mounted level the brakes won't bleed the air from the master cyl. Jack the car up on one end or the other to level the MC and then the air trapped will bleed properly.

GM's are famous for this problem when the MC is not mounted level. The air bubbles simply go back -and-forth but never out.
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Old 02-27-2009, 02:11 PM
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Quote:
Originally Posted by joe_padavano

I don't know what bleeders you're using, but every one I've ever used is a straight thread with a tapered surface on the bottom for sealing.

Having said that, you are correct that air will still leak in around the threads. I use a dab of grease around the threads to seal them when using a vacuum bleeder.
I am not sure either...

Thanx for the tech tip...
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Old 02-27-2009, 03:39 PM
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The Meaning of Getting Old

Quote:
Originally Posted by by KULTULZ Originally Posted


The most difficult part of vacuum bleeding is that the bleeders are NPT *. As you turn them out, air will be drawn around the threads.
* THAT'S NATIONAL PIPE THREAD-NOT TAPERED

Quote:
Originally Posted by joe_padavano

I don't know what bleeders you're using, but every one I've ever used is a straight thread with a tapered surface on the bottom for sealing. Having said that, you are correct that air will still leak in around the threads. I use a dab of grease around the threads to seal them when using a vacuum bleeder.
I've had time to consider my origional statement, and it is correct (I thought I was wrong once, but I was mistaken).

NATIONAL PIPE THREAD comes in two flavors, tapered and straight. What you are describing is machine thread, which if used would not let air be drawn into the actual fitting.

Bleeder screws are NPT straight. And they are machined to seal @ the seat. They could not use a tapered thread as it might require overtightening on the seat to get the correct torque value to keep the screw from backing out.

I also got to thinking that along with the pain in the posterior of removing the screws to lube them (can one use a grease gun here? ), it may lead to contamination of the fluid, that being alike using teflon tape on the threads.

It is not nice to try and trick old people young man. You tricked me, although momentarily extended...
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Old 02-27-2009, 03:41 PM
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I Wish He Would Make-Up His Mind!

Quote:
Originally Posted by KULTULZ

My reply is incorrect. Ignore...

The most difficult part of vacuum bleeding is that the bleeders are NPT. As you turn them out, air will be drawn around the threads.
My origional reply is correct. Please read following explanation.
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Old 02-27-2009, 06:57 PM
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Quote:
Originally Posted by KULTULZ
My origional reply is correct. Please read following explanation.
Sorry, but I must disagree with your original reply and all subsequent ones in this thread. NPT stands for National Pipe Thread and it is most certainly tapered. The thread form is defined per ANSI/ASME B 1.20.1. Here is a table that lists the dimensions:

http://www.unifiedalloys.com/product...pe_threads.pdf

NPT always requires a sealant to work. There is also a dryseal pipe thread. This is still tapered, and is based on the NPT dimensions, but the thread form is modified to allow sealing without a sealant. They are defined per ANSI/ASME B 1.20.3.

Quote:
Originally Posted by ANSI/ASME B 1.20.3

Dryseal pipe threads are based on the USA (American) pipe thread, however, they differ from the USA (American) pipe thread in that they are designed to seal pressure-tight joints without the necessity of using sealing compounds. To accomplish this some modification of thread form and greater accuracy in manufacture is required. The roots of both the external and internal threads are truncated slightly more than the crests, i.e. roots have wider flats than crest, so that metal-to-metal contact occurs at the crests and roots coincident with or prior to flank contact, see Figure 1. Thus as the threads are assembled by wrenching, the roots of the threads crush the sharper crests of the mating threads. This sealing action at both the major and minor diameters tends to prevent spiral leakage and makes the joints pressure tight without the necessity of using sealing compounds, provided that the mating threads are in accordance with standard specifications and tolerances and are not damaged by galling in assembly. The control of crest and root truncation is simplified by the use of properly designed threading tools. Also, it is desirable that both external and internal threads have full thread height for the L1 length. However, where not functionally objectionable, the use of a compatible lubricant or sealant may be used to minimize the possibility of galling. This is desirable in assembling Dryseal Pipe Threads in refrigeration and other systems to effect a pressure tight seal.
Neither of these threads are used on normal brake bleeder screws. Here is a photo of a typical brake bleeder screw. Note the straight threads. Note the tapered seat on the left end.

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