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> Rear Brake bleeding question
Frankvw
post May 21 2020, 10:09 AM
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Hi all, I replaced the calipers and pads and flex hoses in the rear. (1973 1,7)
Old brake fluid from reservoir removed with siringe and filled with new fluid.
I did set the clearance on the inner and outer on both sides.
Then I did bleed the brakes and checked the clearance again (was still OK)
Now the proportioning valve part....do I need someone to push the pedal to the floor, keep pedal at floor and then I bleed again while pedal is down? Or does it work another way ?
Or is it not needed after what I already did ?
Thanks for your reply !
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davep
post May 21 2020, 10:49 AM
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Do you have a proper solid pedal feel? If you circle the block and stop at each corner, does it feel normal? The proportioning valve should not really need any special consideration.
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Frankvw
post May 21 2020, 10:54 AM
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well...thanks for the reply ! But it is still on jackstands, so no testdrive possible......that is why I asked if I have to do an extra step.
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IronHillRestorations
post May 21 2020, 12:46 PM
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Here's how I bleed a 914 brake system, from my post back in Mar 05.

Remember the "Search" function is your friend!

Get a spare cap for the brake fluid reservoir.
Get a tire valve & stem.
Drill a hole in the center of the reservoir cap, the same size as the hole in a wheel (or measure the narrow part of the tire valve).
Pull the valve stem through the hole.
Remove the plastic screen in the reservoir.
Fill the brake reservoir completely, not to the fill line, all the way full to the bottom of the tube that holds the plastic screen.
Put on your new modified pressure bleeder cap.
Drain your air tank to 10 psi, for cheaper compressors setting the regulator at 10 psi may not work. If you put too much pressure in the system, you'll blow off the blue lines that connect the supply lines to the reservoir, or worse.
Take a clip on air chuck and clip it on your new pressure bleeder cap.
Bleed the brakes, starting at the furthest bleeder from the master cyl, and finish at the bleeder nearest the master cyl.
Bleeding sequence (RR-LR-RF-LF) EDITED FROM ORIGINAL POST
Pump the pedal hard about ten times and repeat the procedure.
Do not get brake fluid on painted surfaces it will ruin them.
If the pressure bleeder cap retains pressure, bleed it down before taking it off the reservoir.
This works very well, and makes it a one person job.
Replace brake fluid every two years.
Properly discard used brake fluid.

PMB has a good method as well: PMB Gravity Bleeding Method
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iankarr
post May 21 2020, 01:07 PM
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(IMG:style_emoticons/default/agree.gif) The pressure system is great. I use the Motive, but Iron Hill's setup is way less spendy (IMG:style_emoticons/default/wink.gif). Here's a video I made on the process...

https://www.youtube.com/watch?v=ymHHD6uKhfc

The fluid has to go through the proportioning valve to get to the calipers, so assuming the system hasn't run dry, you shouldn't need to do anything special. If it has run dry, you may need to tap on it with a rubber mallet to dislodge any air bubbles.

I replaced my calipers a few months back and it was a PITA to get them fully bled. Here are a few tips that seem to accelerate the process. You may not need all or any of them. YMMV.

– Open the lower and upper bleed screws on the caliper(s). Take some tubing and a fat syringe and inject some brake fluid in the lower one and let it overflow out of the upper one.

– With the pressure bleeder at 5-7psi and fluid coming out of the calipers, have someone ALSO step on the pedal, firmly and slowly. don't go all the way to the floor, though! Keep a close eye on fluid level and pressure on the bleeder.

– After you have a decently firm pedal, drive the car over some rough road or train tracks for a few minutes, then come back and bleed again.

If you also installed pads and rotors, don't forget to "bed" them per the PMB process.


Be safe! Brakes command respect...
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914Toy
post May 21 2020, 01:18 PM
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I use a similar system as the post above, but use air from one of my tires, between 20 and 25 psi., and mini garden hose plastic tube connecting tire air to the brake fluid reservoir via the overflow tube, with the filler cap on tight. Here is a pic of my contraption! One word of caution, keep an eye on the break fluid reservoir, and be sure the fluid level does not get too close to the bottom or you will be pushing air into the system and will have to start again!

Attached Image
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twistedstang
post May 21 2020, 01:54 PM
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Pressure bleed with a homemade setup or a Gunson eezibleed and never look back.
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Frankvw
post May 21 2020, 02:32 PM
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thanks all for the replies. System did not run dry, so I guess I will forget the proportioning valve for now.
I do not have a pressure bleeder and did not use a compressorr, I used a handpump style vacuumpump to suck through the fluid on the caliperside, keeping an eye on reservoir level (top taken off), I filled it up when needed (two times) I bought this pump for this purpose but I did not really like it to be honest. I do not have a overflow tube on my reservoir, I have a 73, they do not have them . I did d the sequesnce as stated by you guys, RR first, LR after that. Front brakes are not yet done, I started with new rear brakes and work my way through the car.
So.....I guess some more bleeding to do ! :-)
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twistedstang
post May 21 2020, 03:00 PM
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I'm probably wrong but I thought I read somewhere on here that suction doesnt work well on the back brakes because of the pressure valve....any truth to this?
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Frankvw
post May 22 2020, 01:22 AM
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"I'm probably wrong but I thought I read somewhere on here that suction doesnt work well on the back brakes because of the pressure valve....any truth to this?"

Well...because of that valve (proportioning) I did ask if any next/extra step was needed.
I was not sure since it is an 'odd' device compared to the setup in my Volkswagens and although I did search for info, I was not sure if I had to take extra steps.


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IronHillRestorations
post May 22 2020, 07:57 AM
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One problem with vacuum bleeding is you pull air around the threads on the bleeders. Putting air over the fluid pushes it through the system and is very effective at purging the proportioning valve as well.

I've never tried the gravity method, it makes perfect sense though.
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