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914World.com _ 914World Garage _ Front Brake Issue
Posted by: PDXBob Mar 4 2023, 07:14 PM
Hi All,
I just finished putting on rebuilt rear brake calipers done by PMB. Also, new braided steel brake lines and set of new Textar pads on all 4 wheels (1975 914). I took it out to do the “bedding” break-in process and I noticed it was pulling to the right.
So, (after doing cool down slow driving)when I got home I checked temperature of rotors. Both back rotors were about 125 degrees. However front right was about 240 degrees. BUT front left was only about 85 degrees. To a novice like me seems like front left is not working.
Any suggestions on diagnostic procedures or what to check out.
Thanks
PDXBob
Posted by: bkrantz Mar 4 2023, 09:20 PM
I would jack up the front and have an assistant gradually depress the brake pedal while you spin both front wheels. See if the braking action is different from L to R.
Also more bleeding on the L?
Posted by: ndfrigi Mar 4 2023, 09:22 PM
When you bled the left front, does it push brake fluid?
You can also try to jack the front and someone will turn the wheel and one person inside to push the brake. To check if left wheel will brake and compare to right side.
Posted by: PDXBob Mar 4 2023, 11:15 PM
Good suggestions about bleeding again and spinning each front wheel.
Thx
Posted by: Krieger Mar 4 2023, 11:36 PM
Recheck the venting clearance again on your rear calipers. Follow the proper proceedure and set at .004"
Posted by: PatMc Mar 6 2023, 07:50 AM
Make sure you're bleeding from the uppermost bleed screw....bleeding from the lower screw will get you nowhere.
Once you're certain all the air is out, have someone run the pedal and make sure the caliper is actually clamping down on the front rotor. Very possible the pistons are locked up in the caliper.
Posted by: Eric_Shea Mar 6 2023, 09:15 AM
Hey Bob,
Are the soft lines new? If not then I would recommend checking those.
https://pmbperformance.com/pages/frequently-asked-questions-faqs
About mid-way down on our FAQ page you'll see that old soft lines lines can swell from the inside. This often retains pressure on your front right (in your case). It will then lock up and pull to the right when you apply nominal pressure. It often drags as well then causing the heating issue you're having.
My rule is, if you don't know when your soft lines were replaced... replace them. Otherwise, every 10 years.
Hope that helps... give us a call if you have any other issues.
Posted by: PDXBob Mar 7 2023, 04:40 PM
Hey Bob,
Are the soft lines new? If not then I would recommend checking those.
https://pmbperformance.com/pages/frequently-asked-questions-faqs
About mid-way down on our FAQ page you'll see that old soft lines lines can swell from the inside. This often retains pressure on your front right (in your case). It will then lock up and pull to the right when you apply nominal pressure. It often drags as well then causing the heating issue you're having.
My rule is, if you don't know when your soft lines were replaced... replace them. Otherwise, every 10 years.
Hope that helps... give us a call if you have any other issues.
Eric, when I had you rebuild the rear calipers I also bought a set of your braided steel brake lines. These were well worth the price, just in piece of mind compared to 40+ year old rubber lines.
No time to work on it until Saturday, but can’t wait to get brakes sorted. Also, my brother who’s a mechanic chastised me for not getting rotors hot enough during “bedding-in” process. It’s tough to drive 60 MPH and slam on the brakes in Oregon when the roads are wet 364 days a year!!!
Bob
Posted by: technicalninja Mar 8 2023, 12:34 AM
Rear brakes are damn hard to get hot enough to "bed" in using street driving as the front do most of the work anyways.
Having the fronts operate as they are on your car would stop me from trying to bed anything.
Fix the fronts first and then worry about bedding pads.
All the suggestions have been good.
I have another...
Do the proper bleeding, make sure both sides squirt equal amounts out of the top bleeders. Re-check the rear pad adjustment, this does need to be correct.
Put both front tires up in the air and spin test them. Both spin free, have an assistant jam on the brakes and release. Both spin free- you have something way weird going on.
One stays locked up?
Break bleeder free.
Squirt like a bitch? You have a restriction in the system.
Old lines are a common culprit but yours are new.
If it's holding pressure against the caliper, you can slowly move up the system releasing each fitting until you find one that's not under pressure. Your restriction will be between the last pressurized fitting and the un-pressurized fitting.
No squirt from locked caliper? Send your front calipers to PMB for the same treatment you just had done to the rears...
Posted by: Eric_Shea Mar 8 2023, 01:33 PM
Hey Bob,
Are the soft lines new? If not then I would recommend checking those.
https://pmbperformance.com/pages/frequently-asked-questions-faqs
About mid-way down on our FAQ page you'll see that old soft lines lines can swell from the inside. This often retains pressure on your front right (in your case). It will then lock up and pull to the right when you apply nominal pressure. It often drags as well then causing the heating issue you're having.
My rule is, if you don't know when your soft lines were replaced... replace them. Otherwise, every 10 years.
Hope that helps... give us a call if you have any other issues.
Eric, when I had you rebuild the rear calipers I also bought a set of your braided steel brake lines. These were well worth the price, just in piece of mind compared to 40+ year old rubber lines.
No time to work on it until Saturday, but can’t wait to get brakes sorted. Also, my brother who’s a mechanic chastised me for not getting rotors hot enough during “bedding-in” process. It’s tough to drive 60 MPH and slam on the brakes in Oregon when the roads are wet 364 days a year!!!
Bob
Let me know if you have any caliper issues. You have a 10-Year Unconditional warranty.
Posted by: Cairo94507 Mar 8 2023, 05:11 PM
@http://www.914world.com/bbs2/index.php?showuser=1110 - Holly molly- 10 year unconditional warranty!!!!
I am telling you guys, those that do not already know, if you need brake work, Eric (PMB Performance) is your man. Additionally, almost anything Porsche related, and Eric is still your man. They are turning out beautiful cars.
Posted by: Eric_Shea Mar 8 2023, 06:57 PM
Thank you Amigo!
Posted by: PDXBob Mar 22 2023, 03:28 PM
So, after performing several of the tests listed above I came to the conclusion that something was blocking one of the right front brake pistons. Making it chronically drag. I had a conversation with one of the people at PMB (which had recently rebuilt my back calipers) and they had a number of good suggestions. I decided to have PMB rebuild my front calipers as well, so shipped to SLC on Monday.
It will be nice to have 4 rebuilt calipers, new steel brake lines and new pads- Now just have to bleed (again). Thanks to all for your advice!
PDXBob
Posted by: 930cabman Mar 23 2023, 05:53 AM
So, after performing several of the tests listed above I came to the conclusion that something was blocking one of the right front brake pistons. Making it chronically drag. I had a conversation with one of the people at PMB (which had recently rebuilt my back calipers) and they had a number of good suggestions. I decided to have PMB rebuild my front calipers as well, so shipped to SLC on Monday.
It will be nice to have 4 rebuilt calipers, new steel brake lines and new pads- Now just have to bleed (again). Thanks to all for your advice!
PDXBob
Having great brakes is near equal to having great tires. Glad you are on the road to safe driving
Posted by: PDXBob Apr 4 2023, 09:36 PM
So, an update:
Had my front calipers just rebuilt by PMB. This solved my problem with pulling to the right. However I still don’t have good brakes, i.e., pedal goes nearly to floor before the car stops. Can’t come close to locking up wheels.
So far, I’ve had front and back calipers rebuilt by PMB. Also, replaced rubber brake lines with PMB braided steel. Bought 4 new Textar pads. Adjusted (vented) the back brakes to within specs. I have a Motive Pressure Bleeder and have bleed brakes using it at least 3 times. Just today did the 2-person brake bleed procedure on back brakes. Will do 2-person brake bleed of front’s tomorrow. Master cylinder only about 3 years old. I’ve pumped about 2 quarts of fluid through system and each time get pure, clean fluid and virtually no air bubbles. I’m Running out of ideas on what else to do.
Any thoughts or wild-a$$ guesses greatly appreciated.
PDXBob (1975 914)
Posted by: technicalninja Apr 4 2023, 09:49 PM
The rear adjustment can be difficult to gauge.
Just for testing adjust the rears until you have no clearance and see if that helps.
Don't drive the car like this but by taking all of the adjustment out you eliminate one variable.
If this works, then back the adjustment off just a bit. .004 is maybe 10-15 degrees of swing from contact.
I recently rebuilt a MSM Miata rear caliper set. It has one adjuster exactly like the 914 on the inside. Set it up as Mazda suggested and had low pedal. Adjusted the clearance more by "feel" than with gauges the second time. Worked fine after a much tighter adjustment than the service manual suggested.
Posted by: rjames Apr 5 2023, 05:00 AM
So, an update:
Had my front calipers just rebuilt by PMB. This solved my problem with pulling to the right. However I still don’t have good brakes, i.e., pedal goes nearly to floor before the car stops. Can’t come close to locking up wheels.
So far, I’ve had front and back calipers rebuilt by PMB. Also, replaced rubber brake lines with PMB braided steel. Bought 4 new Textar pads. Adjusted (vented) the back brakes to within specs. I have a Motive Pressure Bleeder and have bleed brakes using it at least 3 times. Just today did the 2-person brake bleed procedure on back brakes. Will do 2-person brake bleed of front’s tomorrow. Master cylinder only about 3 years old. I’ve pumped about 2 quarts of fluid through system and each time get pure, clean fluid and virtually no air bubbles. I’m Running out of ideas on what else to do.
Any thoughts or wild-a$$ guesses greatly appreciated.
PDXBob (1975 914)
Virtually no air bubbles isn't good enough. You need to bleed them until all of the air is out of the system. Try the long hose method (bonus, only 1 person is needed). I couldn't get mine properly bled until I switch to speed bleeders. Good luck!
Posted by: Olympic 914 Apr 5 2023, 07:02 AM
Just ran through this myself.
Adjusted rear brakes just until they let the disc turn free. no feeler gauges. You will gain air gap as the brake pads wear in anyways.
Also used Motive pressure bleeder.
The proportioning valve is at a high point in the system. Very hard to get a wrench on the top of the banjo bolt. Try pumping up the motive to 15 lbs and loosen each of the lines from the banjo union to each side, one at a time. Then follow up with another round of bleeding the rear calipers.
I would crack the bleeder on the rear caliper then reach inside the car and press the brake pedal slowwly 3-4 times, the pressure from the Motive should keep fluid moving out.
Posted by: Superhawk996 Apr 5 2023, 07:31 AM
Raise the rear of the car to help move air through the proportioning valve and up to the rear calipers.
Posted by: brubou Apr 5 2023, 10:03 AM
I would start at the beginning of the system. Throw some barb fittings in the outlets of the master cylinder, run tubes from those over the fender into the brake reservoir. Then pump the pedal until not even a rumor of bubbles is present. Sitting in the driver seat gives you a great view. These master cylinders looks small but I swear mine had an oil barrel amount of air trapped in it. Once there were no more bubbles I bled the rest of the system as normal and now I can lock my brakes if I'm not too careful.
Posted by: PDXBob Apr 5 2023, 02:08 PM
So, an update:
Had my front calipers just rebuilt by PMB. This solved my problem with pulling to the right. However I still don’t have good brakes, i.e., pedal goes nearly to floor before the car stops. Can’t come close to locking up wheels.
So far, I’ve had front and back calipers rebuilt by PMB. Also, replaced rubber brake lines with PMB braided steel. Bought 4 new Textar pads. Adjusted (vented) the back brakes to within specs. I have a Motive Pressure Bleeder and have bleed brakes using it at least 3 times. Just today did the 2-person brake bleed procedure on back brakes. Will do 2-person brake bleed of front’s tomorrow. Master cylinder only about 3 years old. I’ve pumped about 2 quarts of fluid through system and each time get pure, clean fluid and virtually no air bubbles. I’m Running out of ideas on what else to do.
Any thoughts or wild-a$$ guesses greatly appreciated.
PDXBob (1975 914)
Virtually no air bubbles isn't good enough. You need to bleed them until all of the air is out of the system. Try the long hose method (bonus, only 1 person is needed). I couldn't get mine properly bled until I switch to speed bleeders. Good luck!
I’m not familiar with the “long hose method”. Can you describe.
Thx
(No Brakes) Bob
Posted by: rhodyguy Apr 5 2023, 02:27 PM
Long hose=speed bleeders in the top caliper bleeder holes on all 4 corners, enough clear hose/tubing to fit the bleeders and stretch from the R rear caliper to the catch jar that will be on the floor next to the drivers door. RR, LR, RF, LF. Buy some extra fluid as this method really flushes the system and the tubing holds a bit of BF. Take care to keep the reservoir full. You don’t need anyone to pump the pedal and HOLD! relax.
Posted by: PDXBob Apr 5 2023, 04:01 PM
Long hose=speed bleeders in the top caliper bleeder holes on all 4 corners, enough clear hose/tubing to fit the bleeders and stretch from the R rear caliper to the catch jar that will be on the floor next to the drivers door. RR, LR, RF, LF. Buy some extra fluid as this method really flushes the system and the tubing holds a bit of BF. Take care to keep the reservoir full. You don’t need anyone to pump the pedal and HOLD! relax.
So, if I understand this correctly, after I have opened a speed bleeder (say RR) I just sit in drivers seat and pump out the fluid (and any air). Speed bleeders keep air from sucking back into caliper. Correct?
Posted by: brubou Apr 5 2023, 04:14 PM
Correct, there is a one way valve mechanism in them, probably using a spring and either a ball or something to block reverse flow.
Posted by: rjames Apr 5 2023, 04:23 PM
When I had my brakes refurbished they came with refurbished bleeders. I suspect they had pitting that was hard to see. One of them leaked from the threads until in frustration I tightened way past spec and it snapped off. Luckily it was a lower bleeder and it stopped leaking after it snapped.
I spent days trying to get all of the air out of the system and couldn't do it. But I after swapping over to speed bleeders I was done in less than 30 minutes.
YMMV
Posted by: rhodyguy Apr 5 2023, 04:25 PM
You will see the bubbles traveling thru the tube with the door open. I used a large canning, glass quart size, jar for the catch. Going thru twice worked best for me. The 2nd time it goes pretty fast. I think they spare the master cyl some abuse too. You’re not under the car forever opening and closing valves. Then I put a lid on the jar and take the spent fluid to recycle.
Posted by: 76-914 Apr 5 2023, 05:51 PM
I run the hose all the way to the reservoir. That way I don't need to keep refilling the reservoir while I'm pumping. You'll need to fashion some wire to hold the end of the hose over the neck of the reservoir. It will take 100+ pumps on the brake pedal at each caliper. Start with the right rear. then left rear, then right front, finally left front. If re-using the old MC don't push the pedal past the point it is used to stopping at. An easy way to do this is to cut a 3" long piece of 2" PVC then cut it length wise on one side, pull it apart until it will slip over the brake pedal. This will keep you from pumping the pedal too far. If you installed a new MC bleed it before you do any thing.
Posted by: rhodyguy Apr 5 2023, 05:57 PM
Return to reservoir….I’m going to get new longer tubing. The pedal block is a good trick too. THX.
Posted by: emerygt350 Apr 5 2023, 06:31 PM
Interesting. How do you seal the line at the bleeder?
Posted by: rhodyguy Apr 5 2023, 08:11 PM
You get tubing that’s a snug fit. The fluid is not under pressure. Just flowing. With the jar on the floor gravity does most of the work. I put the jar in a small plastic tub. No concrete mess to wipe down.
Posted by: emerygt350 Apr 6 2023, 06:09 AM
I figured if you are running it all the way back it's gonna have a little more pressure. Wonder about leaks at the bleeder.
Posted by: rjames Apr 6 2023, 12:51 PM
I figured if you are running it all the way back it's gonna have a little more pressure. Wonder about leaks at the bleeder.
No leaks if your tubing fits snuggly over the bleeder and your bleeders are in good shape. Mine allowed air to go back in, which is why I switched to the speed bleeders.
After you've removed all of the old fluid, have other end of the tube go to the reservoir so you're not wasting fluid or constantly having to refill the reservoir.
Posted by: emerygt350 Apr 6 2023, 04:21 PM
The rear adjustment can be difficult to gauge.
Just for testing adjust the rears until you have no clearance and see if that helps.
Don't drive the car like this but by taking all of the adjustment out you eliminate one variable.
If this works, then back the adjustment off just a bit. .004 is maybe 10-15 degrees of swing from contact.
I recently rebuilt a MSM Miata rear caliper set. It has one adjuster exactly like the 914 on the inside. Set it up as Mazda suggested and had low pedal. Adjusted the clearance more by "feel" than with gauges the second time. Worked fine after a much tighter adjustment than the service manual suggested.
I just went back and tried this (PMB calipers just installed on the back) and I have to say I am pretty impressed. My brakes (after I installed the new rears) were ok to start with but this gave them quite a nudge. Much more confident in the stop. I could lock them up before but the pedal was getting pretty low. Now it is not even going down half way before we are into a "scare the neighbors" stop.
I do notice a little variability from stop to stop. I always give it a little double tap so it isn't that the brakes are pumped up sometimes and sometimes not. I suspect I still have some air in the fronts that needs to be worked out.
Posted by: PDXBob Apr 6 2023, 06:17 PM
I’m going to try the long hose bleeding method suggested by rJames and others. Just ordered speed bleeders from Pelican. I think I’ll route the hose from bleeder valve to reservoir and get some kind of mesh to use as filter; however the fluid looks super clean since I’ve been working on brakes for some time and pumped a lot of new fluid through system.
Posted by: emerygt350 Apr 6 2023, 07:08 PM
I am not there yet. I have been bleeding crappy old brakes for 35 years now and I just don't buy you have to go to that crazy extent if you have a friend. The only thing that makes me question that is the weird valve on the rear system after the firewall. That may require something extra but so far my rear brakes (after setting the venting as metioned) are great. For the fronts, a good old pump, pump, pump, hold, bleed should be enough (if you have a friend).
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