Chasing a firm brake pedal, What next? Options

[robkammer]

Teeners: It's been over two years since our 74 BB arrived. A Caliper blew out as it came off the transporter in 12 degree temps. Really no surprise as the PPI pointed out a leaky caliper. So I did what I thought would be appropriate for this little beauty, I sent all of the hard bits out, calipers and regulator, to a widely recognized firm for 'restoration'. Put in a new EZ master from 914. And all should have been fine. But, even now, after 1800 miles, a second set of calipers from the 'restorer', a new ATE MC from the restorer. ( I threw out the EZ MC). I still have squishy pedal.
I do not suspect the pedal box area as the car has absolutely no rust.
I just rebuilt the 'restored' front calipers with new square cuts from AA, took out the springy metal pieces that are supposed to keep the pistons from rotating, and the pedal is much better. I have about 50 miles on this but after bleeding it again the bleeders were leaking and I put it back on the lift. ( I was told: maybe: we left the calipers in the acid too long)
So: Now that the pedal seems like I might be on my way to GOOD braking, I can hear the pressure regulator knocking when I press the pedal, at a standstill, in the shop. Is this normal and to be expected? Note: During attempts to bed the brakes and get them working, I was only ever to lock up the rears, and it was really difficult to do. ( difficult may not be accurate, violent might be more appropriate)
The newly rebuilt calipers seem fine, just like the calipers in my 911's that I rebuilt.
As for bleeding, I've done it every way known to man. And some new ones too. Just picked up a 6th quart of Super 4. $26.00!!! A fifth of Weller was only $23!.
I'm really frustrated with this little car. Any input will be appreciated.

I'm thinking of putting in a Tee in place of the regulator, just for testing. If anyone has a Tee that they would be willing to let me borrow, I would be willing pick up all of the shipping just so I don't have to mess with the fab work.
Thanks,

[yeahmag]

Might try cracking the brake line at the pressure regulator for the rear brakes. I haven't had the problem myself, but I've heard of folks fighting with air trapped in there. As part of my bleeding routine I use a Motiv pressure bleeder (dry as to not contaminate anything) and a nylon faced mallet at each corner while bleeding. If it's at all stubborn I'll add a few pumps of the brake pedal to get any air trapped in the MC moving along.

[VegasRacer]

A brace on the Master Cylinder is helpful in providing a firm pedal.

[peteinjp]

I can only lock up the fronts on my car. Generally speaking the fronts should lock before the rear to keep the front- in front. Imagine needing to brake hard in a corner for some unforeseen reason and the rears lock...

If the rears are locking I don't think a T will be making any difference as the regulator is supposed to limit pressure to the rear specifically to keep them from locking first. I suppose it wouldn't hurt as a temporary problem solving effort and not a bad idea to pull the regulator apart and check its condition.

Sounds to me as if either your front circuit is not doing its job or the regulator is not working correctly.

[bkrantz]

A brace on the Master Cylinder is helpful in providing a firm pedal.

It sure made a difference for me.

"I do not suspect the pedal box area as the car has absolutely no rust."

Perhaps true, but never assume. You need to watch the MC while somebody strong pushes on the pedal really hard.

[Krieger]

Make sure you adjust the venting clearance properly. I had a problem getting the air out of my back calipers after I replaced them. I left the ass end of the car on stands for a day. A few times over that time frame I took the plastic handle of my screwdriver and tapped on the solid lines and the pressure regulator. Then I bled the rears. That solved the mushyness I had. Good luck

[Arno914]

Just to be sure: Did you replace all 4 brake lines?
I fought with "stuck" pistons for a while only to find out that the old lines were totally clogged, thus preventing the brake pistons to move as they should.

[robkammer]

All: Thanks for the replies. I did bleed the top of the regulator, all the rubber lines are new as well. Today I'll pull the cover off and find someone to push the pedal so I can see if the MC moves at all. If anyone has a pic of a MC brace it would be helpful.
Cheers!

[ChrisFoley]

Tangerine Racing Master Cylinder Brace

[jhynesrockmtn]

As explained in my RR thread, we got stuck in Bend OR and were put back on the road by a mechanic who runs the "classic" shop at the Porsche dealership. Not a certified Porsche Classic Center but an old school mechanic who only works on the older cars. Anyway, he saw my new PMB restored calipers in my BB and after backing my car up to get it out of the shop, commented on my somewhat squishy pedal. I installed new flex lines and the calipers, but left my regulator and MC in the car untouched, as the brakes were fine when I first got the car.

He said he uses PMB for all of his rebuilds but when doing an initial bleed, does it with the pads removed, and something thinner like a screwdriver in place to keep the pistons from moving too far, but further than they could with the pads installed. He swears this has been the key to getting a firm pedal with restored calipers.

[rfinegan]

I may have missed this ...but did you set the air gap on the rear pads?
This will give you a low pedal, more travel and a softer feel

[Mikey914]

As you can see these are notorious for having issues with bleeding. Sounds like you are driving it, so normally they (air bubbles) will work their way through the system. If you are using a 19mm MC the pedal should be firm. Flex would be the only other variable. Perhaps you can look underneath while someone pumps the brakes. Then you would know for sure.

-Mark

[Superhawk996]

I can hear the pressure regulator knocking when I press the pedal, at a standstill, in the shop. Is this normal and to be expected?

Yes - normal to hear the piston in the regulator move with the engine off and in a quiet environment.

Do not replace with a T - you’ll just set yourself back and introduce more air into the system again. The regulator has absolutely zero proportioning effect upon the front brakes. It only reduces the rear pressure in proportion to the fronts.

You do not want to lock the rear brakes before the front - ever! Focus on getting the air out of the front brakes.

Stop using $26/quart brake fluid while you’re working on getting air out of the system. Once you have a good pedal feel you can bleed out - replace with expensive fluid if that’s what you desire.

Don’t underestimate pedal box flex. A reinforcement bracket is not necessary to be able to lock the front brakes when bled properly but these cars all had flex that degraded pedal feel when they were young and none have improved with age, rust, and metal fatigue . Tangerine makes a nice bracket to reduce the flex.

Leaking bleeders isn’t right. If they aren’t tight you’re letting air into the system as well as losing fluid. If they are tightened properly and still leaking, I’d be returning them to whoever rebuilt them - not sure what to make of the acid comment (IMG:style_emoticons/default/unsure.gif)

[rudedude]

I've used old worn out thin pads when initially bleeding new calipers to help with the soft feeling. I think it helps somehow with the seating of the new piston seal and then put new pads in and haven't had any issues with pedal feel. I also have had issues with any but ate master cylinders but I see you have replaced the non ate. By the way I'd be glad to take the problem off your hands, looks to be a beautiful car.

[robkammer]

All great input. Stopped the leak and took it for a drive again yesterday. Pedal is getting much better. I’m going to pull the pads the next bleeding session. The MC does move a bit with really hard pedal pressure, but I shouldn’t have to be on the pedal that hard once the brakes are proper.
Pulled temps after the run yesterday, fronts in the higher 300’s and rears higher 200’s. Drove it pretty hard and I’m starting to get some lock. The new seals seemed to do the trick! Had to cut the drive short when I realized my fuel light was on!
Thanks again all!

[iankarr]

You've gotten great advice in this thread. Also important to keep in mind that it's normal with these cars/calipers for it to be a bit of work to get firm pedal when the system is fresh. There are literally dozens, if not hundreds of threads about trying to get a hard pedal. Just to summarize, in order (with a few things that have worked for me)...

– "Bench Bleed" master cylinder first (see video in my signature for how)
– Replace rubber lines
– Ensure venting clearance is correct
– Replace bleeders with speed bleeders
– Use a motive pressure system AND stomp on the pedal (this is where the speed bleeders really help)
– Repeat bleeding 2-3X
– If pedal is too soft to drive, crack the fittings on the regulator and pump pedal (closing after each pump) to get air bubbles out. Can also tap with a hammer.
– If pedal is STILL too soft, try using a syringe to shoot fluid through the bottom bleeder, with the upper one open
– Take the car for a bumpy drive
– Bleed again
– Bed the pads
– Pedal will not be rock hard for about 100 miles or so...until the seals loosen up.

As Superhawk mentioned, you definitely want to keep that regulator in service. Otherwise you run the risk of the rears locking up before the fronts, which could be a really dangerous thing.

One general note...I'm an amateur mechanic who knows just enough to get by...and sometimes get myself into trouble. If I send something out to be restored by experts...especially experts who specialize in something...and I can't get it to work, I generally assume the problem is mine – not the shop's. Of course, things can and do happen. But if you're still learning, like I am, jumping to conclusions that a shop didn't do right by you may not be fair. Just my .02

Hang in there!

[mskala]

Haven't seen this mentioned yet, but with new seals in calipers sometimes they are strong enough to pull back pistons slightly and this will get better by itself fairly quickly.

[Root_Werks]

Good thread with good tips. Reminds me I should get a MC brace. Nothing indicates I need one, but have installed them before. They make a difference.

(IMG:style_emoticons/default/driving.gif)

[jhynesrockmtn]

Haven't seen this mentioned yet, but with new seals in calipers sometimes they are strong enough to pull back pistons slightly and this will get better by itself fairly quickly.

This is why a couple of us have mentioned bleeding with something thinner than new pads in place. Exactly what the mechanic in Bend described.

[Krieger]

I also had a problem with brand new bleeders leaking. I compared them to the old ones. The tip of the new ones are not as pointy as the old ones. I replaced them with speed bleeders. They were just as pointy as the original ones. Leaks solved!