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DavidSwedem's Avatar
 
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Location: Gothenburg Sweden
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Brake are weak

I recently bought a 914 2.0 from 76. Drove the car from England to Sweden the brakes were a nightmare so I decided to rebuild them. Got the seal kits and split the calipers and rebuilt both front and rear calipers. Bled the system and looked forward to having some decent brakes.
No such luck, the brakes are a lot better but compared to my Saab the stopping power is bad.

How good should they be and where did I go wrong?

Thanks
Old 06-07-2014, 08:34 AM
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John Rogers's Avatar
 
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I would say there is air in the system and the best way to bleed the brakes and remove all of it, including the prop valve is to buy a pressure bleeder and use that. I used the two person method for many years but the bleeder is way better!
Old 06-07-2014, 10:50 AM
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Thanks for the tip.

I will pressurize the fluid reservoir tomorrow. Will let u know how it goes.
Old 06-07-2014, 11:13 AM
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When I used to bleed the race car brakes, I used about 4 to 5 pounds pressure. Just enough to force the air out but not high enough to blow things up.
Old 06-07-2014, 12:45 PM
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How are the brakes bad? Does the pedal feel soft? Do you have a hard pedal but the car just does not slow down? Something else?

--DD
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Old 06-07-2014, 04:22 PM
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The Saab has Power assist(?) the 914 not, thats one major difference.

Im still not fully happy with the brakes on my 914/4 -72 either but stopping ability was greatly improved when i shifted to another brand of brake pads. I guess the new ones are softer, I can now lock upp the front wheels quite easy which I could'nt before.


/Lars S
Old 06-07-2014, 11:27 PM
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Thanks for the feedback.

The pedal is hard but the brakes take a long time to stop the car. Maybe this is normal I i just dont know.

Bled the brakes again today and have put in total about 2 - 3 liters of brake fluid through the system, I dont believe there can be air in the system. The brakes are the same.

regarding the pads I have know idea what make they are they were on the car when I bought it, they look pretty new.
Old 06-08-2014, 08:47 AM
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So the pedal is hard? Good.

Can you lock up the wheels? That is, apply so much brake that the wheels stop turning and the car just slides? If you can, then you can stop faster by getting tires that offer more grip.

If you cannot lock the wheels up, then change the brake pads for ones that offer more grip. We keep hearing good things about the Porterfield street pads, for instance.

And remember, as Lars said, you may have to press harder on the brake pedal in the 914 than you are used to, if you have primarily driven cars with power-assisted brakes. So try putting a lot of leg into the pedal application and see if that works better.

Oh, a couple more possibilities:

If there's still some "give" to the pedal, it can be caused by air trapped in the proportioning valve (on the lower firewall in the engine bay, just behind the driver's butt) which is difficult to properly bleed. Or it can be caused by the mount for the brake master cylinder flexing. People have made a number of different braces for this.

Here's an example of the flexing:

https://www.youtube.com/watch?v=CUdPmitJ9XQ

--DD
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Old 06-08-2014, 12:22 PM
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Dave thanks for the reply,

No the front wheels will not lock up, not a chance and I pressed good and hard on the pedal.
Yes there is a little give in the pedal, I noticed that this disappears if you put the hand brake on and then press the pedal.

Now I'm going to show my ignorance, regarding prop valve, doesn't the valve only affect the rear brakes, there are 2 brake circuits why would air in one affect the other?

Yes I have seen the prop valve I considered cracking it to get a good bleed but its difficult to get to. Do you access the valve from under the car or is it possible via the engine lid?

I will check out the master cylinder for flex but I dont think its a problem.

Whats the story regarding upgrading front calipers with BMW 320i is it worth it?

Thanks

Last edited by DavidSwedem; 06-08-2014 at 12:53 PM..
Old 06-08-2014, 12:50 PM
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Originally Posted by DavidSwedem View Post
Thanks for the feedback.

.....
regarding the pads I have know idea what make they are they were on the car when I bought it, they look pretty new.
Even if the pads are new they can be (too) hard.
I bought new pads at "Biltema" front no 65-9034 and rear no 65-9009 (havn't fitted the rears yet so I cant verify) .

The fronts are the thinner (15mm) ones for early cars; (up to chassis #4722919032) your '73 may have the thicker pads (maybe the thinner pads will fit also later calipers?)
I did not fit the anti-squeek plate behind the pads since it felt at bit soft and I want to keep the pedal as stiff as possible.


/Lars S
Old 06-08-2014, 09:25 PM
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The prop valve is under the engine shelf, so you cannot access it from the top.

The two circuits in the brake system are joined in the master cylinder, and we have seen air apparently go from one end of the car to the other.

You might want to re-adjust the rear brake pad clearance. The spec given in the manuals is about double what it should be.

The 320 brakes are IMHO not really worth the bother. The stock brakes can work very well when everything is in good condition. The different piston size will mean that the brake bias (front to rear effect) changes, which is often not what you want. The larger pad will wear a little slower, but it will also keep air from a little more of the rotor. And that won't help you get rid of the heat any faster, which means the brakes won't really go any longer before they start to fade.

Get some good pads in there and see how the brakes work.

--DD
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Old 06-08-2014, 09:28 PM
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No mention of new brake lines,blocked/delaminated ones provide a nice hard pedal for the wrong reasons...just an idea.
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Old 06-09-2014, 12:37 AM
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Yes thats a thought, but the fluid runs through when I bleed or have I missed the point somewhere
Old 06-09-2014, 02:20 AM
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Yes thats a thought, but the fluid runs through when I bleed or have I missed the point somewhere
A brake hose could teoretically block only when it is pressurised but anyhow new hoses should be stiffer and expand less when pressurised and therfore giving you a stiffer pedal. Not to mention the feeling of not having 38 years old brake hoses...


/Lars S

Last edited by lars s; 06-11-2014 at 08:41 PM..
Old 06-11-2014, 08:36 PM
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The typical failure mode of the rubber hoses is that (after a few decades) they swell shut. Your foot on the master cylinder can generate enough pressure to force its way past the blockage, but the seals in the caliper cannot generate enough to push the fluid back past it. So the brakes go on, and they don't let go.

That isn't what is happening here, so chances are that the hoses are not to blame.

I still suggest putting some good pads on the car, maybe scuffing up the rotors with an abrasive, and seeing how the car stops then.

--DD
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Old 06-12-2014, 08:00 AM
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Dave,

Thanks for the advice I will scuff the disks.

I fitted the Biltema brake pads Lars suggested these cost about $15, there was a slight improvement.
I know nothing about brake pads, you recommended fitting Porterfield street pads have you tried them yourself, they are not cheap what makes them so good?
Old 06-12-2014, 09:13 AM
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I have not tried them myself--yet. I have a set on the shelf for when the current pads wear out. I know a number of people who have, and they are excellent pads that offer a lot of grip. They are evidently a good street/autocross pad. (Race pads are not good for the street, because they often have almost zero bite when they are less than very hot!)

--DD
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Old 06-12-2014, 02:05 PM
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the car should stop hard enough to make you lose your teeth.

So, I would suggest that maybe you either have not bled the system properly (most likely not true) or your master cylinder is old and needs to be replaced...

It can also be that your floor board under the master is so rusty that it flexes alot when you press the brakes hard.

You should be able to lock up the front disks in a hard stop.

Rich
Old 06-13-2014, 07:13 PM
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Yes, I have ordered a new master cylinder, just waiting for it to be delivered.
Old 06-13-2014, 10:09 PM
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Sounds to me that your pads are glazed. I would replace pads, clean scuff your discs and then bed the pads in appropraitely. You can find a procedure on the web, but I normally start with full on stops from 20 mph, then work up to 60 mph stops, careful not to over do it. Its also fun!
Old 06-13-2014, 10:21 PM
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