Braking Power Options

[lsintampa]

75 2.0 FI

So I just got my car finally on the road. It's been a long journey, and this is my first 914, so if my question sounds "dumb" - just give me a new 914 driver break.

All of the latest "old" cars I've owned (74 TR6, 74 BMW) all had brake boosters. The 914 has no "boost".

I find the braking power to be really somewhat below what I expected.

What was I expecting? Well, since I have no prior 914 driving experience I really don't know.

I'm curious if my "newbie" experience is just that I'm not familiar with the lack of braking power, or if perhaps I may have some issue with my brakes?

Rotors all new, pads in good condition, good pedal pressure, 19MM ATE MC from PMB.

Any "road tests" I can do to give me some sort of clue if all is well in brake land?

Thanks,

Len

[ThePaintedMan]

Have you bedded the pads yet Len? What exactly are you not happy with? You should have no problem locking the fronts up, even with a stock setup

[URY914]

Is the pedal firm? Getting all the air out can be a PITA sometimes.

[Elliot Cannon]

(IMG:style_emoticons/default/agree.gif) Make sure they are bled completely. This may help if you haven't seen it. http://www.pmbperformance.com/bedin.html

[lsintampa]

system was bled and bled again

as far as "bedding" the pads, not sure what that really means

[ThePaintedMan]

system was bled and bled again

as far as "bedding" the pads, not sure what that really means

Check out the link that Elliott provided to you. I can show you how to do it one night this week as well. Basically need to find a big parking lot and do some hard braking (without stopping).

[McMark]

If the pedal is soft, you need to bleed it more. Especially because you replaced the master cylinder. The MC really should be bench bled before it's put into the car because it can hide so much air.

If the brakes feel safe enough to drive, go do the pad bedding procedure Elliot linked to. When you get back, do some more bleeding. You'll probably need to do the bleeding process a few more times.

I've tried all the tricks and products, but nothing beats a two person bleed with one person to push the pedal and one person to open the valves.

Oh, and one other thing, make sure there is a little 'free travel' at the beginning of the brake pedal travel. You should feel a bit of space before the plunger actually contacts the piston inside the master cylinder. If there isn't any free play, it may not bleed correctly/completely.

[Dave_Darling]

system was bled and bled again

Again and again does not necessarily mean properly... If air has gotten into the proportioning valve on the firewall (behind the driver's butt!) it is just about impossible to bleed it out the normal way.

Some have had luck cracking open a fitting on the prop valve itself--though then you have brake fluid going everywhere, and that stuff does eat paint if you let it sit on there. So prompt clean-up (with water!) is needed after that.

--DD

[yeahmag]

If the pedal is firm, but low you need to adjust the rear venting clearance. If the pedal is firm and high, but doesn't have the "bite" or "power" you would like you need different pads. Get a nice pad from Raybestos or Carbotech.

The ST43's on my car will throw you through the windshield. The Pagid Orange was plenty when I had all stock, 4 lug stuff.

[Eddie914]

Len,

What do you mean by stating?

"I find the braking power to be really somewhat below what I expected"

Does mean the brakes will not lock up the wheels?

or

Does it mean you have to push harder than expected on the brake pedal to achieve the desired deceleration?

[thelogo]

As far I know this is one of the best braking 40+ year old car on the rode

I seem to get better brake leverage by only contact ing
The very top of my break pedal as opposed to my foot flush
On the pedal ( call me crazy +-)


But of course ,vented rotors will improve fade and
power boost will increase leverage but decrease FEEL!


I'll stick with old stocky stock setup , good enough to stop 2100 lbs

And decent feel

[mepstein]

Bedding the pads or new ones from Eric are probably the solution.

or the proper 17mm master (IMG:style_emoticons/default/stirthepot.gif) (IMG:style_emoticons/default/happy11.gif)

[brant]

Did you reuse pads?

[jmill]

or the proper 17mm master (IMG:style_emoticons/default/stirthepot.gif) (IMG:style_emoticons/default/happy11.gif)

Omg!! Lets not go there.

Anyhow, dont forget about changing out the old flexible lines if you already havent done so. They
plug up and reduce volume and sometimes swell to reduce pressure.

[nathansnathan]

Lupawali's "brake faq" mentions the 19mm master cylinder improving pedal feel but actually reducing braking power.

What about the 19mm master cylinder upgrade?

This is pretty much a "feel" issue. The ratio of master cylinder piston area to total caliper piston area determines the mechanical advantage you get in applying pressure to the brake pads. The smaller the master cylinder piston (or the larger the caliper pistons), the more "advantage" you have (more force on the pads for less force on the pedal). However, while you apply less force, you have to push the pedal farther to get the same amount of movement at the pad. With a larger master cylinder piston (or smaller caliper pistons), you have LESS advantage, so you have to push the pedal harder, but you don't have to push it as far. The pedal feels firmer, but you're actually getting less braking. Some people like the feel this gives, so the upgrade isn't entirely a bad thing. However, many people make the upgrade because they think they're actually improving their brakes, when they're actually making them worse, just improving the feel.

[ThePaintedMan]

I have a 19mm - love it.

Its very possible the brakes weren't bled enough/properly. Are they spongy, then get harder as you pump them Len?

My money is still on bedding. You have new rotors on the car, which means that initial mechanical/chemical transfer of pad material has not been done. You're still working off the glaze of the rotors as well. Going through the bedding procedure (assuming the car is braking well enough to be SAFE) is the first thing I'd try before climbing back underneath the car.. and it gives you a excuse to go (IMG:style_emoticons/default/driving.gif)

[era vulgaris]

All of the latest "old" cars I've owned (74 TR6, 74 BMW) all had brake boosters. The 914 has no "boost".

I find the braking power to be really somewhat below what I expected.

I also owned a 74 TR6 - sold it last fall after spending two years with it. I used some of the money from it to buy my 914. I know exactly the brake feel you're used to.

The 914 will require more effort than the TR6 did. But the 914 is also about 400lbs lighter than the TR6, so it's not a significantly greater amount of effort. I actually prefer the 914 because once you get used to it, you can "feel" what's happening with the brakes better than you can with a booster system. Just drive it for a while.

The test though is being able to lock up the brakes. If you can't do that, then they're not working correctly.

[lsintampa]

sorry guys,

I didn't realize how many of you posted a response. I thought I had set email notice on, but haven't gotten any notices.

Recap - to answer most of your questions.

Pads are NOT new, rotors are. The pads were (IMO) in decent shape.

I have NOT bedded anything - yet.

By not what I expected, I haven't really tried to "lock them up", but the feeling I have is that isn't going to be easy to do.

I'm on my way out to pick up some lunch. I'll do some testing and get back in a while. Don't worry, I'll do it safely.

Thanks,

Len

[McMark]

Len, the real question that needs answering is,

Is the pedal too hard? Or too soft?

Then we can help you find a solution.

[flash914]

What about flex if the floorboard? That is what I will be fighting next on mine. Gordon