Long brake pedal travel

[83_Silberpfeil]

I'm experiencing long brake pedal travel in my 83 SC. It hasn't always been like this.

I know that 911's --- especially from the air-cooled years --- have always had very firm brakes and had very little pedal travel. Seems like less than 1 inch of travel, then the remaining is based on "pressure".

So, with my 83 SC, it seems like travel is 3-4 inches before it become's "pressure-based" braking.

What are the causes? Low brake fluid level? Worn brake pads? Booster or MC needing some rebuilding --- perhaps replacing the seal or o-ring in the MC?

Went out for a ride this AM and wanted to test out the grip in my new BF Goodrich G-Force Sport Comp2's. But, because of the brake symptom, I did not want to push it.

Thanks in advacne!

[tonythetarga]

I think you need look at a couple things, master cylinder and caliper rebuilding. The most likely suspect is the mc. If the calipers were failing you might see evidence of brake fluid on the ground but don't rule out the rebuild even if the there is no leakage. If the mc is original it might be time to upgrade from the stock size to the turbo 22mm(I think) master cylinder. Do one repair at a time and check performance.

[RWebb]

or pedal cluster

[83_Silberpfeil]

TonyTarga ---

Thanks for your reply and your advice.

I've been planning to remove all 4 calipers and send to Eric at PMB. So this is the perfect reason to begin the removal process.

As for the MC, the records I have on the car does not indicate it was replaced. So, certainly could be factory original ---- thus almost 30 yrs old!!!

I would be open to paying $275 for the 23 mm Turbo MC vs the original spec 19 or 20 mm MC. What does the 23 mm MC buy me? Will it actually provide that much better stopping power? The factory brakes (before this pedal travel incidence) was pretty darn good.

Also, I've read in posts here somewhere with 'experts' indicating that upgrading to 23 mm will require upgrade of the booster as well --- otherwise no performance gain? What's your thought on this?

Much thanks again!

Originally Posted by tonythetarga

I think you need look at a couple things, master cylinder and caliper rebuilding. The most likely suspect is the mc. If the calipers were failing you might see evidence of brake fluid on the ground but don't rule out the rebuild even if the there is no leakage. If the mc is original it might be time to upgrade from the stock size to the turbo 22mm(I think) master cylinder. Do one repair at a time and check performance.

[83_Silberpfeil]

Originally Posted by RWebb

or pedal cluster

RWebb ---

Thanks for chiming in.

What should I be looking for in the pedal cluster? Worn out bushings?

Please advise.

Thanks!

[Flieger]

23mm master cylinder will make the brake pedal a lot shorter and much firmer. With a booster it might be do-able but they will probably feel very touchy/grabby.

[na2ub]

My 79 master cylinder operates great. I don't see any need to "upgrade." Usually if your master cylinder is leaking, the pedal will slowly depress, with the same amount of foot pressure on it, as the fluid leakes past the seals in the cylinder. When was the last time you replace your brake fluid, or bled them, for that matter? I would start there.

[RWebb]

[1]the parts of the pedal cluster can distort over time; [2] it collects rust underneath (where you cannot see it w/o removal); and [3] yes, the bushings will eventually fail

you need to remove it every xx years anyway, so this is an "opportunity" - some good threads on redoing it

[83_Silberpfeil]

Thanks for pointing out the "suspects".

I failed to mention that I've been experiencing vibration on the brake pedal. This is fairly recent.

You can hear the pedal vibrate as you step on it. Small but high frequency vibration. After the first push on the brake I hear this. Then, on subsequent pushes (immediately following the first), there's no vibration. Cruise down a few miles, then first push on the brakes, you hear it again.

Seems like something connecting the brake pedal or the brake rod is loose.

Originally Posted by RWebb

[1]the parts of the pedal cluster can distort over time; [2] it collects rust underneath (where you cannot see it w/o removal); and [3] yes, the bushings will eventually fail

you need to remove it every xx years anyway, so this is an "opportunity" - some good threads on redoing it

[euro911sc]

On my SC I have about 1/2-3/4" of travel in the pedal before it engages the MC. I tried to adjust it out using the rod to MC but that just moved the pedal out. It seems to be in the booster linkage. There are a few threads on this subject that are recent:

Deep Brake Pedal at Homestead DE

Deep Brake Pedal at Homestead DE

Though I may return to the site in this thread and see if they have a better solution...

Thread: Brakes: Upgrade to drilled lines?

Site: http://kalecoauto.com/index.php?main_page=product_info&cPath=11&products_id=39

-Michael

[83_Silberpfeil]

Took a peak at the brake fluid reservoir this AM. No fluid visible inside the reservoir. Shook the car a bit, and did not see any fluid level line oscillating.

So, I used DOT4 and slowly poured ~ 5-6 ounces into the reservoir.

Upon startup, the pedal immediately felt fir resistance after about 1 inch of pedal travel. Additional braking power from this point on was extering additional pressure on the pedal --- but with minimal pedal travel.

Still will go through the brake overhaull, but not quite in such a hurry anymore. I will take my time and do a step at a time.

Hopefully, the fluid level stays and does not slowly leak/drop.

X my fingers.

[Walt Fricke]

So, where did all your brake fluid go?

Yes, with pad wear the fluid level will drop. But not that much.

I replaced my fluid, and after some futzing with bleeding, all was well. Then, at the track in the afternoon of day 2, my spouse said the pedal went to the floor just driving to the grid. Fluid missing - what the F?

Refilled, bled (hardly a bubble), and all has been well.

Suggestion from a shop owner friend: the vacuum in the power assist reservoir sucked fluid out of the MC past a seal. The seal probably worked fine with the braking pressure against its insides, but not against the vacuum on its outsides.

Haven't pulled the MC off to see if there is a reservoir's worth of fluid in the pie tin. Ran a track day (not hard on brakes at that track) and an autocross with no issues.

So there is something else to check.

[83_Silberpfeil]

Walt ---

Slow down here! You're going way to fast. You lost me after "But not that much".

What are you suggesting? Where do you speculate the fluid is hiding or puddling up?

Thanks!

JC

Originally Posted by Walt Fricke

So, where did all your brake fluid go?

Yes, with pad wear the fluid level will drop. But not that much.

I replaced my fluid, and after some futzing with bleeding, all was well. Then, at the track in the afternoon of day 2, my spouse said the pedal went to the floor just driving to the grid. Fluid missing - what the F?

Refilled, bled (hardly a bubble), and all has been well.

Suggestion from a shop owner friend: the vacuum in the power assist reservoir sucked fluid out of the MC past a seal. The seal probably worked fine with the braking pressure against its insides, but not against the vacuum on its outsides.

Haven't pulled the MC off to see if there is a reservoir's worth of fluid in the pie tin. Ran a track day (not hard on brakes at that track) and an autocross with no issues.

So there is something else to check.

[tonythetarga]

It can collect inside the booster. I agree with Walt, you lost too much fluid to think your problem has fixed itself.

reference this thread:
Brake booster full of brake fluild

The m/c allows fluid into the booster. you'll need to empty the booster and flush it and put in a new m/c.

[83_Silberpfeil]

Thanks for the warning on the floodded booster. Looks like a MC replacement is my next project.

[kodioneill]

Yes the fluid went somewhere. I would not even think of driving your car until you locate that leak. Very Dangerous!

[83_Silberpfeil]

So, I'll be checking the luggage boot in the area around the MC and the Booster to look for signs of leak or wet spots (brake fluid). If I don't see any, then can I assume the fluid went into the Booster? I don't see any signs of leaks of brake fluid at the caliper piston (slave cylinder) area.

Also, when I remove the MC and booster together as 1 piece, do I have to siphon out the fluid in the reservoir first? Will the fluid still seep out of the MC or booster upon removal? Sounds like a messy job.

Please advise.

Thanks!
JC

[Walt Fricke]

I've not had to deal with this before, so no practical knowledge. However, without a vacuum in the booster, you shouldn't have any more fluid leaving the MC. There would only be gravity trying to get past the seal, and not much of that.

Turkey baster with a flexible tube on its end should allow you to get into the booster once the MC is separated from it.

I can't recall if you can remove the booster without having to disconnect the brake lines to move the MC.

[TahonNifan]

Slow down here! You're going way to fast

[83_Silberpfeil]

Just checked under the front hood. Completely dry --- between the MC and the booster, under the MC and under the booster, at all brake lines, reservoir lines, etc. I even opened up the cover for the "smuggler's box". The lines in there felt dry also.

Went for another drive today. Brakes worked fine. Fluid level stayed same.

Should I still be worried about leakage into the booster?