Brake problems - rebleed when using Motive??

[sigchuck]

Hi guys, I just wrapped up replacing a sticky left front caliper with a centric rebuilt unit and replaced front pads while I was at it.

I bought a motive pressure bleeder for this project, and while the instructions seemed fairly simple, once everything was buttoned up the pedal is incredibly soft. Obviously there’s either air in the lines or I screwed up my MC by wedging my pedal down while changing the caliper - something I read on a thread here and that I now know is a completely unnecessary step.

Some additional facts/questions:

- pedal feel fluctuates - it never feels close to good, but sometimes it definitely feels better than others - Just symptoms of air in system, or any way to tell if possibly bad MC? Another note is that the front brakes completely locked on a hard brake at about 5mph. I know the braking system doesn’t care how fast you’re going when you apply enough pressure to lock, but does anything about this sound funny?
- I was unaware a rebuilt caliper should be exercised/tapped during bleeding. I didn’t do this the first go around, but is it necessary with a motive pressure bleeder? FWIW, the new LF caliper with pads definitely had a bit more drag than the RF caliper with new pads.
- I drained out around a half quart of fluid during the initial bleed of all 4 wheels, which I did RR, LR, RF, LF. I never saw any evidence of air, but I’ve also never used a pressure bleeder, only the two person method. Am I looking for big air bubbles, the size you’d see in a carbonated drink, or smaller? I would have assumed half a quart of fluid between the four corners would have done it, but the motive is unchartered territory for me.

Thanks for your help guys!

[kyngfish]

I’ve never really had a ton of luck with bleeder “systems” the motive is pretty good though and it shouldn’t introduce air in the system. It’s possibly an MC issue but more than likely you just need to re-bleed. I’m sure you already know this but start at the corner furthest from the MC and work your way to the front.

The problem with looking for air bubbles is that air can actually also flow up your tube as you pump and as the brake fluid flows downward. Generally I just look for new looking fluid and go from there.

I recently bought speed bleeder screws for mine. Like 60 bucks for all four. They have a ball bearing and spring inside and all you do is loosen the screw and pump then hold at each corner (rubber hose and jar attached) - it took me all of 10 minutes to completely bleed my brakes and my pedal feels rock solid.

[Lyle O]

Sometimes the with new caliper seals, the seal is so good that the pistons stay close to the caliper (there is suction when they are extended from pushing the brake pedal, and when you release they go back too far, creating a longer pedal travel/soft feel). This is a known/common phenomenon. However, in your case, with only one new caliper, this may not be what you are experiencing...

With a pressure bleeder, and after bleeding out a half quart of fluid, you should have seen some bubbles (at least from the LF / new caliper). I have the Motive, and have been very happy with it. Be sure you are at proper pressure, and try bleeding again. Also be sure you have completely clamped off the MC vent tube.

[sigchuck]

Well on further inspection this morning, it looks like there may have been a long term MC leak... at least that’s what I’m trying to convince myself of after jamming the brake pedal while changing the caliper.

Just to be clear, there shouldn’t be any other grease, liquid, etc. that would attract that much dirt, right?



Also, is replacing the MC really that big of a job? I noticed the tech article gives it a 5 out of 5 for wrenching, but I don’t see the difficulty based on what’s in the article and Bentley’s. Maybe some contorting, but doesn’t appear to be any more difficult than replacing plugs, etc.

[Locker537]

Is that area currently wet with fluid? It looks like it from the picture.

My master cylinder has some of that paint deteriorating crud on the back of it, which I have concluded it from someone spilling fluid in the past and having a hard time cleaning it all up.

I marked my reservoir when I fill it so I can monitor the level and watch for leaks.

[sigchuck]

It is a bit damp, but I had another screw up and used a hemostat clamp on the overflow hose when I was using the Motive, which I think may have caused a bit of weeping. I also have a fluid drip right above the brake pedal which I suppose could be residual fluid from this.

[75 911s]

With a brand new caliper a lot of people will bench bleed it first. It's not really motiv vs human. They are performing the same task. A lot of motiv users don't fill the tank with fluid at all, they simply use it as an air pump. I've done it both ways and the air tank method is way better. The trick is you have to unscrew it off the reservoir often so that you can refill the fluid. If you don't keep it full, you introduce air into the system.

Another trick is to lightly tap on the new caliper with a rubber mallet as you bleed to get the extra air loose. I'd do all that before replacing the MC. You can clean it up and replace the lines. I think aircraft spruce sells the blue brake line and the plastic fittings are here on pelican.

[Mahler9th]

Looks like you are on the right track. I encourage you to investigate any apparent MC leakage until you are satisfied everything is ok.

I have experienced failures of the seal between the MC and booster on a different Porsche model and it caused some strange problems until I was able to diagnose and remedy. In that case, fluid got into the booster and I replaced the booster.

With respect to bleeding, I have used many different methods. And because I have had a Porsche racing hobby for about 20 years, I have had many occasions to bleed brakes. My standard method is vacuum using a Mityvac. I also have a Motive unit-- usually use that on street cars, but sometimes on my race car. It has worked really well for me. I know the owners of Motive and have visited with them in Gilroy. Car folks just like us.

[sigchuck]

Thanks, guys. I'll definitely try re-bleeding tonight, but went ahead and ordered a MC so I can install this weekend if need be.

One thing I haven't had much luck finding an answer to is whether the replacement ATE MC comes with the necessary seals (I think there are maybe two grommets and the booster/MC seal), or whether I should buy these separate. Does anyone have any experience with the product?

Thanks for your help!

[Locker537]

Originally Posted by sigchuck

It is a bit damp, but I had another screw up and used a hemostat clamp on the overflow hose when I was using the Motive, which I think may have caused a bit of weeping. I also have a fluid drip right above the brake pedal which I suppose could be residual fluid from this.

I would thoroughly clean the area and inspect for the leak. Hold the brake pedal with firm pressure and see if it drops and then start looking for the leak near the master cylinder.

[Otter74]

Originally Posted by Lyle O

Sometimes the with new caliper seals, the seal is so good that the pistons stay close to the caliper (there is suction when they are extended from pushing the brake pedal, and when you release they go back too far, creating a longer pedal travel/soft feel). This is a known/common phenomenon. However, in your case, with only one new caliper, this may not be what you are experiencing...

With a pressure bleeder, and after bleeding out a half quart of fluid, you should have seen some bubbles (at least from the LF / new caliper). I have the Motive, and have been very happy with it. Be sure you are at proper pressure, and try bleeding again. Also be sure you have completely clamped off the MC vent tube.

Interesting to know that. When I replaced my front calipers with PMB units and flushed and bled the brakes, I ended up with a substantially softer pedal. The brakes just got another flush & bleed last month, a couple of years later, and same soft pedal.

[NYNick]

Re-bleed all 4 wheels. Make sure the cap seal between the Motiv and the reservoir is tight. I removed the gasket from my cap and used it inside the Motiv cap.

Make sure your overflow hose is well clamped. I went out and bought new tubing from HD as mine was hard as a rock anyway.

Pump and Re-pressurize the Motiv after every wheel.

Took me 4 or 5 times to get it right on my 72.

[jlex]

I normally use a vacuum bleed system (Mityvac) on my cars when I want to get it done quickly, but when I overhauled the front calipers on my '88 last year, I had extra time so I decided to just gravity bleed the brakes. Takes a bit longer, but was very effective for me. Just open the valve and let it drip while keeping an eye on the fluid level in the MC reservoir. Old fashioned, but worked well for me.

[Locker537]

Another tip - remove the overflow and replace it with a short piece of tubing that you can fold over and clamp very tightly, guaranteeing no spills or leakage. Maybe overkill, but easy.

[sigchuck]

I checked the drip on the interior after returning home from work and it’s definitely a fairly active leak. I‘m thinking this means bad MC, no ifs, ands, or buts, right? Any experience on what additional is needed other than the ATE MC (seals, etc.)?

[Trackrash]

You probably know, but I did not see it mentioned, but old brake hoses should be replaced. They will give you grief, causing all sorts of braking problems.

I have also found that if you drive the car a while and then re-bleed the brakes you will notice a firmer pedal.

There have been some issues mentioned here about new master cylinders. Maybe the experts can chime in on the best solution.

[sigchuck]

Well, sorry to be schizophrenic on my path, but after removing the floorboard, the leak appears to be coming in through the heater duct that sits behind the MC, and not traveling down the brake pedal pushrod (which is I think where a failing MC typical leaks). I’m thinking if it’s leaking in through the heater duct, it’s either spilled from when the hemostat stressed the overflow line, or the brake line grommets are bad.

Back on the “bleed it again” train.

[997at]

My $0.02 I just replaced my entire brake system on an 82 SC. The ATE MC will come with the two grommets for the hoses from the reservoir as well as the one gasket between the MC and the booster. The only things I didn’t replace in the entire system were the hard lines. I used the old fashioned methods for the bleeding. I did not pre prime the MC...not necessary. I did gravity bleed all 4 corners although the front right did require a pedal push to get flow started. Typically you will get flow within a couple minutes. After gravity bleed I got one of the kids to pump the pedal the old fashioned way. I took a drive and the pedal felt like it was too soft and had too much travel. Drove for 20 min with lots of stops and then bled again via the pedal method. Pedal feel is great now. New or refurbished calipers will take some use before the pistons settle close to the pads.

[frankc]

It looks to me like a leak in the MC to me. I had the similar leak and replacing the MC resolved it (see first photo).

Regarding the brake fluid that you noticed getting into the cabin, on my '77 there is a hole at the bottom of the "well" under the brake booster. You can barely see the hole in the second photo (circled in red). My assumption is that the purpose of this hole is to allow brake fluid from a leaky MC to go somewhere and hopefully be noticed before all the fluid is gone (plus not pooling and destroying the paint).

[sigchuck]

I had a chance to pump the brakes and observe over the past couple days and it looks like the MC definitely has a bit of a leak. Any harm in removing MC today and cleaning the area while I wait for the new one to arrive? Would this introduce mush moisture to the otherwise pretty full system? I do plan to do a complete flush once the new MC is in.