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Brake pedal won't return completely
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joezapp
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Oct 7, 2017, 6:08 PM
Post #1 of 15
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Brake pedal won't return completely
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Hi all. I have the dreaded Bendix 10 brake system on my 1992 Town & Country, and the system recently acted up with the common "no brake assist" fault. The brake assist on this system is through the ABS hydraulic assembly (no vacuum). I had another hydraulic assembly (which includes the master cylinder) sitting around, so I had my mechanic install it, and we bled the brakes. While the replacement hydraulic assembly still brings the ABS and BRAKE warning lights, I DO have brake assist now, and I have an appointment with the dealer for further diagnosis as this system has a recall.
But where I'm stumped is, since this bone-yard unit got installed, the brake pedal doesn't return completely. Hence, the rear brake lights stay on. I have to lift the pedal about 1/2 inch to 3/4 inch with my foot or hand to get a complete return and for the rear lights to turn off. I've been back to the mechanic 3 times, and he played around under the dash with a screwdriver and WD40, and each time he improved it. The improvement would last until I'd get home, and that's about it.
The mechanic tells me that the hydraulic assembly may not be powerful
enough to return the pedal all the way back. This is all new to me, as
I've never had a master cylinder give me a problem before (lucky I
guess), so I don't know what to think with this. Any thoughts on cause
possibilities would be appreciated! Thanks so much.
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Hammer Time
Ultimate Carjunky
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Oct 7, 2017, 6:22 PM
Post #2 of 15
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Re: Brake pedal won't return completely
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The service info I have says you have a vacuum booster.
There is no such thing as an ABS booster.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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joezapp
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Oct 7, 2017, 6:58 PM
Post #3 of 15
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Re: Brake pedal won't return completely
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Hi Hammer Time. We've been through this before. Double J correctly presented to us that I do not have a vacuum booster. I have the Bendix 10 brake system, which uses hydraulic boost.
http://autoforums.carjunky.com/Automotive_Repair_C1/Brake_Systems_F51/Intermittent_hard_brake_pedal_P190500/
There ARE models of my vehicle that have the non-ABS/vacuum system, and I am considering making the switch. I have the instructions on how to do it.
But for now, I need to know why the brake pedal will not return completely after installing a different ABS Hydraulic Assembly (which includes the master cylinder).
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Hammer Time
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Oct 7, 2017, 7:03 PM
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Re: Brake pedal won't return completely
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Yeah, I remember that now.
Are the brake lights the only symptom? Are there any issues with the brakes when driving around?
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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joezapp
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Oct 7, 2017, 7:26 PM
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Yes, the brake lights are the only symptom here...though when I'm driving around, sometimes it's obvious to my foot that the pedal didn't return all the way, especially upon the next application of the brake.
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Hammer Time
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Oct 7, 2017, 7:32 PM
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That doesn't add up because if a master cylinder doesn't entirely return to it's stops, it will build up pressure and cause the brakes to lock. Are you sure it's not just the rubber bumper that the brake light switch rests against has fallen off.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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joezapp
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Oct 7, 2017, 8:05 PM
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Being that the Bendix 10 system operates differently than the vacuum systems, we can't say that the end result would be the same when the pedal doesn't return completely. For example, the Bendix 10 is already very high pressure. It works off of a pump pressurizing the hydraulics (accumulator) to between 1600 and 2100 psi.
I can ask the mechanic if there was a rubber bumper, but he already told me about plastic being around the brake light switch. This may serve the purpose that you are describing.
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joezapp
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Oct 8, 2017, 10:37 AM
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Re: Brake pedal won't return completely
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Anybody else have causes for a brake pedal to not return completely? I can't be the only person this has happened to.
But to begin with, I really don't know the mechanics behind what makes a brake pedal return completely when stepping off the pedal. Maybe someone on here can explain.
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Tom Greenleaf
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Oct 8, 2017, 10:58 AM
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I can only guess as never saw this and how much is different than everything else? Pedal pivot and you said your mechanic sprayed presumably up there and it helped.
That's a clue if nothing else. WD-40 does lube on its endless list of uses but IMO isn't a very great lubricant! It's light, wears out faster than an oil or grease. If that shaft assembly has to be dismantled to re-lube the whole shaft with an OE suggested grease meant no doubt to last about forever it could be just that. It's hard to believe they changed the entire van over the type of booster combined with master inside would be wasted extra engineering IMO. Master to just bench bleed any other since all time is spring loaded to be OFF - meaning back to "home" position apparently not strong enough for whatever friction is preventing that.
Others have been carpeting made too large/tall up interior and dumb things like that. This part alone if lubing helped is the strong clue I just said and would just do that better with an oil or grease whatever it takes to do that.
Already mentioned if brake isn't really returning any design I know of it would prevent fluid from returning to master hence brakes would be dragging a little or a lot to a wild problem?
T
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joezapp
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Oct 8, 2017, 1:17 PM
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Thanks, as always, Tom. Good explanation. I'm with ya!
So you say that the pedal is spring loaded to be back to the "home" position, and that there is friction preventing that from happening which the WD-40 satisfies only for about an hour of driving because it's not a long-lasting lubricant. Since you never saw this before, I suppose the spring function does not go bad or weaken? If it does not go bad or weaken, then I believe the problem lies in these 2 instructions from the factory service manual. Please let me know if you agree. These are from the instructions for installing the hydraulic assembly (master):
(3) Using lubriplate or equivalent, coat the bearing service of the brake pedal pin
(4) Connect push rod to pedal pin and install a NEW retainer clip. (It also refers to the push rod being installed in the correct position, which I will check into).
*My mechanic used the existing retainer clip, though NEW was capitalized in the instructions. He said the old clip was OK.
*He made like he didn't know what I was talking about when I read instruction 3 to him. (Admittedly, I never heard of lubriplate either, but I got the gist of it).
(This post was edited by joezapp on Oct 8, 2017, 1:27 PM)
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Tom Greenleaf
Ultimate Carjunky
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Oct 8, 2017, 1:44 PM
Post #11 of 15
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Re: Brake pedal won't return completely
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Please understand I haven't messed with this exact system - you said it was unique and sure is. The pushrod and a bearing IDK about. Pushrods on an assortment of vehicles must be free to work as intended. Some center themselves, some may be clipped into place INSIDE the vehicle on now ancient stuff with no power assist at all.
May or may not use springs and may or may not be adjustable - lost with this exact thing but it just can't be working as intended. When you said it improved with WD-40 is a real clue to me.
Side note is also IMO is WD-40 stinks as a lubricant with harsh forces better for light lube and it "displaces" water named "WD" for Water Displacing" and 40 is how many tried it took to achieve that if you believe the lore on it.
I use it more for cleaning, protecting things from rust - tools etc.
There are other lubes that are better if real lube is required. I saw ONE by 3-IN-ONE oil with an extendable stem of pure silicone so it said. Whatever you use should be rubber friendly just because with brake anything. WD-40 is somewhat? The spray silicones are either almost dry or some are just so light not enough IMO.
Where it binds is where it needs the real lube that will last my best guess. I'd use pure silicone grease stating rubber friendly and whatever it took to take apart what is clearly not lubed well enough and do it up well again - strong guess that would end this.
There are brake specialty places, one near me once sold only to the trade and like ''DYNATEX, PURE SILICONE BRAKE GREASE" for several things it's totally water proof is one good reason,
Tom
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joezapp
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Oct 8, 2017, 8:18 PM
Post #12 of 15
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Thanks so much, Tom. Impressed that you even knew "Water Displacing, 40th try!" You and I have inquisitive minds. One day I said to myself, why is it called WD-40, anyway? And Google finds the answer! If they were a little sharper, it could be called WD-29, lol.
I googled lubriplate, and this was apparently the commonly recommended lubricant on cars "back in the day". Apparently it was a white lithium grease. I know that white lithium grease works well. Do you favor rubber friendly pure silicone over the white lithium grease?
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Tom Greenleaf
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Oct 8, 2017, 10:18 PM
Post #13 of 15
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I use all of those for specific reasons - household, vehicles or whatever. Which tolerates heat, doesn't harm something else and last for desired reason. You need to know what materials the lube with be touching. I chose pure silicone not a mix as it doesn't wash away, both tolerated high and low temps and harmless to plain rubber or plastics so far.
Google it out - WD-40 I think was a request for the Air Force to make a product to clean and polish aircraft! What the final version is mostly is FISH OIL! It does wash off with most plain soap and water though.
Just beware of claims of so many product's claims of what magic they can do it's to sell it with no regard if it works.
I'm just focused (again) that it parts helps with less than the and could end it with the right stuff. How to access, apply product and put back together it would really help to look how that's done - this isn't all the common to me to happen at all which is why it's being such a PITA to find, do and be done with this,
Tom
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joezapp
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Oct 9, 2017, 5:51 AM
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Fish oil! That's good for health. If I run out of capsules before I get to the drug store, I'll just spray some down my throat. So many uses, indeed! (For those reading this, don't try this at home!)
Always great tips, Tom. Thank you. I'll post back to let everyone know if proper lubrication at the friction points is all that was needed here.
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joezapp
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Oct 10, 2017, 9:31 PM
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Re: Brake pedal won't return completely
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So my mechanic was convinced that there wasn't enough pressure coming from the master cylinder (in my case, ABS hydraulic assembly) to push the brake pedal all the way to the home position. He determined that we should bleed the system again. He's the most meticulous brake bleeder I've ever come across. "Make sure you're pumping the pedal hard", he says. "Are you pumping hard?"
And that resolved it. So for those who experience this and find this thread, first lubricate all the friction points of the brake pedal well with white lithium grease or 100% silicone. If that doesn't do the trick, re-bleed the brake system, and take your time doing it. If that doesn't work, I'm told that the master cylinder will need to be replaced.
Many thanks, everyone, for all your tips!
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