Binding brakes/faulty master cylinder; mystery solved???

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sansouci
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by sansouci »

JCS wrote:Ken,

You can do it,
the 4 - 13 mm hex nuts holding the booster to the firewall are difficult but doable. you need about 18 inches of extension pcs for your 3/8 drive and a swivel with tape on it (that you've done) I used a regular long 13 mm socket, (pull the sound insulation block with 4 holes out of the way - remove it).
Make sure you have a very bright light,

And when you do the install, you can hold the nut edge to the socket with tape.

Now on the booster high pressure line you need a flare wrench for the hose fitting, it is very tight, and a normal open end wrench will round over the high pressure hex nut, and you will not get it removed, it will strip. I've got flare nut wrenches to attack this, both regular flare and crowfoot flare
You mentioned your crowfoot wrench, is it a crowfoot flare?
Most experienced mechanics learn that hydraulic fittings need a flare wrench. All of your comments you've made are showing its time to hang up your tools, I suggested to you to go to a mechanic before, because of the questions that you are asking. I also am an old guy and i have a very bad back, and when i work an hour i then go lay down for two hours, and repeat.

As I work full time, I only get to the car on weekends and can allocate time between the "honey-do's" I wish I had the opportunity to do 1 hour of work/2 hours of rest and not have to button up the car between work sessions

If your booster has the tall hex nut on the top of the booster high pressure inlet you can use an open end wrench on it to counteract the flare wrench on the high pressure hose flare wrench, and squeeze the two wrenches together, using both hands. The top flare undoing and the bottom wrench holding the tall hex nut still.
If you need a picture send me your e-mail address to jay_c_stratton at hotmail.com
Thanks for the tips....
--Ken
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by sansouci »

Jay,
Thanks for the tips.
As I work full time, I only have selected weekends (warm weather needed) to work on the car between "honey-do's." I'd love to have a window of time for 1 hour of work and 2 hours of rest and not have to button up the car to put it back in the garage between work sessions.
Since I've had the M/C on and off a few times, this should not be much more difficult other than access. Maybe some yoga would help!
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by ron »

Brucey wrote: BTW I took a look at Ron's failed MC and I think it is the guide bushing, just like all the others I have seen. The guide bushing was so tight in Ron's MC that I couldn't get it out; tipping a kettle full of boiling water over the rear end of the MC made it bind worse immediately too, so it is pretty conclusive.
This was a 750i M/C so it's not just the E24 M/Cs that seize up!
They are ALWAYS rustier than you thought!!!!!!
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by JCS »

Fellow Forum Members,

I have solved my problem with my brakes locking on all 4 wheels.
When I put in a new booster, I set the shackle length the same as the one that came out of the car.
I found that the length was incorrect by 5.71mm of threads showing, for this car it should have been about 0.0 (first photo)
The booster in the bottom (5.71mm) of photo was the one that came out of the m6, and the top was the setting I changed it to, 0.0mm.
Once the ATF reached operating temperature the BAR or PSI increased dramatically. 3rd photo.
This caused the booster to come on by itself. And locking on the brakes as the BAR increased.
This is evident in the Bentley 5 series Manual. Shackle setting.
Chapter 19 page 16.(2nd photo).

NOTE : IT WAS NOT THE BRAKE MASTER CYLINDER!!!
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Best,
Last edited by JCS on Wed Mar 02, 2016 12:08 am, edited 2 times in total.
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by Brucey »

IIRC the servo works opening a proportioning valve; if the servo is not sufficiently extended towards the rest position when the clevis pin is fitted then there will be a preload right through the brake system.

I guess there are build tolerances in the servo and the pedalboxes that may affect the point at which the servo starts to function, hence the adjustment built into it.

If anyone else is in any doubt about whether the servo is faulty and/or set wrongly, there is a fairly easy test for this. Just run the car up to normal temperature, then turn the engine off.

Next remove the two bolts holding the MC onto the servo; it will move forwards a little without straining anything too much provided the clips for the hard lines are released where necessary.

If the servo is set wrongly (i.e. as per JCS's), as soon as the MC is moved, the pushrod will push out of the servo under its own steam (with a force of ~15lbs or more) and if the rod comes out, oil will burp out everywhere. If there is enough force to overcome the spring inside the MC, then the brakes will come on.

If the servo is just fine, (then provided you have hydraulic pressure from the 'bomb'), the pushrod will more or less stay put until you push down a little on the brake pedal; if you push down like that (even a small amount) the pushrod will be fired out with some force (and may get damaged/lost) so it is best if you have someone (or something) ready to catch the rod if/when it comes out. NB the rod can come out with a force of up to about 1000lbs, so don't put flesh and blood in the way as a hard stop.

If in doubt about the setting for the servo adjustment, I have usually taken the view that the servo should be fully extended when the pedal is at the top of the stroke. Possibly there is better guidance than this in the workshop manual.

BTW IIRC I detailed that I tested the servo operation in a way that was similar to above in my lead post in this thread; when my brakes were binding the servo was behaving properly but the MC was jammed in the 'brakes on' position. When this happens (with a healthy servo) it is obvious because there is actually a gap between the rod end and the MC; when the brake is applied there is a slight (but audible) 'clunk' as the rod clears the gap and starts to work on the back of the MC.

cheers
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by JCS »

Hi Brucey,

Thanks for the reply,
I found out the solution by disconnecting the clevis pin from the shackle.
While the brakes were (very HOT) frozen and the car would not move, and they (brakes) unlocked immediately.
Be careful if you are on a slope as you may get your foot run over. Set the emergency brake.

Best,
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by Brucey »

I guess if the slot isn't very deep and there isn't much articulation in the actuator rod, it might be that you could release the clevis and the brake pedal might still restrict the movement of a servo that is out of adjustment?

cheers
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by BenM635i »

After reading this thread and musing for a few weeks its been on the mind to swap out brake MC on mine.

Went for a drive yesterday, front right caliper is running hot and i get a judder once all is warmed so pretty sure the MC is at fault.. also the front right caliper is new as of 2008 so doubt its binding.

Got me a shiny new brake MC from Eurocarparts who are running a 20% off Easter weekend deal and a free easter egg into the bargain :) £175.99...
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Car has ABS and the MC looks different to those in this thread, part is right for the car so tomorrow its Easter Sunday in the garage making a mess. Hope all goes smoothly, the brake line captive nut near the inner wing looks like it might be tricky. The existing brake MC looks very rusty along with nuts so i have doused in WD40 to soak overnight.

Hope can get away without a full brake bleed as per Brucey's technique by bleeding captive nuts only - will report back.
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by Brucey »

before you start, discharge the 'bomb' by applying the brakes repeatedly until the pedal goes firm and the PAS reservoir level is static. Then remove the brake pads from each caliper, and replace them with worn backings or timber strips the thickness of backings. Then pump the brake pedal until the pistons bear lightly against the timber strips.

Once you have replaced the brake MC, bleed out via the union nuts and leave the reservoir almost empty. Then simply push the brake pistons back, reinstall the pads, top up the fluid if necessary and you should have bled the system out nicely.

cheers
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by BenM635i »

Brucey wrote:before you start, discharge the 'bomb' by applying the brakes repeatedly until the pedal goes firm and the PAS reservoir level is static. Then remove the brake pads from each caliper, and replace them with worn backings or timber strips the thickness of backings. Then pump the brake pedal until the pistons bear lightly against the timber strips.

Once you have replaced the brake MC, bleed out via the union nuts and leave the reservoir almost empty. Then simply push the brake pistons back, reinstall the pads, top up the fluid if necessary and you should have bled the system out nicely.

cheers
Ta Brucey, as always you are a legend... Saved me hours of frustration with that wisdom :D one day if I'm your neck of the woods I'll buy you a brewery by way of thankings.
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by reddo »

@Brucey.

Hi Bruce - just to say many thanks for your detailed breakdown on dismantling the Master Cylinder. I was directed to this forum via another Audi forum as I had exactly the brake binding issues described on my Audi UR Quattro. I now have the MC dismantled on the work bench and the piston & seals are all good but the phenolic bush was tight as described being the cause of all this. I have now abraded it on the internal diameter and will be doing the same on the outside and re-assembling next week. The MC (or prop valve or servo) had no leaks at all, so hoping this exercise will have given it all a stay of execution (replacement) since mine is the Cast Iron version and will be around 200 Euros to replace.

Just to say many thanks again for your detailed and clear description and which was a massive help =D>

Regards
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by fallon58 »

Hi Brucey,

I have an 89 635csi highline which demonstrated exactly the symptoms you described in your excellent article. Having now stripped down the mc the spacer was indeed out of tolerance and I have cured this as per your supplied tolerances. Whilst on the bench, I decided to renew all of the seals in the mc supplied by Big Redd as per your article. The rear piston was really easy, flick off the spring clip and replace the seals. Now the front piston is a bit of a mystery (I have a cast body with the poppet valve). Does the front piston dis-assemble in order to easily slide the new seals onto the shaft? It looks like it should as there are two flats on the piston, one in the middle and one at the front which both take a 15mm open jaw. There is also a cross head at the rear which looks like it should unscrew? Having tried to dis-assemble the piston I am now not too sure. Do the front seals have to be levered off the seats on the front piston whilst it is in one piece? I can do this but I am loathe to destroy the existing seals in the process of removal, equally I don't wish to damage the new seals by an incorrect fitting process.


Your advice would be greatly appreciated.


Best regards,

Kevin.
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by GazM3 »

Both my e23 & e24 had same issues with locking brakes when hot. Both solved with 1” e32 750il master cylinder replacement
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by Brucey »

fallon58 wrote: Sat Jun 16, 2018 4:15 pm Hi Brucey,

I have an 89 635csi highline which demonstrated exactly the symptoms you described in your excellent article. Having now stripped down the mc the spacer was indeed out of tolerance and I have cured this as per your supplied tolerances. Whilst on the bench, I decided to renew all of the seals in the mc supplied by Big Redd as per your article. The rear piston was really easy, flick off the spring clip and replace the seals. Now the front piston is a bit of a mystery (I have a cast body with the poppet valve). Does the front piston dis-assemble in order to easily slide the new seals onto the shaft? It looks like it should as there are two flats on the piston, one in the middle and one at the front which both take a 15mm open jaw. There is also a cross head at the rear which looks like it should unscrew? Having tried to dis-assemble the piston I am now not too sure. Do the front seals have to be levered off the seats on the front piston whilst it is in one piece? I can do this but I am loathe to destroy the existing seals in the process of removal, equally I don't wish to damage the new seals by an incorrect fitting process.


Your advice would be greatly appreciated.


Best regards,

Kevin.
there are several different ways of assembling the front piston and in many cases the front piston has a valve built into it so that there is some compensation port function. A screw in the middle of the piston could be part of the piston construction that allows the seals to be fitted easily or it could just be part of the valve built into the piston. Any flats on the piston may well be for spanners as you say but if the assy is assembled with threadlock it will not come apart easily, not without heat anyway, which may knacker the poppet valve and the seal anyway. So I don't know offhand what the best route is there, sorry.

I'd suggest that seals are pretty stretchy when they are new so it might be that they can just slide over?
If anyone has a scrap unit to experiment with, maybe they could try disassembling it and see how it goes.

If trying heat, boiling water will heat stuff usefully and probably won't ruin rubber parts so that would be what I'd try first.

BTW I'm glad that this has been useful to Audi Quattro owners too; all we need is some Maserati owners and maybe we have a full set of this type of brake user?

cheers
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by tonomontt »

GazM3 wrote: Sun Jun 17, 2018 8:56 pm Both my e23 & e24 had same issues with locking brakes when hot. Both solved with 1” e32 750il master cylinder replacement
Do you have the part number for that cylinder you bought?
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by JCS »

tono,

the larger bore e32 750 # is 34311156643, make you get the 1988/89 year!
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by 1bhp »

@brucey & @Ron

Hi. Rather than start a new thread I'm intrigued if your experiences are anyway connected to what I'm experiencing - I recently drove the car ('89 RHD, Highline) back from the Cotswolds to London, on coming through town in light traffic I noticed the brake pedal softening to an mildly-alarming degree, I can stop well enough but there was a lot of travel and a distinct pull to the right. When I got back to the garage after gingerly crossing town, off-side front was noticeably hotter the the other 3 corners.

After limited investigation I'm told that the MC heats up due to its location in relation to the engine, hence the pedal softening/ nearest brake binding. Since cooling and driving again the pedal returns to 'normal' but then this evening after a shortish drive on a hot evening in some traffic the soft pedal returned slightly whilst driving, but most noticeably after it was sat for a few minutes with the engine off whilst I cleared the garage.

I'm also told that fitting protective heat wrap to the MC will protect from heat and should resolve the problem. I'm inclined to try that anyway as a first try, but also inclined that the problem might be more likely an MC on its way out...

Any thoughts or advice gratefully received.

best. Ben
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by bm635csi »

1bhp wrote: Tue Jun 02, 2020 9:09 pm @brucey & @Ron

Hi..When I got back to the garage after gingerly crossing town, off-side front was noticeably hotter the the other 3 corners.
After limited investigation I'm told that the MC heats up due to its location in relation to the engine, ..... Any thoughts or advice gratefully received.
best. Ben
I had/have the same issue being a RHD 1989 . In my case the issue is a combination of age , not much use of the shark and proximity of MC close to the exhaust manifold. The front Left wheel will lock and placing a heat wrapper on the MC and wrap the metal brake line will help but not a permanent solution especially in Summer. Yesterday it happened again so remove the calipers and wire brush the rusts , lubricate and change/bleed the brake fluid Front left Caliper.

Its holding ( I mean releasing ) so far but solution is to find a proper shielding of MC & brake line IMO. I had similar issue on E28 but not so much on E34 . The E32 MC is a good solution and with age a good option to replace the old E24 MC too , but without proper shielding , it will happen again IMO. I am still experimenting n looking for solution. My MC wrap workaround
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by jps635 »

There's plenty of heat shielding products around, like here. https://www.heatshieldproducts.co.nz/header-armor.html
The header armour is easy to work with and mould to shape. I've seen plenty used on race cars to shield hydraulic reservoirs and had an AU Falcon with a factory exhaust manifold shield made from a similar product. See also the velcro tubing to wrap lines in situ.
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by bm635csi »

jps635 wrote: Tue Jul 21, 2020 8:13 am There's plenty of heat shielding products around, like here. https://www.heatshieldproducts.co.nz/header-armor.html
... See also the velcro tubing to wrap lines in situ.
Great find jps635. Just looking at the site and the velcro tubing will definitely do the job. I am calling them first thing tomorrow. thanks
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by 1bhp »

bm635csi wrote: Tue Jul 21, 2020 9:02 am
jps635 wrote: Tue Jul 21, 2020 8:13 am There's plenty of heat shielding products around, like here. https://www.heatshieldproducts.co.nz/header-armor.html
... See also the velcro tubing to wrap lines in situ.
Great find jps635. Just looking at the site and the velcro tubing will definitely do the job. I am calling them first thing tomorrow. thanks
Be good to know which one you go for and how you get on with fitting it etc. I'm having a new MC fitted tomorrow anyway, but want to wrap it as best as I can - I've got some of the traditional DEI titanium exhaust wrap, as a more heavy duty product from https://funkmotorsport.com/product/tita ... gIXmfD_BwE was too bulky to fit in place...
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by JCS »

1bhp wrote: Tue Jun 02, 2020 9:09 pm @brucey & @Ron

Hi. Rather than start a new thread I'm intrigued if your experiences are anyway connected to what I'm experiencing - I recently drove the car ('89 RHD, Highline) back from the Cotswolds to London, on coming through town in light traffic I noticed the brake pedal softening to an mildly-alarming degree, I can stop well enough but there was a lot of travel and a distinct pull to the right. When I got back to the garage after gingerly crossing town, off-side front was noticeably hotter the the other 3 corners.

After limited investigation I'm told that the MC heats up due to its location in relation to the engine, hence the pedal softening/ nearest brake binding. Since cooling and driving again the pedal returns to 'normal' but then this evening after a shortish drive on a hot evening in some traffic the soft pedal returned slightly whilst driving, but most noticeably after it was sat for a few minutes with the engine off whilst I cleared the garage.

I'm also told that fitting protective heat wrap to the MC will protect from heat and should resolve the problem. I'm inclined to try that anyway as a first try, but also inclined that the problem might be more likely an MC on its way out...

Any thoughts or advice gratefully received.

best. Ben
Ben,

A heat shield is not the answer, if you read more closely, it is the (EDIT phenolic) plug that is squeezing the shaft, is as though the brake fluid as impregnated the plug and caused it to swell with heat. Getting a new M/C is the solution.

Jay
Last edited by JCS on Wed Jul 22, 2020 1:09 am, edited 1 time in total.
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by bpoliakoff »

Jay, can't find a definition for pholihic Could it be phenolic which is some kind of strange plastic with a molasses base with all kinds of porous filler? Just one more thing to learn for me
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by hornhospital »

Phenolics are a lot more complex than that.

https://en.m.wikipedia.org/wiki/Phenol_ ... hyde_resin

Typically they are resin impregnated linen cloth of various densities. Still used in electrical circuits as insulators, but largely replaced by high density fiberglass.
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Re: Binding brakes/faulty master cylinder; mystery solved???

Post by 1bhp »

JCS wrote: Tue Jul 21, 2020 10:21 pm
1bhp wrote: Tue Jun 02, 2020 9:09 pm @brucey & @Ron

Hi. Rather than start a new thread I'm intrigued if your experiences are anyway connected to what I'm experiencing - I recently drove the car ('89 RHD, Highline) back from the Cotswolds to London, on coming through town in light traffic I noticed the brake pedal softening to an mildly-alarming degree, I can stop well enough but there was a lot of travel and a distinct pull to the right. When I got back to the garage after gingerly crossing town, off-side front was noticeably hotter the the other 3 corners.

After limited investigation I'm told that the MC heats up due to its location in relation to the engine, hence the pedal softening/ nearest brake binding. Since cooling and driving again the pedal returns to 'normal' but then this evening after a shortish drive on a hot evening in some traffic the soft pedal returned slightly whilst driving, but most noticeably after it was sat for a few minutes with the engine off whilst I cleared the garage.

I'm also told that fitting protective heat wrap to the MC will protect from heat and should resolve the problem. I'm inclined to try that anyway as a first try, but also inclined that the problem might be more likely an MC on its way out...

Any thoughts or advice gratefully received.

best. Ben
Ben,

A heat shield is not the answer, if you read more closely, it is the (EDIT phenolic) plug that is squeezing the shaft, is as though the brake fluid as impregnated the plug and caused it to swell with heat. Getting a new M/C is the solution.

Jay
Thanks Jay. All a bit beyond me I’m afraid, but appreciate you flagging. Car was dropped off this morning to have a new MC fitted. Planning on trying to pretect the new one from heat as best as possible anyway. Fingers crossed!
Ben
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