TheSamba.com :: View topic - Discuss deteriorating rubber brake lines holding pressure

Mon Jan 06, 2020 12:00 am

Friends and Countrymen,

OK, so there is a common position that a rubber hydraulic brake hose can deteriorate internally in a way that when you press on the brakes and release the brake pedal, the caliper fed by the hose can remain pressurized, causing the brake pads to press on the rotor. It's all over the internet and has been for years.

I do not believe this can happen, so I'd like to discuss it with all the minds here on Samba.

I"m all ears. Someone take a crack at how this happens by explaining what's going on inside the hose.

Doug

Mon Jan 06, 2020 1:31 am

it definitely can!
and we had something similar happening on the rear brakes of our old silver shadow. it wasnt a full lockup following pedal release, but a very very very slow release and dragging.

its a common issue on those cars due to their unique brake system, relative lack of use they typically get, and the complexity/expense of renewing all the hydraulics.

i snapped a pic of one of the ancient lines i cut in half to see how theyd deteriorated on one of the offending corners.
the hose is multi layered, and fluid begins to creep around the collapsing inner-most layer which folds on itself and prevents the pressure from releasing once youre off the pedal.

i suspect more modern brake hoses dont have this issue as the inner most material is probably something more durable, and i dont know whats on these vans, nor have i bothered to cut open a modern car hose to confirm

heres the RR hose for reference, you can make out the folded/collapsing inner layer.

in case the picture is downsized - heres the flickr link
https://www.flickr.com/photos/valvecovergasket/6999098773/in/album-72157625244043432/

Mon Jan 06, 2020 3:21 am

IdahoDoug wrote: Friends and Countrymen,

OK, so there is a common position that a rubber hydraulic brake hose can deteriorate internally in a way that when you press on the brakes and release the brake pedal, the caliper fed by the hose can remain pressurized, causing the brake pads to press on the rotor. It's all over the internet and has been for years.

I do not believe this can happen, so I'd like to discuss it with all the minds here on Samba.

I"m all ears. Someone take a crack at how this happens by explaining what's going on inside the hose.

Doug

Doug, most often you speak truth, in this instance I disagree with your stance,

My brake hose.....

Brake systems generate what? Five hundred to a thousand PSI under normal braking? Even more on a panic stop.

You've got a rotted closed hose, you can force fluid through that hose with 1000 PSI.
Once through the hose, how it it coming back to the Master Cylinder?
Sure, drum brakes have Springs ti pull the shoes back.
Disc Brakes? Good luck with that.

The lack of applied foot pressure will lessen the force upon the pistons, they may even bleed off but it'll take a bit of time, not the free flow back and forth that you have in a clear hose.

I think you'll find that such minor organizations such as the ASE disagree with you as well. They teach brake line clog as truth.
Raybestos is another believer in internal brake hose failure creating dragging brakes.

Dave

Mon Jan 06, 2020 5:14 am

It does happen. It was more noticeable on the early front drum brake VWs. You’d get a pull because one brake could get ahead of the other under braking.

It’s very easy to diagnose. If you have a dragging brake when you rotate the wheel by hand, if cracking the bleeder open, frees the wheel, you have a restricted flex hose. If not, you’ve got a caliper or wheel cylinder sticking.

Sorry.

Mon Jan 06, 2020 5:47 am

Mine.

Theory goes before they completely swell shut they act as a one way valve. I suppose the way to check would be to crack the bleeders and see if that unsticks your brakes.

Mon Jan 06, 2020 7:08 am

we were discussing this in the sheer bolt thread...this is a cut and paste from there

I said he was kidding, and I have done 100's of hoses for this

Quote:
I have no doubt you've been paid to replace 100s of hoses. But I doubt a single one of them had a piece of rubber inside them holding hydraulic pressure in the hose. Check my new thread and state your case.

which thread is that?

every one of them was confirmed by a dragging brake. open bleeder, brakes free up. change hose and problem gone. been a tech since the 90's so you'll have a real hard time changing my mind. never had a come back after a proper diagnosis either.

not looking to start WW3...but I am really interested in your thought process. I have even sliced hoses open and found the breech in the liner where brake fluid has gotten between the layers. everyone thinks it's a random flap of rubber...it isn't. brake fluid gets behind the "liner" and essentially makes an internal "balloon" restricting flow.

think of a bubble on the sidewall of a tire...but internal. that's what happens. 99.9% of the time it happens where the hose has the most flex

same thing happens on hydraulic systems (plows, hydrostatic drives etc) I have witnessed it, that's why I will stand behind the phenomenon

Mon Jan 06, 2020 7:16 am

old_man wrote: Mine.

Theory goes before they completely swell shut they act as a one way valve. I suppose the way to check would be to crack the bleeders and see if that unsticks your brakes. Wow , is that a bad one or what!!!! :shock: :shock:

Mon Jan 06, 2020 7:33 am

Since I work on much younger vehicles in terms of age, I neatly get to avoid this issue as a day to day 'thing'... :D
But I have seen it in the flesh as it were, several times. The 'hold' as noted, was a gradual release of pressure. First time I encountered it, I was sure it was a bad rebuilt caliper with an internal issue[ fixed frame, 2 halves style]
Obtained another caliper, and the same dragging issue happened again.
Replaced the rubber flex line and all was well. Cut open the rubber hose and saw issues as posted here . Made a believer out of me... :P

I have heard, but not seen , that Teflon lined brake hoses get into similar trouble if the Teflon lining goes bad. I had wondered if that issue was more of a lack of pressure getting to the brake cyl or caliper versus a holding pressure issue, but again, haven't encountered that one yet personally.
Maybe someone with more Teflon Brake hose experience as they age can add to this.

Mon Jan 06, 2020 8:56 am

Great topic! I wonder if we should all be replacing our 30 year old brake lines, no matter how good they "seem" to feel.
My 90 Syncro's brakes [big brake kit in front] develop a noticeable issue ONLY descending when Little Cottonwood Canyon in Utah, 3000 feet in 6 miles. They make a rubbing noise after severe braking, even after releasing the pedal. This goes away after the brakes cool [?]. There is no pulling and the rotors and drums seem true upon inspection.
I wonder if the brake lines could be an issue. Any recommendations on best replacement brake lines?

Mon Jan 06, 2020 10:14 am

Wow, that last photo is crazy, but illustrates how this can happen. I've always felt that the flow can be slowed, but not stopped, as even a tiny pinhole would allow the fluid to escape the caliper and release piston pressure back to zero. If its swollen shut like that last one, I can see how it would be able to maintain some gentle pressure - for instance 5psi - by being so swollen the spot generates its own pressure in pinching itself shut.

I don't think the other ones - partly pinched off - would delay the bleeding off of pressure more than a second or two as there's barely any fluid movement needed to release the piston. The piston only moves a fraction, turning the square piston seal cross section into a parallelogram, which when it springs back to its square shape is what pulls the piston back from pressing on the rotor.

Amazing.

Edit: The braided Vanagon brake line kit is pretty cheap from Van Cafe. I put them on a year or two ago, removing the originals and finding deterioration, etc. Rock Auto also sells replacements for a number of vehicles. I paid some $40 for an 8 piece kit for one of our cars recently on Rock Auto. Very cheap, and of course you'll end up bleeding and having fresh fluid in the system as well. Highly recommended. Buy the correct brake line wrenches and use penetrating fluid on them for days in advance and you'll have little trouble.

Mon Jan 06, 2020 10:18 am

Well that got tucked into bed rather cozily.

I haven't encountered the hose blockage myself but it's a well-known thing, I'd heard of enough instances that I never questioned it. What I wonder is if it's a result of the changes in brake fluid formulations. Going from glycol to silicone bases, Si may be incompatible with the older liners. Or maybe inadvertent mixing makes some nasty chemical stew that swells the liner.

Allowing absorbed water to become excessive may cause the liner material to swell.

Or it's just delamination of the inner tube, possibly age-related, which seems to be what people have seen. Flexing below the minimum bend radius and foolish clamping of the hoses (which I warned someone off recently) would certainly hasten the latter as well.

Quote: I wonder if we should all be replacing our 30 year old brake lines, no matter how good they "seem" to feel.

Yes, at 30 years old, flex hoses are overdue for replacement. Soft goods are susceptible to age regardless of mileage.

Mon Jan 06, 2020 10:27 am

replace hoses when you replace/rebuild calipers..

drain and bleed the brake fluid every 2 years.. 3 years MAX..

if you can't operate the brake bleeder.. see step 1 above (rebuild or replace the calipers).

in my VWs with fixed opposing piston calipers I also Exercise the caliper pistons when I flush brake fluid. I do this by removing the pads, and using a wood/plastic shim to keep the piston from over extending.. I press the brakes till the piston extends out some from it's 'regular' resting place.
then I open the bleeder when I push/compress the piston back in. and repeat till the fluid is clear, then assure air is bled out..

replace the piston rubber dust boots from a rebuild kit or fear a corroded piston bore shortening the life of your caliper..

Mon Jan 06, 2020 10:27 am

tencentlife wrote: Soft goods are susceptible to age regardless of mileage.

Applies to me as well.....

Mon Jan 06, 2020 10:36 am

I have no problem using steel braid brake hoses on my racecar. They are inspected regularly and do give better pedal feel. They are not DOT approved.

For my vanagons, I prefer the rubber hoses that should be DOT approved. They see a lot more road hazards and conditions vs what a race car does on a closed circuit. Also way less miles compared to what you can run up on a vanagon in one year.

Mon Jan 06, 2020 10:42 am

Mark,

For clarity, the braided lines I got were merely rubber lines with steel mesh over them to help prevent expansion with high internal pressures, and also a vast improvement against cutting or nicking from driving through brush, etc. I'm (pretty) sure VC is not selling something that is not DOT approved. They were on sale, and the fit and finish was beautiful and they went on just like factory replacements.

Mon Jan 06, 2020 11:14 am

Quote: with steel mesh over them to help prevent expansion

The thing is, the stock hoses already have that reinforcement, most that I've cut into are a combination of steel wire and fiber braid. If they didn't they would burst on first use. So unless the external braiding you favor is in addition to an encapsulated reinforcement, the outer braid alone would be inferior to the encapsulated braid, because the encapsulation helps prevent the braid from shifting and allowing the inner tube to rupture thru. Plowing thru brush would be a good way to get external cover wire separation to begin. Overflexing the hoses would hasten the same.

So better know what you're buying so you know you're actually getting something better. The external SS-covered hoses I've seen were much smaller OD than conventional hoses, leading me to doubt there is another encapsulated layer within.

Mon Jan 06, 2020 12:25 pm

IdahoDoug wrote: Wow, that last photo is crazy, but illustrates how this can happen. I've always felt that the flow can be slowed, but not stopped, as even a tiny pinhole would allow the fluid to escape the caliper and release piston pressure back to zero. If its swollen shut like that last one, I can see how it would be able to maintain some gentle pressure - for instance 5psi - by being so swollen the spot generates its own pressure in pinching itself shut.

To put it into perspective, that last photo is from my 67 Type 3. I'm assume it was the original lines. The car also sat for 20 years. So not only dealing with 50 years old rubber but 50 year old rubber formulations. For the record I tried to put 120 psi through it for fun......no dice.

Mon Jan 06, 2020 1:23 pm

I too can confirm that this has happened before. I started wrenching on VWs professionally in the 80s. At the time I lived in north Florida. Restricted brake hoses cost me so much time in quality control then that I started removing and inspecting all brake hoses during brake repairs.
I now live in western Washington. I rarely see this anymore. I had a theory that heat and humidity combined had something to do with it. I am old enough now to doubt my theories. Maybe materials are better now. Maybe I just do not tolerate people who will not maintain their vehicles now.
All rubber has a limited service life. If tires time out, so do brake hoses.

Mon Jan 06, 2020 3:11 pm

danfromsyr wrote: replace hoses when you replace/rebuild calipers..

drain and bleed the brake fluid every 2 years.. 3 years MAX..

if you can't operate the brake bleeder.. see step 1 above (rebuild or replace the calipers).

in my VWs with fixed opposing piston calipers I also Exercise the caliper pistons when I flush brake fluid. I do this by removing the pads, and using a wood/plastic shim to keep the piston from over extending.. I press the brakes till the piston extends out some from it's 'regular' resting place.
then I open the bleeder when I push/compress the piston back in. and repeat till the fluid is clear, then assure air is bled out..

replace the piston rubber dust boots from a rebuild kit or fear a corroded piston bore shortening the life of your caliper..

Yes.

or every 15 - 20 years for the rubber hoses (they swell internally from the brake fluid)

a benefit of rubber hoses is that you can squeeze them every couple of years to make sure they are ok

Mon Jan 06, 2020 9:23 pm

I’m another one who has never happen but have heard it referenced enough from trustworthy sources to over come my experience bias.

Replacing hoses every caliper service is overkill. I have six cars from 1999-2006 all on original brakes hoses. I do replace my DOT 4 every 2 years, or whenever I crack a bleeder.

I’ll guess those experiencing hose collapse are using cheap parts or old fluid