What to do about an NLA brake line w/ a flexible hose in the center?

While driving down to NJ from CT the other day, both of the front brakes on my 2005 Chrysler Town & Country locked up on the highway during an area of heavy traffic.   I was able to limp it to the next exit, and arranged a u-haul to retrieve the van.    By the time I got the u-haul down there to pick it up, it worked perfectly fine, as it does driving around my driveway.  

This sounds to me like the classic "expanded rubber brake line" issue, but I've only had that on one caliper.   But alas!  Chrysler, in all their infinite wisdom, put flex hoses between the master and ABS unit!  So it could be that this rubber line was the culprit!

However, only one of these hoses is available!  The other is NLA.  I've spent hours trying to find them.  If anyone is better at speaking Mopar than me, they're part #s 04721331AA & 04721330AA

So my questions are:

1. How likely is this to be my culprit?   I'm planning on replacing all soft lines now anyway, and this seems like it would fit.
2. What would be an acceptable substitute?    Do you think it would be okay to just do a bit loop of regular tubing to act as a spring in between them?  That was my plan if I could find a section of M12x1.0 6mm tubing. 

Thanks for any ideas!

My wild ass guess would be a bad caliper or stuck slides. 

Which wheel or wheels locked up?

Never mind sounds like both fronts locked up. I would still take things apart and look for a mechanical failure, before suspecting a hose. 

The flex hose is there to decouple ABS Pump vibration from the firewall.  A hard line with a loop in it will be OK.

I have never seen those fail aside from the hardline rusting through.

That said, if those were the problem, all four brakes would have been affected.  Your vehicle like every other transverse engined vehicle has a split diagonal system.  The circuits are split LF-RR and RF-LR not front/rear.

Folgers said:

My wild ass guess would be a bad caliper or stuck slides. 

Which wheel or wheels locked up?

 

Never mind sounds like both fronts locked up. I would still take things apart and look for a mechanical failure, before suspecting a hose. 

Yeah, that was my initial checklist as well...  I was leaning towards mechanical, but the fact that it was both fronts at the same time with no prior history of dragging/issues leads me to think the suspect lies somewhere other than spontaneous failure of both sides at the same time/same place. 

Pete. (l33t FS) said:

I have never seen those fail aside from the hardline rusting through.

That said, if those were the problem, all four brakes would have been affected.  Your vehicle like every other transverse engined vehicle has a split diagonal system.  The circuits are split LF-RR and RF-LR not front/rear.

Are you sure that these use a split LF-RR setup?  From what I can tell from the service manual, it seems that the traction control system modulates the front wheels via the ABS unit, but I don't believe it's attached to the rear the same way.  It looks like a normal rear ABS control.

Unfortunately, I can't find a clear hydraulics diagram, but they refer to the primary circuit controlling the drive wheels. 

AngryCorvair (Forum Supporter) said:

The flex hose is there to decouple ABS Pump vibration from the firewall.  A hard line with a loop in it will be OK.

Thanks for confirming my thought there...

I have been finding that Summit has a good selection of lines, including stainless braid, in several lengths and end types. I had been looking at mostly M10, but they had some M12, too.

WonkoTheSane said:

Pete. (l33t FS) said:

I have never seen those fail aside from the hardline rusting through.

That said, if those were the problem, all four brakes would have been affected.  Your vehicle like every other transverse engined vehicle has a split diagonal system.  The circuits are split LF-RR and RF-LR not front/rear.

Are you sure that these use a split LF-RR setup?  From what I can tell from the service manual, it seems that the traction control system modulates the front wheels via the ABS unit, but I don't believe it's attached to the rear the same way.  It looks like a normal rear ABS control.

Unfortunately, I can't find a clear hydraulics diagram, but they refer to the primary circuit controlling the drive wheels. 

100% certain.

It is four channel ABS, they can do what they want to do in there.

In reply to Pete. (l33t FS) :

Any other good hypothesis about why the brakes would be applied fairly heavily (and apparently evenly?) On the two front wheels?

Pete. (l33t FS) said:

I have never seen those fail aside from the hardline rusting through.

Well, it looks like the reason you've never seen these fail is because they really can't.  It's not a traditional rubber-wrapped teflon-lined brake line, which explains why they felt weird to flex.  It's just straight up nylon/plastic hose with a stainless wrapper:

I cut both up both front soft lines as well, and those look fine too internally.    I even tore down the calipers to make sure they looked okay:

For the record, I replaced the rotors and pads when I bought the van in 2017, and I replaced the pads & fluid last July 2021 again @ 30k (151k), all of the hardware was greased at that point and came apart fine.  That was probably 10k ago or so.   Pads still have plenty of life, although the rotors show some surface flaking from rust. 

So, to recap, what other things can cause both front brakes to drag/lock up to the point of smoking after an hour of heavy highway traffic, sometimes stop-and-go? It is possible that the rears were suffering from the same fate, but weren't smoking so I didn't notice them.

Should I replace the master or ABS unit or anything?  There was no dash light for ABS failure, but I'm not sure if this van has that.

I've seen boosters do this on multiple platforms. 

I've also seen brake hoses fail simultaneously on both front do this.

Abs module failures I've normally seen cause a soft pedal.

I'd get them to lock up and then loosen the master cylinder bolts, allowing it to come slightly forward, if they unlock I'd assume booster.

I did an escape the other day that was a hose failure, and when they were locked if I loosened the upstream brake hose fitting, I'd get just a dribble of fluid, and when I loosened the hose fitting at the caliper I got a spray, and the caliper released. A hose fixed that one.

I've never seen one of those braided abs lines fail except on F250s where its common and they leak

Opti said:

I've seen boosters do this on multiple platforms. 

I've also seen brake hoses fail simultaneously on both front do this.

Abs module failures I've normally seen cause a soft pedal.

I'd get them to lock up and then loosen the master cylinder bolts, allowing it to come slightly forward, if they unlock I'd assume booster.

I did an escape the other day that was a hose failure, and when they were locked if I loosened the upstream brake hose fitting, I'd get just a dribble of fluid, and when I loosened the hose fitting at the caliper I got a spray, and the caliper released. A hose fixed that one.

 

I've never seen one of those braided abs lines fail except on F250s where its common and they leak

Interesting, I figured a booster failure would be lack of power assist, poor idle due to vacuum leak, hissing, etc.

I was busy loading up the parts cannon, grabbing a boneyard ABS unit, new master, all 4 soft lines... But a booster wasn't on the list.

This was straight up like I was holding the brakes down.  Acceleration was greatly diminished, and shortly you could start smelling the brakes.  Lots of smoke when I came to a stop 1/4 mile down the highway later.

I'm not sure I understand the original symptom.  Did you apply the brakes and they didn't release or did they apply on their own?  Both front brakes were showing signs of being hot?

The ABS will not self-apply the brakes without being commanded to for traction control purposes, and it would have also cut throttle.  You would have also heard/felt the ABS pump buzzing.

Likewise, flex hoses checkvalving would not self apply, and they generally cannot build THAT much pressure.  And it is not sudden-onset.

It's really smelling like a failing booster, like the apply valve was leaking and allowing air into the back side of the diaphragm.

I should note that about 80% of the boosters I have replaced have been Chrysler products.  Normally the failure is rusting through or binding up internally.  I'd take the master cylinder off and check for fluid in the booster (IIRC it is an open chamber that is sealed by the end of the master).  If there is fluid in there,  the master cylinder was leaking into the booster and damaged it.

APEowner said:

I'm not sure I understand the original symptom.  Did you apply the brakes and they didn't release or did they apply on their own?  Both front brakes were showing signs of being hot?

After much stop and go traffic on a highway, accelerating from the latest stop up to 40ish mph felt very sluggish.  Pulling over showed that my front brakes were smoking, and after limping to the next exit about 1/4 mile down the road the smoke was quite bad from both fronts.

Pete. (l33t FS) said:

The ABS will not self-apply the brakes without being commanded to for traction control purposes, and it would have also cut throttle.  You would have also heard/felt the ABS pump buzzing.

Likewise, flex hoses checkvalving would not self apply, and they generally cannot build THAT much pressure.  And it is not sudden-onset.

 

It's really smelling like a failing booster, like the apply valve was leaking and allowing air into the back side of the diaphragm.

 

I should note that about 80% of the boosters I have replaced have been Chrysler products.  Normally the failure is rusting through or binding up internally.  I'd take the master cylinder off and check for fluid in the booster (IIRC it is an open chamber that is sealed by the end of the master).  If there is fluid in there,  the master cylinder was leaking into the booster and damaged it.

Alright, I like the hypothesis, and it's significantly better than the fat lotta nothin I can figure out, I'll pull off the master in a bit and let you know the result.

In reply to Pete. (l33t FS) :

The master looks nice and dry both inside and out of the boot in the rear:

The booster looks dry inside:

Any suggestions on how to test it?

In reply to WonkoTheSane :

When the brakes are locked, loosen the nuts for the master cylinder so it can slide forward. If it releases, Replace the booster.

If it doesn't free up, move downstream. When they are locked up crack a brake line at the top of the brake hose. If the caliper doesn't unlock move downstream to the hose/caliper connection. Crack it. If you get a fluid spurt and it frees up, replace the hoses.

My guess is booster, but I've seen two front hoses fail simultaneously, and it was a chrysler product

In reply to Opti :

Thanks for the walk through.. I won't get to use it this time, but I appreciate all the help.

I've got a new master, all 4 soft lines and a new booster going in.  The calipers looked good on disassembly, so I left them.