URGENT - Is it possible / advisable to clamp brake lines?

I've been having some problems with my brakes, and I asked my mechanic if he would be willing to perform a "line-lock test" to help determine the problem. A line-lock test involves clamping off each brake line to keep brake fluid from flowing through. If all lines are clamped, the pedal should be high and hard.

Anyway, the mechanic said that he would never clamp brake lines because they have metal mesh inside of them and he would be worried he would crimp the metal, or at the very least create a weak spot in the line where a bulge or even burst could occur.

Can anyone else weigh in on this debate? I'm planning to take my car to him this afternoon - so quick response would be helpful! Thanks!

Reply to
saxman
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I dont remember anyone on here that has recommended this type of test. Maybe Im wrong.

You seem determined to do this, so go with it and take your lumps.

Brakes are in general not rocket science. I understand you are anxious to get this system working properly, but suggest you find a mechanic you trust and let him do it, or you do the job yourself, however you want to do it.

Reply to
<HLS

I agree with the mechanic. Clamping a brake line closed seems like a very poor idea no matter the internal construction. If the mechanic is a good one I would describe the symptoms, i.e, soft pedal, slowly sinking pedal, grabbing brake, etc., and ask that it be fixed. I would avoid the temptation to either lay out the tests for him to undertake and or otherwise direct the repair.

Reply to
John S.

quoted text -

The problem I'm having is that the mechanic says he "thinks" it's a rear caliper - but he says he can't prove it to me, that there are no real 'tests' that can point to a bad caliper, and he says that all he can do is replace it (for ~$600) He has also admitted that there is a small possibility that he is wrong, and he will replace the caliper and brakes will still feel the same.

Oh, yeah, it might be important to mention that the symptoms I'm having are spongy brakes with farther pedal travel than I'm used to. I just had the mechanic replace the front brakes pads & rotors - that's when the problem showed up. He said he had to unstick a rear caliper because the rear wheel wouldn't turn. Up to that point, I had seen no symptoms that the rear caliper was stuck (no excessive drag, no pulling to one side during braking, no smell, etc). So the mechanic is sure the rear caliper is stuck or sluggish, but he says that there's no way to prove it.

Anyone have any advice?

Reply to
saxman

quoted text -

Jack up the rear wheel and see if it spins freely

I always thought a 'line lock test' was performed by disconnecting the line in question and plugging it with the proper fitting not putting vise grips on the rubber line.

Reply to
RayV

quoted text -

Well, if the rear caliper was indeed stuck then you may very well have found the culprit. But rust can cause a rotor to stop from turning too. If this is a competent mechanic who has done good work for you before, then I would go with his judgement.

Reply to
John S.

quoted text -

$600 seems pretty high for a rebuilt caliper. And a faulty caliper seems like an unlikely diagnosis for the symptoms you described. What you haven't described is probably far more important. How do the brakes perform when you need to make a panic stop at 60 mph on dry pavement? Does the pedal level change when you pump the brakes? The symptoms you are describing might be due to a weak brake hose. Your test may solve the problem if it causes the weak hose to rupture. Your best bet is to find another mechanic and get a second opinion.

-jim

Reply to
jim

Your mechanic is correct.

I don't know about modern vehicles with rear calipers, but on an older vehicle that has a low pedal after a brake job, usually the rear brakes are just out of adjustment.

Having a seized caliper can accentuate that trouble. The caliper was seized so the brake pedal was higher than it 'should' have been. Now the caliper moves so the pedal is now 'normal'.

In other words, you were used to the feel of screwed up or broken brakes....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > I've been having some problems with my brakes, and I asked my mechanic
Reply to
Mike Romain

Yup that sounds about right and for $800 dollars the mechanic will "fix" what he already fixed for free :)

-jim

Reply to
jim

Reply to
saxman

Reply to
Mike Romain

A change that occurs gradually over 7 years is pretty hard to notice. You get used to it. But something must have changed to prompt you to have brake work done in the first place. As far as I know you have never said anything about how effective the brakes are at stopping the vehicle (before or after the work was done). So why did you have the brakes worked on? Why just the front pads replaced?

A single caliper has a much bigger bore than the master cylinder and you have 4 calipers. A very small amount of movement of the caliper pistons translates to a very large move of the master cylinder piston.

Are you very short? Do your legs not reach far enough? The reason you should take it somewhere and get a second opinion is that they will have the necessary facts to give you an opinion about what to do. Anyone responding to you on Usenet doesn't have much in the way of facts. They only have the limited information you have chosen to reveal. If your brakes are not stopping the vehicle like they should you need to have someone else look at them.

-jim

Reply to
jim

I also agree with the mechanic. I would not do such a test unless I was planning on replacing my brake lines in the near future anyway. And I can not think of any reason why you would want to do the test (what's the need)?

Reply to
scott21230

Your mechanic is correct. This line-lock test you have found is not a good idea. First off it isn't going to tell you a damn thing and secondly you stand a good chance of damaging the hoses.

Steve B.

Reply to
Steve B.

Patience wears thin, huh, Steve.

Reply to
<HLS

I don't know that they actually have metal inside them; all I've seen have a fiber that looks like cotton or nylon. Maybe even fiberglas? Anyway, it is perfectly OK to do this - IF your brake hoses are new and in good shape. If they are iffy, he is correct that damage could occur, and then you'd have no choice but to replace them.

When I worked with ABS development, it was common practice to clamp off brake lines when replacing calipers etc. but then again we were dealing with development vehicles where the hoses were maybe a year old at the very oldest. I thought it was a bad practice then, but experience showed no perceptible difference in performance after proper bleeding (on a fully instrumented test vehicle, so even a slight change in the restrictiveness to flow would have been evident,) so at least the new hoses were able to spring back effectively. This was done because on a modern ABS-equipped vehicle, the bleeding procedure is rather involved if air gets into the HCU.

good luck

nate

Reply to
Nate Nagel

Actually, that test *could* in fact tell you something. It would tell you if the spongy soft pedal was due to the master cylinder leaking brake lines or with one of the calipers. If you clamp off all brake lines, the fluid has nowhere to go (can't go to move the pistons), so the pedal should be high and hard. IF there was a problem in the master cylinder or one of the lines up to the clamp point, the pedal would sink or be soft. Also, if everything was fine with the clamps on, by unclamping brake-by-brake, you could pinpoint which caliper/ piston is having the problem.

Now, I've discovered you really shouldn't clamp the line - but plugging the line would have the same effect. While not entirely feasible/useful, please don't immediately shrug off a test because you don't think someone should do it. Think it through.

By the way - while my mechanic said the test wasn't good for the brake lines - he actually liked the *idea* of the test and agreed that it would help with diagnosis (if it was possible to do the test without possibly damaging the brake lines)

Reply to
saxman

quoted text -

Could it just be that the new pads haven't seated yet? That could explain the brake feel. The last time I replaced pads and rotors it took over a thousand miles to start getting the brake feel I expected. Scared the crap out of myself a few times in those first miles.

Reply to
why, me

I would look for a warped rotor that was forcing the pads to retract and physical damage to the caliper. My personal guess is that there is air in the line somewhere along the way.

The OP's brake caliper stuck ON while the car was at the shop overnight and the mechanic had to do something to the caliper to make it release. It is quite possible that he broke the caliper in the process of making it release.

I don't agree with the steps the OP is looking to perform to have his brakes diagnosed but I do believe that there is a problem with his brakes. Presumably he has been driving the car a few years and knows how far the pedal travels and how much force it takes to operate the pedal. I don't buy this theory that the rear calipers were stuck off then magically stuck on while sitting in a bay overnight and are now working fine.

As for the line lock test I still see the test as useless. If the master cylinder developed a bad enough leak to cause the pedal to drop another couple of inches over night then that leak would not magically seal up at three quarters of the travel.

Steve B.

Reply to
Steve B.

I think someone cut some corners when they did your brakes, or used low quality materials.

With properly surfaced rotors and pads of good quality, assuming proper installation, (adjustment if applicable) and preliminary drive-in, braking function should be up to optimum in a very short period of time.

Reply to
<HLS

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