Manager Forum

On some threads relating to brake diagnosis, there is various opinions on the idea of clamping off a brake hose. To the critics of this method, my question is this: "How do you diagnose a brake system when you want to isolate a certain wheel"? If clamping with a device in a modest manner is not a good option, what do you use? Or do you simply start replacing parts?

I am not interested in starting a word war. I'm simply trying to find my way through these issues we face.

Old school verses new school, best way I can categorize it. At one time I always clamped off the hoses, now it's rare if at all since I started getting pieces if hose innards inside calipers. Quickest way I now fine a bad hose or caliper issue is through the bleeder screw. I don't allow a flow from a bleeder when its opened to answer any issues or thoughts I'm having. I'll have a tech in the vehicle pump up the brake and i'll watch how the piston and caliper acts. Sometimes on 4 piston units I'll notice only one piston moving. Abnormal pad wear is a huge tell. Caliper guides are another tell. If after foot is removed from pedal and I open the bleeder and get a good shot of brake fluid the flex is probably collapsed and needs replacement. I will not replace just one, both front will be done. Clamping off just raises the chances of the interior lining breaking apart.

Steve, I can understand what you are saying and I agree with it. But, suppose you are trying to isolate an imbalance issue within the braking system, how do you handle that?

I cannot say I have ever seen an issue with an imbalance of braking that was not caliper related. We block off the master its self to test it. We do not clamp lines or hang calipers from lines. Air in the system can be checked. Master cylinders can be checked. Fluid leaks can be checked. It's a process of elimination in testing for us.

Say you have an issue with a fading pedal. You block off the master cylinder and there is no fading brake pedal. What is your next step?

First I would have checked for leaks or air in the system. If none was found Id block of m/c. If pedal was firm then the next steps would be based on the abs set up on the vehicle.

Suppose the vehicle has only rear anti lock brakes.

Then id separate the front and rear systems to see were the problem is.

brianp87 wrote:Then id separate the front and rear systems to see were the problem is.

I'm with ya on this but I'm failing to figure out how to isolate the one from the other without clamping hoses or breaking open metal lines and capping them, only needing to rebleed everything.

Sorry I am so dense.

OK, lets deal with a generic vehicle, when you speak of rear abs only and its a Ford it gets complicated. Some vehicles have load valves that control the amount of pressure applied to rear brakes. I've lost count of how many Toyota's have arrived from other shops with a spongy pedal and the rear valve had trapped air. Todays vehicles for the most part need a scanner attached to run the abs module forcing air out that pressure can't accomplish. I collapse calipers and clamp them closed with C clamps to test issues like this and can tell if there is a restriction by the fluid flow when I open the bleeders with a pressure bleeder attached. I also have a set of line caps I made using line unions and bung plugs. There are many different ways to get the same results without crimping the flex hoses and I'll tell you usually crimping is a lot quicker but I use alternate methods so I can avoid damaging them. If I get extremely frustrated and crimp one off I do with all intention of replacing it no matter what the outcome.

Well Steve, it looks like you have given me some ideas worth trying. As I mentioned before, I tend to agree with your not clamping off brake hoses but we are getting desperate to solve this problem. I think one thing I am gonna be doing is to remove the front brake calipers and retract the pistons, install my large c clamps and see if we still have the problem.

Will keep posted here.

Thanks.

Before removing I would suggest having someone pump the brake pedal and inspect them for hanging up. I'm sure you already checked for bearing movement to see if its leaning against the piston. That would give you exactly the symptoms you are experiencing. Good luck.