Author Topic: UK MOT's (Read 25032 times)

Darren · « **Reply #25 on:** September 22, 2009, 05:05:31 PM »

Hi Don, just two wheels at a time, front or rear. Imbalance is left/right front only as the back seems to be fine. There is no ABS on the back.

I need to get to the bottom of this in case it is a problem that leads to a greater failure.

No1_sonuk · « **Reply #26 on:** September 22, 2009, 05:15:15 PM »

Front to back imbalance isn't dangerous but left to right can be.

dsquire · « **Reply #27 on:** September 22, 2009, 05:22:28 PM »

Quote from: Darren on September 22, 2009, 05:05:31 PM

Hi Don, just two wheels at a time, front or rear. Imbalance is left/right front only as the back seems to be fine. There is no ABS on the back.

I need to get to the bottom of this in case it is a problem that leads to a greater failure.

Darren

Hang in there. I am typing up a reply and will post it in a few minutes.

Don

Darren · « **Reply #28 on:** September 22, 2009, 05:25:51 PM »

There should be a front to back imbalance, but not left to right.

The machine says 60% imbalance which should be not only hard to control on the road but downright dangerous.

Thing is it doesn't show up on the road at all. brakes really nicely. Even the tester was surprised when he took it out for a spin, he was expecting exactly what the machine told him. The spin which I insisted on was the only thing that persuaded him to let the car pass the test.

Where do I go from here? What am I supposed to believe?

I put two new front tires on for the MOT, both were well worn, but evenly........should that be any indication...I doubt it.

dsquire · « **Reply #29 on:** September 22, 2009, 05:36:24 PM »

Quote from: Darren on September 22, 2009, 05:25:51 PM

There should be a front to back imbalance, but not left to right.

The machine says 60% imbalance which should be not only hard to control on the road but downright dangerous.

Thing is it doesn't show up on the road at all. brakes really nicely. Even the tester was surprised when he took it out for a spin, he was expecting exactly what the machine told him. The spin which I insisted on was the only thing that persuaded him to let the car pass the test.

Where do I go from here? What am I supposed to believe?

I put two new front tires on for the MOT, both were well worn, but evenly........should that be any indication...I doubt it.

Darren.

Just talked to my son about your situation.

You may have a flex line that is starting to come apart from the inside. When you step on the brake pedal a piece of rubber that is deteriorating flexes off the inside wall and tries to block off the hose causing a pressure build up.

Another possibility is with disc brakes sometimes as the calipers get old they can stick and require extra pressure to expand them.

I am not sure what parts you replaced but I seem to remember that you had to do some work on the front end to get it ready for your MOT check.

I'll keep thinking on this end and we will get it figured out yet.

Cheers

Don

Darren · « **Reply #30 on:** September 22, 2009, 05:41:02 PM »

Thanks Don really appreciate the help. The hose is new and both the callipers have been stripped down fully twice. Everything is free as it should be.

I wonder if I took the fuse out for the ABS if the problem would still be there when on the machine? Is there a fuse, there must be?

dsquire · « **Reply #31 on:** September 22, 2009, 06:08:50 PM »

Darren

Were both hoses brand new?

Here is what happens when you put the brakes on. You have to become the brake fluid and try to make your way to the wheel cylinder so you can do your job and stop the wheel. This is how I try and think it through.

When you step on the prake pedal you push brake fluid out of the master cylinder. Some goes to the front and some to the rear. What goes to the front goes into a "T" so that it can split up for the left and right front wheel. It now goes to each wheel where it has to pass through the flex hose then into the wheel cylinder or caliper.

I know it would be a pain in the butt to do but if you were to disconect the brake caliper and put a pressure guage on the end of the flexible brake line and put an equal pressure on the brake pedal while you tested both right and left sides. This would at least eliminate your hoses and brake lines as being suspect.

If you take the vehicle for a short drive in the country without using the brakes very much. Stop and pullover and put your hand on each wheel. Is one warmer than the rest? If it is that may be where the problem is.

I had a car one time that had that problem. Get to work after a 15 minute drive in the country and one wheel was hot. thought is was a bearing. Nope. It was the flex hose holding slight pressure on the brake.

That all I can think of for now.

Cheers

Don

Darren · « **Reply #32 on:** September 22, 2009, 06:32:36 PM »

New hose on the low side only...

Circuit is a tad more complicated,
master cylinder-abs splitter-wheels

Great thinking about the disk temps, I'll have a quick drive and test that tomorrow.

Now that I have a MOT I can drive it. Driving without one in the uk is now a serious offence and as the MOT results are now computerised you get caught pretty quickly from number plate recognition devices fitted in police cars.

dsquire · « **Reply #33 on:** September 22, 2009, 06:41:49 PM »

Quote from: Darren on September 22, 2009, 06:32:36 PM

New hose on the low side only...

Circuit is a tad more complicated,
master cylinder-abs splitter-wheels

Great thinking about the disk temps, I'll have a quick drive and test that tomorrow.

Now that I have a MOT I can drive it. Driving without one in the uk is now a serious offence and as the MOT results are now computerised you get caught pretty quickly from number plate recognition devices fitted in police cars.

"
"New hose on the low side only..." --Is this the side that has the low braking pressure?

Don

Darren · « **Reply #34 on:** September 22, 2009, 07:03:19 PM »

Yes, it was changed but made no difference to the results.

dsquire · « **Reply #35 on:** September 22, 2009, 07:15:49 PM »

Quote from: Darren on September 22, 2009, 07:03:19 PM

Yes, it was changed but made no difference to the results.

I am running out of thing to look at. This is what happens with a bad flexible hose.

When pressure is put on it restricts to movement of the brake fluid. The more pressure you put on the more it restricts. After a period of time the pressure will slowly bleed thru. It is acting like a one way restrictor valve. It is the reverse of the problem that I had with my car that caused the brakes to stay on and drag causing heating of the rotor and wheel.

I will try and talk to my son again and see if there is any way that the abs system could be causing any of this.

Cheers

Don

rleete · « **Reply #36 on:** September 22, 2009, 07:36:24 PM »

With the wife's Buick, I could not properly bleed the brakes because of the ABS. Seems you need some electronic doohicky (technical term) to hold the system open while you bleed. Costs a lot more than having it done at the garage.

Air in the line will give lower pressure reading on one side.

dsquire · « **Reply #37 on:** September 22, 2009, 08:09:13 PM »

Darren

Talked to my son again about the abs system and he dosen't think that is the problem as you would know when that comes on.

Lets walk thru this again.

Low brake pressure to one front wheel. Why?

Restriction in brake line? where? In steel brake line? Did it get pinched when you were making repairs? It could be pinched off enough to allow a bit of brake fluid through to apply the brakes and bleed the brakes but not as much as the other side causing an imbalance, therefore low braking pressure.

In flexible brake line? Same symptoms as steel line above.

Are calipers operating properly? Does piston expand and retract easily? Do calipers slide freely on mounting bolts? Have calipers been rebuilt? Have calipers been replaced? Has both sides been replaced or rebuilt or just one side?

My son says that when doing major brake work he would always install new or factory rebuilt calipers. If one flexible hose needed replacing, replace them both. Be sure the calipers are free on their mounting so they can work the way they were designed to.

If I think of anything else Darren I'll put up another post.

Cheers

Don

Darren · « **Reply #38 on:** September 23, 2009, 05:03:54 AM »

I think we've pretty much covered everything that has been tried.....

One question, in a hydraulic system if air is present in one calliper or line wouldn't it effect both brakes?

dsquire · « **Reply #39 on:** September 23, 2009, 05:18:47 AM »

Quote from: Darren on September 23, 2009, 05:03:54 AM

I think we've pretty much covered everything that has been tried.....

One question, in a hydraulic system if air is present in one calliper or line wouldn't it effect both brakes?

Morning Darren. For Me it's just about bed time but I keep weird hours, I'm a bit of a night hawk.

Now to the question. I don't think that it would Darren because air compresses differently than brake fluid.

Cheers

Don

Darren · « **Reply #40 on:** September 23, 2009, 05:21:34 AM »

Morning Don, now get yourself off to bed......what is it there 5.30am?

Bernd · « **Reply #41 on:** September 23, 2009, 08:18:31 AM »

Have been following this thread for a while now.

After reading Don's questions I came up with a few more. Does the car have front wheel drive or rear wheel drive? And is it an automatic shift or standard shift?

I'm wondering, if it is front wheel drive, if the drivetrain is having an effect on the test? I'd also question the set up on the machine.

Regards,
Bernd

Darren · « **Reply #42 on:** September 23, 2009, 08:23:40 AM »

Hi Bernd,

Front wheel drive manual shift....auto's are quite scarce here unlike the US. The engine is not powering the brake tester, the brake tester turns the wheels and the brakes are applied to stop the testing machine's rollers.

I think I need to take the car to another test station to verify if the car has actually got a problem and then take it from there. I'll try to find one with a different machine though.

CrewCab · « **Reply #43 on:** September 23, 2009, 01:15:58 PM »

Quote from: Darren on September 23, 2009, 08:23:40 AM

I think I need to take the car to another test station to verify if the car has actually got a problem and then take it from there. I'll try to find one with a different machine though.

Agreed

from all you've done and has been suggested / dispelled the next issue has to be check the test equipment, I'm not saying it will be wrong but you need to know for sure or there is no apparent way forward.

As for the question of air in the system etc, yes air will compress at a lower pressure, hence it gets better with pumping, however the pressure in the system has to be equal at all points afaik that's a simple law of physics.

hth

CC

andyf · « **Reply #44 on:** September 23, 2009, 04:46:51 PM »

Bit of a long shot, and I'm not sure

if it would make any difference, or whether any difference it did make would be only slight, but are the tyres the same brand, with the same wear and at the same pressure?

Andy

Darren · « **Reply #45 on:** September 23, 2009, 04:53:19 PM »

Both tires brand new for the MOT.....

I realise I keep knocking all the suggestions flat having already covered them. But please keep them coming as someone might hit the nail as it were....

Bernd · « **Reply #46 on:** September 23, 2009, 05:46:01 PM »

Have to agree with CC. Time to check the test equipment.

Bernd

CrewCab · « **Reply #47 on:** September 23, 2009, 06:41:31 PM »

Just a random thought Darren, did the same rollers give equal pressure on the rear brakes

CC

Darren · « **Reply #48 on:** September 23, 2009, 06:46:35 PM »

Quote from: CrewCab on September 23, 2009, 06:41:31 PM

Just a random thought Darren, did the same rollers give equal pressure on the rear brakes

CC

Yes, but there is no ABS on the rear of this car.

No1_sonuk · « **Reply #49 on:** September 23, 2009, 06:49:32 PM »

I'd have thought the chances of getting the same imbalance on the front and the back would be remote enough to warrant blaming the test equipment.

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Author Topic: UK MOT's (Read 25032 times)