Brake Force Limiter (Seat Ibiza 6K)

Hi.

I have a 1995 Seat Ibiza 1.4 6K here that I got from a friend, and I'm having trouble with the rear brakes. The braking effectiveness is off by at least 50% during normal operation, while the handbrake works fine.

I replaced everything: the calipers, brake cylinders, and hoses in the rear. It's a standard procedure for me, but the right side brakes are only working about half as strongly as the left side.

Now, as the last culprit in this whole mess, I'm left with this piece here.

Quote:

Seat Ibiza 6K Brake Force Limiter 1H0612151A

"One of these is screwed into the main line at the rear of the hydraulic brake booster. My question is, and I hope someone knows the answer, which of the two is more likely to be faulty: the one where less braking force is reaching the rear, or the one where more braking force is reaching the rear?"

These parts are relatively rare because they were only installed in the Golf III 1.4, the early-production Seat Ibiza 1.4, and various Astra F models.

"Thank you."

These are essentially throttle valves, and the limitation is not dependent on the load.
Since this concerns the brakes, I recommend having the relevant original RLF (Richtlinie für Leichtbauflanschen - guideline for lightweight flanges) document at hand and using only genuine new parts. Replacing two new parts should definitely solve the problem.
hg
Herbert.

Hi!

When it is written that the work is routine for him,
I assume it is well known that Volkswagen has been using brake cylinder pistons with diameters of 14.3 mm and 17.46 mm for a very long time.
I just wanted to remind you...

"These are pressure relief valves; they allow pressure to pass through up to a pressure of XXX bar, after which they close."
The background is that during very strong braking, it is assumed that the front of the car will compress (dive), while the rear will become unloaded, and this is done to avoid the rear wheels from locking up or being over-braked.

I've never seen that at VW or any of its subsidiaries.
In East Germany, there were similar valves in the Wartburg car, and they looked exactly the same.

Interesting: Renault offers brake cylinder assemblies with an integrated pressure relief valve.

I suggest you provide us with the braking values, including those for the front axle if available, as well as the total weight and axle loads of the car.
Then we'll tell you which braking values are correct.

I'll just say that the values around 0.8 to 0.9 are probably correct.
What exactly is happening inside the valve, whether it's no longer limiting the pressure or limiting it too early, is something that probably no one can tell you.

What does a braking value of 0.8 to 0.9 mean?

Herbert.

Kilo-Newton is the unit that a brake testing machine displays.

Well, that would be 900 N.
On my Polo 6R, the rear brake calipers have a clamping force of 190 daN, which is equal to 1900 N.
And it's not that much heavier.
Replace both valves with new ones (RLF), bleed them thoroughly, and then put them on the test bench!
hg
Herbert.

Hi.

Both valves will be replaced, and the shipment is on its way. However, I would still like to know which of the two valves is faulty.

"The brake cylinders are the ones that should be installed, and they are the same size on both sides. I replaced the hoses after an initial brake test because one of them might have been swollen."

I didn't use a dynamometer, but it's only 15km to a workshop where I can. I built something myself (a torque wrench with a pointer and an adapter that engages two opposing wheel studs) to compare the braking force on both sides beforehand. If there are any differences there, I can save myself the trip to the dynamometer. In this case, the difference is more than 50%, compared to the parking brake, which brakes relatively evenly.

It's important to remember that the new brake pads need to be properly bedded in with the old drums. I only removed the burrs from the drums and slightly angled the pads so that they would make proper contact with the drums.

The initial setup, including the release of the brake cables, was also performed.

Once completed, the Ibiza will be presented to a DEKRA inspector for a technical inspection (TÜV), which ensures that all braking systems function correctly.

"What is the torque wrench size so that you can simulate the braking force on the wheel rim? You need up to 2 kN at the rear. Will it slip on the wheel studs? And how can you ensure that the brakes on the left and right sides are working equally within the tolerance range if you're not performing a simultaneous test of the axle?"
The vehicle needs to be tested before it is put into operation; hopefully, the DEKRA inspector will do that.

Herbert.

I always perform this test whenever I've worked on the rear brakes, preferably on drum brakes. If it's compatible with my equipment, I'll put it on the rolling road in the workshop. If everything is clean there, the vehicle will then undergo the mandatory technical inspection (TÜV), also on the rolling road.

I am doing this test by myself to see if the effect is uniform or not. If it's not working properly, I can avoid the trip to the workshop and investigate the issue as I am doing now.

Attached are some photos showing my "device."

Okay, but 100 Nm is even pointless for the handbrake.
With drum brakes, the pads still make contact.
hg
Herbert.

Herbert wrote:

Nice, but 100 Nm is even pointless for the handbrake. With drum brakes, the pads still come into contact. hg Herbert

Again: This is a preliminary check solely for me to test the evenness of the braking force from one side to the other on site, so that I can avoid having to go to the workshop with a brake tester if there are any deviations.

So far, all the drum brakes I've built myself have been within the acceptable range of values, and they've been working well enough on the brake tester that the inspector has been able to issue the required sticker without any problems or hesitation.

Status update: Parts arrived today, installed, brakes bled, preliminary inspection revealed an estimated deviation of 5-10%, more details next Monday after the technical inspection (TÜV).

Hi!

Did you notice that one side was working slower or less effectively than the other when bleeding the system, using the old pressure relief valves?

And then, again, about the torque wrench.
"I no longer have a brake testing machine because it's broken, too old, and spare parts are no longer available. It also can't print a report, and I'm not doing TÜV inspections anymore either."

I've been thinking a lot about the test using the torque wrench.

And what forces are at play during braking.

When testing brakes, for example, when checking the handbrake, the test ends when the wheels slip on the rollers, or when the vehicle is lifted off the rollers.

It has happened to me before, when I was tightening the front wheel hub nut on a car, that the wheel slipped on the garage floor, and someone else had to step on the brake to prevent it from moving further.

If the braking force on the test bench, as I understand it, is around 0.9 kN at the rear, that doesn't necessarily mean you have to apply a torque of 900 Nm using a torque wrench to simulate that. I also don't really have a good idea of how to calculate that.

How did you check the brakes?
Someone is sitting in the driver's seat, pressing the brake pedal, and you are applying torque with the torque wrench.
Did he fully depress the brake pedal, and if so, was the engine running to provide brake assist?

Quote:

If the braking force on the test stand, as I know it, is around 0.9 kN at the rear, that doesn't necessarily mean that you have to use a torque wrench with 900 Nm to simulate that. I also don't have a good idea of how to calculate that....

Force x Radius = Torque.
hg
Herbert.