Brakes too Good - Not normal for a MK2!

After tracking several issues not related to this I heard somewhat of a whistling sound. I found that one of the hoses right before the accuvac was cracked.After replacement every thing seemed ok until most recently.

Just touching the brake pedal is a scary event. I need to put the car up on the rack to see if I have a seized caliper but none of the wheels seemed hot after a short drive. There is no fluid missing from the brake reservoir. If I had a vacuum leak I believe the brakes would not work as well. There is only about an inch of travel on the pedal before the car slams to a halt with me hitting the steering wheel. Obviously not safe to drive, I will add to this thread after I inspect all calipers. I’m thinking the master cylinder or booster have died after being replaced 15 years ago. All thoughts welcome.

Gerard

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This seems a defect brake booster, I would go for a new replacement.
I am using the LR18230 from SNGBarratt on both my Mk1 and my S-type.

I recommend you replace the rubber brake hoses at each wheel. When these get old, they can swell shut from the inside and trap fluid. That can cause a symptom similar to what you’re describing.

Two good ideas here. I’ll be headed to the lift soon to check for brittle hoses and seized calipers. Replacement booster and hoses are not too expensive.

Gerard

Could the SNG model be the same as Moss Motors LR18230 just $130 more?

G

If I were to plug the hose to the booster would this not give me the same effect as having standard non assisted brakes. Would this narrow down that the booster was not at fault.?
So, we just lifted the car and found that all wheels spin freely. All brakes work on each wheel with engine off. The brake lines are stainless steel so no internal collapse? Looking more and more like the booster that might have blown a seal when the accuvac hose was broken and maybe too much foot pressure on pedal was needed to compensate for lack of assist?

I would say the mk2 on a stock setup with just proper pads (ebc greenstuff for instance) has a pretty modern feeling (modern as 90s+!), so I don’t think you should be surprised by the pedal pressure at all.

Rubber hoses. If they’re old they can clog up or swell shut and the brakes will stop but not release.

Sounds like the booster to me. Disconnecting it and trying sounds viable. You can test a booster by only giving it a little vacuum, master disconnected, and see if it boosts in a controlled way.

Yes, just be careful, as they can take a long time to pull up without air assistance

No, this is a scary, massive, all of a sudden halting of the vehicle and just a minute touch to the pedal at a certain point throws me into the steering wheel.

Does “pull up” mean a long time to slow down? I’ll do that on a wide open space of road to test.

I presume you mean using vice grips on the hose to the booster to reduce vacuum and what do you mean by disconnecting the master?

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It sounds like a faulty break booster. Disconnect the vacuum and test the breaks. If all is well (of course you will have higher pedal pressure) you found your fault

Danke, Ich glaube dass das Booster ist die probleme Does everyone agree that I should “clamp” of the hose going to the booster rather than just removing it as that would cause a lean condition affecting the operation of the engine while testing.

It does appear than the consensus is the booster.

Yes you must clamp the hose to the engine, you can leave it connected and iuse vise grips
You can test the booster in the driveway/around the block like that and if inconclusive you take the hydraulics off the booster and see if the booster works smoothly. Der Booster ist bestimmt das Problem, viel Glück.

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Yes or disconnect the hose and put a little cap or screw in it. As long as it doesn’t suck air you should be all right! (plus it wouldn’t destroy your engine to run a few meters with a lean mixture anyway, I guess the most obvious issue would be your idling which would be too fast)

[quote=“The_Jag_Man, post:14, topic:424483”]
It does appear than the consensus is the booster.
[/quote]I can’t think of something else either. Still, it’s a bit strange that it assists the brake too much. I would tend to think that given a particular vacuum the only thing it could do it leaking and hence provide less assistance than more, but there must be a sensible explanation about it. And it’s just a couple of minutes test to unplug it so it’s the thing to do for now, I guess.

No, it is not that simple. There is a valve in there that closes and stops the vacuum assistance. If that doesn’t work properly you can get too much boost.

Maybe this picture helps:

Cheers,
Harald

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Yes I do have a similar diagram on page L21 in the original manual. Not sure if I noted that originally I had a NO BRAKE condition after fiddling with the knurled nut on the back of the intake manifold. We had to remove a LOT of pieces to replace the starter (long story) Huge headache! I DID find a crack in the short hose piece going to the booster. Then this over sensitive pedal occurred and slams me into the steering wheel on the slightest application of the brake pedal. My thought is that this hose leak has been there for a long time and allowing less air/vacuum to the booster and not giving too much assist? TO be this is indicative of the booster being bad or the check valve? We do have 1" to 1.5" inches of travel from the back of the pedal to the firewall. Which I am told is within specifications?

That valve is internal and I believe a new booster from the usual vendors comes with that valve. No way am I going to mess with the components which could lead to brake failure.

G

Thanks, interesting.
But I see the check valve which just maintains the vacuum when the car is not idling and another valve at the atmospheric pressure side so they way I understand it the assistance is only dependant on the vacuum with cannot exceed a 1 bar differential with the 1 bar absolute of the atmosphere (given a perfect vacuum which is obviously very far from reality, but anyway)?
I may be missing something from the diagram but I would say the assistance is only dependant on the booster piston/diaphragm diameter?