Brake Symptoms

[ftm1776]

Just asking here because this is where I hang out................

Pumping the brake pedal frequently when coming to a stop from, say, 60 mph, I notice that the pedal gets harder to depress, seems to have less stroke and the braking effectiveness diminishes quite a lot with each pedal push. It seems that if I then lay off of the brake pedal for a while and continue driving, everything returns to MY normal brake pedal feel and effectiveness.

I haven't bled the brakes for some time, but I thought that would just cause a "mushy" feel to the brake pedal.

I think that the vacuum pump is ok. Never have looked at the power brake diaphragm.

Comments, please.

[damac]

Make sure vacuum pump is putting out.  But I'm guessing its the brake booster.  Same thing has happened to me on a few different chasis, but to be fair these were old runners with probably original parts so they served their purpose.

If its real bad sometimes in the stroke you can hear it hiss out under the dash like my 79 did to me a few months back.

Sometimes they work ok and have fits at other times.

[vanbcguy]

Definitely sounds like a vacuum leak. Check the cheapest stuff first - make sure the vacuum hose from the pump to the booster is in good shape and properly sealed. From there check the pump and booster. If you still have the old style giant round diaphragm pump now would be a good time to replace it with a vane pump.

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[theman53]

Kind of relative here. How fast are you pumping? Do you realize even with the vacuum pump and all brake parts working vacuum takes longer than .3 of a second to build to full vacuum in the booster again, right? Everything could be ok if you are trying to do abs style breaking in the old car it just won't do it. My stuff is all brand new in the brakes in the last 2,000 miles and it will not do it, all but the vacuum pump, but it works as new.
I guess what I am getting at is could you explain what pumping you are trying to pull off

[Renax]

Yea, why are you pumping the brake anyway? Its designed to be pushed and held down until you are stopped/have low enough speed.

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[ftm1776]

Here are a few photos of the test gauge, pump, and booster(?) As far as I can tell the pump, hoses, cap(green), brake booster(if I am using the correct term) are A-ok.
,
Vacuum seems strong at 29 inches with my ancient gauge. Photo taken at idle....no real change when revved a little.

Its a little unnerving with the pedal "stuck" up with no stopping power.......just a little pm in mind.

[DieselBalz]

I am having the same issues although what you describe happens only if i pump the brakes too much. In my case I am double pumping for the right feel. About two weeks ago the pedal started going almost too the floor before good feel, and I have been double pumping cause I am not looking forward to replacing the brake booster, which is probably your problem as well.

Easy enough job but can only find em for about 249$ unless re-manufactured. I replaced the master a year ago. I knew I should of changed the booster at the time.

I referred to the handy chart of symptoms in the Bentley to diagnose.

[damac]

I am having the same issues although what you describe happens only if i pump the brakes too much. In my case I am double pumping for the right feel. About two weeks ago the pedal started going almost too the floor before good feel, and I have been double pumping cause I am not looking forward to replacing the brake booster, which is probably your problem as well.

Easy enough job but can only find em for about 249$ unless re-manufactured. I replaced the master a year ago. I knew I should of changed the booster at the time.

I referred to the handy chart of symptoms in the Bentley to diagnose.

You have a different problem I think.  Booster is for assist so if you lose it it makes braking harder.

If your pedal is sinking and has to be pumped up I would go over your brake system.  After I bleed my cars I don't have a sinking pedal if you brake and hold hard.

 If lines are good and its not leaking I assume its the master.  I had this happen on vw I junked months ago, and found fluid in the booster as well.

[ftm1776]

We could be having the same problem.....if it is a "problem".........DieselBalz and ftm1776, that is.

Pretty difficult to get across what exactly is going on under what circumstances, etc.

Good clues, though..........

So, how can I tell if it is the brake booster???

Added: By the way, the booster holds the vacuum pretty well after I stop the engine....eventually it does leak down.

If I am correct, that is the large round "can" to which the master cylinder is attached. My center photo. Yes?

Question: is it possible to remove the booster and convert to non-power brakes??
My pop's old 61 Ford didn't have power or disc brakes and it weighed a  lot more that my 1991 Jetta.

[Dakotakid]

If these are Jetta problems, you need to crawl under the car (better to use a light when dark out) and check to see if your rear brake actuator is leaking. Common Jetta problem.

[ftm1776]

No leaks from the brake proportioning valve near left rear wheel..........

[Renax]

I still think the symptoms you wrote down is how a good vacuum brake booster should work, all mine has been about the same...
2-3 brake pumps in less than 5 seconds then the pedal gets hard and brakes poor for a few seconds...

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[ftm1776]

Yeah, Renax. that's about what I am getting....probably not worth messing with.

However, if this is normal, couldn't it cause problems if one does not have ABS and rather pumps the brakes to stop on a slippery road surface.

I can live with what I have for now. Got to prioritize !!!

[Renax]

We have snowy roads 4-5 months a year and I've never seen this as an issue. I guess if your on the snow power brakes is not needed anyway...

The easy way to give it some extra capacity is to add a vacuum reservoir. My van has a few extra pumps in it just because of the 4-5meter pipe from pump to booster, add a liter tank and you'll be golden:-)
Still pretty unnessesary...

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