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CorwinB

Brake Troubleshooting - looking for help

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Hi all,
I hope I can draw on the hive mind's experience with this one before it costs me a fortune to fix. I have also posted this on LandyZone but would like to appeal to you too.

Car is a 1996 300TDi 110

Brakes on this were great and could stop big heavy trailers, lock up the wheels etc. no problem until last week.

On the way back from the Dordogne, as we got to Normandy for a few days camping, the brake pedal went very stiff and it became hard to stop, needing almost double-footed effort to stop.

The vacuum pump was replaced a few months ago, but I popped the vac hose off and tested it with my finger while the engine was running and it still sucked my finger onto the pipe.

Some googling of various forums on my phone pointed towards the problem being the booster. Ordered a new one from Bearmach and fitted it (including the new o-ring between Booster and Master Cylinder).

Now there is a different problem - lack of braking force. Whereas a month ago the car would stop fine, then a week ago the pedal was stiff all the way down, now there is very little braking force at all and it's really hard to stop the car. A test of an emergency stop from 40mph on wet tarmac (which would previously have locked the wheels) required far more room to finally stop and was quite scary in the lack of braking force.

Fluid level in the reservoir seems the same as before, I did not open up the hydraulic system when I changed the booster.

Here's the odd thing - when braking in reverse, the stopping power and brake effort seems much more similar to how it was originally (ie. good).

The amount of brake pedal travel to make the brake system start working is much more than before, and it feels spongy.

I've read a lot of threads on this but not found many people who actually had the same sounding problem and went on to solve it.

I have tried to do this test:
1. With engine off, pump brake pedal until it goes hard
2. Start engine with brake pedal held down to see if pedal moves.

BUT the brake pedal just does not go hard at all, nothing seems to change.

My mechanic friend suggested the master cylinder could be at fault.

No evidence of brake fluid leaks in the pipes as far as I can tell.

Has anyone had experience of this? I am loathe to start replacing bits willy nilly without a good steer on the likely cause.

Many thanks

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maybe the new servo pushrod needs adjusting, I had to adjust mine after fitting a new servo.

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29 minutes ago, western said:

maybe the new servo pushrod needs adjusting, I had to adjust mine after fitting a new servo.

Hi western, thanks for the swift response. Were your symptoms the same (basically having half/quarter braking power that it should do)? If so, how did you adjust the pushrod?
 

EDIT: I've given it some more thought and it does make sense, as I know for sure that the old booster was broken (as changing it for the new one got rid of the stiff brake pedal issue), and it would be odd for the booster and the MC to break at exactly the same time as the brakes were totally fine before the booster/stiff pedal issue.

I found this post on how to adjust the pushrod (albeit for a disco 1) so will try that:

https://www.aulro.com/afvb/discovery-1-a/209538-brake-misery.html

Edited by CorwinB

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I had to much free play between servo pushrod end & master cylinder piston, it gave me a long pedal travel & not very good braking, 

 

at theservo rod is a hex nut & a ball end, undo the nut & adjust the ball end, I used bluetac or plasticine to measure the gap, I settled at a gap of just over 1mm, so the servo when brakes are off is not pressing on the piston.

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Hello western, thanks for the advice so far.

I removed the unit, then the push rod on the new one has an 8mm hex head on the stem of the push rod, and a dome headed 6mm nut on the end. I was able to get a spanner on the stem, hold it with pliers, and wind out the dome headed nut by about 10mm (did initially adjust it to 5mm as the original had a 5mm gap). Oddly the older booster does not have this, just a dome headed nut on the end of the stem. The new brake booster is also much deeper than the old one.
What this has done is raise the biting point of the brake pedal up to near where it was before the first booster went kaput (after fitting the second booster the biting point was much further down than before). I now have a lot more braking force with less pedal effort than when the old booster was broken. I am still not certain if this has fixed the issue, or masked the problem, because.....
Did the servo test. Pumped brake pedal which felt stiffer (though not rock hard). Started engine, thought I could feel movement but maybe I was subconsciously pushing harder.
Emergency braking test from 40mph much better as I am able to exert more brake force. 
Started to pour down so packed up for today. More testing required I think.

Edited by CorwinB

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Following with interest.... my brakes are great at first push on pedal but if you are on the pedal for a length of time, you need to push harder to get the brakes to work well. 🤔

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@DC_, petrol or diesel? At idle or more than idle?

 

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@Bowie69 diesel 2.5na, for example if I go down the hill close to my home, I’m on the brakes for about 6-7 seconds. By the time I’m at the bottom I need to press a bit harder to get them stopping me. Checked vacuum and seems ok. It’s like it needs 5 seconds or so to recover then the brakes are very good again. 

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If you find it improves by holding the engine revs a bit higher, either by engine braking or left foot braking, then it will be your vacuum source, or a leak.

Doesn't sound too serious a problem though :)

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I’ll give that a try, also put a new vacuum pipe on but didn’t improve it. The connection into the servo looks a tad wobbly 🤔

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connection on servo is actually a non return valve, it should be held bu a big rubber grommet, I had to replace the grommet on mine as it was part torn through, I robbed a spare of a old 300tdi brake servo. haven't seen the grommet listed seperatly in the parts info I use.

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It doesn’t look too great on the servo, if I wiggle on it a little I’m sure air would get through. Also don’t see a part number on my allbrit parts 🤔

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I wonder if I could pull it out and seal it with gasket sealer? 

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Hmmm. 

I have tested again this evening, the servo test does not make the pedal dip when I start the engine, so I suspect all I have done is to move the bite point.

Moving the car back and forth and applying the brake, it doesn’t feel like it is ‘biting’ down on the discs properly. It’s quite easy to overpower the brakes with the clutch. 

Might try swapping the non return valve for the old one (edit: did this to no effect)

 

Edited by CorwinB

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@CorwinB reading through your original post again, are you certain there is no leaks towards the front braking system? Even the slightest weep? Strange when you say in reverse it seems better. 🤔 

others will be better than me to comment but it does sound like a ton of air in the system. 

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You mentioned the new booster is much deeper than the original 1.

How much deeper is it ? Is the diameter the same or is smaller, but has stepped diameters ?

It's probable that the new booster has a different specification to your old one - the amount of assistance or amplification of your pedal effort. This could make it feel very different.

Did the booster have any manufacturers name on it other than Bearmach's name (Bearmach don't make boosters) ?

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Thinking about the spongy pedal symptom, yes it could be the usual culprit of master cyl, or air in system but I once had a pressure reducing valve go bad with the same symptom - squishy pedal and no stopping power. The valve appeared to be shutting off the rear brake fluid supply, and this may be consistent with your finding of good brakes in reverse. Then again I'm not sure that 110's had a prv at all (but might be worth a check). 

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When you did the servo test, did you exhaust the vacuum first with the engine off by pumping the pedal until there was no hissing and the pedal went hard?

If you did, and there is no change in the pedal when you start the engine, you need to look at the vacuum pipe in its entirety as a start. Is there anything teed into he pipe from the vacuum pump to the servo?

You say there seems to be more brake effort in reverse, so perhaps verify this by jacking up each wheel in turn and trying to turn the wheel with the wheel-brace while someone stands on the brakes. Were you off reading in France? Could you have damaged a brake pipe at the front?

if you post your general location, you might find there is someone close by who could help.

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I ended up giving the landy garage a call and went there after work yesterday. I had not tested a healthy vacuum so I did not know what I was meant to be comparing it to. When he tested the vacuum on the pipe, there was not enough, which points to the (new) vacuum pump (or the cam, which is more expensive so I hope it's actually the pump that's failed). Going to take it in on Friday to get a new pump fitted and to check the cam.

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I had a similar problem with my old man’s defender. We changed the vac pump and fiddled about with the servo but nothing worked. By coincidence we noticed the rear pads were worn out and when we changed them discovered that both calipers were seized. Changed the calipers and put in new pads the brakes performed much much better.

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7 hours ago, CorwinB said:

I ended up giving the landy garage a call and went there after work yesterday. I had not tested a healthy vacuum so I did not know what I was meant to be comparing it to. When he tested the vacuum on the pipe, there was not enough, which points to the (new) vacuum pump (or the cam, which is more expensive so I hope it's actually the pump that's failed). Going to take it in on Friday to get a new pump fitted and to check the cam.

How did they determine it wasn’t enough? 

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4 hours ago, DC_ said:

How did they determine it wasn’t enough? 

Apparently it's supposed to create enough vacuum to stick the pipe to your finger, whereas I was having to hold my finger to the pipe. It was enough to pull my finger on to the end of the pipe, but the slightest effort would take it off.

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Good to know, here’s hoping you’re all good to go soon 👍😊

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If you are measuring, a new Wabco pump does a bit over .8 bar at tickover. After a similar odyssey to the above, I measued a tired one at .3 bar.

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