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-   -   Brake booster (http://www.madabout-kitcars.com/forum/showthread.php?t=5997)

mcramsay 25th June 2016 19:48

Brake booster
 
I have the Marlin supplied dual brake booster, coupled up to a Sierra master cylinder. With the engine off pedal goes rock hard with only a little bit of force on the pedal. However with the engine on the booster is doing its job so well the pedal goes to around 3/4 travel before you actually get any feed back. It's almost like the booster is working too well

I know this is a widely covered topic on her so how do others find it? Have I got something wrong on my set up? It's hard to tell how much braking I'm doing as the car is only creeping forward and back on the driveway!

Mike 26th June 2016 10:33

Quote:

Originally Posted by mcramsay (Post 80573)
I have the Marlin supplied dual brake booster, coupled up to a Sierra master cylinder. With the engine off pedal goes rock hard with only a little bit of force on the pedal. However with the engine on the booster is doing its job so well the pedal goes to around 3/4 travel before you actually get any feed back. It's almost like the booster is working too well

I know this is a widely covered topic on her so how do others find it? Have I got something wrong on my set up? It's hard to tell how much braking I'm doing as the car is only creeping forward and back on the driveway!


Due to the design of the dual servo, there is more pedal travel with it than without, as the first 10-15mm of travel is soaked up in a compression spring movement which is required to allow the vacuum/external air pressure valve seal to seat correctly.
I think we have all found there is more pedal travel before the brakes start to bite than compared to no servo, but then the brakes will bring the car to a safe stop with ease. Without a servo, or indeed with the under powered Metro servo this was just not the case: they were just unsafe in today's traffic


Wait until you get onto the road (private one of course!) to test the travel and their efficiency. If they don't stop you from 70mph with half pedal travel, you have an issue that I do not experience.

Whatever you do though, do not try to over extend the adjuster screw to over compensate for this additional travel: this only results in the servo being slightly activated with the pedal at rest, letting atmospheric pressure create pressure on the diaphragm, which can (has) lead to severe binding of the brakes.

Make sure you fit a pedal return spring as well to ensure the vacuum seal is properly closed.

phil.coyle 26th June 2016 10:49

You could also check the one way valve is working correctly in the vacuum hose between intake manifold and servo.

mcramsay 26th June 2016 12:33

Got to the bottom of it, there was still a little bit of air trapped in the system. I bled through the system again and the pedal feels much much better. Surprisingly the pedal feel is like a modern car, unlike my old gbs zero which had no servo and required one hell of a push to get the thing to stop!

phil.coyle 26th June 2016 13:23

Good news, another problem solved.
Are we becoming softer as drivers with assisted everything, I know technology is a good thing but I can't help feeling that the driving feel/experience is slowly been taken from us, and don't get me started on driverless cars, this validates my opinion.
It also stops us from repairing our vehicles when they go wrong, and we become fitters and not mechanics, oh well nostalgia ain't what it used to be.

mcramsay 26th June 2016 14:26

I agree with you to a point, but every aspect of life changes with technology. i wouldn't say we are becoming softer as drivers, not every one wants a car that shakes and rattles, lets you feel every bump and handles like its on rails. For those who want that the choice will always be there. I had a 7 type car, and I loved it, but there was no luxury with it, it was hot and no good on a long commute. But around a track it was great fun. I'm hoping the sportster will be the opposite.

phil.coyle 26th June 2016 17:06

I'm just an old retired international truck driver, and I have become accustomed to bumps rattles and bangs, and after 16 years I still don't have a roof on my roadster, less hair means I get sunburnt, it's cold in the winter, but I wouldn't change it for anything, the grin factor is what I appreciate most, and I would hope that many more people feel the same.

Nigbo 12th August 2016 14:36

Problems overheating & binding
 
I 've now got my dual booster fitted and an amazing transformation to the brakes. BUT........they start binding on if stuck in traffic/ low speed . Had to pull over open bonnet and cool off. I can feel the pedal "hardening up", so there's no slack in it before the brakes come on.

Its worse on hot summer days. Driving to work early in the morning i get no problems. Driving home on warm/hot summer days i can't even get home without having to pull over. So i undertook wrapping the whole manifold . No improvement. Put some heat shielding on the underside of the booster and the master cyl. No great improvement. Took the master cycl. off and shortened the pushrod from the booster to the MC about 3-4 mm, thinking the whole thing was expanding. No great improvement.

What is noticeable is the copper brake lines ( which are now much longer ) get very hot almost too hot to touch and the MC is also very hot. I've got some heat protection lagging for round the brake pipes from Demon Tweeks and going to extend the manifold wrap further down to include the collector pipe.

I've a M3 3.2 lump which clearly generates a lot of heat but this was never a problem before fitting the dual servo.

Before anybody mentions i have the Landcover return spring fitted and anyway its not that the pedal is sticking down , i can feel that , its as if somewhere is the whole system its expanding and taking up slack.

Am not hopeful that the pipe lagging will really stop the problem. Its like the brake fluid is expanding as it gets hot, which i would not have thought it would. There is a exhaust heat guard which normally fitted to the engine of an M3 which might help a bit although it could make things worse.

Getting exasperated ......any ideas

Nigbo 12th August 2016 14:45

Faulty MC ?
 
I've found a unrelated posting about problems with brakes binding when hot related to a faulty MC. It's not a big cost so maybe i will replace the MC.

Mike 12th August 2016 23:03

Nigbo
These servos seem prone to "vacuuming themselves on" - you are not alone in experiencing this problem. As you have fitted the Landrover return spring, have you checked to see that there is small gap in the servo output adjuster to master cylinder? It is critical that the servo can close off the atmospheric pressure with the pedal at rest.
Try shortening your adjuster and see if the problem disappears. It leaves you with a slightly longer pedal, but helps prevent binding brakes.
Mike

Quote:

Originally Posted by Nigbo (Post 81845)
I 've now got my dual booster fitted and an amazing transformation to the brakes. BUT........they start binding on if stuck in traffic/ low speed . Had to pull over open bonnet and cool off. I can feel the pedal "hardening up", so there's no slack in it before the brakes come on.

Its worse on hot summer days. Driving to work early in the morning i get no problems. Driving home on warm/hot summer days i can't even get home without having to pull over. So i undertook wrapping the whole manifold . No improvement. Put some heat shielding on the underside of the booster and the master cyl. No great improvement. Took the master cycl. off and shortened the pushrod from the booster to the MC about 3-4 mm, thinking the whole thing was expanding. No great improvement.

What is noticeable is the copper brake lines ( which are now much longer ) get very hot almost too hot to touch and the MC is also very hot. I've got some heat protection lagging for round the brake pipes from Demon Tweeks and going to extend the manifold wrap further down to include the collector pipe.

I've a M3 3.2 lump which clearly generates a lot of heat but this was never a problem before fitting the dual servo.

Before anybody mentions i have the Landcover return spring fitted and anyway its not that the pedal is sticking down , i can feel that , its as if somewhere is the whole system its expanding and taking up slack.

Am not hopeful that the pipe lagging will really stop the problem. Its like the brake fluid is expanding as it gets hot, which i would not have thought it would. There is a exhaust heat guard which normally fitted to the engine of an M3 which might help a bit although it could make things worse.

Getting exasperated ......any ideas


phil.coyle 13th August 2016 08:52

Have you checked the one way valve in the Hose to the servo.
Some are obvious in the Hose, and others are at the point of entry into the Servo.

Mike 13th August 2016 23:08

Quote:

Originally Posted by phil.coyle (Post 81874)
Have you checked the one way valve in the Hose to the servo.
Some are obvious in the Hose, and others are at the point of entry into the Servo.

It is unlikely to be the non return valve in the vacuum hose.
If this is faulty you will lose vacuum, which is not your experience - quite the opposite!

The cause will be one of two issues:

The inlet valve on the servo not quite seating, allowing atmospheric pressure to exert a force on the servo's diaphragms, or

The mater cylinder is not returning fully, so retaining hydraulic pressure in the system.

Nigbo 17th August 2016 21:31

I have already shortened the adjuster once. I originally set it up pretty close to no gap. Have shortened it by 4mm and still have the problem. Do you think I should shorten it further?

If the problem is with the servo would I be right in guessing the pedal will not be fully returned e.g. The brake light switch might even be activated! If it was a M/C problem the servo would fully return and therefore the pedal. Should that logic not diagnose where the problem lies.
One other piece of info is that the whole setup was fine initially, it's come on with time.

Mike 17th August 2016 23:07

Quote:

Originally Posted by Nigbo (Post 81985)
I have already shortened the adjuster once. I originally set it up pretty close to no gap. Have shortened it by 4mm and still have the problem. Do you think I should shorten it further?

If the problem is with the servo would I be right in guessing the pedal will not be fully returned e.g. The brake light switch might even be activated! If it was a M/C problem the servo would fully return and therefore the pedal. Should that logic not diagnose where the problem lies.
One other piece of info is that the whole setup was fine initially, it's come on with time.

You should only need a marginal gap (when it is hot) - 4mm is way too much gap.

How have you connected your servo to your pedal? - have you used a clevis or a rose joint?
How well did the servo input and the pedal line up?

My guess (and it is a guess) is that your servo input valve is not seating totally, and is allowing atmospheric pressure to activate the servo slightly.
Since you had no problems with your old servo, logic suggests the problem is due to the set up of the new servo, and its connection with the pedal on the input side and the master cylinder on the output side. As you have a huge (4mm) gap to the M/C I doubt this is the problem. So it comes back to the input side of the servo.
Does your brake pedal switch prevent your pedal from coming back further?

Nigbo 18th August 2016 21:37

I have a Rose Joint connector and the alignment looked pretty good to me as best as one can tell. Don't know what else i can do, i not sure putting a bigger return spring on will help. I will check next time and see if the pedal is actually depressed or should i say pull down by the servo.

This looks like a faulty servo. Big sigh......... am not impressed with Pirate Jack. I've sent them an email but the chance of them sending me a replacement FoC is probably nil. if i had to fund buying another one then it will have ended up costing over 600 all in just for the servo, let alone all the other costs

The first one they sent was the wrong part and i had to replace it at my own cost. I thinking i going to take the whole thing off and put the old servo back on ( inadequate thought it was ), I've thrown the old servo out, does anybody have their old one i could buy off them.

your very depressed.


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