Setting up new brakes.

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davidimurray

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posted on 4/4/12 at 09:32 PM

Setting up new brakes.

Hello

When I first got my car out of the garage the brakes stopped the car quite well but the pedal was very poor with lots of travel. Setup is standard Sierra Kit with the servo and deceleration valve removed.

I struggled to bleed the brakes so I invested in a vacuum brake bleeder which is great. Having got all the air out I found that while the pedal went hard, it never came to a dead stop and would travel all the way to the bulkhead.

Having heard of a few people having trouble with old master cylinders being left dry I invested in a new one. I setup this up and put a couple of bleed nipple in the ports to check it was ok and the pedal was rock solid. Connecting it all up to the system the pedal felt stronger, but still didn't got solid before hitting the bulkhead.

Checking the car over I found both rear brake cylinders leaking. I bought new cylinders and took the opportunity to fit smaller escort units as a couple of people have had problems with overbraked rears. Fitted and bled the system again and the pedal was further improved but still I could get the pedal to the bulkhead. Now getting fed up I made sure the system was totally bled and left the brakes jammed on for a few days. On my return I noticed a small drip from the front caliper. Biting the bullet I bought a new set of front calipers

So basically we have new master cylinder, rear cylinder, front calipers and I have replaced the brake pressure sensor with a bleed nipple for testing. I've put about 3 litres of brake fluid through each line. After all this I can still get the pedal to the bulkhead. Asking a mechanic mate of mine he has suggested that once I get the car on the road and bed the brakes in then the pedal will come back and should go solid away from the bulkhead when bedded in.

Is this likely to happen? Does anyone have an experience of this and if so how did you cure it?

All help much appreciated

Dave

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posted on 4/4/12 at 09:44 PM

for me, some air is still in there. could be seized piston in a caliper?

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posted on 4/4/12 at 10:08 PM

If you pump the pedal quickly then hold it does it creep down until it hits the bulkhead?

YES creeps slowly until hitting bulkhead - you have a leak either external or internal in MC

NO pumps up and stays hard - You have either air or a siezed / misaligned caliper or something else which is flexing.

Davie

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posted on 5/4/12 at 07:28 AM

i had the same problem got a new master cylinder and still had the same problem. turned out the new master cylinder was duff too. finally i fitted a third and it sorted it out. i two replaced both callipers and cylinders trying to track it down. any chance you got your new master cylinder from brakes int like i did?

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posted on 5/4/12 at 08:44 AM

I also had this problem, and it turned out that the brake pushrod was too short, meaning that the brake pedal was reaching the end of its stroke before the plunger in the master cylinder had gone through its full travel, made the pushrod 10mm longer, bled the brakes again, and now have superb brakes!

Always worth checking the simple things first!

Cheers

Adrian

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posted on 5/4/12 at 09:09 AM

Assume from the description that you have drums at the back. When you bleed the brakes you need to do it with the adjusters fully let off then (manualy) adjust them up. If they are already adjusted the pistons can be far enough out to alow air to sit in the ends above the level of the bleed nipple.

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posted on 5/4/12 at 09:26 AM

certainly wouldn't take a chance driving it like that

davidimurray

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posted on 5/4/12 at 11:34 AM

Thanks for all the comments everyone.

With regard to the pedal creeping, firstly the pedal does not pump up - i.e. no matter how hard I pump the pedal does not get any harder. Secondly if I press the pedal down hard and hold it there it does not drop or creep.

Ash - having heard about your problem I did avoid brakes int and got one from a local motor factors. I did fit the M/C into the car and then plug the outlets with bleed nipples, followed by a bleed and the pedal was absolutely rock solid.

Adrian - that's an interesting thought - I had wondered about this. Will have a play and see if it has any affect. Out of interest are you using the standard haynes pedal box? If so is there any chance you could measure the distance from the back of the pedal at the top to the the bulkhead?

Adithorp - do you mean the adjusters should be fully released - i.e. the shoes all the way in. Mine are adjusted out at the moment.

Cheers

Dave

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posted on 5/4/12 at 11:36 AM

Are your calipers on the right way round, bleed nipple should be at the top.

davidimurray

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posted on 8/4/12 at 08:44 PM

Had another play with the brakes. I've extended the brake push rod as far as I possibly can while still keeping some play in the push rod. This has moved the pedal footplate about 50mm further back and if I press with all my force I can get the pedal to within about 15mm of the bulkhead - however it seems like there is an awful lot of travel in the pedal. To demonstrate this I took a video showing the pedal being actuated -

http://www.youtube.com/watch?v=EJmhBe9oM1g&feature=youtu.be

Does this look normal? Am I just being paranoid about the amount of travel?

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posted on 9/4/12 at 07:01 AM

That's more travel than I have. Have you bled the brakes again since extending the pushrod? I had to bleed them again once I was getting full stroke, and now they are really good. Does the pedal feel spongy or solid? It looks a bit soft in the video clip.

Cheers

Adrian

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posted on 9/4/12 at 09:07 AM

Hi Adrian

Thanks for the quick reply. I've quickly gone through and rebled them. I'm using a vacuum bleeder that I hook up to the compressor and then suck the fluid through. I've probably put about a litre through each line and there is no sign of any air bubbles.

The feel of the pedal is - strange. As you press the pedal it slowly gets harder and harder. But probably the first 50% of the travel seems to do nothing. The pedal does get to a point where it goes hard but still feels a bit spongy. Totally different to the feel of the tin top with the engine off. The car is currently up in the air but when it was running despite the terrible feel to the pedal the brakes were strong and did lock up.

I can't help but think it must be air related in some way. My rear brake lines run down the tunnel up over the top of the diff structure then back down to the wheels - I wonder if this high area could be giving me trouble??

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posted on 9/4/12 at 09:23 AM

quote:
Originally posted by davidimurray
Thanks for all the comments everyone.

Adithorp - do you mean the adjusters should be fully released - i.e. the shoes all the way in. Mine are adjusted out at the moment.

Cheers

Dave

Yes, bleeding should be done with the adjusters released so the shoes push the cylinder pistons fully in as a general rule. Otherwise there can be air in the cylinder above the bleed nipple hole. You can often get away without but it can be a problem. Quick way to do it is just to remove the drum, open the nipple and push the pistons in with a pair of screw drivers, hold them there and lock up the nipple.

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posted on 9/4/12 at 09:36 AM

I'm not sure whether this will help (or will even apply) but I just thought I'd chime in. When my discs were warped, I was finding the first part of the brake travel did very little, and the pedal had to go a lot further down than I would have expected. What I think was happening is that the discs were pushing the brake pads (and therefore the pistons) further back than they should have been, and I was having to take up that slack before the brakes were effective.

Although it sounds like you're doing all your work on a stationary car so this wouldn't be what you were seeing.

I'm not 100% with how brakes work, what causes the pads to back off under normal circumstances but still allows for pad wear?

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posted on 9/4/12 at 09:41 AM

Don't assume that the pedal should feel anything like a modern car either with the engine running or not. The pedal will feel a lot stiffer than a modern, heavily servo'd car.

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davidimurray

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posted on 9/4/12 at 10:59 AM

quote:
Originally posted by DIY Si
Don't assume that the pedal should feel anything like a modern car either with the engine running or not. The pedal will feel a lot stiffer than a modern, heavily servo'd car.

Mine definitely does not feel anything like the tin top - much much more travel and nowhere near as hard in the roadster. I was expecting the pedal to be much harder.

When I first fitted the new master cylinder I plugged the outlets with bleed nipples and the pedal was rock solid almost instantly. I appreciate that there will be some flex etc in the system but I was expecting a similar case when everything was hooked up - i.e. very little travel and a hard pedal.

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posted on 9/4/12 at 11:36 AM

Might be worth clamping each flexi hose (if they are the normal rubber type)then when holding the pedal down release each hose clamp in turn to identify which wheel(s) are causing the problem.

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posted on 28/3/13 at 09:39 PM

Hi Dave,

Watching your video about the foot pedal movement, I can't but help notice that your have a certain amount flex in the bulkhead as you press the pedal???

It's interesting to read the post as I have just solved the exact same issue on my Locost 7. It's a long winded explanation but here goes?

I have cortina callipers up front and mk5 cortina drums at the rear. I recently changed engines, thus had to make changes to the brake circuit and the position of the servo which was using a 19mm MC. Having bled the brakes with an easy bleed kit I thought all was well, firm pedal, wheels locked under foot pressure on the Axle stands so I presumed all was well.

Until I took her on the road....

OMG the shock of my life.... No brakes... Just the front right appeared to work. After further investigation and many hours of scratching ones head I thought I found the cause to my problem.

Having removed the servo and removing the master cylinder from the servo some small fragments of bakerlight were found loose inside. I split the servo apart to find that the servo had cracked and broken in half, thus no servo pressure, thus no brakes. Just brut force.....!!!!!

So next I sourced a replacement servo, but unfortunately I couldn't find like for like.

On the positive side though, this meant I could change from hung above pedals to floor mounted pedals. The pedals I fabricated myself modifying the current set of pedals to floor mount.

I set my pedal ratio to 8 to 1 which I hoped would prove successful and produce a nice firm pedal once bleed. The pedal length to the ball of the foot was 200mm and the mc pickup point was 25mm from the pedal rotation centre point. All good, so I thought.

Having bleed the brakes several times, and using 4 litres of brake fluid I now found myself with your exact symptoms you have. Spongy pedal with full pedal travel until the pedal hit the bulkhead !

So to my solution, I found that if I increased the pushrod length of the MC this had little or no effect, next we checked the callipers on the front in case they were sticking, we adjusted the rears manually on the take up adjusters, still no success.

So, further mods to the pedal box where needed, I lowered the centre pivot point of the pedals by 1/2 inch, raised the mc pivot point to 45mm from 25mm,this resulted in a pedal ratio of 4.4 to 1.

However the subsequent increase of throw on the stroke of the mc was over 1/2 inch increase in stroke length acting on mc. SUCCESS

Having looked back at what I found and making several tests I discovered that the offset of 25mm for the pickup point of the mc was too close to the centre of the pedal, thus the moment of travel was never enough to act on mc correctly as the movement in simpler terms meant the circumference change in pedal arc wasn't sufficient to generate enough brake pressure. Having raised the pickup point to 45mm the difference was incredible.

I now have firm brakes and short pedal travel. If I could make further improvements I would increase the overall pedal length to 360mm, but sadly there's no room for such a long pedal.....

Another test I intend to perform before taking her back out the road is to actually use a pressure gauge at each wheel cylinder to check the line pressure. If I get 1100 to 1200psi all is well

The simple things get overlooked ???

Lesson learnt the hard way.

I hope other readers find this post useful, as I wasted such a lot of time and effort on this issue.....

Cheers

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posted on 1/4/13 at 08:18 AM

A non-servoed brake should have a rock solid pedal ie almost no movement of pedal -- anything else and there is something wrong.

Making the master cylinder push rod longer is likely to lead to the expansion of the fluid as the brakes warming up cause the brakes to bind and completely lock all 4 wheels.

If the system is bled properly which should take no more than about 250ml fluid on an IRS Locost this usually requires unbolting the rear callipers and inverting them so as to put the nipple at the top.

The most common cause of a soft sinking pedal is a leak in the system, a leak can be very hard to detect as often it will be a one way leak no fluid can be seen leaking out but air is drawn back in on the return stroke.

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posted on 1/4/13 at 10:27 AM

This would have been the ideal opportunity for sending one on an april fool/wild goose chase solution and this sounds like one but ....

It may be that the master cylinder seals are not 'flaring' properly. They don't flare open (and make a proper seal) until they've travelled down the cylinder quite a bit, flare then seal then start to work. This can come from the rubber sitting on the shelf too long and becoming stiff (this is impossible to judge by hand)

I'd go for a new set of master seals....

We used to get master cylinder seal problems on vauxhall fleet vans - when you opened the brake circuit to change a caliper or whatever - they'd relax and be really hard to return to decent pedal travel until you changed the master cylinder seals for fresh ones.

The seals/travel may well improve with use but I'm not sure that's the way to go.

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