davidimurray
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| posted on 4/6/13 at 09:15 PM |
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Aaaarrrrrgggghhhh - damn brakes
I have been trying to get a firm pedal on my car for over a month and I'm now more confused a ever. Any advice would be much appreciated.
New master cylinder, calipers and rear cylinders all standard sierra items. I've blocked off the m/c ports and the pedal is solid. I though the
problem was at the rear, so bled like hell,adjusted shoes and released handbrake and with just the rears connected to the m/c I get a solid pedal with
about 1/4 of the total pedal travel
Then connected passenger side front and rears, bled and got a solid pedal about 1/2 way down the travel.drivers front m/c port bocked
Then connected both front and rears and the pedal went to the bulkhead. Removed the brake switch which is in drivers side front line and rebled.
Still pedal to bulkhead. Then disconnected passenger side front and plugged pedal then went solid 1/2 way down again
Basically is seems that if I connect either front brake in isolation, but with the rears connected, I get a solid pedal.But as soon as I connect both
fronts the pedal goes soft.
What could the problem be? I thought both fronts were driven from the same piston so surely if one works both should? Could my master cylinder be
knackered
All help much appreciated.
Gallery 1 http://www.facebook.com/media/set/?set=a.116893465324.130778.601005324
Gallery 2 http://www.facebook.com/media/set/?set=a.245243755324.181913.601005324&l=a9831a9319
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Ben_Copeland
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| posted on 4/6/13 at 09:45 PM |
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Are all the bleed nipples at the top of the calipers and drums ?
Ben
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davidimurray
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| posted on 4/6/13 at 09:50 PM |
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Yeah all the nipples are at the top. I've also removed the front calipers to lift them high up while bleeding.i'm using an easybleed to
bleed them with.
Gallery 1 http://www.facebook.com/media/set/?set=a.116893465324.130778.601005324
Gallery 2 http://www.facebook.com/media/set/?set=a.245243755324.181913.601005324&l=a9831a9319
Gallery 3 http://www.facebook.com/media/set/?set=a.440671625324.232627.601005324&l=3f0d42c523
Gallery 4 http://www.facebook.com/media/set/?set=a.490098255324.297598.601005324&l=efb083b7df
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AdrianH
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| posted on 4/6/13 at 11:16 PM |
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Hi David.
From viewing your archive you are using the same pedal arrangement as me, the same sierra MC, you mention drums on the back may I ask what size they
are, 8 or 9".
Are you on the vented front disks?
Reason for my questions are I am on vented fronts and 9 inch drums at the rear and know with the same pedal set-up I have enough travel.
From some of my past problems with brakes, I would look initially at the brake pedal movement itself.
With your foot off the pedal, do you have a small amount of free play between the push rod and the cup in the MC, allowing the MC to come back fully
to the end and at what position does the brake pedal rest.
There is a stop underneath the pedal through the floor (Bolt and nut), drop the stop down and allow the pedal to move further away from the bulkhead
at rest and use a slightly longer or adjust the push rod to just give some allowance and try again. I quick check of a MC here and the maximum travel
is 30mm, just wondering if you are getting near that travel on the push rod.
I did change my rear cylinders down in size for the 9 inch drums to get brake balance to meet IVA , that would therefore take less fluid to fill them
and less movement on the MC.
Adrian
Why do I have to make the tools to finish the job? More time then money.
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hughpinder
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| posted on 5/6/13 at 06:56 AM |
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Sounds to me like the master cylinder hasn't got enough volume to provide flow to all the calipers as AdrianH says.
Regards
Hugh
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davidimurray
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| posted on 5/6/13 at 09:09 AM |
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Hi Adrian
Thanks for posting. I actually followed your build blog while you were building your car. I've put some answers to your questions below in red.
The bit that really confuses me is that rears is fine, and the rears plusone front is ok. But the moment you connect both fronts the pedal goes to the
bulkhead. I should also explain that when is say goes to the bulkhead, the pedal does go hard about half way along the travel, but then you can
continue to push until the pedal runs out of travel. With rears and one front connected the pedal goes solid and you cannot push it any further no
matter how hard you try.
quote:
Originally posted by AdrianH
Hi David.
From viewing your archive you are using the same pedal arrangement as me, the same sierra MC, you mention drums on the back may I ask what size they
are, 8 or 9".
Are you on the vented front disks?
Reason for my questions are I am on vented fronts and 9 inch drums at the rear and know with the same pedal set-up I have enough travel.
I've got vented fronts and 9" rear drums. My rear cylinders were actually leaking so I bought some new smaller sized ones based
on the sizes in your build diary.
From some of my past problems with brakes, I would look initially at the brake pedal movement itself.
With your foot off the pedal, do you have a small amount of free play between the push rod and the cup in the MC, allowing the MC to come back fully
to the end and at what position does the brake pedal rest.
Currently, I've got about 3-5mm of slack between the push rod and the master cylinder. When I first press the pedal, the first 20mm
or so of pedal travel (at the footplate) is just taking up the'slack'
There is a stop underneath the pedal through the floor (Bolt and nut), drop the stop down and allow the pedal to move further away from the bulkhead
at rest and use a slightly longer or adjust the push rod to just give some allowance and try again. I quick check of a MC here and the maximum travel
is 30mm, just wondering if you are getting near that travel on the push rod.
I haven't checked exactly how much m/c movement I am getting,will check tonight, but my pedal does hit the bulkhead rather than reach
the end of the travel. With the bleed nipples open, the pedal moves freely in the master cylinder with no sign of the pushrod binding or
similar.
I did change my rear cylinders down in size for the 9 inch drums to get brake balance to meet IVA , that would therefore take less fluid to fill them
and less movement on the MC.
Adrian
Gallery 1 http://www.facebook.com/media/set/?set=a.116893465324.130778.601005324
Gallery 2 http://www.facebook.com/media/set/?set=a.245243755324.181913.601005324&l=a9831a9319
Gallery 3 http://www.facebook.com/media/set/?set=a.440671625324.232627.601005324&l=3f0d42c523
Gallery 4 http://www.facebook.com/media/set/?set=a.490098255324.297598.601005324&l=efb083b7df
Gallery 5 http://www.facebook.com/media/set/?set=a.10150244028550325.366987.601005324&l=583fd5cd3a
Gallery 6 http://www.facebook.com/media/set/?set=a.10150550640070325.430417.601005324&type=3&l=fe779b358c
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owelly
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| posted on 5/6/13 at 11:17 AM |
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Can you wedge the front pistons back to stop them moving and see what the pedal travel is like. Use wooden wedges or G-lamps. This should rule out any
volume issues as the pistons won't be moving.
http://www.ppcmag.co.uk
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davidimurray
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| posted on 5/6/13 at 11:53 AM |
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Hi Owelly
I assume you mean the caliper pistons? Will take them off tonight and try and wedge them solid.
I do notice that you can see the calipers physically sliding a fair distance.
Cheers
Dave
Gallery 1 http://www.facebook.com/media/set/?set=a.116893465324.130778.601005324
Gallery 2 http://www.facebook.com/media/set/?set=a.245243755324.181913.601005324&l=a9831a9319
Gallery 3 http://www.facebook.com/media/set/?set=a.440671625324.232627.601005324&l=3f0d42c523
Gallery 4 http://www.facebook.com/media/set/?set=a.490098255324.297598.601005324&l=efb083b7df
Gallery 5 http://www.facebook.com/media/set/?set=a.10150244028550325.366987.601005324&l=583fd5cd3a
Gallery 6 http://www.facebook.com/media/set/?set=a.10150550640070325.430417.601005324&type=3&l=fe779b358c
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britishtrident
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| posted on 5/6/13 at 11:57 AM |
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Unless something is wrong in a disk brake system the volume of fluid that is actually pumped when the pedal is moved is practically zero.
(1) Make 100% sure you don't have a leak.
(2) Take each calliper off and check it slides freely and evenly on the guide pins.
(3) Check the moving pad moves frelly in the calliper and the outer pad is seated properly.
(4) Check the anti-rattle retaining spring clip is properly in place
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davidimurray
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| posted on 5/6/13 at 12:13 PM |
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Hi BritishTrident
Thanks for the response.
I will recheck everything again tonight.
Out of interest, how tight should the calipers be on the sliding pins.They seem to slide nicely but i am surprised how much deflection you can get in
the caliper.
Cheers
Dave
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Gallery 6 http://www.facebook.com/media/set/?set=a.10150550640070325.430417.601005324&type=3&l=fe779b358c
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johnemms
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| posted on 5/6/13 at 12:53 PM |
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I put smaller bore 17.8 rear cylinders on - made a lot of difference from the 20.6's i had on.
Master cylinder push rod had to be perfect size a few thou play.
Good brakes now bedded in 
M16 front 8'' drum rear
Available sizes:
BWC 5080 20.6mm
BWC 5090 19.0mm
BWC 5084 17.8mm
Own chassis & Build - First time pass!!
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Ivan
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| posted on 5/6/13 at 03:20 PM |
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Maybe the clue is in the amount you say the caliper is moving - you should barely see any movement of the pads never mind the caliper.
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Theshed
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| posted on 5/6/13 at 03:48 PM |
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quote:
Originally posted by Ivan
Maybe the clue is in the amount you say the caliper is moving - you should barely see any movement of the pads never mind the caliper.
Just what I was thinking! Try a g clamp on each calliper. If that cures it then either something is forcing the calipers back when the brake is off OR
they are being "sucked back" because fluid is not flowing into the master cylinder from the reservoir
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AdrianH
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| posted on 5/6/13 at 07:37 PM |
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quote:
Originally posted by davidimurray
Currently, I've got about 3-5mm of slack between the push rod and the master cylinder. When I first press the pedal, the first 20mm
or so of pedal travel (at the footplate) is just taking up the'slack'
I would try to reduce this down to 1-2mm if at all possible
There is a stop underneath the pedal through the floor (Bolt and nut), drop the stop down and allow the pedal to move further away from the bulkhead
at rest and use a slightly longer or adjust the push rod to just give some allowance and try again. I quick check of a MC here and the maximum travel
is 30mm, just wondering if you are getting near that travel on the push rod.
I haven't checked exactly how much m/c movement I am getting,will check tonight, but my pedal does hit the bulkhead rather than reach
the end of the travel. With the bleed nipples open, the pedal moves freely in the master cylinder with no sign of the pushrod binding or
similar.
In theory you want it to hit the end of travel before hitting bulkhead, but I can honestly say I have never measured the amount of travel
that is possible on the hayes pedal/push-rod
You mention there is a lot of spring back in the callipers,as others, I would certainly say this is not helping, this is minimal movement normally.
Adrian
[Edited on 5-6-13 by AdrianH]
Why do I have to make the tools to finish the job? More time then money.
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davidimurray
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| posted on 5/6/13 at 07:59 PM |
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Been out and had a look at the car tonight. Checked the push rod travel and my pedal hits the bulkhead after the push rod moves 23mm. Should I extend
the push rod say 5-10mm
Took the calipers off and tried to get a g-clamp on them which was difficult due to the brake pipe inlet.When I did manage to get my record 6"
g-clamp on it I could see the g-clamp flexing so I didn't push it. Instead I left the brake pads in and packed between them. With both packed
out the pedal went to the bulkhead easier than it did when fitted to the car. So you could see I took a video of both sides
passenger side
Drivers side
Any thoughts?
To me it looks like both calipers are doing the same. I've ordered another master cylinder just in case.
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Gallery 2 http://www.facebook.com/media/set/?set=a.245243755324.181913.601005324&l=a9831a9319
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Gallery 6 http://www.facebook.com/media/set/?set=a.10150550640070325.430417.601005324&type=3&l=fe779b358c
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AdrianH
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| posted on 5/6/13 at 08:27 PM |
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looking at the video I would say they are fine, took me a while to recognise what bits were missing but I guess you could not demonstrate with them
on.
Not sure what you are using as push rod but I used a clevis pin with 6mm threaded hole in the end, use of threaded bar screwed as far in as I could
and a lock nut allowed be to play with the length, once worked out I went for an cut down M6 bolt type 8.8 to ensure a bit more strength.
In the video if you are putting a lot of effort on the pedal, believe me when driving that would have had all wheel locked up and the car skidding to
a standstill. I worked it out one and around 20KG weight on the pedal would lock all wheels.
Yes go for a longer push rod.
It's called the joys of kit cars, and I wonder why I still have not started my second build.
Adrian
[Edited on 5-6-13 by AdrianH]
Why do I have to make the tools to finish the job? More time then money.
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britishtrident
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| posted on 5/6/13 at 08:34 PM |
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If the spring clips are missing or not installed properly the hydraulic part of the calliper will droop in the slider and when pressure is applies
will wobble about causing a spongey pedal.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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davidimurray
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| posted on 5/6/13 at 09:47 PM |
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Thanks for having a look.
The calipers were taken off the slides and just laid on their backs with the pads and packers installed, with no spring clips.
At the moment I have a homemade push rod but I've just ordered a proper threads clevis so I can easily adjust the length.
In the video I'm not pushing that hard, I has to push much harder when the calipers are fitted.my worry is that if I can push the pedal to the
bulkhead then so can the iva inspector:-(
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Gallery 6 http://www.facebook.com/media/set/?set=a.10150550640070325.430417.601005324&type=3&l=fe779b358c
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