The Brick-yard Homepage Brickwerks
Forum Home Forum Home > T3 Section > T3 Tech help
  New Posts New Posts RSS Feed - brake imbalance???
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

brake imbalance???

 Post Reply Post Reply
Author
Message
sam_seed View Drop Down
Groupie
Groupie


Joined: 21 Sep 09
Location: NI
Status: Offline
Points: 81
Post Options Post Options   Thanks (0) Thanks(0)   Quote sam_seed Quote  Post ReplyReply Direct Link To This Post Topic: brake imbalance???
    Posted: 05 Nov 10 at 14:10
Ok folks had the van up for it's MOT yesterday
 
It failed on three things:
Fog light refused to work on the day - working fine the evening beforeAngry
Window washers weren't hitting the windows square - can't belive I was failed on thatShocked
Front Brakes were imbalaned - no idearConfused
 
After speaking to a few lads on an irish forum they advised me it was the offside wheel that was at fault and more than likley a sticking caliper.  armed with this info I went at it this morning and ripped off the offside caliper took it apart and cleaned it then fitted it back on again.  I also went and got some brake pads the disks look fine to me.  Thing is...when I go to fit the nearside caliper back over the new pads it don't fit. The piston of the brake caliper is now hitting the new brake pad.  now, i reckon this is probably due to the fact that the old pads were a bit thiner.  The question is how do I move the piston back in a bit so I can lower the caliper over the new pads???
 
Thanks in advance folks
 
heres a snap of the mot rap sheet if it helps
 
Back to Top
Andytee View Drop Down
Groupie
Groupie
Avatar

Joined: 25 Jan 08
Location: Leeds
Status: Offline
Points: 179
Post Options Post Options   Thanks (0) Thanks(0)   Quote Andytee Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 10 at 14:36
Use something like this:
 
 
There's cheaper ones out there. I've got a Laser bargain basement one that does the job... from Halfrauds. You can use g-clamps to achieve the same effect... but this does the job better.
 
 
 
 
Atlantic poptop
Nissan Leaf
Really want a Tesla!
Back to Top
sam_seed View Drop Down
Groupie
Groupie


Joined: 21 Sep 09
Location: NI
Status: Offline
Points: 81
Post Options Post Options   Thanks (0) Thanks(0)   Quote sam_seed Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 10 at 14:39
G-Clamp! Good man - Why didn't I think of that -runs outside to rummage in garage
Back to Top
sam_seed View Drop Down
Groupie
Groupie


Joined: 21 Sep 09
Location: NI
Status: Offline
Points: 81
Post Options Post Options   Thanks (0) Thanks(0)   Quote sam_seed Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 10 at 15:31
you the man!Clap
 
g clamp worked a treat.
Back to Top
kamperman View Drop Down
Yardie
Yardie
Avatar

Joined: 07 Jan 10
Location: kidderminster
Status: Offline
Points: 340
Post Options Post Options   Thanks (0) Thanks(0)   Quote kamperman Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 10 at 21:31
a big pair of pipe grippes work well too and are cheaper than the brake winding kit Thumbs Up
life is for fixing,Not living

1981 westfalia 1.6 td
Back to Top
CaliforniaDream View Drop Down
Yardie
Yardie
Avatar

Joined: 07 Mar 07
Location: United Kingdom
Status: Offline
Points: 838
Post Options Post Options   Thanks (0) Thanks(0)   Quote CaliforniaDream Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 10 at 00:04
The brake 'winding' kit is for rear calipers that have a combined handbrake mechanism within the caliper to take up the free play as the pads wear. The tool actually turns the piston as it pushes which you don't do with front calipers.
A G clamp is fine but the proper ATE tool looks like this....
 
I doubt if you will ever see any of these for sale tho...mine are getting on for 20 years on now....
 
Martin
On wings like angels whispers sweet

my heart it feels a broken beat

Touched soul and hurt lay wounded deep

Brown eyes are lost afar now sleep xxHayleyxx



Back to Top
CaliforniaDream View Drop Down
Yardie
Yardie
Avatar

Joined: 07 Mar 07
Location: United Kingdom
Status: Offline
Points: 838
Post Options Post Options   Thanks (0) Thanks(0)   Quote CaliforniaDream Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 10 at 00:10
I would also be concerned that the piston is seizing in the caliper.....
Give the brakes a bleed at the same time...there could be some air in the fluid and besides...it needs changing every two years anyway as brake fluid is hygroscopic (absorbs water from the surrounding air) which if you didn't already know lowers the fluids boiling point which leads to a phenomenon called vapour lock (basically the fluid boiling creating gas bubbles) foot to the floor job...very scary if you live to tell the tale.
 
Martin
On wings like angels whispers sweet

my heart it feels a broken beat

Touched soul and hurt lay wounded deep

Brown eyes are lost afar now sleep xxHayleyxx



Back to Top
sam_seed View Drop Down
Groupie
Groupie


Joined: 21 Sep 09
Location: NI
Status: Offline
Points: 81
Post Options Post Options   Thanks (0) Thanks(0)   Quote sam_seed Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 10 at 10:47
I suppose the next question then is...
 
how far should the piston move back when you take your foot off the brake?
Back to Top
CaliforniaDream View Drop Down
Yardie
Yardie
Avatar

Joined: 07 Mar 07
Location: United Kingdom
Status: Offline
Points: 838
Post Options Post Options   Thanks (0) Thanks(0)   Quote CaliforniaDream Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 10 at 12:30

Interesting question......and the answer is very little. As the pressure is released the unique lip design of piston seal flex's to it's pre-formed shape drawing  back the piston by a fraction of a millimetre.

Unlike rear shoes which have 'return springs'
Martin
On wings like angels whispers sweet

my heart it feels a broken beat

Touched soul and hurt lay wounded deep

Brown eyes are lost afar now sleep xxHayleyxx



Back to Top
sam_seed View Drop Down
Groupie
Groupie


Joined: 21 Sep 09
Location: NI
Status: Offline
Points: 81
Post Options Post Options   Thanks (0) Thanks(0)   Quote sam_seed Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 10 at 19:27
so in that case, are the pads are in continual contact with the disk then only gripping when you brake...?
Back to Top
CaliforniaDream View Drop Down
Yardie
Yardie
Avatar

Joined: 07 Mar 07
Location: United Kingdom
Status: Offline
Points: 838
Post Options Post Options   Thanks (0) Thanks(0)   Quote CaliforniaDream Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 10 at 23:02
Well yes and no......the pads are in contact with the disc but the amount of contact 'drag' is a careful design characteristic of piston groove/seal design and the deformation/re-formation of that seal when the brake is applied and released (in other words the amount of deformation of the piston seal is responsible for piston retraction when brake pressure is released) 
The greater the amount of piston retraction the higher the volume of fluid needed to re-apply the piston but we are talking about fractions of a millimeter.
Read the following pdf....very technical but the info is there to see:
 
Martin
 


Edited by CaliforniaDream - 07 Nov 10 at 23:05
On wings like angels whispers sweet

my heart it feels a broken beat

Touched soul and hurt lay wounded deep

Brown eyes are lost afar now sleep xxHayleyxx



Back to Top
CaliforniaDream View Drop Down
Yardie
Yardie
Avatar

Joined: 07 Mar 07
Location: United Kingdom
Status: Offline
Points: 838
Post Options Post Options   Thanks (0) Thanks(0)   Quote CaliforniaDream Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 10 at 23:14
The mechanism for pulling back the pistion in a caliper is quite different to that of a rear wheel cylinder. 
With rear brakes the pistons in the wheel cylinders are pulled back by the brake shoe return springs. The amount the pistons 'pull back' is determined by the brake adjuster bar which acts as a stop.
Badly adjusted rear brakes will result in excessive piston movement before the shoes eventually come in to contact with the drum (long footbrake travel)
The front caliper is 'self adjusting' and sets it's own clearance by the deformation of the piston seal. Rear drums are often 'self adjusting' but the mechanisms rarely work properly so need a hand when they are initially setup (basically manually adjusting an automatic adjuster) yes I know it sounds wrong but that is the reality of crude mechanical rear brake adjusters on drums.
 
Martin  
On wings like angels whispers sweet

my heart it feels a broken beat

Touched soul and hurt lay wounded deep

Brown eyes are lost afar now sleep xxHayleyxx



Back to Top
sam_seed View Drop Down
Groupie
Groupie


Joined: 21 Sep 09
Location: NI
Status: Offline
Points: 81
Post Options Post Options   Thanks (0) Thanks(0)   Quote sam_seed Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 10 at 21:20
That's intense reading is thatConfused  I'm more clued up on the breaking mehanism now tho thanks.  Front break calipers are now stripped cleaned and back on again with new break pads.  Van's now booked in for an MOT tomorrow morning again. Fingers crossed.
 
Thanks for the help & education
Back to Top
sam_seed View Drop Down
Groupie
Groupie


Joined: 21 Sep 09
Location: NI
Status: Offline
Points: 81
Post Options Post Options   Thanks (0) Thanks(0)   Quote sam_seed Quote  Post ReplyReply Direct Link To This Post Posted: 09 Nov 10 at 14:36
Van passed today guys! WooHoo! Thanks again.
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.

The WebThis site