Rear Brakes Locking on...
Discussion
Just picked up my GTR tonight but notice the rear calipers lock on sometimes. Any simple solutions to sort this out e.g. brake bleed, caliper lube (if so, where abouts?) etc..
Cheers for the info.
Robin.
PS Note there's no seperate handbrake caliper, the handbrake cable just feeds onto the main calipers.
Cheers for the info.
Robin.
PS Note there's no seperate handbrake caliper, the handbrake cable just feeds onto the main calipers.
GreenV8S said:
Do you have a separate master cylinder for the rear brakes? If so it could be that the pushrod is adjusted too tight - that can cause this problem.
I'll check that tomorrow. If so then back off the pushrod? Just wondering how that would effect the brake bias though.
I've a trackday on Thursday 7th so might have a play with the bias then (hopefully it'll be a wet day then I can see which wheels lock up first etc..).
As Peter said if a rod is too long then it prevents the master cylinder from opening the fluid return port leaving the brakes locked on.
This should not be possible with a brake bias bar as it should just twist and allow the master cylinder to return.
If both rods are too long and the pedal is as far back as possible then it will be the rear that will be affected because the rear brake system has far less pressure in it as demonstrated by peoples issues with brake light switches not coming on (P).
Steve
This should not be possible with a brake bias bar as it should just twist and allow the master cylinder to return.
If both rods are too long and the pedal is as far back as possible then it will be the rear that will be affected because the rear brake system has far less pressure in it as demonstrated by peoples issues with brake light switches not coming on (P).
Steve
What type of brakes do you have? If the car originally had the servo assisted Ford brakes, which were upgraded to AP or similar, then the servos need to be disconnected, just the vacuum feed, not the hydraulics. I had this problem, and before I disconnected the servos, the only way to unlock the rears was to really "stamp" on the pedal!
On my bike I find that I get an in balance of fluid in the calliper itself. Sometimes one piston on one side of the calliper will lead or lag the other pistons in the calliper by a significant margin. Holding the leading piston back against the body with a pair of pliers or vice grips while some light pressure is applied to the lever/pedal allows the fluid to equalise in the calliper. The end result is that all the pistons in the calliper work at the same time and the pad now contact the disc evenly. This greatly improves the feel attained through the lever/pedal as the slight mushiness that is initially felt prior to hard brake applications is now gone.
May not be you issue.
Will require someone to move the brake pedal slowly as you watch the relative motion of the pistons. This will require the car up on stands with the wheels off.
ryan
May not be you issue.
Will require someone to move the brake pedal slowly as you watch the relative motion of the pistons. This will require the car up on stands with the wheels off.
ryan
I have AP's on the rear, no servo. The problem also occurs if you operate the handbrake but it does free itself if you bang away at the pedal.
I suspect the plunger being too long is the problem e.g. fluid can't return as per someone's suggestion. I'll try to shorten the rear brake plunger on the weekend and see how I go.
Need to get it sorted as pulling up with smokin' rears is becoming a pain!
I suspect the plunger being too long is the problem e.g. fluid can't return as per someone's suggestion. I'll try to shorten the rear brake plunger on the weekend and see how I go.
Need to get it sorted as pulling up with smokin' rears is becoming a pain!
Steve_D said:
I can't remember if the rods are adjustable but pretty sure they are.
If you do make an adjustment you may need to adjust both rods. What you want is for the bias bar to be square with the rods when the brakes are applied.
Steve
I found this an interesting read. If you do make an adjustment you may need to adjust both rods. What you want is for the bias bar to be square with the rods when the brakes are applied.
Steve
http://www.wilwood.com/Products/005-PedalAssemblie...
Don't be concerned where it says that the distance of lateral movement (A+B) should be 0.20" - 0.25". I suspect that is for vehicles wilth a whole lot more pedal travel than ours. I spoke to Ted yesterday and he said that this gap (A+B on the diagram) should be 1-1.5mm. Of course, you should double check that both clevis do not bind to pedal over the whole travel.
The puch rod adjustment I'll let you read, but again, different master bores have different throws, so the static unpressured stance may seem a little off perpendicular. The article says mid pressure to be 90 degrees (but I found very little shift in the bar as the travel is so short).
Finally the off pressure 'slack' in push rod, this should be noticable but not excessive. Just grab the pushrod and feel for play fwd and aft. A small amount is right, none is definately wrong!!
HTH
Lucks
Edited by LuckyP on Thursday 31st July 11:28
Oh an incidentally, in setting the clevis/pedal gaps (which required one turn in on the rear master cylinder side), I got my brake lights to work to what I would would call, 'roundabout braking'. Still nothing on 'M25 traffic braking'
Now just a bit woried that I've biased too much to the rears.....only time and a mildly moist Sunday morning will tell
Now just a bit woried that I've biased too much to the rears.....only time and a mildly moist Sunday morning will tell
LuckyP said:
Steve_D said:
I can't remember if the rods are adjustable but pretty sure they are.
If you do make an adjustment you may need to adjust both rods. What you want is for the bias bar to be square with the rods when the brakes are applied.
Steve
I found this an interesting read. If you do make an adjustment you may need to adjust both rods. What you want is for the bias bar to be square with the rods when the brakes are applied.
Steve
http://www.wilwood.com/Products/005-PedalAssemblie...
Don't be concerned where it says that the distance of lateral movement (A+B) should be 0.20" - 0.25". I suspect that is for vehicles wilth a whole lot more pedal travel than ours. I spoke to Ted yesterday and he said that this gap (A+B on the diagram) should be 1-1.5mm. Of course, you should double check that both clevis do not bind to pedal over the whole travel.
The puch rod adjustment I'll let you read, but again, different master bores have different throws, so the static unpressured stance may seem a little off perpendicular. The article says mid pressure to be 90 degrees (but I found very little shift in the bar as the travel is so short).
Finally the off pressure 'slack' in push rod, this should be noticable but not excessive. Just grab the pushrod and feel for play fwd and aft. A small amount is right, none is definately wrong!!
HTH
Lucks
Edited by LuckyP on Thursday 31st July 11:28
I also lengthened the front brake pushrod and backed off the rear so hopefully that'll apply more front.
What does worry me slightly is the front brake pushrod moves okay when pressure applied but the rear pushrod has virtually no movement.
It may be that I have a problem with one (or both) of the rear calipers or the reservoir (which I wouldn't be surprised about as I drove for about 15 miles with them on pretty hard = smoke, heat and brake smell).
I'll do some testing tomorrow to see the impact of my changes.
Cheers,
Robin.
Robin,
When you say the rears calipers lock on, is it one side or both?
I'm guessing here, but one side would indicate a localised caliper issue, but both sides would surely have to come from a master cylinder or pedal problem. See what I mean?
If it is one side not the other, try to see if the pads are worn symmetrically. If there is a difference on one pad, top to bottom or side to side, then perhaps the piston is binding in the caliper? No ammount of pedal or pushrod adjustment will rectify that!!
All this comes with a disclaimer. It's all guess work!!
When you say the rears calipers lock on, is it one side or both?
I'm guessing here, but one side would indicate a localised caliper issue, but both sides would surely have to come from a master cylinder or pedal problem. See what I mean?
If it is one side not the other, try to see if the pads are worn symmetrically. If there is a difference on one pad, top to bottom or side to side, then perhaps the piston is binding in the caliper? No ammount of pedal or pushrod adjustment will rectify that!!
All this comes with a disclaimer. It's all guess work!!
LuckyP said:
Robin,
When you say the rears calipers lock on, is it one side or both?
I'm guessing here, but one side would indicate a localised caliper issue, but both sides would surely have to come from a master cylinder or pedal problem. See what I mean?
If it is one side not the other, try to see if the pads are worn symmetrically. If there is a difference on one pad, top to bottom or side to side, then perhaps the piston is binding in the caliper? No ammount of pedal or pushrod adjustment will rectify that!!
All this comes with a disclaimer. It's all guess work!!
LuckyP, it's both sides so suspect master cylinder problems, also the rear plunger just won't move more than a few mm into the master cylinder, that for some reason concerns me more.When you say the rears calipers lock on, is it one side or both?
I'm guessing here, but one side would indicate a localised caliper issue, but both sides would surely have to come from a master cylinder or pedal problem. See what I mean?
If it is one side not the other, try to see if the pads are worn symmetrically. If there is a difference on one pad, top to bottom or side to side, then perhaps the piston is binding in the caliper? No ammount of pedal or pushrod adjustment will rectify that!!
All this comes with a disclaimer. It's all guess work!!
While my fronts are AP's the rears are what I presume are Ford calipers.
I'll give it a test tomorrow and see what difference I've made. If no joy I think I'll hand back to the Factory to check over and advise as I'm not so sure how to progress. Only problem is I rang them Monday and they're busy with the show, then busy next week and maybe the week after so could be up to three weeks before they can look at it.
You don't know anyone else in the Midlands who is good with these cars?
I also need a couple of other things looked at (door locks stuffed, wheel alignment/suspension set up is out etc..), basically the car needs a bit of TLC.
Cheers,
Robin.
Apart from the suspension alignment all the other issues are quite normal work for your local back street garage. There is very little on an Ultima that a decent mechanic will not be able to work out for himself how to deal with it.
With respect to your brakes the next step is to push back the pads in the rear callipers to first confirm they are not seized and to then see if the master cylinder pushes them back again or is the master seized. If this is not a job for you then, as I said, this is straight forward stuff for your average mechanic.
Even the suspension is not difficult just time consuming. Have a look around for someone local who either does race car prep as their business or more likely one of the mechanics runs his own race car. This is usually quite easy to spot as the garage probably sponsors him to the tune of storing the car and allowing him to use the garage facilities.
Steve
With respect to your brakes the next step is to push back the pads in the rear callipers to first confirm they are not seized and to then see if the master cylinder pushes them back again or is the master seized. If this is not a job for you then, as I said, this is straight forward stuff for your average mechanic.
Even the suspension is not difficult just time consuming. Have a look around for someone local who either does race car prep as their business or more likely one of the mechanics runs his own race car. This is usually quite easy to spot as the garage probably sponsors him to the tune of storing the car and allowing him to use the garage facilities.
Steve
Gassing Station | Ultima | Top of Page | What's New | My Stuff