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MGF Rear Calipers 
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Post MGF Rear Calipers
I've just finished fitting a servo and rear disc set up with MGF rear calipers (pics to follow sometime) and I'm having a job getting the brakes bled. I've done them at least 6 times with an Eezibleed but the pedal is still soft and goes half way down so I suppose I'll have to try it the proper way next with somebody pumping the pedal (the calipers are fitted upside down on the wrong sides but I unbolt them and turn them up so that the bleed nipple is at the top before bleeding).

Anyway, when Googling these calipers I've several times come across somebody stressing that you MUST NOT apply the handbrake before seating the pads using the foot pedal first but nobody says why this is. I've never come across it before with any other car and it's bugging me that I don't know why or what happens if you do - can anybody put me out of my misery :cry: ?

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Tue Mar 26, 2013 9:58 pm
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Post Re: MGF Rear Calipers
Taking the calipers off and holding them bleed nipple up is exactlly what I do with mine.

How I bleed them
Calipers off.
Wedge/hold the piston so it cannot move.
Position calipers so bleed nipple is highest point.
Bleed as normal.

I have never used an ezibleed always pump the pedal method.

The only reason I can think of for not activating the handdbrake is due to moving the piston out of the bore and causing a pocket for trapping air?

SO just push, wind the piston back in and try the above.

On the GT cars I worked on we would bleed the calipers as normal then pump the pistons out, hold the pedal down, crack open the bleed nipples and push back the pistons to ensure all the little air pockets were found in the big multipot calipers.

Neil

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Wed Mar 27, 2013 10:20 am
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Post Re: MGF Rear Calipers
if u have pulled the handbrake up before the foot brake has been pumped up youll not get a good pedal youll have to undo caliper wined the piston back all the way, then wined the piston back out by hand till its very tight fit! then pump the brake pedal up till hard if still spongy rebleed dont forget the fronts could also have air in them even though they have not been touched! when you get a good pedal pump it till hard hold it on and lift the handbrake up and down serveral time then hold on release foot brake and then hand brake repeat a few times. hope this helps! but dont tell everyone the trick of the trade ;-) lol laters alex


Wed Mar 27, 2013 2:19 pm
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Post Re: MGF Rear Calipers
Things to try! 8) I've been using the Eezibleed because I've been doing this on my own. I recently bought a Sealey vacuum bleeder but it's either not much good or I haven't got used to it yet (probably the latter :roll: ) - it seems to be drawing air in from around the bleed nipple while it's loose. As a matter of interest I should also mention that I have an adjustment valve in the rear brake line and this fully open so shouldn't be affecting things.

Alex - I definitely didn't pull the handbrake on before bleeding because I didn't have one fitted at that stage :lol: but I'm not sure that I had the pistons wound fully back before fiting the calipers and pads. What puzzles me is that if I do as you suggest (which I will) ie wind the pistons fully back and then out again by hand so that the caliper is a tight fit before pumping the pedal etc how does that differ from pulling the handbrake on first? I don't doubt you for a second but I'm just trying to understand how this works and failing miserably!

Another thing while I'm at it, if I may - my servo has two master cylinders (photo on my thread in 'Projects') and the front and rear systems are completely separate, the only common area being the servo diaphragm chamber . Am I correct in thinking that if the brakes were working well and I then had a failure in one of the systems that I should still have a pedal because the other system is ok and assuming that the master cylinder is also ok? I'm just trying to narrow it down a bit because if that's the case I either have air in both systems or in the only common area which is the Metro twin master cylinder. Maybe I'm concentrating too much on the back brakes.

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Wed Mar 27, 2013 9:53 pm
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Post Re: MGF Rear Calipers
normaly the pipes off the master cylinder should work across the diagonal ie. nsf and osr and the other osf and nsr. not both fronts and both rears. because if one stage fails the car would pull up in straight line on the one stage thats still in tack so it would feel like half a pedal. if it was fornts and rears and the rears stage failed in could cause you to loose rear end whilst trying to stop hope you understand that lol. if you were to pull hand brake on first it fills up chamber behind handbrake lever rather than the the fluid been compreesed by the lever chamber. if that does work still get 4x molgrips or hose clamps and flexi on each corner and see if that is better if still sh1te then take pipes off mastercylinder and put blanks in to eliminat master. vacume bleeders always look like there pulling air try puttin pipe in j shape so that bleed tool higher than bleed nipple should see fluid pooling at lowest part of pipe. i uses mitte-vac with fluid chamber on it.
not to shore on the bias valve try checking out some race/ rally or trackday forums of the instruction ;-) hehe laters alex.


Thu Mar 28, 2013 2:52 pm
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Post Re: MGF Rear Calipers
Vacuum bleeder systems, whether hand pumped or compressor driven like the Sealey unit do have a tendency to suck air in around the bleed nipple threads even if you try to seal them with Teflon plumbers tape but this air does not actually enter the brake system. It just reduces the efficiency of the system a little.

What I normally do is to use the Sealey tool to pull the fluid through the empty system then finish off by pumping the pedal in the conventional way.

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Thu Mar 28, 2013 7:35 pm
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Post Re: MGF Rear Calipers
Thanks for the explanation and for all the tips, Alex. I understand what you are saying about the system being in a front/rear arrangement and this is because the servo I used is meant to be done this way - I used it to avoid having to use two separate servos and still keep separate circuits for IVA which doesn't specify exactly how the brakes should be plumbed, just that a wheel on each side should be operated separately if you see what I mean. However, I now know why systems are plumbed diagonally! I'm not sure about clamping the flexis because I have Goodridge stainless braided ones all round - would they not be damaged by Mole grips? I think I'll have another shot with the vacuum bleeder too after what you and gtmdriver say about it and then I get the missus to flex her leg and do a bit of pumping for me to finish it off :wink: Hopefully I'll get back to it over the weekend if the Easter Bunny doesn't get in the way :lol:

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Thu Mar 28, 2013 9:51 pm
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Post Re: MGF Rear Calipers
Well, I managed a few more hours at the brakes today and didn't get very far. They were thoroughly bled again by pumping the pedal this time and the end result is that the pedal still goes almost to the floor even after trying all Alex's tricks:x However, with the benefit of somebody at the pedal I discovered that with the pedal down the front discs are firmly clamped and can't be turned but the back ones can still be turned no bother at all as if the back has not been connected up! I'm as sure as I can be that there is no air left in the system, fluid came through the calipers ok and the pieces of timber that I fitted into the calipers to keep the pistons in place during bleeding and which were a neat fit had to be tapped out with a hammer so there must have been at leastsome pressure there. I'm now wondering about the adjusting valve which is fitted in the rear line. I've checked it a dozen times to make sure that it is plumbed correctly and the valve was wide open as recommended during bleeding so I'm wondering if it's faulty. The only way to prove that is to remove it and join the pipes up which is what I'll do next. I should have bought some shares in a brake fluid factory :roll:

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Sat Mar 30, 2013 10:47 pm
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Post Re: MGF Rear Calipers
Try bleeding the rear circuit at the master cyl first, I had trouble once on a clutch and had to bleed the master first, it can be messy as you have to bleed at the fitting coming out to the rears.

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Sat Mar 30, 2013 10:57 pm
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Post Re: MGF Rear Calipers
Sounds messy all right :lol: I've already bled the master cyl at the nipple which blanks off the place for fitting a reducer/proportioning valve/whateveritis that's fitted as standard on a Metro and also there are two bleed nipples (one each for front and rear cylinders) on the servo but that's something else to have a go at. Thanks.

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Sat Mar 30, 2013 11:21 pm
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Post Re: MGF Rear Calipers
is there a bleed nipple on the bias valve? if its been well bleed cant see there been any air it but worth a try. also try closing the bias valve down as this may increase force been applyed to rear brakes, what make is the bias valve ill try and find out some info on setting it up maybe something on race, rally and trackday forums!!! :? laters alex.


Tue Apr 02, 2013 1:38 pm
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Post Re: MGF Rear Calipers
Hi Alex. There is no bleed nipple on the bias valve. I got it from McGill Motorsport on ebay and it looks identical to others for sale by the likes of ProTec who have anodised their's blue. The valve screws down to increase pressure and I have it down as far as it will go. I have also checked the plumbing against the instructions to make sure that I've got it the right way round - the highest port is the inlet and the lower one is the outlet. I haven't got back to it for a few days (work is a necessary nuisance!!) but my next tactic is to remove the pipe from the inlet port and put a bleed nipple on it (the pipe) and bleed it - if I get a good pedal then the master cyl and servo should be ok in which case I'll reconnect the inlet pipe and remove the outlet to fit a nipple which will allow me to check the valve. If that's ok then the problem is with the calipers. This is the only way that I can think of to break the system down into sections to help narrow the problem down. I hope all that makes sense!

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Wed Apr 03, 2013 9:06 pm
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Post Re: MGF Rear Calipers
I spent most of today faffing around with this and made some progress...of sorts. First off, I removed the inlet pipe from the adjusting valve, fitted a nipple, bled it and got a perfect pedal 8) Reconnecting that pipe I did the same with the outlet from the valve and still had the perfect pedal so the problem isn't with the master cyl, servo cyls or adjusting valve therefore it has to be the calipers. I tried everything I could think of to get these right but with little success. I made sure that the pistons were screwed fully back (one of them doesn't go back as far as the other but only by a couple of mm) and a couple of times I opened the bleed nipples for good measure. To cut a long story short I still have far too much pedal travel - the first pump goes almost to the floor and then it gets a bit better. It doesn't feel spongy, more like it's taking up some slack as if the caliper pistons have a long way to go. I have checked that the pistons are operating ok but, on the first pump, the back wheels can still be turned with a bit of effort, second pump they can be turned with a lot more effort and third pump they can't be moved at all which is an improvement on what they were before. I spent a lot of time trying Alex's routine with foot pedal and handbrake and it gets much better but if I leave it for a few seconds the pedal goes back to the floor again :? Just to make sure that the adjusting valve wasn't somehow interfering I disconnected the pipes from it and joined them up so the valve is bypassed. I can only think that somehow there must still be some air in there but I don't know what to do to get it out - it's been bled by pumping the pedal, by Eezibleed and by both at the same time. (With the Eezibleed still connected and all bleed nipples closed ie the system pressurised to approx 15 psi the pedal is fine) There are absolutely no air bubbles coming out in the fluid and I'm as satisfied as I can be that there's no point in bleeding it any more. Other than buying a pair of (expensive :shock: ) reconditioned calipers in case the ones I have are wonky I'm really stumped as to what to do next, maybe it's time to get some professional help but that really is a last resort because I've got ths far on my own :roll:

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Sat Apr 06, 2013 9:59 pm
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Post Re: MGF Rear Calipers
The syptoms you describe are same as you would have if you have fitted new brake pads onto unevenly worn brake discs. i think the caliper is not at 90 degrees to brake disc so one edge will contact disc and it then takes three pumps of pedal to get it in full contact with disc. this would improve with use if this is the problem but the pads will wear slightly wedge shaped.you could try removeing calipers and try it with some sort of packing in place of disc to see if you get good pedal with less travel . onother option is try it with fixing bollts loosened so it can find it own correct angle in relation to disc to so if this reduces travel.I have seen this several times on transit front axles on stock cars when stub axles get bent during race . hope this helps if not one more thing to rule out


Sat Apr 06, 2013 10:48 pm
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Post Re: MGF Rear Calipers
Thanks Mark. I'll try that first chance. Actually, I have noticed that the outside pads are very slightly not flat against the disc but put this down to their not being settled down properly due to the pedal travel problem and that it would sort itself out as the pads bed in. I can live with the pads being slightly wedge shaped because the car will not be doing a high mileage anyway. When I get the engine going again (starter motor and other bits have been removed to give more room to work with handbrake cables) I can get the back off the floor and run it in gear with the brake on slightly to settle it in.

I've just had another thought while typing this - the caliper on one side is not central on the disc by 3mm so would require a 1.5mm shim between the caliper mounting lugs and the hub to get it spot on (the piston side has the greater clearance). Because it's a sliding caliper I thought that it would be ok and left it alone but maybe I should shim it to rule that out too...

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Sat Apr 06, 2013 11:10 pm
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