MGA / Midget Master Cylinders
- Steve Simmons
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MGA / Midget Master Cylinders
Has anyone had problems with MGA or Midget master cylinders returning slowly, or being difficult to bleed? I'm at wit's end trying to solve this problem in my MGA. The only big change to the system was rebuilding and re-sleeving the master. I've even had the bores polished and opened up oversize to .877 in hopes it would help, but no joy. I'm not getting any air out of the lines but the brakes act as if they are full of air, and they return a bit too slow.
Deleted return valve, no change. The rear brakes seem to activate less than the front, so I replaced the original cylinders that I had rebuilt (and were leaking anyway) with brand new ones. No change.
Argh!!!
Deleted return valve, no change. The rear brakes seem to activate less than the front, so I replaced the original cylinders that I had rebuilt (and were leaking anyway) with brand new ones. No change.
Argh!!!
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Re: MGA / Midget Master Cylinders
Steve, I don't have experience with those particular masters, but...
You said the brakes act as if they have air in the lines. Do they pump up significantly?
Does the pedal creep down after you come to a stop and hold your foot on the brake?
Have/can you peel the dust boot back to see if there is fluid leaking out the back of the master?
By return valve, I assume you mean the residual pressure valve?
4-wheel drums?
Is it a conventional style master with both a large and tiny hole from the reservoir into the bore and the outlet near the end (opposite the pushrod)? Or is it a Girling style with the reservoir at the end and the outlet in the top middle?
You said the brakes act as if they have air in the lines. Do they pump up significantly?
Does the pedal creep down after you come to a stop and hold your foot on the brake?
Have/can you peel the dust boot back to see if there is fluid leaking out the back of the master?
By return valve, I assume you mean the residual pressure valve?
4-wheel drums?
Is it a conventional style master with both a large and tiny hole from the reservoir into the bore and the outlet near the end (opposite the pushrod)? Or is it a Girling style with the reservoir at the end and the outlet in the top middle?
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Re: MGA / Midget Master Cylinders
You said the brakes act as if they have air in the lines. Do they pump up significantly?
Yes, three or four pumps gives a firm pedal.
Does the pedal creep down after you come to a stop and hold your foot on the brake?
No, it holds pressure even if I stand on the pedal for 60 seconds.
Have/can you peel the dust boot back to see if there is fluid leaking out the back of the master?
No leaks anywhere that I can detect.
By return valve, I assume you mean the residual pressure valve?
Correct!
4-wheel drums?
Yes, I'm waiting to install the discs until I get this problem sorted out.
Is it a conventional style master with both a large and tiny hole from the reservoir into the bore and the outlet near the end (opposite the pushrod)?
Yes, precisely. Click here for a photo of the re-sleeved masters.
Yes, three or four pumps gives a firm pedal.
Does the pedal creep down after you come to a stop and hold your foot on the brake?
No, it holds pressure even if I stand on the pedal for 60 seconds.
Have/can you peel the dust boot back to see if there is fluid leaking out the back of the master?
No leaks anywhere that I can detect.
By return valve, I assume you mean the residual pressure valve?
Correct!
4-wheel drums?
Yes, I'm waiting to install the discs until I get this problem sorted out.
Is it a conventional style master with both a large and tiny hole from the reservoir into the bore and the outlet near the end (opposite the pushrod)?
Yes, precisely. Click here for a photo of the re-sleeved masters.
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Re: MGA / Midget Master Cylinders
Okay, since it pumps up significantly, there is air in the system.
Since it holds when you keep pressure on the pedal, it is probably not bypassing the pressure seal.
In that twin bore M/C, I assume one bore supplies the front and the other the rear? If so, are there two sets of holes connecting the reservoir to the bore(s)? One set for each bore?
Triple check that the reservoir-to-bore holes are drilled though the sleeve, all the way up to the same size as the original, especially the tiny hole. This is critical for bleeding.
Have you tried bench bleeding the master? That is connecting hoses from the M/C outlets back into the reservoir (submerged), pump the pedal until the master is completely bled. You can probably do one cylinder at a time. That is the single best way to bleed a master cylinder.
Since it holds when you keep pressure on the pedal, it is probably not bypassing the pressure seal.
In that twin bore M/C, I assume one bore supplies the front and the other the rear? If so, are there two sets of holes connecting the reservoir to the bore(s)? One set for each bore?
Triple check that the reservoir-to-bore holes are drilled though the sleeve, all the way up to the same size as the original, especially the tiny hole. This is critical for bleeding.
Have you tried bench bleeding the master? That is connecting hoses from the M/C outlets back into the reservoir (submerged), pump the pedal until the master is completely bled. You can probably do one cylinder at a time. That is the single best way to bleed a master cylinder.
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Re: MGA / Midget Master Cylinders
In that twin bore M/C, I assume one bore supplies the front and the other the rear?
No, one for brake and one for clutch. This is a single circuit brake system.
Triple check that the reservoir-to-bore holes are drilled though the sleeve, all the way up to the same size as the original, especially the tiny hole. This is critical for bleeding.
They are drilled, but I'm not sure what the original size was. I suppose I could drill them a bit larger but that would mean pulling the darn thing out and I've already lost a lot of skin getting it back in...
Have you tried bench bleeding the master?
I only went so far as to pump the piston until fluid came out the rear hole, which is about halfway up the fluid level in the reservoir. Then as fluid continued dribbling out, I connected the hard line. Since the hard line exits upward, any air should have continued to be pushed away from the MC.
You really have me thinking about that smaller hole. I just can't imagine that's my whole problem. The slow return rate, the feeling that the pedal has some extra effort to it, etc. I should also note that this is DOT5 fluid but there are more than enough reports of MGAs running it that I'm not worried about that being an issue.
One last note, it seems like the rears aren't working as smoothly or strongly as the fronts. Could be due to the longer pipe I suppose. It's a single circuit system so not much to consider unless maybe the rear hose, which was replaced at the same time the first MC was replaced, is sticking too far into the 3-way on the rear axle and limiting the amount of fluid going through? Nah, that doesn't seem right. Argh.
No, one for brake and one for clutch. This is a single circuit brake system.
Triple check that the reservoir-to-bore holes are drilled though the sleeve, all the way up to the same size as the original, especially the tiny hole. This is critical for bleeding.
They are drilled, but I'm not sure what the original size was. I suppose I could drill them a bit larger but that would mean pulling the darn thing out and I've already lost a lot of skin getting it back in...
Have you tried bench bleeding the master?
I only went so far as to pump the piston until fluid came out the rear hole, which is about halfway up the fluid level in the reservoir. Then as fluid continued dribbling out, I connected the hard line. Since the hard line exits upward, any air should have continued to be pushed away from the MC.
You really have me thinking about that smaller hole. I just can't imagine that's my whole problem. The slow return rate, the feeling that the pedal has some extra effort to it, etc. I should also note that this is DOT5 fluid but there are more than enough reports of MGAs running it that I'm not worried about that being an issue.
One last note, it seems like the rears aren't working as smoothly or strongly as the fronts. Could be due to the longer pipe I suppose. It's a single circuit system so not much to consider unless maybe the rear hose, which was replaced at the same time the first MC was replaced, is sticking too far into the 3-way on the rear axle and limiting the amount of fluid going through? Nah, that doesn't seem right. Argh.
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Re: MGA / Midget Master Cylinders
Is the master cylinder mounted lower than the wheel cylinders or higher like on an MGB?
I would not recommend drilling it out larger, but the sleeve must have the same diameter hole in it as the original hole. I assume the original hole is still intact in the reservoir, right? You should check that the matching hole in the sleeve is not smaller, or not there at all.
I would not recommend drilling it out larger, but the sleeve must have the same diameter hole in it as the original hole. I assume the original hole is still intact in the reservoir, right? You should check that the matching hole in the sleeve is not smaller, or not there at all.
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Re: MGA / Midget Master Cylinders
Oops, hit submit before I was done...
The DOT 5 fluid will be a bit spongier (is that a word?) if you had DOT 3 or 4 in it before, but not to the point of pumping up significantly.
It is highly unlikely that the distance to the rear has anything to do with it. The fact is, pressure is equal throughout the system, especially with a single M/C system...Pascal's Law of fluid pressure. There is virtually no flow in a brake system. You'd be amazed at how small some passages are in various brake devices. The only time I've seen an issue where flow was restricted was in decades-old brake hoses that swelled or collapsed internally. It happened to me.
I think your issue is just air.
The DOT 5 fluid will be a bit spongier (is that a word?) if you had DOT 3 or 4 in it before, but not to the point of pumping up significantly.
It is highly unlikely that the distance to the rear has anything to do with it. The fact is, pressure is equal throughout the system, especially with a single M/C system...Pascal's Law of fluid pressure. There is virtually no flow in a brake system. You'd be amazed at how small some passages are in various brake devices. The only time I've seen an issue where flow was restricted was in decades-old brake hoses that swelled or collapsed internally. It happened to me.
I think your issue is just air.
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Re: MGA / Midget Master Cylinders
It's mounted up high like an MGB. The hole in the sleeve is much smaller than the hole in the MC, but I'm not sure if the hole in the MC is the original size. It seems pretty big for the "smaller" of the two. I've been told in the past that drilling the small hole the next drill size larger helps the MC work better, but the hole in the sleeve now is half the size of the hole in the cast iron. Hmmm... I guess I need to find an original, unmolested MGA master cylinder to measure.
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Re: MGA / Midget Master Cylinders
Checking an original is the best bet, but I can tell you that about .023" to .030" diameter should work well. Any bigger and you risk prematurely wearing out the cup seal as it has to travel across that hole on every stroke. Smaller makes it harder to bleed. So you want it as small as possible while still being able to bleed it.
For comparison, the area of a .023" hole is .0004 sq-in, and a .030" hole is .0007 sq-in. That is a huge difference.
With the master above the wheel cylinders, during bleeding you should have seen air bubbles coming out of both holes in the reservoir, especially the small hole. It's nearly impossible to push the air from the master cylinder down to the wheels.
Check that the hole size is right and "bench" bleed the master.
I'll check back with you tomorrow.
For comparison, the area of a .023" hole is .0004 sq-in, and a .030" hole is .0007 sq-in. That is a huge difference.
With the master above the wheel cylinders, during bleeding you should have seen air bubbles coming out of both holes in the reservoir, especially the small hole. It's nearly impossible to push the air from the master cylinder down to the wheels.
Check that the hole size is right and "bench" bleed the master.
I'll check back with you tomorrow.
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Re: Still Spongy ?
If so , it's time for : The Stick Trick !
.
You won't believe how well this simple trick works until you've done it.....
.
Simply wedge a stick between the seat and the brake pedal and go off and leave it for a few days , atmospheric pressure will draw those pesky bubbles out and you'll once again have rock hard brake pedal .
Metropolitans suffer this malady ~ many Metters back fill the system from the bleeder valves and say that works too , I just do the Stick Trick once or twice and it's good to go until the next time I open the system for new cylinders .
I made up a pressure bleeder and that got me 3/4 brakes but only the Stick Trick works 100 % .
![Bow :bow:](./images/smilies/bow.gif)
You won't believe how well this simple trick works until you've done it.....
![Wink ;)](./images/smilies/icon_wink.gif)
Simply wedge a stick between the seat and the brake pedal and go off and leave it for a few days , atmospheric pressure will draw those pesky bubbles out and you'll once again have rock hard brake pedal .
Metropolitans suffer this malady ~ many Metters back fill the system from the bleeder valves and say that works too , I just do the Stick Trick once or twice and it's good to go until the next time I open the system for new cylinders .
I made up a pressure bleeder and that got me 3/4 brakes but only the Stick Trick works 100 % .
-Nate
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Re: MGA / Midget Master Cylinders
Believe it or not I've tried that and it didn't work! Maybe I didn't do it right.
- VWNate1
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Re : The Stick Trick
Trust me , I believe it !
.
My red '59 FHC Met is maddening as it often take several tries before the brakes come up proper .
I'm on a Road Rally now and I've been seriously abusing the brakes to - day as I missed as turn off and got 1,000 % LOST ~ I've not seen another since before lunch on Rt. 154
I made my way by dead reckoning via tiny back roads to King City only to discover we no longer stay in King City.....
I even asked the Road Captain if we'd be staying in King City this morning & he said yes , just a different Motel .
They're 50 miles away in another town , I'm going to bed then home in the morning .
I really need to learn how to follow directions better
Or , maybe buy some maps...![Jester :jester](./images/smilies/icon_jester.gif)
![Mad :x](./images/smilies/icon_mad.gif)
My red '59 FHC Met is maddening as it often take several tries before the brakes come up proper .
I'm on a Road Rally now and I've been seriously abusing the brakes to - day as I missed as turn off and got 1,000 % LOST ~ I've not seen another since before lunch on Rt. 154
![Shocked :eek:](./images/smilies/icon_eek.gif)
![Confused :?](./images/smilies/icon_confused.gif)
I made my way by dead reckoning via tiny back roads to King City only to discover we no longer stay in King City.....
![Hammer :hammer:](./images/smilies/hammer.gif)
I even asked the Road Captain if we'd be staying in King City this morning & he said yes , just a different Motel .
They're 50 miles away in another town , I'm going to bed then home in the morning .
I really need to learn how to follow directions better
![Razz :P](./images/smilies/icon_tongue.gif)
Or , maybe buy some maps...
![Jester :jester](./images/smilies/icon_jester.gif)
-Nate
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Re: MGA / Midget Master Cylinders
Steve - it may be a seal issue. Sorry for being slow to respond here but I had a similar issue on the Bugeye (same MC) and it turned out to be the seals being oversized and needing to be worked some to get them to fit properly.
http://mgaguru.com/mgtech/hydraulics/ht204a.htm" onclick="window.open(this.href);return false;
http://mgaguru.com/mgtech/hydraulics/ht204a.htm" onclick="window.open(this.href);return false;
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Re: MGA / Midget Master Cylinders
That was my feeling at one point, but it seems to return OK on the bench. I will be pulling it apart AGAIN in the next day or two to try opening that rear hole up slightly. I'm fairly certain it is too small.
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Re: MGA / Midget Master Cylinders
Definately the by pass ports are too small ! .
Once you open it up , don't forget to de burr the cylinder inside where the rubber cup passes over the by pass port....
I've polished a few of these aluminum cylinders with some old leather duct taped to a drill bit , the result is a mirror finish that allows good sealing and less drag when the piston returns....
Once you open it up , don't forget to de burr the cylinder inside where the rubber cup passes over the by pass port....
I've polished a few of these aluminum cylinders with some old leather duct taped to a drill bit , the result is a mirror finish that allows good sealing and less drag when the piston returns....
-Nate
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Re: MGA / Midget Master Cylinders
I agree, it is critical that the hole is deburred. Nate's method sounds fine to me.
Do not go too big on the hole size. Definately keep it under .030" diameter. The larger the hole, the faster it will wear out the cup seal.
I suggest checking the current diameter size and trying to bench bleed it before opening the hole. This will be your benchmark. Then open it in maybe .003"-.005" increments and bench bleed each time to see what effect it has on bleeding. I know it doesn't sound like a big change, but when you calculate the area of the hole before and after a .005" change, you'll see it equates to a substantial percentage difference.
On the seal oversize posibility, I'd say the cup seal OD should be roughly .020-.050" larger than the bore. That being said, there are a lot of variables and it is difficult to accurately measure an elastomer. Believe me.
Call me if you have any questions.
Do not go too big on the hole size. Definately keep it under .030" diameter. The larger the hole, the faster it will wear out the cup seal.
I suggest checking the current diameter size and trying to bench bleed it before opening the hole. This will be your benchmark. Then open it in maybe .003"-.005" increments and bench bleed each time to see what effect it has on bleeding. I know it doesn't sound like a big change, but when you calculate the area of the hole before and after a .005" change, you'll see it equates to a substantial percentage difference.
On the seal oversize posibility, I'd say the cup seal OD should be roughly .020-.050" larger than the bore. That being said, there are a lot of variables and it is difficult to accurately measure an elastomer. Believe me.
Call me if you have any questions.
-
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Re: MGA / Midget Master Cylinders
Under the theory of KISS, might the seal just be too small? Have you tried another one?
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Re: MGA / Midget Master Cylinders
Definitely not too small! The seals were way too tight when this all started, but now seem to be working properly. I'm also replacing the springs on the next rebuild, which will be tomorrow.
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Re: MGA / Midget Master Cylinders
Girling used to sell a special brake grease (NOT ! white Lithium grease !) you'dd work into both the bore and the rubber cups to alieveiate this dragging issue .
If the M/C is fully released then the braking system is back filled , the brakes will work fine as the cup beds in and begins to slide easily .
This gave me fits as I don't lack back filling the system .
If the M/C is fully released then the braking system is back filled , the brakes will work fine as the cup beds in and begins to slide easily .
This gave me fits as I don't lack back filling the system .
-Nate
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Re: MGA / Midget Master Cylinders
Someone measured an original MGA MC for me. The small hole in his MC is .023" (.57mm). Mine is somewhere around .050". I don't have anything exact to measure with but it's larger than .048 and smaller than .062. Much close to .048.
The large holes are the same at 3/16".
The clutch side is a little bit sticky but the brake side moves very free and smooth. I've replaced the springs "just because", but I don't see anything else that can possibly be wrong with it. I just can't get it to bleed!
The large holes are the same at 3/16".
The clutch side is a little bit sticky but the brake side moves very free and smooth. I've replaced the springs "just because", but I don't see anything else that can possibly be wrong with it. I just can't get it to bleed!
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Re: MGA / Midget Master Cylinders
I had a similar issue with my brakes on the '66 b when I tried to bleed them for the first time. No amount of pumping of the brakes would push fluid through the system. Finally I created a cap for the MC that I could attach an air hose to and create positive (about 10-15 lbs) pressure in the lines. Then is is a simple matter of going around to each corner and letting the air out till the fluid runs clean. With silicon it took three sessions spaced out to let the ir settle out to do the job right. I am very pleased with the results now.
I don't know if the cap is the same as it is on the early B's, if it is you are more then welcome to try my bleeding tool.
I don't know if the cap is the same as it is on the early B's, if it is you are more then welcome to try my bleeding tool.
Chris Gorman
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Re: MGA / Midget Master Cylinders
I've already tried my power bleeder. No dice. Hopefully upon reassembly it will work this time, either because of the new springs or by magic.
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Re: MGA / Midget Master Cylinders
Hmm, I asume the cup seals were ok, not swelled up or gummy (sticky)? That would indicate a material incompatibility issue.
Since the holes are over .035", double check with a paperclip that the cup seals are not partially (or completely) covering the small holes when the piston is fully returned. They must not be blocking the small holes at all.
Assuming that all checks out, my suggestion is to "bench" bleed it. Fill the reservoirs about half way after connecting flexible tubing to the outlets and routed back into the reservoir (submerged in the fluid). Pump the master cylinder as long as it takes, until no more air comes out. Then connect your lines. I prefer to do this mounted in the car, as long as you can get to the lines to reconnect them.
Since the holes are over .035", double check with a paperclip that the cup seals are not partially (or completely) covering the small holes when the piston is fully returned. They must not be blocking the small holes at all.
Assuming that all checks out, my suggestion is to "bench" bleed it. Fill the reservoirs about half way after connecting flexible tubing to the outlets and routed back into the reservoir (submerged in the fluid). Pump the master cylinder as long as it takes, until no more air comes out. Then connect your lines. I prefer to do this mounted in the car, as long as you can get to the lines to reconnect them.
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Re: MGA / Midget Master Cylinders
Well I think the small holes may have been partially blocked, but it was hard to tell because of how small they are. The only thing I had that would fit in there was a piece of solder, which obviously isn't very solid. Investigating the possible cause of this issue led me to a couple interesting things.
First, I compared the cup seal to a brand new one I just bought. Both were from Moss. The one in the MC now is longer than the new one. To account for swelling, I compared the old cup with another new one that I had purchased (also from Moss) at the same time as the old one. They were the same size.
With this in mind, I believe it's safe to conclude that there has been a variance in the size of the cups in recent past with Moss' supplier. That was issue #1.
Next I discovered that the two seemingly identical pistons are not identical. The one on the brake side was 20 thou longer than the other. Combined with the longer cup, this could be the problem. I shaved the shorter piston about 5 thou, and the longer one 25 thou so that they are now the same size and will give a little wiggle room for rubber that may be too big.
The MC is now back together with all new (smaller) cups, new secondaries and new springs. The clutch side is even more sticky now, but it should be ok since it has a strong return pressure.
EDIT: Another note on the rubber cups, I noticed the longer ones are also much stiffer than the shorter ones I just got and the finish on the rubber is a little different. The markings are all exactly the same. I'm running the shorter, softer one now on the brake side. I accidentally put the stiffer one on the clutch side but I'm not doing it over. Even when it was super sticky before, the clutch worked fine, probably because of the pressure plate forcing it home.
First, I compared the cup seal to a brand new one I just bought. Both were from Moss. The one in the MC now is longer than the new one. To account for swelling, I compared the old cup with another new one that I had purchased (also from Moss) at the same time as the old one. They were the same size.
With this in mind, I believe it's safe to conclude that there has been a variance in the size of the cups in recent past with Moss' supplier. That was issue #1.
Next I discovered that the two seemingly identical pistons are not identical. The one on the brake side was 20 thou longer than the other. Combined with the longer cup, this could be the problem. I shaved the shorter piston about 5 thou, and the longer one 25 thou so that they are now the same size and will give a little wiggle room for rubber that may be too big.
The MC is now back together with all new (smaller) cups, new secondaries and new springs. The clutch side is even more sticky now, but it should be ok since it has a strong return pressure.
EDIT: Another note on the rubber cups, I noticed the longer ones are also much stiffer than the shorter ones I just got and the finish on the rubber is a little different. The markings are all exactly the same. I'm running the shorter, softer one now on the brake side. I accidentally put the stiffer one on the clutch side but I'm not doing it over. Even when it was super sticky before, the clutch worked fine, probably because of the pressure plate forcing it home.
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Re: MGA / Midget Master Cylinders
Wait ~ tell me again how you don't know enough to be a Journeynam Mechanic ?
.
I hope this works out ~ I too was going to suggest bench bleeding but I was too late .
Sadly , one of the front blind brake cylinders I installed in December , is seeping a tiny bit so I'lll have to go back in and re - do the entire system right after the TT Ride in two weeks .
I'll prolly have to fight the bleeding thing again too
.
![Laughing :lol:](./images/smilies/icon_lol.gif)
I hope this works out ~ I too was going to suggest bench bleeding but I was too late .
Sadly , one of the front blind brake cylinders I installed in December , is seeping a tiny bit so I'lll have to go back in and re - do the entire system right after the TT Ride in two weeks .
I'll prolly have to fight the bleeding thing again too
![Mad :x](./images/smilies/icon_mad.gif)
-Nate