Moss Motors, Ltd

If I understand your description correctly, the answer is Yes, that will cause you a problem. The brakes will not work at all. Those seals form a cup that the fluid pushes against to force the pistons out. With them backwards, the pistons will stay in place as the fluid simply flows past and leaks out into your drums.

It sounds like you may be trying to do this with the cylinders still on the car. That's not a good idea. You really should remove them to see if they need honing or if they are even salvageable. The problem you are experiencing is caused by compressing the air in the cylinder as you try to insert the pistons. If the cylinders were off the car, the fluid inlet would be open to allow the air an escape path rather than just pushing the other piston out. You can probably verify this by opening the bleed valve, if it works. You're still much better off to remove the cylinders and do it right.

 

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Bayless
Never express yourself more clearly than you can think
'48 Prefect
'67 Sprite (project)

enfoprefect,

Accually, I did have the complete wheel cylinders off of the car.  It does seem like air is being trapped inside when I push the piston in, though the bleed valve was completely off as well as the brake line.  So the air should have been able to escape easily.  I had this problem with both wheel cylinders.  The inside of them looked good, i did not see any pitting or anything of the sort.  Is there a speacial method to get these pistons in or should they slide right in?  I've seen lube made for this in the moss catalog, is there any other lube I may have around the house that would be safe to use that I may have around the house or garage?

joel

I have only used brake fluid for lubricating the cup seals and bore.

which is what I've been using so far.

Sometimes silicone spray helps here, and it is inert: it will not be a problem in the system. You often have to sort of work the piston/cup assembly around in a "swashing" motion to get it to start into the cylinder. These days we find it unusual that an original cylinder is clean and pit free enough to take a rebuild.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

update,

I honed out the wheel cylinders and used some silicone spray to put the pistons back in...it worked great!  Thank you all for your help.

though, there is yet another problem...of course...I was bleeding the rear wheels...yet again...and the bleeder on the drivers side stripped out, not the bleeder screw, but the hole the screw turns into.  So, I am ;looking into just puchasing 2 new wheel cylinders...guess I shoulda done that from the start, I knew it would happen in the long run...I found them $12 cheaper than MOSS but they are .8125" instead of .800".  Question is, Will the size difference cause a problem.  They said that the larger size is made for my make and model.   they accually told me 13/16" which equals out to be .8125".  any advice is greatly appreciated.

joel

joel,

I doubt you'll get into trouble with this switch. Be aware, however, that doing so decreases the forward bias of your system. In other words, it trades a little front brake for a little rear brake. All cars come with heavily forward biased brakes. This makes for less than optimal dry smooth condition braking, but it keeps you out of trouble in poor traction conditions, such as wet or snowy roads. Your front brakes, by neccessity, must exert more of the total stopping effort. This is because of forward "weight transfer" under decelleration. I use quotes because the actual static weight of the two ends of the car remains the same. The effect of decelleration changes the dynamic load on the two ends of the car. We've all seen old softly sprung cars which seem to want to stand on their noses under hard braking.

Race cars are stiffly sprung and don't do this as noticably, though the effect is still there to a degree. In an effort to get absolutely maximal braking effect, they install twin cylinder systems with a "balance bar" to make this bias adjustable. While the track is dry, the crew or driver dials in as much rear bias as the car can live with short of making it unstable during braking or turning while braking. The car is less stable but much faster in terms of lap times this way. This is how race drivers earn their pay, by living just on the edge of control with a car which wants to turn and bite them at any oppurtunity. When it rains, the driver/crew makes several adjustments. First among them is to dial forward bias back into the brakes. Next is to soften the sway bars, particularly the rear, but this isn't about that.

If you wonder about the dynamics involved, drive into a big open parking lot in the snow sometime and yank up on the handbrake. You won't want it on for long....Though it can be fun, I'm certainly not advising it.

By installing larger diameter rear cylinders you are changing the effort ratio, or mechanical advantage (MA), between the master and wheel cylinders. It will, in effect cause you to have to pump more fluid into the wheel cylinder to achieve the same linear motion. This will also cause the cylinder to have a greater pressure potential when the shoe meets the drum. As I said, I doubt this will be a big problem. I have two reasons.

One is that I've seen a lot of people install MGBGT cylinders on their roadsters with no ill effect, and those are .875" in diameter, which is quite a bit more than you are considering. The other is that the jump you will make just isn't all that much, and car manufacturers have traditionally built cars to have massive front bias in the brakes, as well as many other design features which are not exactly complimentary of our abilities.

I hope this gives you the information to make an informed decision. I want to make the point that I do not seek to counsel anyone to modify their car outside of the parameters of the original design. I have given this explanation for informative purposes only. I offer my own anecdotal experience as someone who has seen many modifications made, but NOT as someone who particularly endorses them. Enjoy.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

i didn't realize that such a change could accually change the dynamics of the braking system.  I was only thinking that if I needed to rebuild them in the future again, if I might run into trouble finding seals to fit.  According to MOSS there are only 2 sizes, .800" and .875".  I think I was more curious about wwhether a .800" rebuild would fit on the .8125" the same way, or if the difference in size though small, would cause more greaf down the road to maintain.  I was shocked to get such a long descripion on what the difference could cause to the braking system' though i am pleased to have been informed.  I think I may now be leaning toward the more expensive ones from MOSS and just get the originals at .800" after reading your response.  thank you.

joel

update,

I ended up purchasing the new .800" wheel cylinders from MOSS and installed them.  After bleeding the brakes yet again...I finally have brakes on my MGB again.  I am still a little unhappy with the front driver's side brakes...when I bleed this one I don"t get a steady stream like the other 3, it more spits but with force.  Not quite the same as if I'm pushing air out of the lines.

Now I can"t seem to get the car started again.  I think it is a problem with the carb. again.  Carb. doesn"t seem to be getting fuel.  If I disconnect the fuel line just before the carb., the fuel flows nice and steady, but if I reconnect it, the fuel will not flow.  I empied out the fuel filter chamber and turned the key for the battery, the fuel pump will not fill the filter chamber unless I pinch open the line just before the filter chamber to let teh air escape, then it will fill up the chamber.  But I still can't get the engine to turn over.  I was thinking that it may also be a vent problem with the fuel line, but I'm not sure where the vent is for it< the books do not seem to be helping me with that one.

 

joel

 

update, 

I have managed to get my B running at a good idle speed around 800-900 rpm.  it does sound like it is a little slugish still...only running on 2 or 3 cylinders, timing off, carb. adjustment, something.  But i believe it to be the fuel mostly.  I have added fresh fuel to it, but the was some old fuel in the tank that has sat for a few years.  I think there may be sediments in the bottom of the tank as well. 

my main prob. right now i think is the fuel FLOW issue.  if i diconnect eh fuel line just before the carb. and turn on the battery, the fuel flows at a steady rate without slowing down.  which tells me that my pump is working properly and tha my fuel line is not clogged.  however, if I empty the fuel filter chamber and leave the fuel line disconnected from the carb. and pinch the end off...the fuel filter chamber will not fill.  the pump starts to pump for a few seconds and stops.  Is there any vent line on the fuel pump of fuel line before the carb.?  could my problem be a blocked vent line?  I have not found one in any of my books, but someone had suggested the posibility.  Or could this be a float issue in the carb.?

thanks,

joel

As I understand your description, it sounds like all is right up to that point. Those pumps do not put out much pressure so you can easily pinch off the line and when the pump feels the right backpressure, it stops pumping. If it didn't do this then it would just pump raw gas right past the float valves and flood the engine as well as the ground around the car.

It could be a float issue. The most common problem with floats is the needle no longer makes a good seal in its seat letting gas leak past when it should shut off flow. There should be an overflow pipe on your carb to divert the excess fuel to the ground instead of flooding the engine. If you turn on the eky and let the fuel pump run without starting the engine, you should see gas running out if this is the case. The other possibility is that the needle has varnish or gum on it causing it to stick in the seat. Since the pump does not put out much pressure, it can't dislodge the needle and no fuel gets into the carb. If this is the case then you might be able to dislodge it by simply tapping on the float bowl right where the fuel line goes in with a screw driver handle. Don't use a hammer here as that could do serious damage. If that still fails, you can remove the top from the float bowl and see if there is gas in it. If no gas or if the needle does not seat then get new needle valves. First see the next paragraph though.

There could be a problem with your float valves but running on 2 or 3 cylinders more likely suggests an ignition or possibly valves problem. And if it is not hitting on all 4 then it certainly will be "a little sluggish." I would start with the ignition. Make sure it is timed right or at least close. You can do that statically with a simple test light. Check your points for excessive wear and replace if necessary. Adjust them very carefully. Pull your spark plugs and make sure they are clean and properly gapped. When all is well there, try it again. If there are still problems then check each plug wire to make sure you have spark. Be careful here. If your body supplies the ground, it hurts a bit. If still problems then it is time to check the valve clearances. You'll have to refer to your shop manual as this is a very important adjustment and too much detail to go into here. When all else is right then it is time to look at the carbs. No tinkering with the fuel system will make up for inadequate ignition or valve clearances.

Finally, gas a few years old should never be run through the system. Best of luck.

Bayless

 

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Bayless
Never express yourself more clearly than you can think
'48 Prefect
'67 Sprite (project)

bayless,

thank you for your help with my problem, it is appreciated.  The distributor has been looked at and reinstalled by someone else more qualified than I and he had also set the timming on it.  If it is not on, it is close I am sure.  I would like to check it though to cover my bases, so I would I accomplish this with my test light?  Do I just need the battery on or do I need someone to crank on the engine?  I have checked my spark plugs numerous times over the past weekend and cleaned them up each time.  They usually look like they are getting too much fuel.  (black and wet, but not oil.)  the last time I pulled them, 1 and 4 were black and 2 and 3 were clean, This is why I feel that maybe only running on 2 clyinders. 

I have pulled out the needleand it seems clean, cleaned it up anyway.  popped the cap off on the bottom of the carb. under the float chamber and turned the key on for the battery and the fuel flowed for a little bit  and then stopped.  I only pulled the cap 1/2 way off due to the air filter being in the way (i was pressed for time) so it may not have been off enough to let the fuel flow. I will pull off the air filter today and pull the cap off all the way off and try it again. I would also like to test those pionts on the ditributor and will check the spark on my plugs.

 

joel

Oops, I'm afraid I may not be paying attention here. I'm thinking of dual SU carbs but it sounds like you have the single Zenith which would be original for your car. Sorry but I know nothing about that device. Still the float valve operates on the same principle. A black wet deposit on plugs is either oil or fuel not being fully burned. From your other symptoms, and the fact that it does not seem to be oil, fuel could well be it. Since 1 and 4 are clean, I would not suspect excess fuel at first. More likely is that 2 and 3 are not firing properly. That could be weak ignition but could just as well be valve adjustment. Let's get the ignition checked or fixed first. The first step is to ensure that the points are right, not significantly pitted or burned and properly gapped. Be very precise in setting that gap. Make sure the rubbing block is on the highest point of the distributor cam.

Check and set the timing as follows. Remove the distributor cap and rotate the engine clockwise by hand until the timing marks line up according to specifications. At this point either number 1 or number 4 cylinder should be firing. It doesn't matter which for our purposes. Connect your test light to the coil post where the small wire leads to the distributor, remove the distributor cap and turn on the ignition key. The test light should light indicating the points are open. If it does or not, loosen the clamp bolt at the distributor base and rotate the distributor clockwise until it does. Once the light is lit, rotate the distributor counterclockwise until it goes out. Now slowly rotate it back clockwise until the light just lights. Your ignition is now statically timed so tighten the clamp bolt carefully without disturbing the distributor. It is a good idea now to rotate the counterclockwise a few degrees past where the light goes out then slowly rotate it back clockwise until the light again lights. Now check the timing marks which should be aligned according to specifications. If not, repeat the above procedure more carefully until all is right or at least very close. The engine should now run well enough to go on to other tests.

Next I would check the spark at each plug. One thing I forgot to mention above is the distributor cap and rotor. While the cap is off, inspect both carefully. Look for excessive carbon in the cap or burning or wear on the rotor. check for cracks in the cap. Look for signs of carbon traces or other anomolies inside the cap. Be certain it is very clean both inside and out and check that the plug wires seat properly and make good contact with the cap. Ok, that's probably enough for today. Best of luck. You will find your problem eventually.

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Bayless
Never express yourself more clearly than you can think
'48 Prefect
'67 Sprite (project)

bayless,

thanks again for your help.  I do have a single zenith carb.  just wanted to make one correction, that plugs 1 and 4 were the dirty plugs that were black and 2 and 3 were the ones that were clean.  I will tackle this distributor and plug spark by the end of this weekend if not sooner and post my results.  thanks again for your help. 

joel

 

p.s.  I pulled the air filter off and pulled the plug from under the floats on the carb and turned the key on,  Fuel flowed continuously and steady though the carb.