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MG TD TF 1500 - brake pedal free travel (again)

Okay, here's what's next! After completing about 90% of my restoration I'm finding my brake pedal free travel to be about 2 1/2" vs. the 1/2" shown in Fig M.3 in WSM! Don't ask me how I let this happened. I should be shot!

Anyway, the question is is there a way to shorten the free travel using the adjusting nut on the MC push rod WITHOUT removing the clevis pin that attaches it to the pedal shaft? It looks like someone in the archives has tried it but results were not posted. I do have the pushrod with the both large and small next nuts unlike the one shown in WSM (picture att). The picture is BEFORE MC rebuild showing about 14 threads. Currently there are about 7 threads showing so I must have screwed the rod in about 7 threads during rebuild - I know not why. If I can turn the thing, which direction will remove the free play?

Thanks all,
Ed


efh Haskell

Hmmmmm...Free play in the brake pedal could be related to air in the system....So I think I would re-bleed the system first....
The other possibility, is the brake-shoe adjustment...
I always adjust my shoes so that there is a very slight rub on the drums.....Just barely, so you can hear the wheel going around, but not enough to drag.
I think the last place to adjust , would be at the m/c
linkage, since you've already got it half-way up the clevis rod....
Edward
E.B. Wesson

Edward, I've done all the things you've suggested a thousand times and that has no effect on the free travel. Look at page M.5, section M.1 "Adjustment of Brake Pedal" in WSM. It says "1/2 play" and Fig. M.3 shows 1/2" play. I have 2.5" play hence I'm only getting about 1" of "effective" brakeing. To fix that it says "adjust the effective length of the rod...". So that's what I'm trying to do.
efh Haskell

Latest: I was able to turn the push rod towards the MC and now have about 1 1/4" of free travel! Yea. To get it to 1/2" per the WSM I have to keep turning it but I have no way to see how much thread is left. I'm afraid the push rod will separate into two pieces! Does anybody know how much thread there is? I didn't take a photo of the pushrod in that detail back when.
Appreciate it,
Ed
efh Haskell

From the WSM drawing, what you show in the pic above is about the absolute limit. The clevis end screws into the fat part, and there must be some metal at the bottom and some unthreaded part at the bottom. I will suggest that the MC piston is not returning to its correct rest position against the circlip in the bore. That will give you a lot of free play, but adjusting it out will make things much worse. Sorry, I know it is a miserable device to investigate.

FRM
FR Millmore

FRM may be right- thle piston may be stuck part way down. Best to pull the MC and check. Look at the length of the fat part (female part w/ threads)- it isn't very long, so if you screwed it way out there can't be much thread left. George
George Butz

It occurred to me that you may also have a loose fit, at the brake-pedal shaft .....If so, that is a geniuine PIA...Something to tackle with the floor out.
Let's face it , since all the bleeding, tightening, and re-building , and adjusting,hasn't done it, there must be something causing the problem, and there isn't too much left.
Edward
E.B. Wesson

Hi Ed, are you talking about the free play before the push rods contacts the piston in the MC, or the total brake pedal travel, including the movement required to apply the brakes? Matt
Matt Davis

Edward, I've already rebuilt the entire @#$%!@# pedal box whilst the floor was out (see my YouTube for a laugh). All the bushings, etc. are brand new. There is no slop at the pedal shaft. Whew!

Matt, I'm talking about the free play BEFORE the rod connects to the piston, NOT the total (the play as shown in Fig. M.3 in WSM ideally as 1/2").

I don't think the piston is stuck because during rebuild I did honing and a bench bleed and pumped that thing for a LONG time! I think I would have noticed it then, but you know how that goes. Of course, that was last summer and it's been sitting all winter waiting for this moment. Perhaps the piston just needs some "waking up"? Possible guys?
efh Haskell

Ed, I've just checked my pushrod, which I carefully set up to provide the 1/2" free play several months ago, and like your photo, it has about 14 threads showing. I would not have thought these cars would vary that much. Assuming the distance from top of pedal to the pivot is about 5 times the distance between the pushrod and the pivot, you would need to extend teh rod by about 0.4" to take up the free play. Are you sure the piston has not become stuck? If it has, I do not know how it could be released without taking the MC apart. Good luck. Matt
Matt Davis

Matt, thanks very much for checking the thread count! That makes me feel much better.

I just did this test to see if piston is sticking:
1. Measured free play. About 3/4".
2. Pump the brakes 3 or 4 times hard.
3. Measure free play. Now about 1 1/4".
4. Let it sit about 5 minutes.
5. Measure free play. Back to 3/4"!!!

This would indeed indicate the piston is sticking, wouldn't it? Rather than pull the MC at this time do you think it's safe to finish the restoration and drive the car a few miles and see if the piston frees up from actual use? I can't see any safety issues, or am I missing something?
efh Haskell

....although in my mind that sounds backwards (more free play after pumping)....try something...pump your brakes, get out of the car and try and roll it back or forewards with it out of gear...if you can't move it cause the brakes are stuck on, then your little relief valve is clogged?
Just a thought....???
gblawson(gordon- TD27667)

Ed, Sure you can finish the restoration, but I hope you are kidding about driving it like that. It could be your last drive when the piston sticks and you plow into whatever. Driving it like that would be like sharpening and waxing a ski and trying out even though you know you have a badly defective binding. Pulling the master requires removing exactly two bolts and one line, about 5 minutes if you work slowly (I know you have to bleed, etc. to reinstall). Never, ever skimp or shortcut on brakes and steering- your life depends on it! George
George Butz

5 minutes! How??? George, I agree with you 100% and your advice is always sound, but ....how can I remove the MC without first removing the dreaded clevis pin and cotter pin on the break pedal which of course first requires removing the clutch counterparts? All this with 2" of clearance for my head. Removing the floorboards would make it easier of course, but this is almost impossible at this point. It was a week of work just putting them in! Is there an easier way to remove the MC?
efh Haskell

My master cylinder came out, leaving the rod in place.... two bolts and the line.....last time I did it I just reached under from the side of the car....
gblawson(gordon- TD27667)

The method Gordon describes is how I remove/replace an MC. I leave the control rod in place too. The rod has a semi-spherical end and fits neatly into a deep chamber in the MC piston face. I also usually slather the inside of the bellows with a silicone nonpetroleum grease, fit it over the rod, and slide the MC onto the rod and bellows in one motion.

warmly,
dave
Dave Braun

The guys are right on. The male clevis end just mates with the cylinder piston- it slides in and enters just like.. well, you get the picture. George
George Butz

D-U-HHHHHH!!!
Sometimes you just cannot see the forest for the trees. I'ld like to say "I knew that" but that would be a lie. And I'm the one who rebuilt this thing? Well, that was last winter.
Out it comes for inspection.
Thanks gentlemen and Happy 4th of July!
Ed
efh Haskell

Gordon, I just tried your test. She rolls just fine in either direction after pumping the brakes multiple times. So I guess the relief valve is fine. I'm positive I cleaned both of those little holes with compressed air last winter. I even remember shining a light in there to confirm.
That said, would you pull the MC anyway just to make sure? Now that I know the trick I guess I'll sleep better if I do?

efh Haskell

Gentlemen,

As a slight aside to these discussions and, from a non-mechanic: Is my 1954 TF equipped and set up the same way regarding the MC. I have just had a brake job sans MC. May have some work to do there but most of you seem to be saying it is not that difficult any more. I APPRECIATE any help/advice/suggestions.

Regards,

Jerry
Jerry Chandler

More free play, after pumping leads me to believe that you are "sucking air" ....literally....
I'm suspecting that your "rebuild" of the m/c, may have left some extra gap around the piston seal....
I've always had a suspicion that these "rebuild" kits, are not all they should be, since the seal is usually the same size as the original, but you have honed out the cylinder, thus it needs a slightly larger seal....
Only way to salvage an oversize m/c , is to have a sleeve pressed in that is exactly the size of the original...Probably more expensive than just replacing it.
All the kits that I have used are the same, and it usually means replacing the m/c.
Good luck with it.
Edward
E.B. Wesson

Edward, well that "sucks" (I couldn't resist). When I pull the MC maybe I should spray some soapy water all over it and pump. I should see something(?) I'll report results here.

If I have to buy a new MC which one do you guys recommend, aftermarket or Delphi-Lockeed. The latter's price is out of the ballpark! I do have an experienced machinest nearby. I wonder what miracles he could do to mine if needed? Thinking out loud...it helps.
efh Haskell

Hi Ed

I tried honing out my original Lockheed MC and had to give up as the corrosion pits were too deep. I've replaced it with an aftermarket MC (made in India), which was about half the cost of the Lockheed. It appears to be exactly the same size as the original. I dismantled it before fitting and the internal components appear to be essentially the same as the Lockheed MC. It appears to be working fine, but I have only driven about 200 miles since the brake rebuild. I am more concerned about my wheel cylinders, which were all honed and fitted with new seals. I am planning to pull the hubs shortly to check that there are no leaks!

Matt
Matt Davis

I have tried honing slave cylinders, as well, and almost always ended up replacing....
Been tempted to email the Moss tech department, about developing slightly larger seals, to compensate for honing...
The pitting is the big downfall...If you get the pits out, the cylinder is too big, and if you don't get the pits out, it leaks.....
Edward
E.B. Wesson

I thought those rubber seals came in all sorts of sizes just for this problem...(or was that in the 'old' days?)
gblawson(gordon- TD27667)

Ed,

Have you checked the brake springs? They provide the force that returns the MC into position.


Jim Barry
J Barry

Okay all, I removed the MC today. Took about 5 minutes. Thanks!

So now what? The MC is clamped into my bench vise in a level position. I want to test that the piston does NOT stick I assume. Since Jim correctly noted (above) that the brake springs are the force that returns the piston, how can I test this on the bench? What is the correct technique? There must be one.

Ed
efh Haskell

"Since Jim correctly noted (above) that the brake springs are the force that returns the piston, "
Not correct.
The piston is returned by the piston return spring - if it doesn't return there is a problem with the seals or the (honed) bore is too rough.
The brake springs do retract the wheel cylinders, which will bring the MC piston back part way, but the MC must return all the way by itself.

FRM
FR Millmore

Ed, The brake springs do not return the piston, that is accomplished by the piston return spring inside the master cylinder. You should now remove the rubber boot and use the push rod to move the piston in and out to see if it is returning against the piston stop which is directly behind the circlip. If not, you will have to disassemble the components and check that everything is fitted in the correct order. Make sure the dished washer between the piston head and the master cup is fitted correctly with the domed side facing the push rod end. Make sure the by-pass port is not plugged. Cheers Phil
Phil Atrill

Oops. Can't get away with anything on this forum!

Jim
J Barry

Oops, I should have known better myself Jim, since I'm the guy who rebuilt the thing. Yes, of course there is a return spring inside. It's been a while...

Results of bench test: MC is mounted in bench vise. Using a bar I push piston aft. Fluid exits MC properly thru aft end. Piston however, does NOT initially return!! It is indeed stuck! I dismantle MC and determine everything is in correct order & orientation (yea). I do notice a few small globs of very soft black or maybe blue "stuff" but all new {Moss} rubber appears still like new (yea). Bore feels smooth to the touch. Both tiny holes inside are clear. I reassemble and, viola, the piston now returns 100% to it's stop unassisted, just like it did during rebuild last winter! Yea (I guess)?

My Options:
1. Take it to local machinest and smooth my amatuer boring on his fancy machine. But will that overboar and cause a leak??? $50 min. charge down the drain? Plus a 60 mile drive roundtrip.
2. Bite it and order the $125 Indian MC from Moss. Reliable or junk? (I refuse to pay $250 for the Lockeed.)
3. Put my MC back in and assume it was just stuck from lack of use?

What would you guys do? Your opinions are valued here!
Ed


efh Haskell

Or...sleeve it in Stainless and never have a problem again..... That is what I did to the MC and all wheel cylinders. Sure it costs more but at least the Stainless won't pit or corode. Pay now or pay later.
L Rutt

"globs of...stuff" indicates chemical contamination, either something you put in or the remains of some process, like cleaning with petroleum solvents, honing with oil, etc. Maybe it is all out now, but if not it might gum up the MC again, or the entire system eventually.
What fluid?
I once had a customer who put some gas station fluid in a freshly rebuilt Jag MKII. It ate all the rubber in the system - MC, servo, hoses, WC seals. Only took a few days and caused catastrophic brake failure, but no crash and only a mile from me.
If it now works, nothing like additional honing will do any good, and will increase the bore size which is not desirable. Since you now know how to remove it easily, put it back and keep aware of how it works. Be liberal on bleeding new fluid through all bleed screws; watch what the fluid looks like.

FRM
FR Millmore

I just honed a little bit more and put it back together with fluid (all new Dot 5 - no cleaning solvents, etc. FRM) just to see how it went. Guess what, it STILL STICKS.

LBCO is having a sale! $92 for aftermarket, $208 for Lockeed MC....looks like it's fate. I'll be placing an order shortly it seems. Safety wins I guess.
efh Haskell

Ed, I assume that you confirmed that BOTH holes in the bottom of the M/C cylinder wall are open. There is one larger one for the fluid and one tiny hole for the pressure relief. I forget the diameter of the smaller hole but most wires will NOT fit through it. I am sure one of the guys here on the board will either know or know where to find the diameter.
Jim Merz

Take a light and look all the way down into the MC....the very last rubber washer could still be in there (it happened to me) and I had small bits of black floating around until I found that washer....pulled it out with a dental tool......
gblawson(gordon- TD27667)

It appears that you have been trying to "make a silk purse out of a sow's ear"....
You are doing the best thing , by replacing the offending device.....
As suggested, the only other alternative would be to sleeve the cylinder(s)....An expensive, though semi-permanent solution....
The sleeving would fix the cylinder(s), but the rubber seals will still need to be replaced, in the future....
Edward
E.B. Wesson

Jim, yep BOTH holes confirmed clear. Used sewing needle on little one (the one inside the other little one) plus air blasts.
Gordon, yep, I know that damn washer! I pulled it during the rebuild and replaced at that time. Still there and looks good.
At least I have an excuse to finish the interior while the MC ships! If the new mc doesn't work I'll just finish the car and put it on a revolving pedestal in the front yard. The neighbors will love it!
Ed
efh Haskell

Ed and all others who have contributed to this post. Thanks. I was having the same problems that Ed was experiencing (I rebuilt my mc with the Moss kit). I was about to go through the troubling shoot efforts that Ed has done, but decided to wait to see what was the final suggestion. solution, before proceeding. I have now ordered the MC replacement from LBCC at $208. Thanks Ed for announcing its availability at that price.

It seem, Ed, that I am always just behind you in our restoration process and progress, and sometime the lack thereof.

Cheers to all -- John
John Brickell

John, glad to be of "help". I just ordered mine as well. I also ordered the adaptor that screws to the back end for the pipe plus a few washers "just in case" my old one won't come off.

Progress? I finished installing my interior today only to realize that the kick panels had to come off (again) to install the Brit Flags! Of course, now the @#$!@#$ right door latch won't work again,

The race is on!
Email me your progress on the MC. I'll be curious how it goes.
Ed

efh Haskell

...ok...when mine was reassembled, the old one was tucked in behind the new one....(made it even harder to figure out the problem).... and yes, a needle is about what you need to clean out the release hole (within the other hole).....
gblawson(gordon- TD27667)

John, et al. For the record I got my new MC yesterday at 3:30 pm and by 4:00 pm I have the proper 1/2" free travel, no more stuck piston and the brakes are going to feel like a new car, I can tell! What a difference!!
Thanks go to you guys for the support and LBCarCo for the sale price and the pack of Scottish shortbread.
efh Haskell

Glad to know that all's well with the brake system. I have yet to receive my mc, but I may get lucky and it'll arrive today.

Cheers -- John
John Brickell

I too just tackled the MC rebuild using the Moss parts kit and had the stuck piston syndrome. My inner cylinder looked pretty good so just replaced all with the new rubber/washer and after reading the horror stories of too much honing decided not to do any. The rubber seal that goes on the piston was a tough to get back into the cylinder though. Filled the MC with fluid and reassembled but doing the first brake's bleeding it became obvious that the piston was stuck.
Dissembled again and decided obviously needed to solve the stuck piston cause. Only real cause I thought was that it could be the new rubber seal on the piston or cylinder too small for it. Archives pointed to new rubber kits were with original sizing and any honing would cause leaks. The old seal on the piston moved ok so I tried some very light honing (actually polishing rather than taking any metal off) but the piston with the new seal still stuck. So since the old seal still looked good I put it back on. Now piston travel seemed firm but it rebounded after manual depression. Bundled it all up and after the rear brakes were bled have good pressure with no need to pump now. Still have the fronts to do but am also redoing brakes shoes too and need to get correct size axle nut socket.
Know brakes are paramount (that's why redoing all) but in my case it seems that the new rubber was slightly TOO big and caused the piston sticking.
Randy
Randy Biallas

Randy, I had mine working great on the bench last winter. No sticking! But things change in these cars all on their own I've decided. If I were you I would order a new one from LBCarCo today while they have some at the $208 price. You will thank yourself someday. The comparison between my attempted honing job with new parts vs. the brand new MC complete wasn't even close during bench bleed yesterday! That new piston pops back like a new part should!
Good luck,
Ed
efh Haskell

Thanks Ed. Will consider that. Still have the cluster/1st gears I bought 30 yrs ago awaiting tranny rebuild some day. Now they are 3x what I paid back then!
Randy
Randy Biallas

Received my MC yesterday and installed, did brake bleed, and all seems to be functioning as should. I now question the wisdom of using the MC rebuild kit in a old MC housing.

Thanks again Ed for starting this series of posts, you and I were experiencing the same problem and now have ended with the same solution.

Yes Ed, the race is on, but it appears certain that you will win this race

John
John Brickell

This thread was discussed between 02/07/2011 and 16/07/2011

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.