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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Tight m/c rebuild

Interesting discovery when rebuilding the53's master cylinder. (I'll probably stretch this out in three pieces for the images.) Here's an image of the components inside of the bore of the master cylinder. A rebuilding kit contains new rubber pieces (#11, #12, #14, #16 and #20) plus the metal washer #49. Ideally, you can hone out the bore of the cylinder, reassemble it with new rubber pieces and you've saved yourself a bunch of money.


Bud Krueger

The problem that I ran into upon reassembling the pieces was that the spring would not return the piston to its normal position after I pushed in the push-rd (#20). A closer look at the piston (#15) shows that it has a ridge about a quarter inch away from the end by #17.


Bud Krueger

The secondary piston cup (#16) has a groove molded into it that fits over this ridge. It's a tight fit. What I found was that the piston would not retract if I put the cup over this ridge. It would would work fine if I just slipped the cup over the piston and just located it against the ridge. After reassembling the m/c that way I hooked it up to the brake system and it worked fine. I'm just not happy with that setup. I see two options. One is to ream the cylinder a wee bit larger. The other is to consider trying silicon fluid after a dab of silicon grease. Hadn't planned to go silicon, but I've replaced all of the lines and rebuilt all of the cylinders. Here's an image of the old cup. If you look closely you can see the groove inside of it. Bud


Bud Krueger

I rebuilt mine also Bud and had no problem using a Moss kit. I was fortunate as the bore was in good shape and needed only a light honing. Your right, it saves quite a sum compared to buying a new one and works just as well, maybe better for all I know. PJ
P. Jennings

The secondary seal must be placed in the groove. If left on the shaft ahead of the groove, you may have problems. It's easy to end up with the rubber not fully seated in the groove. The fit is tight but it will go in. Carefully get a thin device like an eyeglass screwdriver under there and help it along, but be careful to not damage the sealing surfaces. Once in place, it may still be a bit tight in the bore but if lubricated beforehand then it should return on its own. If you are using a new piston, measure everything and make sure it wasn't made incorrectly. I've seen this happen as well. Assuming everything was working before, then I would NOT open up the bore since it's probably already beyond spec from normal wear, and opening it further may cause internal and external leaks.
Steve S

Bud, I think this problem has been kicked around on the board recently. I wonder if there is a problem with some rebuild kits? If it is just the one seal, if you open up the bore you are loosening the fit of the other one. George
George Butz

Further honing would be the last thing that I would do. I'm wondering about the tolerance on the cup seal from the rebuild kit. That's the one part that's not listed from Abingdon Spares (Moss has no innard parts). I'm going to give them a call today and see if they may not have one kicking around.

I just finished cleaning up an old master cylinder. It looks good, but has no innards. After honing it I'm going to take the new innards out of the tight one and see how they perform in this one. If still tight, I'll see how they behave with silicon fluid.

BTW, if anybody has any old innards, especially a piston that they'd like to sell, I'd be happy to take them (it) off of their hands. Bud
Bud Krueger

Bud,

The problem is likely the seal. It may or may not wear in, but I think it will. I've found that the parts supplied by Abingdon Spares are often not the same parts as supplied by Moss, especially with regard to rubber. In this case, getting the Abingdon parts is probably a good idea.

Another thought is that silicon is considered a universal brake fluid... i.e. you can use it with DOT 3 with no ill effects (but with none of the advantages of the DOT 5 by itself.) So assembly with the silicon is OK, and then you could run with DOT 3. In fact, the old Lockheed brake assembly lube tins were silicon grease.

And I am an advocate of DOT 5 in our cars. I know that Dave DuBois and I have both run tens of thousands of miles using DOT 5 exclusively. In fact, I'm putting DOT 5 in "The wire wheel conversion that turned into a full restoration" MGB project.

And... I see that I never bothered to photograph the MC when I was assembling it. It went together so effortlessly, exactly like the diagram, that I just noted which diagram I like best... the one a page after the one you are showing! If you put the clevis rod on the pedal and then into the cup as the MC is mounted, it mounts and unmounts rather easily, leaving the clevis and rod attached to the pedal during these processes. I might be inclined to mount it and try it before I ding around with it too much.

Hope this helps,
dave
Dave Braun

Experienced an extra tight seal with the Moss rebuild kit when I re-did my mc too. The new rubber piston seal kept the piston from returning after pushing it in despite repeated attempts during bench test. Did try a very light hone but still the same sticking. Didn't want to really hone out the cylinder more and thus potentially cause more issues. Finally ended up using the old seal since it still looked pretty good. Got good piston return with it and the pedal pressure remains firm now so one of the new parts cured my pedal pressure droop.
Randy
R Biallas

The rubber sold by Moss and Abingdon are not the same, or at least they weren't last year when I went through a similar situation. Measure the rubber once it is mounted. If it is larger than 0.875" then you have found your problem.
Steve Simmons

Had a long chat with Bob Seymour (owner of Abingdon Spares). The m/c rebuild kits are (and have been) assembled by a UK source. He knows of no one that sells the cup washer as a separate item.

After a bunch of measuring and r/r I have come to the conclusion that the problem area is that the groove on the inside of the washer is undersized. This afternoon I mixed up a bit of J-B Weld and inserted into the new washer and an old one that I have from a rebuild that I did a bunch of years ago. I'm hoping that the J-B will give me a positive mold on which I can make some measurements. More to follow. Bud
Bud Krueger

The cup is a standard size. You can buy them at any "real" auto parts store. Size is .875".
Steve S

NAPA here I come. Thanks, Steve. Bud
Bud Krueger

Looks like we found the part in a NAPA catalog. They're calling it a 7/8" boot. Their computer image looks about right. They'll be coming in from Washington (State). Should have them in about a week.

The J-B Weld was tough to remove from the washer. But, it looks as if the groove in the new one is about .020" narrower and about .020" shallower than the groove in the old one. That would explain the symptoms. Bud
Bud Krueger

The words 'Made in England' are molded into the cup. I've learned that they're produced in the UK by Brovex Nelson.
Bud Krueger

Bud Be very careful of rubber parts made in England. They seem to use a natural rubber that does not like DOT 5 fluids. I found that my local auto parts store had 7/8" cups that seem to stand up to DOT 5 fluid just dandy. (neoprene?)
Cheers,
Bob
Bob Jeffers

Bob Seymour would second that motion. Had disastrous results with Dot 5 in a Rolls. I'm anxious to see the ones from NAPA. Bud
Bud Krueger

I emailed Brovex Nelson about the problem. They have responded and have asked for more details. Bud
Bud Krueger

As George said above, this has been kicked around recently. I was the "kickee". The piston would just not return properly after a Moss MC kit rebuild + honing. I finally bit it and purchased a new Lockeed MC when they had a good sale going on. It took a few minutes to install and worked first time and I think about it every time I push the pedal.
Ed
efh Haskell

I'm not impressed with the response from Brovex Nelson:
Dear Mr Krueger,
Thanks for your email, we are sorry to hear you’ve had problems with our product. An investigation by our ID department did not find any problems with our tooling, and though it was remade in 1997 there isn’t a significant change. I am advised this is a fairly popular kit which has not previously caused any issues, it may just be a difference in whether the cylinder or piston is an original. We can send you another seal, let us know what we can do to help – did you buy from us previously? DBABJ would refer an order placed several years ago.

Kind regards,
Richard

Richard Chaplin
Nelson Stokes Ltd
Camelford, Cornwall
01840 213711
Website & Online catalogue
http://www.nelsonstokes.co.uk/

After this one:
Dear Richard,
Thank you for the response. I may not be the only one who has experienced this problem. Perhaps I'm the first to identify it. A few months ago another TD-TF'er on the MG UKBBS reported symptoms that would match this. There are reports of folks having problems with kits purchased from Moss Motors (USA). The cylinder and piston are originals, probably installed in about 1952. The old seal, that fit fine and would work, was found in a kit labelled Nelson Brovex 50567 CJJH. The kit contains the parts that I replaced when I installed in ca. 1960. The recent 50567 DBAJB (labelled 'Made in England') kit was purchased in this past month from Abingdon Spares. I have never purchased directly from you. BTW, please note that the kit is DBAJB, not DBABJ. I couldn't guess how long Abingdon Spares had this in stock. I understand that, except for the bellows, the same components are contained in kits for TC master cylinders. I suspect that the fear of silicon brake fluid being incompatible with rebuilt, i.e., honed, cylinders has significantly reduced the number of us that rebuild ours. I would be willing try another seal in hopes that the one that I have is an anomaly. I've been led to believe that this particular cup washer is available from other sources of parts for Lockheed master cylinders and have such a search underway. Please send the seal to: ****

They said:
Thanks for letting us know, the heads up on any potential issues is appreciated - a new seal will be sent over to you this afternoon.

I'm still waiting for the seals from NAPA.
George Butz sent me some used parts, including a piston and seal. I assembled a m/c using his parts and it worked fine. Assembled it with the new seal causes it to jam.

It'll be interesting to see what they send me. Bud
Bud Krueger

The new seal has arrived from Nelson Stokes. Same thing! So far, with testing on two master cylinders with two different pistons and four cup washers, the master cylinder jams if the cup washer says "MADE IN ENGLAND" rather than "LOCKHEED". I've brought this to the attention of Moss (USA).

Maybe I'm wrong with my belief that the groove in the cup washer is intended to fit over the ridge in the piston. Any experts out there? Bud
Bud Krueger


Below is an image of sample S7031 on a good piston. Notice that the seal diameter is slightly greater than the diameter of the piston. This difference is enough to cause the piston to bind in the cylinder. Bud



Bud Krueger

That looks very much like a seal that is not seated. Sometimes you really think it is, but it isn't. I use a small angled pick to get under the seal and work it into the groove. Just be very, very careful with the rubber. The smallest nick can cause a leak.

Also, is it a trick of the light of do you have a shim behind the seal? There should be nothing there.
Steve S

The groove in the seal does fit over the small ridge on the piston. I always turn the seal once installed on the piston, as this helps to seat it; seals have a habit of not seating correctly on installation, esp. if not lubed with brake fluid.

The seal shown is incorrect. Typical piston diameter is on the order of .002 under bore diameter on a new cylinder. Seals never protrude above the piston shoulder, except for the lip; normally the seal is visibly smaller than the piston at the shoulder. If the seal does protrude above the piston, it acts as a very bad bearing, drags, and wears out quickly.

The lip itself is not as much larger than the piston diameter as it usually appears, but this may be a visual effect of the too large shoulder.

One possibility is that the seal is too long for the space allotted on the piston, which would compress it lengthwise, and expand the diameter.

In hope of avoiding confusion, and Since I do not have a T cylinder to examine, can you provide a clear picture of the piston without seal, showing the "small ridge" in question? Accurate dimensions would be good too, and are there any actual numbers on the seals, esp the ones marked "Lockheed"? I want to compare to other NOS Lockheed parts I have.

FRM
FR Millmore

No shim, Steve. Just an illusion. I spun, and did all that I could to seat the seal.
FRM -- George Butz did some castings of old and new seals and confirms that the groove is too small to avoid pressure from the ridge. Pistons:



Bud Krueger

Bud=
Thanks for pic, not quite the one I was envisioning, but no material difference. Later designs tend to have a ridge at the back end of the seal, so the whole seal is in a recess, with a very small secondary ridge somewhere in the middle.
Not sure that comparing new parts to ones that have been in service is much good, since the old ones take a set. I've always hated trying to measure rubber bits, since you can't tell what degree of stretch or compression is designed in.
I'm pretty sure that the ridge is meant to exert pressure, in order to seal the inside of the seal bore. But too much certainly won't do!

FRM
FR Millmore

Latest from Nelson Stoke:
Hello,

I’ve been advised an alternative number with very slight difference it’s dimensions, I will send you a couple of these to test.

Let's see what these bring. Bud
Bud Krueger

Bingo! The alternative seal (S7464) fits like a glove. Its base circle is slightly smaller than the diameter of the piston. So it doesn't jam up in the cylinder. The flare of the cup is a good seal in the cylinder. I'll assemble a master cylinder with it tomorrow and try it. Anybody know how much pressure a master cylinder should be able to supply? Bud


Bud Krueger

Looks as if this issue has once again shown up. Maybe somebody else can convince Moss that's it's worth clearing up. Bud
Bud Krueger

Sorry, I missed the pressure question first time round. You can figure that most brake systems run around 1000psi hard stop normally, and 1500 panic conditions.

FRM
FR Millmore

Bob , my compliments for this research . We all wil benefit.

Gerard
Gerard Hengeveld

Back in 1950 when caddy's had hydraulic brake light switches we found that power brakes were generating over 2500 lb's/sq in. That pressure was enough to undo the crimp in brake light switches. Then no brakes! That was one of the prime reasons they went away from hydraulic switches.
Cheers,
Bob
Bob Jeffers

Reactivating for Gerard. Bud
Bud Krueger

Thanks Bud, I am sure others will benefit to .

Gerard
Gerard Hengeveld

Reactivating thread that George Butz mentioned. Bud
Bud Krueger

Does anyone know if the "fix" (ie. the S7464 part vs the S7031 part) to the M/C rebuild kits has been incorporated yet into Moss or A/S kits yet? (or will? and have "old" kits containing the S7031 rubber cup pulled from inventory?)
Will we need to contact Nelson Stokes directly to obtain the S7464 rubber cup ike Bud did? I did a search on their online catalog but no S7464 part # comes up.
Randy
R Biallas

I'm reactivating a thread that George Butz and I did some work on about 6 years ago. It may, or may not, have any relevance to the present brake problem, but it may be worth having a look at. Bud
Bud Krueger

All good information for me as the piston is not fully returning. I dismantled my newly refurbished master cylinder to check all was well, check the recuperation hole, and clear any contamination. At the same time I spotted the master cup was marked "Lockheed". I did not remove the secondary seal. If I have to dismantle again (unfortunately that appears likely) I will check the secondary seal fully. Thanks.
Dave H
Dave Hill

This thread is of interest to me as I rebuilt my MS and used a Moss kit. It works perfectly, but saying that, I bought the kit about 5 years ago and possibly their supplier has changed. PJ
PJ Jennings

Absolutely true, in 5 years manufacturers can change all sorts of things (I spent all my working life in manufacturing). Nelson Stokes, mentioned above, seem to major on brake hoses now, and no sign of the Part Nos mentioned. I bet all those rubber seals are made in the Far East now.
Dave H
Dave Hill

I just bought a master cylinder seal kit from B&G. The particular seal in question above in my case looks exactly like seal S7464 rather than S7031, short barrel section and longer sloping seal part. It has no number and just says "Made in England". I'm just going to have to remove the master cylinder yet again and try it for size.
Dave H
Dave Hill

This thread was discussed between 23/10/2011 and 07/07/2017

MG TD TF 1500 index

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