| Author | Message | ||
     Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 342 Registered: 4-2015 |
Re: 1959 Silver Cloud LSMH109 In the process of assessing the brakes, a few questions have come up on which I would appreciate any input. To begin, what are the problems caused when brake drums wear, get resurfaced, and eventually become overly wide in internal diameter such that they are beyond the recommended maximum specs, which I believe is 50/1000 inch over. I presume this is measured on the diameter, rather than the radius, and if so, a mere 25/1000 inch of additional ID on the radius is the maximum recommended tolerance for the drums. Is this correct? Second, what is the problem that is caused with over sized drums? 25/1000 inch on the radius in not much and it is hard to visualize that it causes the drum become overly thin such that it is susceptible to cracking and breaking, but perhaps even that small amount is cause under protracted or heavy braking for the heat generated to not be able to dissipate and cause the braking effectiveness to diminish or fade? Third, I can also visualize that the shoes must be moved out further in order to contact the over dimension drums and that as a result the small drum/cylinder and seal in the bore of the brake cylinder gets moved out towards the end of that bore just a bit...the same 25/1000 inch that the brake drum is over sized. As the brake shoes wear, that also causes the seal and drum to move even further out on the bore of the brake cylinder. Is it possible that with the combination of oversize drums and worn shoe material thickness that the internal drum/seal gets moved so far out that it pops out of the brake cylinder bore? Seems unlikely, but is it possible? These are the potential problems/issues that I can visualize. Are they realistic and accurate causes for concern? Are there others that may be of even more cause for concern? | ||
| christopher carnley Unregistered guest Posted From: 5.80.18.89 |
Christian, Post 55 Parts are selling some really good new,all cast iron drums at a realistic price along with new cylinders.They are a little heavier than the original steel/ iron but you know what American iron is like! Fit ,em. No worries moit! (Message approved by david_gore) | ||
| Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 343 Registered: 4-2015 |
Christopher... Yes. Thank you. I see that they have just what I will need. Many of the parts appear to be for Could II and III so I will give them a call to verify compatibility with Cloud I. What I was really wondering was the "why", the academics of the situation, and just what problems are created beyond the 50/1000 (25/1000 on the radius) limitation. Does not seem to have a logical reason and I was just wondering. If, arguendo, the brake shoes were made 25/1000 thicker, would that not bring the combination of factors back to square one? or if the end of the shoe that rests on the end of the brake cylinder piston end was, again arguendo, 25/1000 longer, or the piston itself 25/000 longer, wouldn't that move the shoe back out into contact with the drum surface and not disturb the location of the piston and seal within the brake cylinder? Somehow it just seems like "much ado" over simply 25/1000...the approximate thickness of a paper safety match book cover and odd that proper function of the whole design is limited within such a small dimension. That's not much "reserve capacity" for wear before expensive components (even at 'Post 55' prices!) have to be replaced. Just wondering! Thanks! | ||
| David Hughes Frequent User Username: wedcar Post Number: 55 Registered: 7-2004 |
Christian All of your observations are valid (albeit to a certain degree), RR have taken a very cautious approach and set grinding limits for safety reasons, a limit has to be stated, RR chose 0.050". Factory brake drum dimension as per the workshop repair manual is 11.250 inches diameter new, grind limit + 0.050 inches (11.300 inches. Wall thickness of the brake drum new is close to 0.500" so that 0.025" wear would seem hardly anything at all, however if your brake drums are approaching this limit replacements should be on your agenda. Your observation regarding the brake cylinder seal exiting the bore would seem almost impossible (never say never), as a test, see how far the piston has to move out of the bore before the seal exits should give you a good indication. The heavy "warning" spring (No3) on page 19 of the manual, alerts the driver that the brake shoes are reaching the wear limit and time for renewal. Trust this helps Regards David | ||
| Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 344 Registered: 4-2015 |
David... Thanks for the response and the reference to the "warning spring". Oddly enough, I could not find any actual written discussion of its purpose...what it is intended to warn of, and when is it intended to give that warning. Helpful as the manual is, it is not 100%. Any ideas there? Also, there was mention of "check valves" in the brake cylinders but absent further information other than that in addition to the "spreaders" (I eventually figured out what those were!) they were added as the series progressed. I guess I don't need to know, but still, I wonder what they are! As you are not doubt aware, many "problems" come up on these older cars when some prior owner or "Detroit" mechanic unfamiliar with the system has "fixed" something. That scenario is always good for creating a mystery as to why things are the way they are, and whether the way things are is actually proper! In this case, the rubber cylinder "boot" supplied with the service "kit" just absolutely would not fit and upon observation, was clearly different from that which came off. Turns out the cylinder had been replaced with one for the Cloud II, which "fit and worked fine" but simply has a different boot, and the service "kit" I ordered was for the Cloud I. The internal seal is the same and was the important issue (bore was clean and unpitted) so I just reinstalled the old boot since it was still in fine serviceable shape. Several other "substitutions" had also been made, but I will spare the details! | ||
| David Hughes Frequent User Username: wedcar Post Number: 56 Registered: 7-2004 |
Christian The warning spring makes the brakes more difficult to apply by increasing the pedal pressure required to overcome the spring, warning the driver. Basically, if (and when) the brakes are set up correctly the spring only comes into play when the linings are due for renewal. The check valves as I understand it were ball bearings inserted to the system to prevent air being drawn into the system on the return stroke of the master cylinders. These components ultimately were deleted. As Bill Vatter often says "the cars when new were very good, if we reinstate them to that standard should still be very good". Unfortunately over 50 or more years people make changes that often weren't beneficial. Regards David | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1611 Registered: 6-2006 |
Briefly, RR are very conservative. If the drums get too thin they are likely to turn oval with hot braking emergency stops . Just reached the bottom of an alpine pass and then lock the wheels up or slam the handbrake on and leave it to cool. In practice. Never seen a problem. The wheel cylinders used to suck air in when the brakes were released. The spreaders kept the rubber more firmly against the cylinders to prevent this. Restrictor valves were tried near the master cylinders as well. | ||
| Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 345 Registered: 4-2015 |
David and Paul... Thanks for the explanations. I'll take a closer look at the "warning springs" next time the drums are off and see if I can visualize their function. Oh! Ball bearings! I had forgotten about that "modification"! It would seem that the ball bearing under the bleeder plug had been replaced with one that is too small and has thus been jammed so tightly into the orifice that even the pressure of fluid against it (with the plug removed) will not dislodge it. The only way we were able to "bleed" the brakes after the cylinder seal replacement was by cracking the fitting where the brake line to the backing plate is located as an assistant manipulated the master cylinders. Any ideas of how to get it dislodged? If the cylinder was removed and on a workbench, what could be done, or is it hopeless? Based on what I see in terms of pricing at "Post 55", they are not that expensive, so I suppose that it could simply be replaced, but I hate doing that if parts can be salvaged, unless brake cylinders with ball bearings jammed into them fall into the "completely expendable" classification? Any advice there? | ||
| David Hughes Frequent User Username: wedcar Post Number: 57 Registered: 7-2004 |
Christian. The only way I can see to remove that ball bearing is to remove the wheel cylinder and strip it. Using a small bent steel rod (scriber) inserted in the bore (protect the bore with a suitable packing strip) and prize the ball out from inside. Regards David | ||
| Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 346 Registered: 4-2015 |
David... Having never had occasion to examine a cylinder on the bench, I was not even clear if the ball would be accessible from the interior and around a corner. Of course now that I have things reassembled and bled, other than the annoyance of the knowledge that it is stuck, it is a moot point. What I may be inclined to do is to back the bleed screw out a turn or two and then drive the car a bit while applying the brakes in the hopes that eventually the hydraulic pressure generated from the whole weight of the car being stopped, rather than simply pressing the brake pedal with the car stationery, may pop the ball out. Of course if it does, I will have brake fluid spurting out as well, so that's the downside. On the other hand, if that does not work, it would indicate that the ball is basically hopelessly jammed into the orifice and I doubt that any amount of prying from the inside will dislodge it. I would not be surprised if in the end the cylinder has to be replaced. | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1613 Registered: 6-2006 |
You can jack the rear up and put it on stands then run the engine and put it in gear to get the servo working. . No need to drive around with no bleed nipples. Just in case. If the pick does not move it. .On the bench . Piston and seal back in. Clamp in vice so piston can not come out. Find a grease nipple that fits in pipe union hole. Grease gun - pump grease in. Much safer and higher pressure than compressed air. Point ball bearing towards a safe zone  | ||
| Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 347 Registered: 4-2015 |
Paul... Thanks. Great ideas. We did try the jack stands idea already without effect. The car was on a lift. I put it into gear, ran it up to about 10 mph and then applied the brakes. Repeated three times. No effect. The idea of doing it on the road was that perhaps the pressure created by the servo trying to stop the entire car might be greater than that created by simply stopping the relatively less significant inertia from only the drive train turning. At least that was the theory. As to the grease idea, the mechanic (extrememly talented) overseeing the project also suggested a variant, but in place rather than on the bench. Time was running out on my $$ budget so we just left well enough alone until another day. His idea was similar except that instead of the cylinger being held in a vise, the piston would be held in place by the brake shoes against the drum. My concern is that the pressure may pop the rubber seal if the ball bearing is truly stuck...or is that not likely? I suppose the worst case is that I just put in another seal. Thanks for the input! | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1614 Registered: 6-2006 |
A g clamp would be safer than using the drum. |
