Kelsey Hayes Brake Restoration & Upgrades Part 3 by Mike Cassidy
Vacuum/Air Bellows Assembly Continued
Though the vacuum and atmospheric valve assemblies are relatively simple devices, the replacement seal set is quite expensive at around £122 in the UK (Pic 39). I examined the components very carefully and decided that, while there was some rust to the rear of the vacuum valve and on the balance washer, they were otherwise serviceable, so I decided to re-use them after cleaning. Fitting is very simple, but care must be taken-to avoid any damage to the rubber components, to make sure the various components are assembled correctly using rubber grease and that all surfaces are clean. My biggest concern was actually with the vacuum integrity of the rear hide seal and the small seal on the air valve because, if worn, these would admit air when braking, as the system was attempting to evacuate the bellows assembly.
With the support rings and end plates re-plated, I fitted the support rings into a new rubber bellows. This is quite a fiddly job. The middle one should be fitted first and then the two end rings, working one into each end minimise the amount of the bellows through which each has to be manipulated. Care needs to be taken to avoid splitting the rubber. I then re-fitted the front bellows plate into the bellows, carefully lifting the end lip of the rubber over the plate circumference. The plate needs to be oriented to make sure the bolt fixing holes will align with the three tapped holes in the valve housing, relative to a small raised section on the edge of the rubber bellows which fits into a recess at the bottom of the valve housing (Pics 40 & 41). It is very difficult to rotate the plate within the bellows, so the alignment should be correct before fitting.
I cleaned the hide seal in the rear bellows end plate with a clean dry cloth, then sprayed it with silicone grease from an aerosol can and left it to soak, repeating the application a number of times to ensure that the silicone fluid soaked into the hide. I have no idea what the composition of the original lubrication was, but felt that either fine vacuum grease or the fine silicone grease from an aerosol would work well in giving a sliding, vacuum-tight seal. If the valve set along with the hide seal has been replaced, this re-lubricating exercise should probably still be carried out.
Once I felt happy with the uptake of silicone grease by the hide seal, I carefully re-fitted the front valve housing into the front bellows plate. Because of the tight fit between the valve balancing diaphragm and the recess in the front bellows plate, the two need to be eased into place gently, making sure once again of the alignment of the three internal bolt fixing holes. Because of the tight fit, the two assemblies cannot be rotated, so it is important to ensure that the assembly fit is made with the fixing holes in alignment. I then fitted three new 1/4in UNC bolts (the coarse thread is used because of the alloy casting), along with locking washers to secure the front plate to the front casting assembly. As a precaution, I coated the threads of these bolts with a pipe-fitting compound, to make the threaded holes air-tight (Pic 42).
I then re-fitted the main return spring into the bellows assembly and, using the rear plate, compressed the spring and bellows by hand until the stainless steel vent tube could be carefully eased through the hide seal. While holding the assembly in position, the rubber buffer, stop washer and circlip can be re-fitted to hold the rear closure plate in place (Pic 43), The rear lip of the bellows can now be eased over the edge of the rear plate, to complete the bellows assembly. Once again, this plate needs to be oriented correctly, so that the fixing studs are in the correct place relative to the rear mounting plate and again, this must be done before easing the rear bellows lip over the plate, as it is too difficult to rotate once fitted.
Simple tests can be carried out using the ‘mouth to tube’ test, checking that at rest it is possible to blow freely through the rear air port. Then, while pressing the vacuum actuator by finger, check that the ability to blow air through the system from the rear tube is prevented. Then try sucking on the vacuum port as in the initial tests. In the relaxed position, with no operation of the vacuum actuator, this should not be possible. However, while it will not be possible to compress the bellows once the actuator is pressed, it should be possible to suck some air out of the system. These are hardly high-tech tests; however, in the absence of a calibrated vacuum/pressure pump, it gives a fair idea whether or not the bellows valve system functions.
The sintered bronze air filter cone can then be re-fitted, followed by the filter securing clip (Pic 44). The various valves and seals are not sophisticated, just sufficient to provide air tightness and to hold the manifold depression during relatively short-term braking actions. Once this is completed, the rear mounting plate can be fitted (assuming it is repainted) and the vacuum assembly placed to one side, or refitted if only this part is being serviced (Pic 45). Once refitted, it will be necessary to set up the eccentric bush which controls the vacuum operation using a vacuum gauge.
Clutch Master Cylinder
The clutch master cylinder is a little harder to remove if the pedal box is left in situ, because the pushrod fork end is connected to the clutch pedal directly with a trunnion and split pin and it is necessary to lie upside-down in the footwell to access this, but otherwise this is straightforward enough.
The original clutch master cylinder is similar in appearance to the brake master cylinders, though the bore is 3/>in rather than 5/8in. The master cylinder is secured to the base casting via a pair of studs and nuts and the pushrod is connected directly to the clutch pedal via a trunnion secured with a split pin. After removing the fixing nuts and the trunnion, the master cylinder can be separated from the casting (Pic 46). Opening up the unit shows an identical arrangement to the brake master cylinders (Pic 47), though again in this case the rear fluid seal was fitted incorrectly by whoever had worked on the unit.
Restoration of the clutch master cylinder was not going to be so straightforward, because while I could have the 1/4 in cylinder re-sleeved in the UK as I had done with the brake master cylinders, I could not find a UK source for a set of seals. I did find a company in California who not only re-sleeved brake and clutch master cylinders in brass but also supplied their own seals for the 1/4 in unit; however, for simplicity and cost, the choice came down to fitting a new replacement.
As a result, I purchased a new replica clutch master cylinder in the UK. For many years the replacement unit for the 3.8 car has been an original of the type fitted to the later 4.2 cars; however, now the replacement is a replica of the later 4.2 part. While very similar in appearance to the original 4.2 unit, the replica is plated and there are a number of differences (Pic 48). In Pic 49, the painted replica is shown alongside the original.
The replica 4.2-style unit is inexpensive and appears to be the only option available in terms of a new replacement product. The unit appeared well made; however, it was supplied with an open-ended pushrod without a fork end. Since the aperture at the rear of the new master cylinder for the piston retaining disc was smaller than the original, this also meant unfortunately that the original pushrod could not be substituted.
After fabricating a screw-on fork end, I found that even at the most extreme ‘short’ setting the pushrod was too long, setting the clutch pedal too high relative to the brake pedal. I have assumed that this may be because they were actually modelled on the original for the 4.2 Series II cars, which I believe may actually have a spacer between the master cylinder flange fitting and the base casting to move the cylinder forward and thereby lower the pedal, though I am not 100% sure of this. As a result, I ended up welding the fork onto a shortened rod, after deciding on the length of the rod through trial-fitting to the pedal box, comparing the pedal position to that obtained with the original master cylinder.
The brake pedal linkage is held in place at the main pivot by a large bolt which passes through both sides of the master cylinder mounting bracket and at the front by the trunnions which secure it to the master cylinder pushrods. In my sequence, both of these will already have been disconnected and removed. At the rear, the linkage is fastened to the power lever by a pin (Pic 50) and the power lever is bolted to the main brake pedal fulcrum shaft by a % UNF lock nut and the castellated nut which locks the eccentric barrel, which is used to adjust the position of the vacuum operating lever relative to the power lever.
The power lever and operating lever are separated from the forged lever which forms the end of the main brake pedal shaft by removing the split pin, castellated nut, eccentric “barrel, rubber bush and a number of small components, as well as the lower 1/4 UNF locknut. Be careful to note how they are assembled and not to lose anything (Pics 51 & 52). After reassembly and refitting to the car, the eccentric bush will need to be adjusted for proper operation of the servo.
Restoration of the linkage will most probably involve replacement of some or all of the five sets of plastic bushes which are used as bearings between the various sections, possibly replacement of rusty pivot bolts and refinishing painted or plated surfaces. After removing the main pivot bolt which passes through both sides of the master cylinder bracket, I found this bolt and the bearing sleeve through which it passes and which holds a pair of plastic bushes was very rusty, so I decided that it would be better to replace it on reassembly.
The linkage can be broken down into its separate components by driving out the pin connecting it to the power lever and by removing the bolt connecting the balance link to the pivot bracket (Pics 52, 53, 54 & 55). Other individual components and plastic bushes can be seen in Pics 56 & 57. The rust found on the two bolts which secure the linkage is obvious on the shorter bolt, which holds the balance link and pivot bracket together (Pic 55).
If the two bolts are to be replaced, rather than cleaned and re-plated, they should be replaced with bolts of the same type and not with set screws, which are threaded down the entire length. This may not be so easy, as both bolts have long smooth shoulders and very short threaded sections. The long bolt shown in Pic 54 is shown fitted in the bearing sleeve and fitted with the plastic end bushes. In this case I found that, though dirty, the plastic bushes were otherwise in good condition and so, after cleaning, I re-used these, though replacements are available.
Some of the linkage components look to have been heat-treated to give a black finish and I decided to re-finish these ‘black steel’ components in satin black paint. I re-plated the power and vacuum operating levers in nickel, using my DIY plating system. Once everything was cleaned up and re-plated, the linkage components were re-assembled and fitted to the power lever (Pic 58).
To be continued…