Hub of Motion: Replacing bearings on a full-floating hub system
By John Gunnell We had done everything outlined in the shop manual to restore the wire wheel hubs and the disc brakes on the front of the Daimler SP250 roadster….
By John Gunnell
We had done everything outlined in the shop manual to restore the wire wheel hubs and the disc brakes on the front of the Daimler SP250 roadster. Since the British sports car had originally been taken apart by someone else and we didn’t have photos, drawings or notes about the disassembly, we thought we did a pretty good job putting it back together. Why was there an extra part left over?
To answer this question, we e-mailed Daimler expert Laurence Jones in England. By the next day we had an answer. “The extra part is a dust shield added to late-production cars,” Jones wrote. “It mounts on the inner flange of the stub axle, up against the vertical link (pivot pin to Americans) and between the link and the dust cover on the end of the inner bearing.“ This added dust shield was never pictured or mentioned in the Daimler shop manual. Since so few SP250s were made, the shop manual was never updated. Jones said we should use the dust shield, so that meant disassembling the hub again.
Although SP250s are rare, their underpinnings are a direct lift from the mass-produced Triumph TR3 and TR3A sports cars. They also have many similarities with other cars (even domestic) that used wire wheels with full-floating hubs. With full-floating hubs, the wheels are mounted to the hubs. This contrasts with semi-floating hubs where the wheels are mounted to the axles. With full-floating hubs, the hubs (not the axles) bear the weight of the vehicle.
There’s a small likelihood you’ll ever work on a Daimler SP250, since only 2,500 were built, but some of the following information and parts sources will be helpful whether you’re working on a British sports car or a Model A Ford. Removing and installing bearings, greasing hubs, brake repairs and tips on tools are pretty much universal, no matter what vehicle you’re restoring.
On the SP250, the hubs are bolted to the brake discs (rotors) with four bolts. The hubs have a small bearing and bearing race at the outer end and a large bearing and bearing race at the inner end. A donut-type felt oil seal fits into the metal ring that is tapped into the outer end of the hub after installing the bearing and race. The “leftover” dust shield goes against the ring. It has a flat, angled bottom lip that hooks into the vertical link to keep the shield from turning.
After installing the smaller bearing and race at the outer end of the hub, slide the hub/disc onto the stub axle. This may knock the small outer bearing loose. If so, just put it back in the hub by hand. When properly positioned, the large inner end of the hub is against the once-forgotten dust shield.
At the smaller, outer end of the hub, a washer with a D-shaped hole goes over the D-shaped axle. Push the washer against the bearing with the castle nut, adjust the tightness of the castle nut and position it so a cotter pin can be installed to keep the castle nut from coming off. The washer is a finger’s length inward from the hub’s outer edge, so the hub has holes through which to install the cotter pin.
Before installing the hub on the axle, position a shield (brake backing plate) over the front suspension members. This will be held in its final position by the same bolts that are later used to attach the brake caliper, but for now, leave it loose. Next, make certain that the pads in the caliper are pushed back and place the caliper over the disc on the rear upper part of the disc. The bolts that attach the caliper are threaded at the ends only, so they need to be tapped a bit to make things tighten. Then, put the bolts through the “backing plate” mounting brackets and the calipers, as well as the shims mentioned below.
Factory shims were used under the caliper bolts to make slight inward/outward adjustments of the caliper on the rotor. The goal was to match the vertical centerline of the caliper to the center of the brake disc’s edge. The thin shims are shaped like a barbell with holes in each end that the caliper bolts pass through. When disassembling a car, carefully note how many shims are used in each side. Since we did not have that information for this car, we played around until the centers were aligned.
The castle nut adjustment mentioned earlier is what actually moves the caliper in or out on the rotor to get it on center. The shop manual states the nut should be tightened until the brake disc just about stops turning. Then, it says to back off the nut from one to two flats (to a spot where the cotter pin will slide though a hole in the axle end). If the correct number of shims were used, the centerlines of the calipers and discs should be close.
Naturally, the hubs have to be greased, and there are no Zerk fittings or provisions for adding grease after the hub and brake assemblies are built. The Daimler’s shop manual says to fill the entire hub between the inner and outer bearings with the proper type of grease. The inner and outer wheel hub bearings themselves (tapered roller bearings on this car) should also be liberally greased.
The proper felt grease seals were difficult to find. Thinking the Daimler and Triumph seals were identical, we ordered Triumph seals from Moss Motors (www.mossmotors.com) and found they were smaller. We found the correct seals from John Carey in Massachusetts, who said that they had been “unobtanium” for a while, but were recently reproduced.
Every part on the hub assembly was removed from the car, cleaned or sandblasted and repainted with Satin Black chassis paint from Eastwood (www.eastwood.com). The calipers were completely rebuilt and upgraded with stainless-steel inserts by Brake & Equipment Warehouse in Minneapolis (www.brakeplace.com). We feel this is the only way to go in preventing rusty brakes on a collector car that will be stored.
Since we had the car completely apart during its chassis restoration, we replaced all of the bearings and races in the hubs. The small bearings and races were a common number used on trailers and were available at any auto parts store. The larger bearings were harder to find and came from John Carey. We also sourced new brake discs (rotors) from Carey’s New England Automotive Restorations. The discs were slightly different than the originals, which had slotted edges. We discovered why the new rotors were different — many of the slots on the originals had fractured.
Driving out the smaller races that were in the hub was easy. They sat up against a ridge on the bore of the hub that had notches on either side. We placed a long punch where the slots were located and tapped with a hammer and the small bearing races flew out. It was a different story with the larger inner races.
To get each of the large inner races out, we took an inexpensive Bearing Race and Seal Driver Set and ground the opposite edges of the purple 50-mm aluminum collar flat. This allowed the collar to slip down into the hub, past the old race. Then, we tapped the collar until it was sitting flat inside the hub, against the old race, and installed the drive handle. Next, we put pressure on the driver handle with our 20-ton bottle jack press.
Since we knew it is hard to press anything in or out that isn’t perfectly flat or level, we avoided generating hub-breaking forces with the press. Instead, we repeatedly applied a little pressure and sprayed lubricant into the hub to make parts slide easier. Each time we stopped to check on our progress, we adjusted things so that we were pressing straight and level. Eventually, the large bearing race, which had sat in the hub for 50 years, dropped out with a telltale “pop.”
Flattening the edges of the 50-mm collar didn’t ruin it and it still came in handy when we were pressing in the new smaller bearing race. Other collars were used to press in the larger race. Sometimes, it seems like the new bearings go in easier with the 20-ton press and sometimes they seem easier to install using repetitive hammer blows. Again, when using a press, things have to be perfectly straight, while using a hammer tends to make “automatic” adjustments with each blow. The important thing to check is that the bearing races seat properly. When things are right, that telltale “pop” or “snap” can be heard again.
One other thing worth mentioning is that experts in a particular type of car often used shortened descriptions for parts. For instance, Daimler expert John Carey referred to the smaller hub bearing races as “1910s,” although the full part number was LM11910. When we asked the Bumper to Bumper counterman for a 1910 bearing, his computer almost crashed. When we then checked the old bearing number and told him we needed an 11910, he found it on the shelf.
