K21 – Four Wheel Disc Brakes

by Dick Nye in the September 1995 RootesReview (reprinted from Tiger Tales Vol. 25 #4)

What do a Sunbeam Tiger, Fiat124, Datsun B-210, $200 and your friendly machine shop have in common? Give up? They’re all necessary to convert your Tiger’s rear drums to disc brakes for an incredible improvement in stopping power.

I’d heard the rumor for years, glimpsed a setup on David Brigg’s Tiger and finally saw a transformation underway on Bob Hertz’s ’66 at Smitty’s place in San Diego. I decided to take the plunge myself. When you realize the hardest part of the swap is finding the correct tool to break lose the hub, you begin to realize just how garage-mechanic friendly this swap is. Smitty’s got a tool that he made himself. If you can lift it, it will defeat the stubbornest hub.

Sourcing the Parts

This fun job began with a visit to Ecology Wrecking Chula Vista where a Fiat 124 donated its rear calipers and mounting brackets. Cost $15.95 each plus tax. Next I visited Foreign Auto Service in El Cajon where I bought a pair of new brake rotors for $18.88 each. Part numbers and crossovers are as follows: 40206-U6700 Nissan 3125 Aimco 141144 Bendix JBR-104 Autosp BD-97306Wagner D9250EIS 9250 Raybestos 4005 MCI.

I also purchased a caliper rebuild kit, Beck Arnley Worldparts P/N 071-4543, which has enough parts to finish one pair and costs only $7.12.

Next I visited Pep Boys and purchased a brass brake line T 3/16″x3/16″x3/16″, P/N37495-43521, cost $2.59 along with four metric bolts at $.56 each and six longer axle flange bolts to hold the bracket adapter to the axle housing, cost $.26 each.

Adapter Assembly and Installation

I gathered up my hubs, rotors, mounting bracket adapter template (courtesy of Smitty) and 4″ of 1.250″ round bar stock and headed to my favorite machine shop. He knocked out the studs and chucked the hubs in his lathe. He first turned the outer surface of the hub so that the rotor would run true. Next he rounded the corners of the hub so it would fit inside the new rotors. He set up the rotors and drilled four holes so they would fit over the Tiger hubs. Next he set up the adapter pattern on a mill and machined a piece of 3/8″ thick steel plate, marking the locations for holes, which I drilled later at Smitty s using standard and metric bits. He sawed the round bar into 4 pieces, 3/4″ thick. I drilled 10mm holes through their flat centres. These will be used to center the calipers over the rotors. Cost $94.

I degreased the calipers then bead blasted them at Smitty’s and rebuilt them at home, using my bench vise to press the caliper puck past the new seal. Bob designed some practical tools for the hydraulic press so we would assemble the Fiat emergency brake part of the calipers, which worked slick. Flexible steel brake lines are optional and are readily available from Earl’s.

Some Additional Improvements

While I was pretending to be a mechanic under Smitty’s watchful eye, my Tiger’s rear end was being rebuilt by Mechanically Inclined Technicians (MIT) in El Cajon, a nice easy to work with group who did the job for $150, including completely painting the housing, checking the internals of my posi and reassembling everything.

I bought all the necessary parts through Tiger Tales, a late model locker from Peter Freiberger for $250, 3:31 gears, new bearings, seals and a new pinion flange , from Barry Schonberger for $212, and internal oil seals, $25.

I had National Spring resize and reheat-treat the front eyes of my rear springs and I added new Teflon slides and polyurethane bushings. I welded the front frame mounting brackets to add a little strength there, then I was ready to reassemble.

Total costs (Ed: 1995 prices!) are shown below:

Disc brake conversion $184 +tax
Spring rebuild $99 + tax
Rear end rebuild plus posi and lower gears $637 +tax