MG Sports Cars

Due to the Covid 19 scare I have plenty of time on my hands.

Off and on there has been discussion about improving the front disc brakes for MGBs. There are pros and cons over the effectiveness and weight of any conversion. All points are valid and any conversion offers compromises as does the OEM design.

What peaked my interest was the conversion using MGRV8 parts. At around $500+, from the usual suppliers, the conversion seems to be appealing. If the caliper is what I think it is, same as Rover SD1 or Princess, The piston surface area is equivalent to the piston surface area of the MGB caliper, no benefit there. Also, being a 4 piston caliper, the weight is greater. The benefit is the pressure is applied to a larger pad. The other concern is the weight of the rotor. Since I have no specs on the rotor is could be heavier than the MGB.

The benefit I see with that conversion is better heat dissipation due to the vented rotor and larger pads with the braking effectiveness being about the same as the MGB. Correct me if I am wrong.

There are several DIY projects that I have seen using Toyota truck 4 piston calipers and and Volvo 4 piston calipers. Those calipers have the same effective piston surface area as the MGB with added weight. I did look at a Toyota Prelude brake conversion that was teased on the British V8 forum. Though the piston surface area is slightly larger than the MGB is caliper is enormous and uses a rotor that is 7/8" wide. All very heavy and would require at least a 15" wheel to get a decent size rotor. On the plus side, the larger rotor and caliper piston could offer better braking performance.

The problem with MGB front brake conversions is the design of the swing axle. That limits the way another caliper can be mounted. That got me to thinking. I decided to dig through the gold mine to see what I have. What I found were the parts I used when I converted the front brakes on the Morris Minor and the Chick Magnette. The caliper I dug out was from a 1995-1999 Nissan Sentra. It's very compact and has the same piston surface area as the MGB. The rotor I found was from a 1985 Toyota Cressida. Though the rotor is smaller than the MGB by .150" it is vented and fits the Sentra caliper. Comparing the weights with the MGB parts, the weight is the same as an assembly. MGB caliper is 7lbs, Sentra caliper is 5lbs. MGB rotor is 10lbs, Cressida rotor is 12lbs. The part to put this all together was the bracket I designed for the Morris.

The Morris bracket did move the caliper out too far to fit the rotor. But as a test fit the concept has promise. All it took was to move in the caliper by 3/8" inch. Now the Sentra pads are near the outer edge of the rotor and the entire assembly fits nicely within my 14" Minitor wheels. So what I have here is a brake conversion with about the same braking effectiveness as the MGB but with a vented rotor with no weight penalty.

As an aside there are possibilities for those folks with 15" or 16" wheels to get better effectiveness using a rear rotor from a 2006+ Nissan Frontier. That will be explored later.

One of the issues I found with using a larger caliper is the caliper makes contact with the suspension near full lock. I don't see any practical way to avoid that problem. Since the Sentra caliper is more compact that problem can be avoided with a simple stop made into the mount bracket. Some may like that some may not. I did discover later that the stop is not necessary.

Here are the costs so far. The Cressida Sedan rotor PN 9911R can be found on Rock Auto for $13.00 each, The Sentra caliper L1792, L1793 can be found on Rock Auto for $40.00 each. The Sentra ceramic pads ZD668 can be found on Rock Auto for $9.00. I made the simple flat bracket from a piece of 1/4"x1.5" scrap steel and you may need some misc bolts and spacers to fit it all together. The brake hose I used is from a MKII 1600 MGA with front disc brakes.

Aside from getting the parts, the pilot bore on the rotor needs to be enlarged to about 3" to clear the front hub. The rotor will be mounted outboard so a provision for set screws to locate the rotor on the hub will need to be drilled, countersunk, and tapped.

The bracket can be mounted on either side of the MGB caliper ears on the swivel axle. If mounted inboard you will need 2) 3/4" long spacers. If mounted outboard the Nissan caliper bracket will need a slight modification for clearance. Either way the caliper will be centered on the rotor.

For about $125.00 (maybe less with some shopping) and some sweat equity you too can have vented front disc brakes using common parts available in North America. The cost of the conversion is awash if you are replacing all of the MGB brake parts anyway during a brake overhaul.

I completed the conversion last night. I am happy with the fit. Took the car out for a spirited drive this morning and am very pleased with the performance. After repeated 70mph panic stops the brake temps hovered around 130 degrees. The surprise is my butt dyno says the brakes are more effective. Win, Win.

Looks like a nice option especially if one was intending to rebuild/replace the factory system

Attached is a simple drawing for the adapter bracket. It is not symmetrical for an alignment of the pad to the rotor. That is not critical.

Thanks, Charles!

Here is a better drawing of the bracket if anyone is interested. Bob Harper gets credit for this drawing.

After I had some brackets laser cut I found that the original drawing brings the pads in a little closer than I like so I had the drawing bring the pads out another 2mm.




Edited 2 time(s). Last edit at 06/26/2020 06:36AM by geezer.

Looks great Geezer, I am working on the rear disc setup from the info that you sent me last year. Something positive from this COVID downtime I guess. Stay safe!

As usual, great work Charlie! I'm putting the final touches on my rear disks based on your design.

Scott

Some folks have expressed concern about the weight of the vented rotors and caliper. I did weigh the parts from the MGB and the conversion parts.

MGB caliper 7lbs, Nissan caliper 5lbs

MGB rotor 10lbs, Toyota rotor 12lbs

In the end the change in unsprung weight is zero

BTW this conversion WILL NOT fit within a stock 14" Rostyle wheel

Here is a pic of the laser cut bracket.




Edited 2 time(s). Last edit at 05/28/2020 05:43PM by geezer.

Well done. Did you buy the 7/16 counter sunk screws on line? What was the reason to use the MGA hose over the MGB hose? Thanks for sharing your work with the MG community.

I did order the screws online. None were available in town. The reason for the mga hose os it has the correct fittings oon each end. The mgb hose does not

Ruben,

I apologize for the short answer. I've been out of town for 5 days and just got in. Answering questions on my phone is a PITA.

The MGA hose has a "banjo" end that will work with the Nissan caliper. The MGB hose has a male threaded that just would not work out. The frame end of the MGA hose is the same as the MGB.

I used a Goodridge branded hose. It worked well with the Nissan caliper, though I did have to widen the locating tangs on the caliper so the hose would fully seat. That just took a minute with a file.

Hope that answers your question

Charlie D

I just got back from 5 days of running the "Pig Trails" in NW Arkansas. The roads are tight, twisty, with some very steep grades that have switch backs. I was the only one without stinky brakes at the bottom of one 17% grade with switch backs. We compared front disc temps. Most were around 165 degrees(with rear disc), and a couple with rear drum were just over 200 degrees. The vented fronts were just 95 degrees. I call that mission accomplished. Very pleased with braking performance with cheap ceramic pads.

Charles, sounds like a well proven setup!

Great job!

Thanks for sharing your project!