I have designed rear disc brakes for my 74 MGB.  I'm not new to this so I know the benefits and pitfalls of rear disc brakes.  My question here is about the master cylinder.  Does the check valve for the rear circuit need to be removed on from the stock MGB master cylinder?  I have everything mocked up to my satisfaction, just need to address the M/C before I install everything on the car..  

On some of my conversions on other cars I did have to remove the internal check valve and then replace it with a 2psi external valve, on other MG's I could leave it in.  I did do a research on rear disc conversions and have not found any mention about the M/C internal check valves in a MGB M/C.

I don't think the MGB master has a residual check valve. People have had trouble with the brass H where the lines meet. I would do away with that and separate front and rear. I do like the aftermarket 2lb residual valves for disk brakes.

Seems to me the '74 had the MC with the big round cap. Later MCs had the rectangular reservoir and there was a built-in brake balance switch. Not sure about any check valves though.

Jim

Yep, My M/C has the round cap.  The parts breakdown for the M/C does show check valves in the ports.  I just can't find the values for those valves.  I'm going to try it without mods and if I need to remove them, add 2lb inline valves.  The valve in question is item 21.  Since both are the same part number in the Moss catalog I doubt they are more than 2lb.

Sounds to me like a good approach.

Jim

Started the install over the weekend and then it stalled out.  Thought I had wheel seals and the discovered I only had one.  Only got the right side done.  Oh well something to do next weekend.

 -- moved topic --

Looking good Charles. Nice work.

Thanks, hope to get back on it tomorrow afternoon or Sunday afternoon.

Took the GT for a spirited test spin today.  The brakes have a good firm pedal.  Temps are 190 front 130 rear.  I really dislike the Wagner PD900 pads.  The box says ceramic but the pads feel and look like metallic.  They squeal  even when just driving down the road.  I'm going to try something else next weekend.  The rear brakes do not lock up first.

I need to make some adjustments with the park brake cables.  That will be simple enough to rectify.

Excellent work Charlie!

Found the noise. The anti-rattle shims that come with the PD900 pads were the cause of all of the ills.  I rounded up another set that are a different shape and now the irritating racket is gone.  The new shims hold the pads more securely.  Rotor temps today were 90 rear and 160 front.  The stops are straight and no surpries during vigorous brake application while turning.    

When I get a chance I may experiment with some 38MM 240SX calipers that I have.  That will be for another time.

I'm happy now.

1st 2 pics are the troublesome shims
last 2 are the good shims

Cool!  But, where in the world were you able to get just the anti-rattle shims?  I've never seen them sold separate from the calipers or pads.

The hardware can be had at Rockauto and I'm sure at NAPA

http://www.rockauto.com/en/catalog/nissan,2002,sentra,2.5l+l4,1388112,brake+&+wheel+hub,disc+brake+hardware+kit,1736

In my case one set came with the calipers and the other with the pads

The next challenge is one of the reman calipers has inop park brake.  Discovered the problem when I raised the car to check things over.  With the park brake set the right was applied solidly, the left not.  I want to see if I can discover the problem with the left side before I move on.

While fiddling today I made a proof of concept mounting for a 38MM 1998 Nissan 240SX rear caliper.  The 240sx caliper requires a different offset for the axle bracket.  I was able to make a simple 4 hole bracket attached to the bracket for the Sentra caliper.  The alignment is good and it uses the same rotor.  Basically it's 4 10mm holes spaced 115MM x 29mm with a cut out to clear the 240sx caliper cylinder.

The 38mm will give more bias to the rear at the expense of a little more pedal travel.

I decided to draw up the adapter.  I'll make a template out of steel this weekend and give it a test fit on the car.  

The adapter provides the required additional offset  and move the the 240sx mount holes out for alignment with the existing rotor.  I did add an additional hole that attaches to a nearby bolt for strength.

I've had several folks ask about the change I'll be making to the Sentra caliper adapter bracket.  I have attached a pic with some hand written notes.  The changes are small.  The bracket works well as is.  The changes are just to clean up some details.

Hi Charlie,

What details need to be cleaned up?

Scott,

Double click on the drawing and you will see my hand written notes.

I now have a CAD drawing for the bracket for mounting the 2002 Nissan Sentra caliper to the tube type MGB rear axle. It will require a CAD viewer to see. The .dwg file can be converted to what ever file system is used for the cutter. Also there is a .jpg file. I have not had this part cut as I am satisfied with the original drawing. This drawing is modified to "square up" the caliper as it sits over the OD of the rotor. The top yellow line was maintained at 115MM. The lower yellow line was extended to 3 11/16". Have your machinist confirm those dimensions before cutting. All else remained the same. When I get time I will experiment with adapting the 1998 240SX rear caliper using the "U" shaped bracket above. That additional bracket provides the correct offset for the 240SX caliper.

Unfortunately I was not able to attach the .dwg file.  Just e-mail me with your e-mail address and I'll send out the file.

I found a problem with the latest drawing.  The hole where the 2 yellow lines intersect is still out of place.  I'll see if I can get it redrawn.

The additional bracket for the 240sx caliper has to be changed.  The difference is the spacing as shown in the pic.  That spacing will also change on the Sentra bracket.

Yesterday I got a chance to make the adapter brackets for the 240sx calipers. Those brackets move the mount holes out and provide the necessary offset. As a precaution, I bolted and welded the 2 brackets together.

I took the GT out for a vigorous test drive with the 38mm bore 240SX rear calipers. The stopping is satisfying, Very little nose dive. almost flat. In checking the temps front to rear and they we within a couple of degrees front to rear. We had a steady rain all day yesterday so there were still patches of wet asphalt. The car braked well on both wet and dry pavement. In places where the pavement alternated between wet and dry the car behaved predictably. I even tried hard braking on a curve both wet and dry and the car behaved. No surprises. I had a buddy with me who has a stock1972 roadster. His gut feeling is the 38mm calipers may give a roadster a little too much rear bias. We'll try the 34mm Sentra calipers on his car sometime in the future.

The 240SX provides for a better routing for the hydraulic hose and the park brake cable, in my opinion. I did have to make a simple modification to the park brake lever by welding a small piece of metal to close off the open hook for the brake cable. That may not be necessary, I just wanted to be assured the cable end could not fall off the arm.

The Sentra 34mm calipers have some benefits in that the pads are longer than the 240sx pads. As I understand it longer pads may not give more stopping power but may have an advantage of lasting longer and operate cooler. The other benefit is the bracket is one piece. The disadvantage is the park brake lever has to be modified and the park brake cable ends up being very close to the boot bodywork.

The benefit for the 240sx caliper is the brake hose port is in a place for better routing of the hose and the park brake cable is in a better location. The disadvantage is the 2 piece bracket and the brake hose routing I used is close to a mount bolt which means the brake hose will have to be removed to change pads. There may be a workaround for that issue.

I had to remove the squealer from the inside pads because of interference with the adapter bracket I made. The bracket could be modified easily.

In the end, I like the 240sx calipers for the GT and the jury is out about those calipers on the roadster without adding a porp. valve.

IMO, the wet pavement brake test should have shown if there was too much rear bias.

Hi Charlie,

For the Sentra 34mm calipers, you mention they are close to the body work. Would clocking the caliper at a different angle help with that? Nothing you mentioned about either caliper sounds like a show stopper though.

Thanks for keeping us informed. Great job!!

Scott