MGB rear disc brakes

[geezer]

Scott,

The caliper is not close to the body work it's the park brake cable on the right side.  In reality it just rubbed so all I needed was a little more clearance.  I solved that problem with drilling another hole in the lever on the caliper.  That brought the cable in enough to clear the boot floor.

It's suppose to rain this weekend so I'll take the GT out and see how the brakes react in the rain.  We have some smooth roads out in the toolies so I can give it a brake test in the wet and on a curve. That should show any glaring balance issues.

I am having the drawing corrected so a laser cutter can cut out the bracket with the one stray hole in the right place.  It would also be easy enough to make one from some 3/8 flat stock if you so choose.

I'll see if I can post a pick of the redrilled lever this weekend.

[geezer]

Attached is a pic of the shortened lever.  That provided enough clearance for the park brake cable.  I did notice that the caliper does get close to the body in full compression.  I did not find any evidence of the caliper contacting the body, however I did take the time to bend over the lip for additional clearance.  If you choose to rotate the caliper down a bit that can be done with the Sentra caliper but not with the 240SX caliper.  There is a clearance issue with the extension strap mount on the axle with the 240SX caliper.

Another change.  I will change the flex hose to a shorter hose.  12 or 13 inches long should clean that up.

I did find a defective 240SX caliper.  That is now changed out for another reman caliper.  I took a vigorous test drive today and the temps are 145 degrees for both rears and 265 for both fronts.  That coincides with the predicted brake balance of 67-33.  It's raining now so I should be able to take it for a wet test drive in the morning.

[geezer]

Unfortunately the streets were dry on Sunday.  It may rain later this week so I'll give it another try then.

[geezer]

OK I'm happy with my rear disc brake conversion.  Bob Harper in Australia was kind enough to correct the drawing for the Sentra/Sunny caliper bracket.  The drawing has been checked and to the best of my knowledge it is correct.  The dimensions have been changed to make it easier to layout on a piece of steel or aluminum with easy to locate reference points.  I'm not going to develop this conversion any farther.

If anyone wants the drawing for the caliper bracket send me a PM with your e-mail address and I'll send the drawing along with part numbers for the caliper and rotors that I have used.  As far as the additional bracket for the 240SX is concerned, it is easy to make at home out if 1/4" flat steel stock so I'm not going to commission a CAD drawing at this time.  If someone wants to make a CAD drawing of the additional 240SX bracket feel free to do so and share.  Also feel welcome to use the finished drawing as a basis for any rear disc brake conversion you care to undertake.  All of the basics are there.

Charlie Durning

[geezer]

FYI.  Using a spare prototype bracket I did a 34mm Sentra install on a 77 RBB roadster.  There are a couple of challenges.  All but one can be resolved easily.  The biggest issue is the boot floor for that car is different from the CBB GT.  There is interference between the park brake linkage and the boot floor.  This weekend we are going to experiment with a different park brake lever on the caliper.  Failing that the 34mm 240SX caliper will be a better choice since the park brake lever on the caliper is located close to the axle housing and not out the back.

We did take the car for a spirited test drive on a rainy day and we feel the 34mm caliper is well suited for the RBB roadster.  We also took out the CBB GT and feel the 38mm 240Sx caliper is a good match for that car.  The early 240sx, target date 1992, has a 34mm bore and the later 240SX, target date 1998, has a 38mm bore.  Both will use the same add on caliper bracket since the exterior and mounting dimensions are exactly the same.

[geezer]

Resolved the park brake clearance on the 77RBB.  Originally I was going to make a new arm for the caliper that would lower the attaching point.  In the end I just shortened the flat arm on the caliper and that gave enough clearance.  I also moved the attaching point for fiber flex for better alignment.

[geezer]

Latest drawing with corrections for Sentra caliper.  It should print full size

[geezer]

I finally got around to rerouting the brake flex hose to the caliper. On the Sentra caliper the hose went straight in towards the center of the car and behind of the limit strap. I was just not happy with that. For the 240SX caliper i sent over and and in to the center of the car. I didn't care for that either. In reality I was using the hose available to me at the time. In doing further digging I found a vendor on eBay who will make custom brake hoses. For the Sentra conversion on the RBB car I had him make a pair of 18" long hoses with the banjo bent at 45 degrees. I thought the 18" hoses would also work for the 240SX. The 18" does fit the 240SX but a better choice would be 20". What the 45 degree bend does is allow the hose to be routed down the back of the caliper and then up and over the axle tube. That routing keeps the brake hose out of harms way. The pictures are for the 240Sx install on the CBB GT. The 18" hose for the 240SX ends up routing behind of the bump stop on the axle. A 20" hose would be better routed in front of the bump stop. With the Sentra caliper the 18" brake hose can be routed in front of the bump stop also.

[geezer]

I had a pair of brackets made from the latest drawing.  I should be able to do a mock up on a spare housing to prove the drawing this weekend

[geezer]

Did a test fit.  The laser cut brackets are a perfect fit.  All I had to do was clean up the bolt holes and make a small radius so it would fit flush against the axle housing flange.

[geezer]

I have had several requests for clarification on the applications for the Rotor and calipers I have used for the disc conversion. Hope this is useful.

Rotor and Caliper Applications

Buyer's Guide : CENTRIC 12140024 Rotor
ACURA CL 1997
HONDA ACCORD 1991-1997
Please refer to catalog for application details.

38MM 240SX caliper applications
Buyer's Guide : BECK/ARNLEY 0771213S Caliper
NISSAN 240SX 1994-1998
Please refer to catalog for application details.

34MM 240sx caliper applications
Buyer's Guide : CENTRIC 14142512 Caliper
NISSAN 240SX 1989-1993
Please refer to catalog for application details.

34MM Sentra caliper applications

Buyer's Guide : A-1 CARDONE 19B2627B Caliper
INFINITI G20 2002
NISSAN SENTRA 2002-2006
Please refer to catalog for application details.

Manufactures names and part numbers are for reference only. Parts from any manufacture for the application will be suitable

Right and left calipers required



The pics below will show specifics on the Rotors and calipers

[MGBV8]

Lot of great info.  Thanks, Charles!

[geezer]

Rhere have been questions about how the secondary bracket for the 240sx caliper and the Sentra bracket fit together.  The secondaty SX bracket is attached to the inboard side of the Sentra bracket.  That provides the necessary additional offset for the SX caliper.  Hope this helps.

[geezer]

Made a handy fixture for boring out the center hole in the caliper with a drill press.  Found a 2.5" washer with a .75" hole.  Used a 7/8" hole saw to make a bushing.  Mounted the washer and bushing to a piece if wood that will also be a handle.  The washer centers the rotor and the bushing guides the hole saw.  Knock out a rotor in 2 minutes.

[geezer]

I've had questions about fitment with wire wheels. I don't have a wire wheel so I cannot give a definitive answer. Hoewer ,here are some shots with a wire wheel hub. From that you should be able to discern if this will clear a wire wheel. The rear axle in my GT is a wire wheel axle. There may be some body clearance issues with the wire wheel axle that may not be an issue with a bolt on wheel axle. The conversion I did on a RBB roadster did not have any clearance issues other than the park levers had to be shortened for clearance with the boot floor withe the Sentra caliper. That is not an issue with the 240sx caliper. I'll post the sx caliper fitment with the WW hub later today.

[geezer]

Here are pics of the 240SX fitment along with a pic with a WW hub

[geezer]

Yesterday I had all of the parts and time all in one place. I made a new mock up and test fit the secondary bracket to be used with the more accurate Bob Harper drawing of the Sentra mount bracket. This 240SX bracket moves the caliper in slightly for better placement of the pads. The previous bracket placed the pads even with the OD of the rotor. This bracket places the pads at the outer edge of the contact surface of the rotor. Bob Harper has agreed to create the cad drawing of the bracket also. I will post when it is available. Attached is the more accurate drawings for those who want to go ahead and make their own bracket. One suggestion is to drill the 5th hole once the brackets are attached together on the axle. I was not able to establish a spot on accurate location for that hole. The attached drawing is a tracing from the mock up bracket. All other measurements are accurate.

Another consideration, my CBBGT is lowered by using 5 leaf rear springs and early roadster front springs and it does have a wire wheel rear axle. With 2 people and luggage it does bottom on the bump stop when hitting a harsh bump. Though measurements show adequate clearance it is very close. As a preventative measure I am adding an Energy Suspension 9.9117G to the bump stop on the axle. I'll get better measurements for the 2 CBB conversions I'll be doing in May. Those cars have not been lowered and have bolt on wheels which moves the caliper outboard in relation to the body. No issues are noted with the RBB roadster at normal ride height.

[geezer]

Bob Harper was kind enough to draw up both a PDF and a DXF CAD drawing of the secondary 240SX bracket.  The DXF file is laser cutter ready.  If anyone wants a copy just PM me your e-mail address and I'll send it right out.  I have not commissioned any brackets based upon the drawings, however, the drawings do match my tracings of the prototype bracket.

[geezer]

The question has been asked about increased pedal travel.  There is some additional pedal travel though I would not consider the additional travel as disconcerting.  

My master cylinder shot craps on me, I was expecting it since it would lose the front circuit occasionally.  While I had the system open I took the opportunity to install a pair of 2 psi residual check valves.  The valves did make a difference and brought the pedal to almost the original position.  I would say try without and see what you think.  If you feel the travel is too long, installing the residual valves may be the answer.

[geezer]

I have posted my closing comments on this conversion here

https://www.mgexp.com/journal/geezer/16968

Unless there are further questions I am putting this to rest

[WernerVC]

Charles,
A question about the connections at the brake lines. How did you make the connection from the MGB brake line to the Datsun or Nissan caliper ? One is British threads and the others metric
Werner

[Nibor1]

Hello Charles I'm new on this site and have just found your post's about disc brakes on mgb and was wondering how thick the mounting plate you made was. Regards Robin

[geezer]

VernerVC, Nibor1,

I apologize, it's been awhile since I visited this forum.

Yes the Nissan caliper is metric.  The flex hose I used has a compatible banjo end for the caliper and the other end is -3 inverted flare for a 3/8-24 thread inverted flare nut.  The hard line has an inverted (double) flare on the 3/16" pipe.

The primary bracket is made of 3/8" flat steel and the secondary bracket is 1/4".  I have positive feedback from one fellow who made the brackets from aluminum.

Hope that helps

[MGBV8]

'I have positive feedback from one fellow who made the brackets from aluminum. That is interesting.  I can cut aluminum much easier.  I am curious what thickness he used.

[MG four six eight]

Carl,

I'm using 1/2" 6061 aluminum for my rear caliper brackets. Different set-up than the OP, with Wilwood calipers on a Mopar rear end but no issues with the brackets at all.
Bill