Miles Posted September 15, 2013 Share Posted September 15, 2013 I just finished installing 85-88 Maxima rear calipers on my 72 240Z using a mounting bracket from MSA. The pads drag on the rotors. I have completed the hydraulic inspection and there is no hydraulic lock or residual pressure build up that would cause the pads to drag. The calipers are new with pistons that move freely. Both sides drag. I am now looking for mechanical issues such as the parking brake and caliper/rotor fitment that would cause the pads to drag. The parking brake functions normally. Looking at the position of the rotor relative to the caliper shows that the rotor is not centered in the caliper. The gap between the rotor and the caliper is about 1 mm narrower on the inboard side (piston side) of the caliper. The only reason I can see for this is that either the mounting bracket was not machined correctly or there is problem with the pad where the bracket bolts to the 240Z strut. Reading old posts from Ross Corrigan (Modern Motorsports) indicates that the bracket mounting pad on some 240Z struts varied enough that his 240SX brackets would not bolt on. He later modified his brackets to allow for this rare variation in 240Z struts. How critical is it for the rotor to be exactly centered in the caliper? Would putting a 1mm spacer between the hub and rotor hat be safe way to center the rotor in the caliper? Quote Link to comment Share on other sites More sharing options...
Akira Posted September 15, 2013 Share Posted September 15, 2013 Not sure if this thread will help or maybe you already read it, but if not, it might be worth a look. http://forums.hybridz.org/topic/105599-need-help-with-dragging-rear-disc-brakes/ Quote Link to comment Share on other sites More sharing options...
beermanpete Posted September 15, 2013 Share Posted September 15, 2013 (edited) The caliper will find its own center due to the floating desing. What needs to be on center with the rotor is the mounting bracket. If the rotor is dragging on both pads the pads are too thick or the rotor is too thick (assuming the caliper piston is fully depressed and not held out due to corrosion or debris in the bore.) Edited September 15, 2013 by beermanpete Quote Link to comment Share on other sites More sharing options...
Miles Posted September 15, 2013 Author Share Posted September 15, 2013 The caliper will find its own center due to the floating desing. What needs to be on center with the rotor is the mounting bracket. If the rotor is dragging on both pads the pads are too thick or the rotor is too thick (assuming the caliper piston is fully depressed and not held out due to corrosion or debris in the bore.) Beerman That floating calipers should be self centering seems logical. By mounting bracket, do you mean the bracket that bolts to the strut or the bracket that the caliper bolts to? Quote Link to comment Share on other sites More sharing options...
beermanpete Posted September 15, 2013 Share Posted September 15, 2013 I mean the one the caliper bolts to. Quote Link to comment Share on other sites More sharing options...
Miles Posted September 15, 2013 Author Share Posted September 15, 2013 I mean the one the caliper bolts to. That is the one I suspect has the wrong offset or I have a non-typical 240Z strut that moves the bracket outward pushing the piston towards the rotor. So even though the floating caliper is self cenetring, the bracket still has to center the caliper on the rotor. Quote Link to comment Share on other sites More sharing options...
DuoWing Posted September 17, 2013 Share Posted September 17, 2013 In my experience in most cases of putting new pads and rotors, even on stock cars with a floating caliper. When brand new you almost always get some drag. As you'll start driving you'll hear it, then do your short break-in drive and usually by the end of that the pads, rotor, has already begun to wear and match to one another and you're good to go. I did have an issue when I put my 240SX rear calipers on my Z where the one side was really tight. I then realized that the pads were not all exactly the same and one of them had a little tab on the back. So I didn't put them together correctly and the little tab was pushing against the caliper, rather than letting it sit properly and was causing more drag. Switched them all around and was good to go. Quote Link to comment Share on other sites More sharing options...
Miles Posted September 17, 2013 Author Share Posted September 17, 2013 (edited) On a hunch, I bought some cheap organic pads and compaired the thickness to the Hawk HPS pads I had installed. The Hawk pads measured 13.62 mm and the cheap pads measured 12.3 mm. With the car on jack stands, the cheap 12.3 mm thick pads allow the rear wheels spin freely with very little drag. The thicker Hawk pads would drag when the wheel was spun and I could hear and feel the pads dragging while coasting. With the cheap 12.3 mm pads the car rolls with no resistance and yet both rear wheels are too hot to touch after only a few miles. I took the car for test ride of about 5 miles and both rear wheels were very hot, but didn't show much rolling resistance. The front wheels were slightly above ambient temperature. Setup: New Wilwood 1 inch MC with residual presure valve removed form rear output port. The MC was bench bled New 280Z booster with push rod adjusted so it is not preloading the MC. System bled with firm pedal. Wilwood PV opened all the way to the rear. The PV was Installed for future brake upgrades e.g, Arizona Z front and rear kits. Stock front brakes. New Maxima rear calipers. Pistons glide in and out during adjustment. The parking brake lever retracts back to its resting position on the stop pin. Bench testing of the parking brake shows the piston moving out when the parking brake lever is moved. New 82-83 280ZX rotors. The 280Zx rotors are 9.906 mm thick as compared to stock Maxima rotors which are 10.16 mm thick. Parking brake cable is not preloaded and is relaxed at the caliper connection. Pistons fully retracted and pads are installed correctly using a caliper piston tool. Slider pins are not binding or show no resistance to movement. I have checked the entire brake system for mechanical and hydraulic problems. Everything appears normal. There is gravity flow and no residual pressure shown at the bleed screws after road test. The only components that I that I have not opened up for inspection is the Wilwood PV and the brake differential pressure switch that is located under the MC. I was thinking of removing both components and reconnecting the brake lines as a test, but since I am not seeing any residual pressure build up and there is good flow at the bleeders that test would be pointless. Edited September 17, 2013 by Miles Quote Link to comment Share on other sites More sharing options...
beermanpete Posted September 17, 2013 Share Posted September 17, 2013 It sounds like the rear brakes are simply doing most of the stopping. Do the brakes work properly in a general sense? You may need to adjust the proportioning valve towards the front. Quote Link to comment Share on other sites More sharing options...
Miles Posted September 17, 2013 Author Share Posted September 17, 2013 (edited) It sounds like the rear brakes are simply doing most of the stopping. Do the brakes work properly in a general sense? You may need to adjust the proportioning valve towards the front. Beerman Yes, the brakes work in a general way, but not impressive either. Rears doing most of the work: I was just thinking the same thing this morning. I am using Hawk HP pads on the front with new rotors, but may not be getting the clamping force for some reason. I never expected the stock front and Maxima rear brake set up would be unbalanced - that is usually a problem when big vented kits are installed on the front. Just looking at the piston surface areas I would expect the balance to around 65% front and 35% rear with this combination. I'll do some test drives with PV set towards the front. Did test drive with PV set to front bias (knob all the way out). No change. Rears still hot. Edited September 17, 2013 by Miles Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted September 18, 2013 Share Posted September 18, 2013 Consider driving around for a while applying no brakes or almost no brakes. Coast to a stop. Check brake temperature. If rears are still hotter than fronts it likely isn't a bias problem but a dragging problem. I can't get good enough rear bite out of my maxima brakes to lock them first even with the PV allowing 100% pressure to the rears. The brake rotors did purple up with heat on my track day, so try are making some contribution just not much. The front pads and rotors were destroyed. Quote Link to comment Share on other sites More sharing options...
Miles Posted September 18, 2013 Author Share Posted September 18, 2013 Consider driving around for a while applying no brakes or almost no brakes. Coast to a stop. Check brake temperature. If rears are still hotter than fronts it likely isn't a bias problem but a dragging problem. I can't get good enough rear bite out of my maxima brakes to lock them first even with the PV allowing 100% pressure to the rears. The brake rotors did purple up with heat on my track day, so try are making some contribution just not much. The front pads and rotors were destroyed. I did that twice today. Once with the PV valve set to full rear and then again with the PV set to max front bias. The wheels still got hot. It is worse if I use the brakes normally. So the pads must be dragging. Even though the pistons glide in and out of the bore easily the seals must be hanging them up just enough to heat up the rotors. I see a lot of complaints about this type of caliper dragging/seizing up on the Nissan 240SX and Maxima websites. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted September 18, 2013 Share Posted September 18, 2013 I'm sure you have already done this and I'm just trying to help. Have you checked to make sure the master is fully returning and failing to let fluid return to the reservoir? My "maxima problems" got resolved by giving the pedal more travel (more on the return swing) and by removing the rear check valve in the master cylinder. You are a brake guy so I'm sure you already tried these things. After a year with Maximas, I'm replacing them with Wilwoods. Yes, they are easier to service than drums, but they haven't been good stoppers for me. Quote Link to comment Share on other sites More sharing options...
Miles Posted September 18, 2013 Author Share Posted September 18, 2013 (edited) Both the pedal and MC push rod are adjusted real loose. Pulled the check valve when I installed the MC. I am starting to think it is time to recheck the Wilwood master cylinder. In the last three years I have had two Wilwood MCs leak internally. The second one leaked out of the rear seal into the booster with less than 500 miles on it. Are you getting the AZC Wilwood kit with the parking brake? Edited September 18, 2013 by Miles Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted September 18, 2013 Share Posted September 18, 2013 Ok. I did have LOTS of trouble with Wilwood and tilton master cylinders on my clutch master. Some of them are bad out of the box. Mine would just slowly leak down with constant pedal pressure. Finally figured out it was bad by putting a plug in the outlet and seeing if it would hold pressure-it wouldn't. I freakin hate hydraulics. I am blowing off the parking brake. I did pay extra for the comparable bracket, but from reading posts, it seems like the AZC p-brake needs more development. I will just park it in gear in flat places and use a block on hills. I just wanna stop! I may also play a little more with my hydraulic handbrake. That sucker is kind of handy for staging. If I don't use it, I'm staging a little too deep and am more apt to red light. Quote Link to comment Share on other sites More sharing options...
Miles Posted September 18, 2013 Author Share Posted September 18, 2013 Have you looked at the Datsun Parts LLC rear caliper with intregal parking brake? Quote Link to comment Share on other sites More sharing options...
Miles Posted September 18, 2013 Author Share Posted September 18, 2013 Attached is a detailed flow chart that I have been using to diagnose rear caliper dragging problems. It seems complete. As a long shot, I have been considering checking out the brake differential pressure switch located under the master cylinder. If you look at the attached pictures it appears that the switch is designed to recenter itself (note springs at each end) once brake pressure is released. I don't see any mechanical feature of the switch that would lock it once it is activated. However, since the switch is over 40 years old the seals may have erroded allowing fluid from the front and rear circuits to leak/mix into the wrong sections of the switch. It may be silted up with dirt as well. Today I am pulling the master cylinder and the brake switch for inspection. If the switch is bad I'll replace it with a 3-way distribution block to connect the front brake lines. The rear brake lines can be joined with a metric union. To test that the return ports in the MC are not blocked I'll use a large syringe and force fluid back through the outlet ports and watch for fluid filling the tanks. Quote Link to comment Share on other sites More sharing options...
Miles Posted September 21, 2013 Author Share Posted September 21, 2013 The off-center rotor is being caused by either the custom Maxima caliper bracket or the position of the outer stub axle flange relative to the brake backing plate mount. I need to verify the dimension between the outer stub axle flange and the brake backing plate mounting face per attached picture. Quote Link to comment Share on other sites More sharing options...
Miles Posted October 9, 2013 Author Share Posted October 9, 2013 (edited) I found a reference to the dimension between the hub mounting point and the stub axle flange here: http://forums.hybridz.org/topic/4672-rear-disc-bracket-fabrication-some-comments-and-a-question/?hl=%2Bcaliper+%2Brubbing+%2Brotor&do=findComment&comment=35335 See post #2 in link above. The dimension is 45.2374mm or 1 25/32" on a stock 240Z. See attached picture. The dimension matches my hub to stub axle flange distance perfectly. So there is no problem with the stub axle position relative to the hub. This can only mean that the custom MSA mounting bracket was machined 1mm too thick where it bolts to the strut. The rotor is definately not centered in the torque member slot. The rotor is approximately 1mm closer to the inboard edge of the slot of the torque member i.e., the torque member is pushed outboard 1mm by the custom mounting bracket. Looks like I'll be returning the brackets. Edited October 9, 2013 by Miles Quote Link to comment Share on other sites More sharing options...
NewZed Posted October 9, 2013 Share Posted October 9, 2013 It's only a 16th but the guy in post #2 said 25/32" not 23/32". May not matter, just sayin'... Feb 2001. Pretty good detective work. Quote Link to comment Share on other sites More sharing options...
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