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510 rear disc conversion brake issues/problems


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I just installed Beebani rear brackets, 200sx rotors, and maxima calipers on my '69 510. I bought this stuff used at a swap meet from a reputable source who said he removed them from a customer's car and that they worked fine. The discs still had cross hatch on them, and the pads appeared to be new. I made new rear brake lines; one stainless hardline over the differential, and two stainless steel braided lines running the length of the trailing arms. I wouldn't have made new lines unless I hadn't cracked one of the original hard lines while removing the old drums (at that point, I decided on all new lines). Also, I installed the calipers on the underside of the rotors so I would be able to keep my parking brake and re-use my stock 510 p-brake cables. I bought aluminum ferules and steel hitch pin bolts that I can cut down to connect to the parking brake hooks on the calipers.


First issue, the calipers weren''t centered over the rotors. I used 5mm washers between the bracket and the calipers to get some clearance, as the caliper's fingers on the non piston side looked to be rubbing the sides of the rotor (on the outer side of the vehicle). I believe a 10mm washer would be ideal, but I'm not comfortable doing that because it would put more stress on the mounting bolts and there would be less surface contact area between the calipers and the caliper brackets.


I then bled the rear (rear pass, then rear driver side, then back and forth several times), then bled the fronts, then bled the master cylinder, front then rear. I did unbolt and place the rear calipers on the upper sides of the discs so the bleeder screw was at the top when I was bleeding the brakes (I heard that mounting them under the rotors could lead to air being trapped in the calipers).


Problem: The brake pedal will go to the floor and the brakes don't grab when I try to stop. However, if I pump the brake pedal once to the floor and then immediately hit the brakes again (while driving) they "pump up" and work like they should (i.e. about an inch, inch and a half of travel and firm pedal pressure). After they're pumped up, I can hold pressure on the brake pedal and there's no loss or brake sponginess. After a second or two of non-use (I let off the brakes completely), the brake pedal will go back to the floor and needs to be pumped once before I have pressure again.


It feels like the pistons in the rear calipers are backing off too much, and I have to pump the brakes once to get the brake pads back onto the rotor again so I get some brake feel. I changed the brake pads in the rear just in case they were worn down (which they weren't, actually the new pads looked marginally smaller than the old ones, haha).




1. Is my symptom a result of bad brake bleeding technique? I'll try bleeding the rear system again tmw with a vacuum pump instead of a helper working the brake pedal.


2. Do I need a larger M/C to go with the maxima calipers? I currently have a stock 3/4" Tokico master, original to the car I believe. Would going to a larger M/C upset the balance to the front brakes (stock 510 discs and calipers). I do not have a proportioning valve.


3. Do I need a metering valve to keep the rear pads in contact with the rotors?


4. When installing rear discs on a 510, is everyone re-using their stock 3/4" M/C??


Thanks for all the help everyone, I'm stumped and frustrated (which appears to be quite normal for a Datsun owner, hahaha).

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Disc brake pistons do not back off when you release the peddle. They are always in contact with the rotor. The master has a small residual valve that keeps several pounds of pressure in the lines to keep the pad gently against the rotor to keep them clean. Sounds like you have air in the lines still. Did you change the master to one used for rear disc brakes like from a zx ?

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Sorry, not Beebani brackets but Compression's. I read through so many threads about disc brake conversions last night before my post I confused myself.


Datzenmike, I did not switch master cylinders because I did not read or hear anywhere that this was necessary when doing the rear disc swap. I'm hoping that other people who have done the conversion can chime in here so I can get a better idea of what's going on with my brakes.

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I'm not trying to throw anyone under the bus here, or make complaints or accusations. I'm just going by what I've been told by the seller I bought these parts from. Datto mentioned he had to pump his brakes for a while after his conversion, anyone else?


Also, did anyone change their M/C to something larger? Just trying to see what problems/ workarounds other 510 owners have had when switching from drum to disc.



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Compressions brackets did not fit perfectly on my car, actually! :) We talked about this at the time. Solution was two common flat washers, which spaced it perfectly. Apparently most 510s are correct, some aren't. I'm also using control arms from a 610, which are interchangeable according to hollander. I suspect there is some difference in between rebuilt calipers.


Either way, mine work fine, BUT I did have a bitch of a time bleeding the brake system when I converted. Ran into the same problem. I think air bubbles like to hide in new calipers. What I did was pump the pedal like a jackrabbit on speed multiple times, then hold it. Did this sequence quite a few times and finally knocked some air loose. This was after regular bleeding, pressure bleeding, and cursing many many times. Just was a real bear to get the air out of the system.


Oh, and I see you have a Toyota. That might be the cause of the problem. Just sayin' :D

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The bleeder screw must be at the top or as close to the top as possible to let the ait out. Check and see if you have the calipers switched side to side. Will switching position the bleeder higher???



Valid point on the bleeder location.


From what motoliam has posted I think he has the bleeder at the high point when he was trying to bleed the system. He noted that the calipers were mounted below the control arm, which is a popular location to utilize the factory e-brake cables, but to bleed the brakes he had removed and rotated the caliper to where the bleeder was at the top.


He also mentioned that he has the stock 510-3/4" master. This is likely a big part of his problem and if he has upgraded to 280ZX fronts (not noted, but I bet he has) then likely that is all of the problem and a change to a 280ZX-15/16" MC will fix it (along with another good bleeding). :D


Below is a picture from EDP's (Compression's) webpage showing an under mounted caliper.


EDP Webpage Link: EDP - Engineered Datsun Products



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Great info so far guys :)


I'm running stock 510 struts and brakes up front, and the stock 3/4" M/C. I believe I've narrowed the problem to either air in the lines, or rear calipers that need more fluid volume to be pushed. The reason behind this thinking is that the brake pedal is firmer when the parking brake is applied, and also the brake pedal pumps up (throw is cut in half for full pressure to be applied) after one pump. If I leave the parking brake on it engages solidly, but within an hour the pressure fades and the car will roll slowly downhill. I park on a rather steep incline, so parking brake is a must for warming up the car.


If the parking brake cable is pulled tight (preloading the calipers), then the M/C doesn't have to push as much fluid to get them to activate. One comment made earlier had me scratching my head - Brake pistons do retract, it's inherent in the design. Not by much, granted, but they roll their seal when they push out, and the seal rolling back is what causes the piston to sit back into the caliper.


I am reluctant to switch out M/C's to something larger simply because I value the front brakes so much more than the rears. If I were to switch to a 13/16", 7/8", or 15/16" (as someone suggested above), my pedal push would become harder and I think I would lose a little of the braking feel when I'm close to the limit. I do Autox this car, and I'm always screwing around when I daily drive it (heel/toe downshifting, breaking the rear loose on corner entry and on power exits). If I was just commuting with it, this wouldn't be so much of an issue for me and I'd simply bleed it every weekend for the next month or until it started feeling consistent. Right now, it's consistently unacceptable to me, haha. One pump and then my brakes are where I want them.


I have tried my darndest to get the calipers as high as possible on the car, but there are other higher spots within the brake line system. I crafted a SS hard line over the LSD, and the t-fitting/junction box for the rear lines is also higher than I can get the calipers. I would have thought that a 3/4" M/C would push enough fluid to the rears that I wouldn't have to worry so much about air being trapped in solid lines, but some have noted that the calipers are notorious for holding "tiny bubbles" (sing it like Don Ho). I've used a helper to pump the brakes and hold while I bleed. I've used a vacuum pump, and also preloaded the pedal with a short baseball bat (my high tech fender roller), and bled the system. Now I'm considering using a reverse bleeding method by pumping fluid through the lines from the caliper side. Does anyone have experience with this technique?


HRH, thanks - I used the same solution - 2 5mm washers did the trick.


Dave, I used your extended wheel studs as the excuse for why I installed this rear brake set-up :) That, and I bought the entire kit for dirt cheap. I wish I'd taken the time to chuck up the studs in a lathe and chamfer the ends . . . . for that extra sexy touch. Perhaps when the car is down for a motor swap next year.


Thanks again everyone.

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Too small a master will result in too much peddle travel ( spongy ) but easier to apply brakes. A larger master will reduce peddle travel but increase effort. It will feel like stepping on a brick. Put a 210 or 620 vacuum brake booster behind the master and this will reduce the effort on a 15/16" diameter one. I used to poo poo power anything but the advantage is reduced fatigue. Simply put, more braking with less effort.

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Here is another thought (I do not know this as fact and it is purely conjecture). The 510 master is designed to work with drum rear brakes, likely there is no residual pressure valve in the rear circuit.


Disc brakes, while they do not have springs to retract the piston/pads, they will retract to some degree. The piston retraction is caused by the seal distorting as the piston moves. Let off the brakes and this seal distortion relaxes and the piston retracts ever so slightly to keep the pads from being in constant contact with the rotor. If there is no residual pressure valve in the system, there is nothing to keep the pistons from over retracting or possibly getting pulled back too far by the e-brake system.


Too much piston retraction will leave you with a long first pump on the brakes to put the piston back into proper position. If there is no residual valve in the 510 MC rear circuit, then the pads/piston could be moving too far away from the rotor. This might explain the shorter pedal travel when the e-brake is applied.


Just some ideas that would need investigation.

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Dave, I believe you are referencing a metering valve. I had read that drum rears would have a 10psi valve, and a disc would be 2psi residual pressure. Either way, it is something I'll have to check out further when I have more time.


I have driven about 2 tanks worth, and the brakes are feeling better and better with less initial sponginess and do not really require a big push to pump up the system. Maybe the pads are wearing flush to the rotors? I don't know why it's getting better, which stumps me even more.


I won't have time to pull the wheels and re-bleed until Sunday afternoon. I'll let you all know how that goes.

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You ae correct that the drum circuit has a higher residual pressure, not none as I indicated.


It appears that the higher drum residual pressure will hold too much pressure on a disc caliper circuit causing them to drag, heat, expand and eventually lock-up the rear brakes. There is a thread on the 510 realm that addresses the issue and offers a solution in changing out the residual pressure valve to a lower pressure valve suitable for disc brakes.


Here is the link:



The residual pressure valves are located in the bottom of the master cylinder. The large hex nuts that the brake lines screw into hold the residual pressure valve systems into the master.


I think the metering valve that you mention (if its mounted to the driver's side front inner fender) is the brake warniing switch. There is a wire that goes to it and both front and rear brake circuits are plumbed thru it. If one side of the braking system fails, it pushes an internal plunger toward the failed side and this throws the switch to illuminate the brake warning light.

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Just an update, since I have been driving for a few hundred miles (SF city streets and freeway). The brakes feel great now, though there's still a tiny amount of mushiness on the initial push on the pedal. My thoughts are that the pads are bedding in, and actually seating correctly against the rotors (previously, there wasn't as much contact between pads and rotors, maybe 30-40%). As the pads are squaring up, perhaps I have to push less on the pedal to make full contact and have some strong brakes? And they are stronger for sure!


I can lock up at will, tested going down hills and such. Overall pedal travel has been reduced when compared to the same set-up I had with drum rear brakes. The difference is enough that I can't heel/toe the same way because my ankle doesn't bend that far! I'm sure I simply have to adjust the rod under the brake pedal to get back to where I was previously, and balance out the pedal heights when I'm hard on the brakes. Not sure if it's related, but I have managed to warp the right rear rotor slightly, and I hear it making squaking/groaning sound (like a seal) when I'm rolling at slow speeds. No pulsing at the pedal however, so I'm reluctant to pull everything apart and re-surface the rotors (15 bucks a pop here in the city). But, I did order some new rotors from Rockauto just now (easier and faster to swap out rotors at one time, rather than take apart, wait, etc).


About the residual valves, I've been doing my own reading, also. Thanks Dave for the good link. I haven't detected any rear caliper heat issues or locking up over time (driven two hours now, using brakes often in the city). I will be keeping my eye on it, though.


So, in conclusion (thus far). I'm happy with the braking performance I've got at this point. It's better than when I was running rear drums, but I couldn't tell you what the weight difference is between the two set-ups because I unfortunately didn't weigh all the pieces before assembling them. It's more stylish, at least on my style of wheel I can see the sheen of the rotors through my spokes, which is a nice touch. I'm still using the stock M/C, so not having to change that out after the fact is a plus, I have less pedal travel than when I was running drums (just barely, almost not noticable), and it's firmer than when I was running drums.


If I do experience any issues with rear brakes locking up, or whatever, I will post in this thread for sure. Thanks everyone!

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The difference is enough that I can't heel/toe the same way because my ankle doesn't bend that far! I'm sure I simply have to adjust the rod under the brake pedal to get back to where I was previously, and balance out the pedal heights when I'm hard on the brakes.




There should be about 2 to 5mm of play or travel before the push rod actually pushes on the master pistons. When the brake peddle is released, the pressure in the lines pushes the master pistons back to their rest position. When the piston moves back it uncovers an opening to the reservoir and any excess will flow back into it. If there is no peddle play the piston can't return and pressure is trapped. Every time the brakes are used more pressure is trapped until the brakes lock up.

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Mike, I think you've misunderstood me again. When I'm hard on the brakes now, the brake pedal height is so high I can't reach the gar pedal with the heel of my foot to blip the throttle and downshift smoothly. I can adjust the brake pedal so that it's closer to the floor.

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  • 2 years later...

I know this topic's been dead for 3 years now... but hoping Motoliam is still active so I can inquire about whether or not his rear brakes every locked up/heated up. I'm doing the 200sx rotor and maxima caliper conversion myself on my 72' 510. Just wondering if the increased residual pressure ever caused problems. I've upgraded to 280zx front brakes without any problems, so I'm asuming the rears will be ok as well. I'm also hoping I wont need to install a proportioning valve, though I will if they don't perform to my expectations. I'll continue browsing through rear disc conversion threads for info.


Any thoughts on whether or not a proportioning valve with 280zx fronts and maxima rears would be necessary? I've got the stock 510 MC

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Any thoughts on whether or not a proportioning valve with 280zx fronts and maxima rears would be necessary? I've got the stock 510 MC


I wouldn't be surprised if you have to get a proportioning valve with the stock 510 MC.


I have 280ZX front brakes, Maxima rear calipers with 200SX rotors, 15/16" 280ZX MC and the brake balance is great.

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Proportioning balance has zero to do with the master cylinder. It has everything to do with the relative stopping power of front vs rear brakes. ZX front a Maxima rear will be fine at lower braking forces. But the real test is with panic braking and loading the car with stuff in the back.

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You're right.  :blush:  I always post in a hurry.. jeez.  However I've heard from ppl with 280zx/maxima brake setup that they lock up the rears quite easily, then again who knows how they have their car setup.  

If you run the stock MC, remove the residual valve.  Also you'll have to hit the pedal harder with the stock MC.


You should only need a proportioning valve if the rear brakes are locking up... if you look at the size of the 280ZX calipers vs. the Maxima calipers (and the brake pad size difference) , you'll see why this shouldn't be an issue.


At low speeds (below, say 40 mph?) my fronts will lock up before the rears.  At higher speeds the balance is great, I can trail brake real nice into turns without the fronts locking up.  If my 510 was a dedicated track car, I would probably be trying to get more rear brake force.  I've had to do a couple panic stops on the freeway with the rear drums as well as with the Maxima setup.  With the drums I had a few close calls.... with the Maxima setup I barely have to use the brakes.  But again, it all depends on how you have your car setup (alignment, suspension setup, tires, etc) 

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