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Disc Brake Conversion on 71 521


MK4A80

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Hello,

 

So i have a 71 521 truck that i want to covert to disc brakes on front and rear.

I been searching a bit for recommendation on disc brake conversion, all i find is expensive kits.

 

Anybody out there has info on stock options from newer Nissan trucks. I don't mind going to bigger wheel.

Any help is highly appreciated.

 

 

Thank you.

 

FYI, im new to Datsun/Nissan so please don't flame me.

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Mklotz makes quality stuff but I believe his upgrade requires different spindles too.... http://www.bluehandsinc.com/

But you can fit under a 14" rim

 

Beebani is on ebay as Beebani1028 ...

He sells the brackets for 160, and fit under 15" rims..... 

 

Both require extra parts you need to buy...

 

Are you increasing the hp at all?

In all honesty you really only need to upgrade the fronts and switch to a dual master and you'll have all the brakes you need..... unless you just dont wanna deal with the rear drums at all.... 

 

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Mike’s kit requires D21 hubs, not spindles. It also requires that one corner of the stock spindles gets cut off.

 

Beebani’s brackets require D21 4wd calipers and Honda passport rotors. They bolt right on. New front lines need to be made to connect to the calipers.

 

I agree with Crash. Rear disc is nice, but not needed.

Edited by mainer311
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6 hours ago, mainer311 said:

Mike’s kit requires D21 hubs, not spindles. It also requires that one corner of the stock spindles gets cut off.

 

Beebani’s brackets require D21 4wd calipers and Honda passport rotors. They bolt right on. New front lines need to be made to connect to the calipers.

 

I agree with Crash. Rear disc is nice, but not needed.

The 1980 to 86 720 hubs ans also the78/79 620 disk brake hubs also work with Mike Klotz's kits.  The 78/79 620 and the 1980 720 hubs have the small centers and fit the stock 521 wheels.  The d21 hubs centers have to be turned down fot the factory 521 wheels to fit.

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With only one post we got to see if he is even qualified to fix anything.or modify ect.....

Otherwise if one has a stock 521 just tighten the brakes up is good enuff and dont cost much. Drive the speed limit and give 2 cars lengths when following

Yes they are better but most 521 owners dont keep the rig that long as most dont even last one your on Ratsun asone never sees them again

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44 minutes ago, banzai510(hainz) said:

With only one post we got to see if he is even qualified to fix anything.or modify ect.....

Otherwise if one has a stock 521 just tighten the brakes up is good enuff and dont cost much. Drive the speed limit and give 2 cars lengths when following

Yes they are better but most 521 owners dont keep the rig that long as most dont even last one your on Ratsun asone never sees them again

 

lol aint that the truth.  

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56 minutes ago, banzai510(hainz) said:

With only one post we got to see if he is even qualified to fix anything.or modify ect.....

Otherwise if one has a stock 521 just tighten the brakes up is good enuff and dont cost much. Drive the speed limit and give 2 cars lengths when following

Yes they are better but most 521 owners dont keep the rig that long as most dont even last one your on Ratsun asone never sees them again

 

Wow Hainz, super informative post. ?

They probably don't last a year on Ratsun because of posts like this.

Edited by mainer311
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Been here a long time most dont last long .Im just a realist on this part not to hurt him but really to get him to think, do I really need to do this? and prevent another 521 from going bad. Or he gets more motivated to prove me wrong. How many I seen, "My carb dont work right" so I pull motor for KA swap?well if you cant handle a Weber carb install then your not going to do a KA install.

Im not stopping him.Lets Wait and see.Maybe the 1st post should be a introduction and a photo of this truck to see where we starting at.Or is this out in the field next to a barn

Hes only the next town over from me.. Ill give 1 free HELP offer in PERSON if a L motor 521.  Which I have done many times. After that more than enough info is out there to keep a L motor running.

Now if this is a super clean beautiful truck then I might see hope as one who has money will more likely do the correct thing. Like Mr Bigtanker.Hes  done his truck  over years . This just isnt a one weekend adventure. If doing a dual masteror a single ect. SAE fitting and or Metric. Lots of stuff comes into play.

 

I can see doing the fronts as most stopping is about 80% front  and the kit is out there. Rear????????

 

 

 

Edited by banzai510(hainz)
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Both of you are right. Most projects never got off the ground floor. How many engine swaps have we all seen started but not completed? That kills me, because it's essentially deducting one good Datsun from the mix.

 

Simple upgrades like a disc brake conversion should be encouraged though, so I am with Mainer on this one too. Keep it positive...but realistic.

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The reality is they will both stop about the same and are limited by the tire's traction. I had a 521 and four 10" drums will easily lock up and stop you. The advantage of discs are you don't have to constantly adjust the drums to keep them at peak performance and you can (with practice, though it takes a lot of discipline in a panic situation) modulate a disc brake closer to lock up, without lock up, (human ABS) than a drum which are like throwing an anchor out. It goes without saying they are a lot less bother to maintain and replace than drums and will accept much more heat and are more fade resistant than drums, but the average driver, even the above average driver would never need this. How often are you going to panic stop from 70 MPH 5 times in quick succession?

 

So ask yourself how bad do I need these advantages? Make no mistake you will be impressed with disc brakes but there may be something more important to address first and this will be lipstick on a pig.

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If you use your 521 truck as a truck I would encourage having front disc brakes, if you want it to stop when going down hill for a extended period of time with a load I would encourage vented rotor disc brakes.

Fact is the reason I put 620 disc brakes on my 521 was because I was tired of doing a counter clockwise spin on the freeway during an emergency stop, and the way I drove back then I had a few of them, I put 620 non-vented rotor disc brakes on the truck and this counter clockwise issue went away, but then my 521 started hauling more and more weight over the next few years and I found a Hardbody V6 setup for sale on craigslist that would bolt right in(being sold by yello620), so I bought them and that was a great upgrade, each upgrade the brakes lasted longer while going down hill with a load of firewood, but I will admit that disc brakes are all right, but you really need power brakes to get the most out of them.

In the 24 years I have owned my 521 work truck, the L20b was by far the best upgrade I ever made,  and disc brakes was the 2nd best upgrade, and power brakes was the most dramatic upgrade I ever made although going from the L16 to an L20b was fairly dramatic.

 

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11 hours ago, wayno said:

If you use your 521 truck as a truck I would encourage having front disc brakes, if you want it to stop when going down hill for a extended period of time with a load I would encourage vented rotor disc brakes.

 

 

I was going to mention that exact thing. Discs are better at handling heat. I live in the mountains, and heavy, constant braking is common here even when just going to town. I use Hawk red pads on my daily driver (Dodge 2500 Cummins) just for that reason. Our family car also has vented/drilled/slotted rotors and Hawk pads.

 

Fact is, disc brakes are much easier to own, drive, maintain...and they work better under harsh conditions.

 

Drums work fine too in most situations, but I think we all agree on the cons of drum brakes.

 

I haven't brought it up here, but how about the complete balljoint front clip install? Better geometry, better bushings/joints, better brakes too. Lots of work though.

 

 

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Well since he only made 1 post, and was saying the brake kits were expensive I assumed he had a budget issue.....

I'd love to do the rear disc upgrade but I have other places to spend my money first.... the biggest reason would be I wouldn't have to adjust them.... 

 

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I rarely adjust my rear brakes as my pedal is always at the top, but maybe that is because of the front disc brakes, I can say this for sure, I had front disc(dual piston)/rear drum(dually axle) on my 521 with a modified 521 frame and even with a power brake booster it only stopped so well, but after putting my 521 cab onto a 1986 kingcab cab/chassis frame with the 1986 front brakes, using the same power brake booster/brake master it stops way better, so there is more going on than just keeping the rear brakes adjusted.

I did not have that all that extra brake stuff on my 521 frame/chassis that the 1986 frame/chassis has like the NLSV, so I do not know if that plays a part in the way better brakes I have now.

I think rear disc brakes on an old Datsun is good for bragging rights, but I do not believe it will make it stop that much better to warrant spending the money.

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2 hours ago, wayno said:

 but after putting my 521 cab onto a 1986 kingcab cab/chassis frame with the 1986 front brakes, using the same power brake booster/brake master it stops way better, so there is more going on than just keeping the rear brakes adjusted.

I did not have that all that extra brake stuff on my 521 frame/chassis that the 1986 frame/chassis has like the NLSV, so I do not know if that plays a part in the way better brakes I have now.

I think rear disc brakes on an old Datsun is good for bragging rights, but I do not believe it will make it stop that much better to warrant spending the money.

 

The 720 had bigger rear wheel cylinders?

 

After  Dec '81 the 720 rear drums were equipped with automatic adjusters.

 

The NLSV (Nissan load sensing valve) senses added weight in the back (actually it's a change in how level the frame sits between empty and heavy) which would increase tire traction and automatically sends more brake pressure to the rears. Something to think about if you lower the rear more than the front.

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I guess I did not word my post right Mike, my 521 work truck cab sitting on a heavily modified 521 frame/chassis had a Nissan dually axle in the rear and 1990 Nissan Hardbody(D21?) V6 dual piston calipers, it did not have NLSV, just a brake line going from the brake master to the rear drums.

Now my 521 work truck cab is sitting on a stock 1986 Nissan 720 kingcab frame/chassis, it has a Nissan dually axle in the rear and 1986 Nissan 720 single piston calipers(what it came with) in the front, using the same booster and master brake cylinder(1979 Datsun 620 dual circuit) this setup stops way better, but as mentioned this chassis has the NLSV, the difference is quite dramatic.

Even with my trailer which does have electric brakes, I suspect if a cop decided to stop me for some reason and I stomped on the brakes, if he was too close he would likely rear end me as the whole thing stops that fast, I was amazed the first time I stepped on the brakes, I would have thought the dual piston calipers would do a better job than the single piston calipers, but maybe the difference  is not that much.

By the way I changed the rear brake cylinders on my 521 work truck in the past and it made no difference, so either the NLSV is playing a part in this, which one needs to keep in mind that the rear of my work truck only squats a couple inches when loaded as I have a very stiff suspension, or the 1990 V6 dual piston calipers are not as good as the 1986 single piston calipers.

The dual piston calipers that were on the work truck are on my 521 kingcab now, I had non-vented rotor 620 brakes before, it stops just fine, but I do not normally haul loads or my trailer behind that truck, and when I do haul the trailer the trailer brakes do not work as I do not have the electric brake stuff in my 521 kingcab, but it still stops fine so the dual piston calipers are good, just not good on my work truck, by the way I believe that the 521 kingcab also has the 1982 version of the NLSV, I do not remove what these chassis have on them when I use them, I work with what I have.

 

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Dodge caravans had a lever on the rear axle to a valve in the brake line for this but not the Nissan one.

 

The NLSV is solidly mounted on the frame under the passenger side at a 10 degree incline to the front. Inside is a steel ball that can roll forward under braking and blocks pressure from the rear brakes. As the rear lowers from added weight the incline increases and the ball is less able to roll forward and more braking is applied.

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No it would be the same as level. Or close to level.... this is the minimum starting point. It only increases the rear braking if the front tips upward and the rear lowers. I guess the rears would lock easier going up a steep hill.

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I tend to delete the load sensing valve on my truck builds, and replace them with a manually adjustable valve from WIlwood. If the brake system is mostly stock, I may leave it in place, but I like the owner to be able to adjust them however he sees fit.

 

The Toyota LSV, which I'm sure is probably identical to the Nissan valve, uses a long, flexible actuating lever that is able to accommodate for bottomed out or topped out suspension travel, meaning that the valve only travels so far, but it will not get damaged if the suspension travel exceeds the valve travel.

 

When making ride height mods, I adjust the height of the LSV mounting point, according to the change in ride height. A 4" lift would get a 4" tab to relocate the mounting point on the axle.

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The Nissan ones (620/720) are bolted to the inside of the frame under the passenger seat. Not the same. And hard to bleed with front and rear lines and 3 bleeders (620 only) if you do keep it. I had to put a manual valve on mine as it was sitting 16" higher than stock and the weight transfer was incredible. Even average stops on dry pavement caused rear lock up and glares from the cars around you.

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