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1985 Nissan 720 4x4 KC rear brakes locked up


stingraylx1

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Truck has 43k miles original miles with original factory brakes.

 

Started truck( Parking brake was not engaged or in use ). Truck rolled about 4 feet and both rear brakes completely locked and truck will not move or drive even with RPM,s. Left in Garage, let sit 24 hours, truck moved 2 feet and again lock up on both rears with applying any brake pressure.

 

i have driven the truck about 1000 miles since buying it almost 2 years ago,  I did notice  the rear brakes dragged slightly when I drove it the first time, also the brakes seems to drag when I would drive it but would quickly release tension on right and left side rear drums. 

 

I left the truck in my Garage up north and will see if the hydraulic pressure releases next weekend.

 

Appreciate recommendations for troubleshooting the issue and the repair.

 

 

Thank you

 

 

 

 

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It's not the brakes.

 

1/ Put transfer case in neutral and try rolling truck forward and back but go at least 6-7 feet or one turn of the rear tire. If it will.

 

If it still jams you probably have something caught in the differential gears, pinion shaft fell out, spider or side gears broken jammed.

 

I don't think it the transfer case or transmission because you said you moved 4 feet. The drive shaft has to turn 4.1 times for one turn of the rear wheel. It wouldn't have moved that far.

 

 

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Does it roll in neutral?

 

If the pedal to master cylinder pushrod is not properly adjusted, it will not allow pressure release and can lock the brakes. Same goes for the clutch master. There needs to be some play between the pedal and the master.

 

One way to diagnose this is when it happens again, try releasing the pressure at the wheel cylinder. If fluid shoots out when you open the bleeder, then something in the hydraulic system is not adjusted properly.

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 Mine did that long ago.My driver side rear tire kept locking up.To unlock it.I would remove the black plug on the back plate and put a flat head screw driver in hole and turn the adjuster down to let tension off that cable.It was doing it real often.So I took it to Jack and he found the problem real quick.It was the emergency brake cable.It done rusted to the return spring.He got the last one Nissan had.Since there are regular cabs and king cabs,means there are 2 sizes. So remove the rear tire,pull off hub and remove cable and see if it is rusted and won't move freely.Ya'll probably think I don't know what I am saying.But this is what happened to my 720 long ago.Something different but 720s are full of mysteries.Ripley's Believe it or not. .Just pull that plug off and turn that adjuster down with a flat head,make sure you do it on level ground with no emergency brake on and in neutral.I did it so many times..I even have it wrote down on my Nissan manual.Turn adjuster down to loosen and up to tighten cable.Don't loosen it too much,it will come apart,then you will have to take hub off to put back on.You will feel the tension being removed when you loosen the adjuster..It will make a clicking noise as you are turning the adjuster.But it will tighten back up and lock again till you get a new cable and spring.

 

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Edited by Thomas Perkins
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Thanks for the input, I will check it this weekend. I currently own 3 720’s.

 

I bought a brand new one in May 83, a 1983.5 2wd for $5999.00 while in USAF. My first one ran with zero issues for 400,000 miles and I gave it away because I could not break it.

 

 My primary use 720 4x4 has 250,000 miles and keeps ticking. Just installed rebuilt TC, rebuilt Transmission, replaced all u joints and had the drive shafts balanced. Front and rear diffs are still are holding up.

 

This 720 4x4 is a Gem from Montana, 1 owner 43,000 miles and 100 percent original. No rust and all parts are original other than the selling dealer installed a new cylinder head when they received as a trade. It still even has the complete OEM emission’s installed and motor looks new.

 

I’m hoping Mike is not correct!!!

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Another common problem with drum breaks is they are confusing, which means that lots of mechanics don't get the assembly correct. Adjusters that are accidentally swapped side to side can also make shoes lock up. But that doesn't sound like your problem. Sometimes even the shoes can be installed incorrectly causing them to grab violently.

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Another problem I had long time ago when K-mart was still open and they had a Automotive shop.Who remembers's that.J.C. Penneys had a automotive shop,so did Sears and Montgomery Wards and foosball was still around.But any way,that was not long after I got my 720.That was in 94.Also Seen Pink Floyd's Division Bell tour in Atlanta that year.32 bucks for tickets.I was in need of some tires and rode by all them stores and K-mart had a sell on tires.They were kelly tires.The first set I put on there.They had a hour till closing and they had my 720 still in the air.So I went to see what was going on.They had both rear tires off and showed me that both wheel cylinders were leaking and leaked on the brake shoes, causing my rear brakes shoes to crystalize and all rear brake shoes were cracked real bad.They wanted over 300 bucks to fix.I told them to just put the tires on and I will pay for the tires and left and drove to Nissan dealer and bought me some new brake shoes and wheel cylinders.K- mart also stripped one of my wheel studs.I just got another from Nissan.They didn't have the blue light special that day.I had 108,000 miles on my 720 back then.Now I have over 381,000 on it.Never had to replace them wheel cylinders since then.I have put new drums on there though when I got the new driver side emergency brake cable and springs.Not much that I haven't replaced on my 720.Back then 720 parts were plentiful from the Nissan Dealer.I paid 3500.00 for my 85 back then.It had bald tires on it.

Edited by Thomas Perkins
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17 hours ago, stingraylx1 said:

Thanks for the input, I will check it this weekend. I currently own 3 720’s.

 

I bought a brand new one in May 83, a 1983.5 2wd for $5999.00 while in USAF. My first one ran with zero issues for 400,000 miles and I gave it away because I could not break it.

 

 My primary use 720 4x4 has 250,000 miles and keeps ticking. Just installed rebuilt TC, rebuilt Transmission, replaced all u joints and had the drive shafts balanced. Front and rear diffs are still are holding up.

 

This 720 4x4 is a Gem from Montana, 1 owner 43,000 miles and 100 percent original. No rust and all parts are original other than the selling dealer installed a new cylinder head when they received as a trade. It still even has the complete OEM emission’s installed and motor looks new.

 

I’m hoping Mike is not correct!!!

Show us a picture.

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On 8/28/2022 at 6:09 PM, stingraylx1 said:

Started truck( Parking brake was not engaged or in use ). Truck rolled about 4 feet and both rear brakes completely locked and truck will not move or drive even with RPM,s. Left in Garage, let sit 24 hours, truck moved 2 feet and again lock up on both rears with applying any brake pressure.

 

19 hours ago, datzenmike said:

Said he didn't apply the brakes, so unlikely they applied themselves after 4 feet. 

 

After '81.5 self adjusters were installed on the rears.

The original statement is confusing.

 

- with applying any brake pressure

or

-without applying any brake pressure

 

Misprint?

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Without, but now I’m second guessing myself.
 

The truck is sitting all week up north. My plan is to place TC and MT in Neutral and push the truck without touching brakes or starting the engine.

 

I posted a photo of the engine bay on my profile for Tommy, still need to read about posting photo’s on Ratsun.

 

Any other trouble shooting suggestions is appreciated, master cylinder, lines, brake proportioning valve and brakes are still factory original, hell the brake fluid could be factory. The truck has 43,000 documented original miles. The underbody is as clean as the engine bay photo I posted on my profile.

 

 

 

 

 

 

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A vehicle that has sat a long time can start leaking from the wheel cylinders, and that brake fluid can destroy brake shoes if sitting long enough. The brake shoes then turn to a fibrous mess and can get stuck in the drums. But once they are stuck, they usually don't unstick, so again, this doesn't sound like your problem.

 

Given your clarification, if it's not the brakes, it has to be some other mechanical interference, but what??? Mike said diff. That could be it. Cross-shaft broke and fell out. Spider gear blown up and lodged inside the R&P. Bad R&P with a tooth that gets jammed. Possible a bearing, but not likely. Driveshaft binding on something. Or even a messed up tailhousing bushing that's grabbing on the slip yoke.

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For now I discount the driveshaft and anything forward as this is an '85 with a 4.11 differential. Thus, the drive shaft would turn up to one turn before jamming and this would only turn the rear tires up to 1/4 turn or at most 1.7 feet. 720 tire circumference is almost 7 feet. Says he moved 4 feet before jamming.

 

If it is something jammed it should be easy enough to back it up a few feet, well maybe.

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20 hours ago, stingraylx1 said:

The Truck is not perfect but for 6 grand it was a great find.Yes,that was a steal for 6000.That would be a good down payment on mine.There is one on Ebay for 17,000 and not clean as your's.Mine is way better than that one on Ebay.Your motor look's new.I would keep it forever.I will never sell mine.20 ,000 couldn't get mine.Gonna get buried in mine with Pink Floyd playing Young Lust.

 

On 8/29/2022 at 11:27 PM, stingraylx1 said:

Thanks for the input, I will check it this weekend. I currently own 3 720’s.

 

I bought a brand new one in May 83, a 1983.5 2wd for $5999.00 while in USAF. My first one ran with zero issues for 400,000 miles and I gave it away because I could not break it.

 

 My primary use 720 4x4 has 250,000 miles and keeps ticking. Just installed rebuilt TC, rebuilt Transmission, replaced all u joints and had the drive shafts balanced. Front and rear diffs are still are holding up.

 

This 720 4x4 is a Gem from Montana, 1 owner 43,000 miles and 100 percent original. No rust and all parts are original other than the selling dealer installed a new cylinder head when they received as a trade. It still even has the complete OEM emission’s installed and motor looks new.

 

I’m hoping Mike is not correct!!!

Show us a picture.

Edited by Thomas Perkins
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Hi StingrayLxi.If you want to put pictures on this site and it says insert image from URL.Do want I did.Go to Imgur.com and join. It's free, then you can load pictures to it from your phone and computer and then you can send them here or anywhere else.This is what I did after I joined Ratsun.net.I just went on the internet and found it and have been using it for a year now.I can also load pictures here from my Library on my computer.I only used my phone once on Ratsun.I like using my computer better.I have a million pictures stored on it and I use my Kodak Z950 camera which it stamps the date on it.Phone's don't do that.Here are some boots I had put on when my front rotors and everything else was replaced.Rotors lasted over 350,000 miles.they were worn out.I sent these picture from my Imugur page.Got Rancho shocks front and back.iiL6DVY.jpgZFRAGjf.jpg

Edited by Thomas Perkins
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Thanks Tommy, appreciate the suggestion.

 

BTW, I have not lurked much on Ratsun for 720 content, working on a 620 so most time reading 620 content.
 

Great content and people, Datsun/Nissan’s are becoming very collectible, seems like younger generations appreciate Japanese simplicity, engineering and style. Toyota, Datsun/Nissan, Mazda, Suburu and Mitsubishi are appreciating big time. Take a peak at Bring a trailer past auctions. I regret not buying a mint 510 in the 80’s, but I could barely afford a New 720 for $5999.00 with 8.8 percent financing.

 

Your 720 looks great, I used to spend time on the 720 world.  I see you have completed many upgrades since then. Very nice paint job and the A/C conversion must be a very nice upgrade for the Georgia heat.

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21 hours ago, stingraylx1 said:

I added a photo to my profile of the newest edition 720. My other 720 kind of looks like yours.

 

How do you add a photo, is their a add attachment button? Check this price out on Ebay.It has been restored.Not original like yours.It doesn't have the power steering dust cap like your's.Mine had it at one time.https://www.ebay.com/itm/394203674720?hash=item5bc85eb860%3Ag%3A9jAAAOSwWApi-9vm&amdata=enc%3AAQAHAAAAoD43Oo4QHU2LlW73aRclME7sl%2FJK0%2BpXuHtIzZfFTQ%2BTEmMgXIpJW%2BkOkeud%2FfYxta6VxtmNksltO%2BFv5T%2Brp6nJavvHcMMDg%2BdDCuXHFPSii%2Bf24jrFuuAm38m0JW2jCTEhqSuiaxKHqQHTDRruiYJaIJ4lUEi7Wy24R%2BO1VfqBKs6qzF05%2FWAQtqc8OmzVMHs8xqp4ffy%2FNXoVOmg5z4w%3D|tkp%3ABk9SR-af1tjeYA&LH_ItemCondition=3000|1000|2500

 

 

 

Edited by Thomas Perkins
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