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Brakes lock after BANG!

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About once per two months, at very low speed in first gear, my Datsun pickup goes BANG and halts. It won't go forward, drive forward or roll forward until I back it up a ways. It rolls/drives in reverse fine.


Does this sound familiar to anyone? I looked at the brakes, they seem to be assembled correctly and not missing any parts. They work excellently.


Could it be the transmission? I'm not certain if it happens when i'm shifting to 2nd or what, it happens so fast I can't exactly pin down the details, but when freed up everything works fine. As I recall it only occurs when the engine is cold, having first started out. I've driven it 1000s of miles and never has it occured at speed.

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While this NORMALLY is something I'd suspect as being brakes, you should be able to overpower it. Generally a shoe that's too loose. But yours only has rear shoes and has front discs, right?


But it could be transmission. Or differential, though I would think either of those COULD happen at speed and would make a big bang followed by parts making their escape.

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Cold trans or diff oil is thicker and may scoop up a chunk that lodges either between the main and counter drive gears or the 1st and 1st counter drive gears.


Drain the oil and maybe it will flush out.

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I am going to put my vote on rear differential.


I say this, because my 510 did this to me with the original open differential. I would try to go forward, but it was as if I had the e-brake on. If I backed up it would make a growling type noise momentarily. Go forward again and thing would be fine. Ended up being a chipped tooth off the ring gear, just small enough as not to disrupt mesh, and not make it noticeable while turning the pinion.


I took the cover off and found that, and assumed that's exactly what it was, since it was slightly chewed up and marred, as were several other teeth on the ring gear. It was a high mileage (>400k) differential anyways, so I took that chance to upgrade to a Subaru Posi.


I'm just glad that it didn't happen whilst driving down the road, because it could have ended ugly.

The snapping sound you mention though, my stock 4 speed had a loud snap from time to time but I never could figure out what it was. You could definitely tell it was coming from the transmission, though. It didn't affect drivability. But, all the stock 4-speeds I used locked up in 4th gear and left me stranded somewhere. When I went to the 5speed, I never had that noise again.

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hmm ... yes it is front disc, rear drum

It won't go forward at all when it happens. I didn't try dumping the clutch but the engine doesn't overpower it. But maybe it's not the brakes at all. Next time it happens I will jack up each rear wheel and see if either turn.


The differential makes no unusual noises, ever -- but I can certainly check that out. I hope it's not that because it has a rare 4.11 gearset for H165.

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I hope it's not that because it has a rare 4.11 gearset for H165.


Yes the L18 automatic equipped 710 had them for the one year. Drain it and poke around inside with a coat hanger see if you can fish out anything.

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Not that long ago while backing out of my driveway my '80 720 rear axle locked up solid.

I pulled forward and backed up again, same thing.


I pulled the axles and dropped out the carrier, a ring gear bolt (half of one) was in the bottom of the axle housing.


No damage to the gearset, shear luck I didn't choose to try to drive it rather than open the damn thing up and look.


My bolt snapped off and left the threaded portion in the carrier, the factory lock tab was intact.


Our shit is getting old, metal fatique is common after 30 years - 38 years (or more)

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yes, i've had all four brakes off and inspected with no problems noted.


Thanks guys.


DRIVEN, that sounds like my symptoms to a T.


I will inspect the pumpkin since it is easier than the transmission, and if it's not the differential, I'll swap transmissions. I have a 5-speed I could put in to replace the 4-speed. Not that I need overdrive -- A-series love to rev all day long. I'd rather have the steeper 1st gear of the 4-speed.

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OK,. found it. It was the brakes.


Took the driveshaft loose, went to pull the left axle and saw this:




It's the 3rd time I've had the brakes drum off since it started, but didn't notice it before, maybe because the brakes work so well (usually) I didn't look close enough.


At least I'm hoping it is the entire cause. Time will tell.

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I was looking at the leaf very closely today. It doesn't seem to be wearing into the main spring. I'll keep an eye on it.



The brake return spring was kind beat up, and wouldn't stay in the top holes. I re-bent the hook and it went in. I'm fairly confident it won't fall it, but we'll see. Next time I'm at the wreckers I'll pick one up. Rockauto has it for $4, but with $9 shipping :no: It is the same return spring as 1982-1986 Stanza or 1979-1982 310.

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According to the 310 info, it's part number 2260 (UP) available out of California from NAPA. Just sayin' ;) Of course, there will be freight from California too. C'mon you cheap bastard, just buy some new springs! :D

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