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Datsun 521 rear wheel cylinders


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I was just wondering why the rear wheel cylinders are twin piston and fronts are single piston? Would this then mean the rears would be getting better and more even grab on the surface area of the shoes in the rear drums? If so could you use a twin piston wheel cylinder on the fronts and also use the rear shoes so they fit?

Just curious.

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It has something to do with the fronts being "self actuating" If you google that, you might get a better answer. The fronts do 80% of the braking.....if the rears were actually a better setup, they'd be locking up all the time. You'd be far better off converting to discs up front.....but the front drums work just fine if you have them setup correctly with good components.

 

flat....I'm pretty sure he's referring to how the front only push out one side of the wheel cyl and the rears push out both sides. I'm pretty sure there's only one wheel cylinder in his rear brakes......but I could be wrong....Australian models were a bit different.

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Both front and rear drums ony have the one wheel cylinder but rear has a twin piston cylinder.

In googling I found this pretty in detail and interesting article about disc brakes

http://www.hotrodheaven.com/tech/brakes/

But also found this on self actuating.

http://auto.howstuffworks.com/auto-parts/brakes/brake-types/drum-brake1.htm

From what I can gather the rears are also self actuating.

My thought was they might have put a twin piston in because it being a commercial vehicle and the 1 tonne load capacity it has, to help the rear braking when it has a load in the tray. All the passenger cars I have worked on with 4 wheel drums normally have twin piston cylinder in the front drums and single in the rear. And my 1500 Fairlady had two single piston cylinders in the front, 1 top and 1 bottom, and a single in the rear.

DSC00250.jpg

DSC00249.jpg

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Those are normal wheel cylinders....same thing we have on all of ours. I'm thinking that the dual piston would have half the travel and pressure....helping to bias the braking since it was on a single circuit master cylinder.

 

 

GREAT links!! I'm definitely going to have to read the Dean Oshiro one completely! :)

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  • 2 months later...

hey guys sorry to thread jack but does anyone know the difference between 13/16 bore and 3/4 bore wheel cylinders? I just bought some 13/16 bore rear wheel cylinders from rockauto and the y pipe dont fit on new ones.

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I had good luck fitting rear wheel cyl. 3/4 or 13/16 isnt much difference.

Mine always fit. ck the part number.

However the taiwan or Italian made ones dont last 5 years.

 

if you have new washers you could use the old Y fitting to make you brake line

well I was planning on reusing the old Y fitting, the problem is the Y fitting has different thread size than the new replacement (Dorman brand). I don't get it. I have to call rockauto and see wtf.

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Just reuse the old Y fitting and if the new Y fitting had the new washers and use them.

 

he 521 front cylinders show a picture of the fitting but when I got them from Rockauto they didnt have the bleed screws or Y fitting . I called rockauto and they called the manf and no they do not come with them. I told them I only order those cause of the photo is was complete.

 

Maybe the cylinder you got was a later 620 type (which could be metric but Im not a 620 expert)

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I believe the difference between 521 rear wheel cylinders and 620 wheel cylinders is only the threads.
on a 521, the studs that hold the wheel cylinder to the backing plate are 5/16-24, on a 620 the threads are M8-1.0, or M8-1.25.
The flare nut fittings on a 521 are 3/8-24, on a 620 are M10-1.0. I believe the same thread is used for the "banjo" bolt fitting the brake line attaches to the wheel cylinder.

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  • 1 year later...

well, I still can't seem to get this going, i tried all the nissan dealerships and none offer y pipes, I tried a repair kit to only have it leak after I cleaned everything up and made sure it wasn't scored.  Anyone else have an option, is there a conversion I can run? or anything, I want my truck back on the road.

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