ZF80A gearbox

[alan pragnell]

I have twin cummins with zf80 a gearboxes,port gearbos takes 1 minute to engage reverse,forward ok ,has electric 24v shift solenoids, test out ok and tried swapping still same ,decided to try swapping control valves over to starboard engine ,same problem but in forward gear ,due to opposite rotation ,still taking 1 minute to engage gear ,have removed and checked all removavable valves and springs ,nothing found .hard to understand why its 1 minute? Appreciate any ideas please.

Topic

[Clark Leighs]

Thanks Tony.

 

I was off base here.

[Tony Athens]

Transmission “Piston Rings”

Clark,  Just an FYI..

 

Most every type / make  of gear I have looked at uses the same method of sealing a rotating shaft to an inner fixed housing that pumps oil to thru the shafts and ckutches.. The “piston rings” or oil rings, or ?? as different manufacturers call them,  are all basically of the same design  Hardened and pricision ground steel,  and split/but interlocking..

[Clark Leighs]

I don’t know this gear at all.   

 

However if those 3 rings are allowing leakage from age then maybe the slow actuation is a result of the rings allowing leakage of the shifting oil OR the main piston clamping oil.

 

All O rings shrink over time and heating.   Maybe they have simply shrunk a hair to much.

 

Just a guess based on Tony’s emphasis on those three rings.

[alan pragnell]

Zf80A

Hi Tony ,No haven’t changed the 3 rings as yet because when swapping the valve body’s from one gearbox to the other the fault stays with the faulty valve block on both gearboxes.we have removed and checked every removable pistons and ports but everything seem ok.

[Tony Athens]

ZF80’s are quite old and most likely you have the early designed block & solenoids.. There was a reason they changed them down the road to a newer style………………………. Did you replace all 3 piston rings with new?

[alan pragnell]

Hi tony ,thanks for reply ,the solenoids are the 24v which i have tried exchanging and are all getting 24v when engaging forward or reverse ,when i change the housing from one gearbox to the other it still not engaging on same valve port.pressure tested both valve blocks, and both are showing 2 .4 bar . Very strange.im thinking possible internal crack in valve block?

[Tony Athens]

Did you bypass the shift control head and just put power direct to the solenoids? If not, try that. If that does not solve it, then repalce the 3 split delicate piston rings that you “see” or saw on the shaft when you removed the entire transmission valve assembly.

[Author]

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