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Gearbox leak


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Had a serious gearbox leak on my PRM150 a month ago. It turned out to be the O-ring rubber seal where the gearbox cable lever is attached  - quite common I understand.  However ever since the gearbox has continued to "weep" oil and on big lock days can lose 100ml of oil. I check and replace oil daily.  Are there any thoughts on using gear box additives which are supposed to seal up small leaks like this? Or might I need to have the the O-ring seal done again? 

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16 minutes ago, Paolo Reale said:

Had a serious gearbox leak on my PRM150 a month ago. It turned out to be the O-ring rubber seal where the gearbox cable lever is attached  - quite common I understand.  However ever since the gearbox has continued to "weep" oil and on big lock days can lose 100ml of oil. I check and replace oil daily.  Are there any thoughts on using gear box additives which are supposed to seal up small leaks like this? Or might I need to have the the O-ring seal done again? 

 

Have it done again, but properly this time- suggest you use a different 'mechanic' as the former one doesn't seem to be capable of doing the job.

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How was the leak traced to the o-ring on the gear selector? Was it actually seen weeping from this point, or was it just assumed to be from there? Is it certain the current leak is coming from the same point and not just assumed to be.

I am wary of any sort of oil additive that is supposed to magically make a mechanical thing better. Usually sold as a resort to someone with a banger that is one step from the scrap yard in an effort to keep it going and a proper repair can't be afforded.

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1 minute ago, Jen-in-Wellies said:

I am wary of any sort of oil additive that is supposed to magically make a mechanical thing better. Usually sold as a resort to someone with a banger that is one step from the scrap yard in an effort to keep it going and a proper repair can't be afforded.

 

Sorta like sawdust in the gearbox just before you go to 'we buy any car' ?

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Have it done again, just make sure that the correct size O ring ( imperial 000 series I think from memory) is used and not a metric close size substituted

It is very easy to scratch the spindle removing the old seal so a flattened brass brazing rod is best. These gearboxes are well made with only the shaft seals or loose drain plug being your other leakage points.

The forward/reverse spindle and output seal are easy to check visually. Input seal with give leakage from the adapter housing. 

Drain plugs are easy to cross thread or overnighten and hence strip thread.

Do not add any magic sealer as the clutch plates rely on the correct oil to prevent slippage and rapid wear

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Speaking from experience, PRM 150 hydraulic gearboxs tend to leak from the output flange oil seal, it is commonly seen when the engine is out of alignment to the prop shaft or if the engine mounts are "on the way" as it were, the extra movement from the engine itself during operations could pull the shaft and flange out of alignment.

Its a simple seal to replace but it would be a good idea to have the engine alignment checked before and after the seal is done.

 

It would also be worth noting that oil additives that can be bought, most commonly "Stop leaks" formally know as, seal swell component additives will damage the internal clutch plates of the box since the hydraulic pump that pumps oil into the hydraulic clutches to engage forward or reverse gears will destroy the component compound and eventually block up the internal oil passages.

 

I have known these boxes to also leak from the input shaft oil seal but its rare, since this shaft is not only supported by two internal thrust roller bearings, its also got the drive plate from the engine to absorb shocks and in the end the drive plate breaks before the box providing a fail safe and avoid damaging the box internally.

 

As for the gear shifter oil seals, these when fitted normally need to be greased with high temperature grease when fitting the seal and the shaft, this grease helps fitment and also prevents damage when fitting the shaft as fitting dry rubber seals can crack and even chip if installed incorrectly in the housing.

Same goes for the input and output shaft seals.

 

 

Mr L

Edited by Mr Lister
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Also the bolts that secure the pump to the back of the box, ''the round thing'' next to the output coupling. There are I think 6 bolts, a couple of which penetrate into the boxes oil space and often leak oil. They have copper washers under their heads, these compress a bit and the bolts can become a touch slack. Tightening the bolts a touch often stops the leak, or fit new washers or anneal the old ones, remove one at a time to do this.

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Check that the remote operating cable is not pushing the gear lever on the box hard against the end of its travel - there should be a couple of mm remaining travel when forward or reverse gear is selected and throttle applied. To do this (with engine stopped) push the morse lever to say about 1/2 throttle ahead, then disconnect the cable at the gearbox end to see if the gearbox lever was being pushed hard against the stop or not, repeat for reverse.

 

If the gearbox lever is being pushed hard against the stop this puts a radial force on the shaft which, with a bit of wear, moves it sideways and away from one side of the O ring, causing a leak.

 

This is covered in the installation manual but it seems most installers don’t read the manual!

Edited by nicknorman
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52 minutes ago, nicknorman said:

Check that the remote operating cable is not pushing the gear lever on the box hard against the end of its travel - there should be a couple of mm remaining travel when forward or reverse gear is selected and throttle applied. To do this (with engine stopped) push the morse lever to say about 1/2 throttle ahead, then disconnect the cable at the gearbox end to see if the gearbox lever was being pushed hard against the stop or not, repeat for reverse.

 

If the gearbox lever is being pushed hard against the stop this puts a radial force on the shaft which, with a bit of wear, moves it sideways and away from one side of the O ring, causing a leak.

 

This is covered in the installation manual but it seems most installers don’t read the manual!

 

Absolutely.

 

Off topic but this is one of the reasons the throttle spindles leak on DPA injection pumps (BMC 1.5, 1.8 etc.).

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