760 GLE Rear Axle Oil Check/Replace.

[griston64]

I was looking at 706 in the 740/760 catalogue https://www.gcp.se/en/catalogues/model/740-760-en/

[diccapilly]

Hello Dave,

Yes, I was confused about the oil filter and oil sump plug washer but I’m ok now.

I see what you mean by the self sealing tapered bolt, one less washer to have to consider.

Headings:-

Page 719 - Rear Axle Limited Slip Differential 1990.
Page 711 - Rear Axle Exc Anti-Spin 1988.

Thanks

Steve

[Laird Scooby]

Originally Posted by diccapilly

Hello Dave,

Yes, I was confused about the oil filter and oil sump plug washer but I’m ok now.

I see what you mean by the self sealing tapered bolt, one less washer to have to consider.

Headings:-

Page 719 - Rear Axle Limited Slip Differential 1990.
Page 711 - Rear Axle Exc Anti-Spin 1988.

Thanks

Steve

It might be one washer less to consider but you have to ensure the threads on both the plug and the diff cover are scrupulously clean - any grit will cause a leak!

[lynns hubby]

PTFE (plumber's tape) applied to the CLEANED thread will give peace of mind.

[Laird Scooby]

Originally Posted by lynns hubby

PTFE (plumber's tape) applied to the CLEANED thread will give peace of mind.

Sorry but i have to disagree with you there for two reasons. First is my experience of it being used in oily environments - the oil tends to cause it to decompose after a period of time and secondly, a listed "property" of PTFE to "creep" which could cause the tapered plug to become loose.

Both could cause potentially catastrophic results. I've also seen PTFE used to seal the ECUs CTS to prevent a leak - the CTS doesn't have a tapered thread but a tapered seat to seal it. Removing the tape and cleaning the area and the sensor restored normal operation of the engine (and economy!) and stopped the leak too!

There is another point that's kind of obvious and that is that the tapered threads are designed to seal as long as they are unobstructed (i.e. clean) and without any products on. The only thing i might consider using is something like Loctite 243 on the area of the thread where it actually seals, usually about halfway along - that would prevent the plug coming out accidentally but as i've already explained, if it's properly clean and tightened sufficiently, it will seal by itself.

Have another look at the pic i posted further up the thread of my drain and filler plugs :



The filler plug is on the right, it's fairly plain to see from the witness marks how far it goes in before going tight and sealing, about 4 threads in. If i was to use a thread locking compound, i would go round the plug on the 3rd thread to the 4th, making a single ring of compound - a complete ring, slightly overlapping perhaps but no more and definitely none on the "lead-in" threads to avoid getting any in the diff.

[lynns hubby]

[QUOTE=Laird Scooby;2656783]Sorry but i have to disagree with you there for two reasons. First is my experience of it being used in oily environments - the oil tends to cause it to decompose after a period of time and secondly, a listed "property" of PTFE to "creep" which could cause the tapered plug to become loose.


Well I have to disagree here on both your counts. PTFE tape, up until fairly recently was used exclusively on various instrument fittings etc in the petrochemical and oil and gas industry both on and offshore to seal threads on tapered fittings, NPT, BSP etc. In most cases these fittings are subject to various chemicals and most certainly various oils etc at pressures up to and sometimes beyond 3000 PSI.
The primary reason for using the tape on fittings is that the fittings are tapered but usually made from 316 stainless steel or various molys and this has a habit of picking up or galling when attempting to unscrew. The PTFE tape is used to coat the threads to prevent this happening.
These fittings NEVER become loose if tightened correctly.
I do however agree that the design of the thread is that seal should be achievable by the "taper" of the thread.

[Laird Scooby]

[QUOTE=lynns hubby;2657123]

Originally Posted by Laird Scooby

Sorry but i have to disagree with you there for two reasons. First is my experience of it being used in oily environments - the oil tends to cause it to decompose after a period of time and secondly, a listed "property" of PTFE to "creep" which could cause the tapered plug to become loose.


Well I have to disagree here on both your counts. PTFE tape, up until fairly recently was used exclusively on various instrument fittings etc in the petrochemical and oil and gas industry both on and offshore to seal threads on tapered fittings, NPT, BSP etc. In most cases these fittings are subject to various chemicals and most certainly various oils etc at pressures up to and sometimes beyond 3000 PSI.
The primary reason for using the tape on fittings is that the fittings are tapered but usually made from 316 stainless steel or various molys and this has a habit of picking up or galling when attempting to unscrew. The PTFE tape is used to coat the threads to prevent this happening.
These fittings NEVER become loose if tightened correctly.
I do however agree that the design of the thread is that seal should be achievable by the "taper" of the thread.

It seems we have slightly different experiences then, a lot of the time when i saw it disintegrated it was also in close proximity to a lot of heat, ~300C which is above the 260C point where the PTFE starts to break down. That said about 15-20 years back when i used to go into a refinery fairly frequently, they wouldn't let PTFE be used. The area i was most concerned with didn't need PTFE tape anyway so wasn't a major problem for me. I've also worked on systems that recover methane from landfill gas systems and again, it was a no-no there at the time.

That said, the two points we definitely agree on are the two most important here - the fittings don't become loose if tightened correctly and the seal should happen due to the intrinsic design of the thread.