Checking transmission oil level

[jco]

Hello,
When I check the oil level through the transmission peephole of my GTO, I have some difficulties to see if the level is right or not. There is a small dot in the center of the peephole, which is currently red, but I am not sure what this means.
Could anyone tell me more on that ?
Thank you for your help !
JCO

[Steve S.]

If you want to be super-accurate, I would just drain the oil and measure what you have.  If it has been recently changed and you want to re-use it just filter it first.  The correct amount should be 2/5 US Gallon, which works out to 1.6 quarts.
Hope this helped.

Steve S.

[jco]

Thank you Steve. That's just what I did a few months ago so I am now just checking to be sure I don't need to top up.
JCO

[Steve S.]

As long as you can see oil in the window you should be good to go.  Have fun!

Steve S.

[disc_valve]

I'd second Steve's comment - I don't think the red dot in the peephole means anything. I just reckon that if peephole shows oil when the engine is stopped then all is well. Once the engine is started, the oil level will drop out of sight, because the Clutch drive gear dips into the oil and sprays it around inside the transmissuion case.

There is one related point here, though. The oil level in the transmission case must be higher than that in the main gearbox, even though it's a common reservoir. When filling the gearbox, the oil first flows into the main gearbox chamber and then overflows across a weir (hole) in the gearbox wall to fill the transmission case. When the engine is running, the oil sprayed up by the clutch drive gear is captured and drained back into the main gearbox chamber. The peephole only shows the amount that's overflowed into the transmission case.

Now, both the transmission case and the main gearbox chamber drain out through the same drain plug underneath the engine, and it's important to fit a long drain plug here (the original is an inch or so long). The short drain plug used on the smaller Bridgestones will fit, but doesn't block off the drain feeds to the gearbox and transmission case, so the levels will equalise leaving the gearbox chamber short of oil. You wouldn't know anything was wrong until the gearbox got noisy, so it's worth checking the drain plug length on an unknown engine.

Graham

[jco]

Thank you Graham for this in-depth analysis... We learn a lot from you guys !

[BRT-GTR]

   To help understand Graham's and Steve's comments/ advise have a look at the cross section shown on Page 24, Part D of the Workshop Manual. There is a very simple but clever oil circulatory system built into the transmission on the GTR. The drawing is reasonably self explanatory, the Clutch driven gear being used to lift oil in the primary transmission case up to the oil baffle plate level where it should spread across the top of the main gearbox and fall onto the gears, returning to the transmission case as described by Graham.

I've never actually taken a baffle plate off and had a look at the top side, but will do so on a disassembled engine. It doesn't seem to have any rim on the top which would retain oil and encourage it to flow to the far side of the gear box. Maybe carry out a test to see how it performs. You do sometimes see significant gear fork blueing in the GTR box though running hot.

The drawing suggests the oil level should be towards the top of the peephole, once the engine has been run and the oil allowed to settle. You can also see the significance of fitting the correct length drain plug. The red dot is moulded into the outer window. Knowing BS there probably was a considered reason for it, maybe better contrast but it looks high tech and a bit fancier than a plain window.

Trust I've used the US terminology correctly. Brian the Brit