G50 Gearbox Oil Level

[Dimi]

Hi All

After having no answers to the question of how much oil should be in a G50 Transaxle I decided to make a concerted effort and find the real answer.

After looking at how the oil sits in a standard G50 Transaxle in relation to the gears and the crown and pinion gears and after making up the mods to my
G50 shown in the picture I now have some real idea as to where the oil level sits in the box depending on how much oil is put in.

I made up some fittings and used the existing sump plug hole for the lower and for the the top fitting there was an existing bolt beside the filler plug that just goes through into the box but doesn't serve any other purpose and was perfect for my need.

I then attached some clear oil and petrol resistant hose to act as a sight glass which allowed me to physically see the level of oil being filled into the Gearbox.

The first horizontal strengthening web up from the bottom of the gearbox is where the oil sits at 3 Litres.
The second horizontal strengthening web up from the bottom is the where the oil sits at 5 Litres.
Four Litres is exactly halfway between the two webs.

Five Litres allows half the crown wheel and pinion to be immersed in oil and is just below the side output flanges.

An allowance would have to be made in the individual situations as mine is fitted with LSD and this would alter the amount of oil although only minimally.

This sight fittings will remain on my car permanently as a guide to the amount of oil and also when the colour changes to dark and dirty it will alert me that an oil change is required.

I decided to do this based on the number of questions being asked and no definitive answers and my for my own peace of mind.

At least now I know how much oil and what level it sits at in the box.

Dimi

[EGLITOM]

Dimi

great help for all of us G50 users.

But how many liters are you putting in now ?

Thanks
TOM

[Craig White]

Thanks, that is really interesting.

For G50, I've always been told to put in 3.5lt if changing the oil. Assume this takes into account that there is still a little of the old oil remaining in the transaxle.



A popular choice locally is Castrol Syntrax 75W-90 oil. That's what I have been using. This is for non-LSD.

[Dimi]

Hi Tom

As per the level of the sight tube I am running 5 Litres.
That ensures that the gear shafts have enough oil but most importantly that the crown gear and the pinion gear have enough lubrication.

Dimi

[Craig White]

Dimi, just grabbed this info that Lynn L posted some time back.

"It seems that best way to get it at the right level, is to pull (or loosen) one of the output flanges and fill until the oil leaks out of the opening. (retorque to 19-22 ft.lbs. for '72+) This will get enough oil in the gearbox to adequately oil the diff gears/clutches (the ring gear will dip into the oil and spray the pinion at much lower levels.)"

It looks like your level is higher than that from the photo.

Not sure of the consequences of this.

[Dimi]

Hi Craig

The level in mine is actually just below the lower edge of the flange.

I personally do not want to have to remove driveshafts & flanges just to fill a gearbox

The big advantage of the sight tube is that it enabled me to get some physical reference levels with regard to the gearbox and the quantities of oil.

Up till now Everyone and myself included have had no idea what level the oil came up to if you put in 3,4,5, Litres

The lower strengthening web on the box shows where the level is in the box with 3 Litres and the second web with 5 Litres.

This now gives everyone a reference point for those quantities.

It now allows you to know that those quantities of oil will fill the box up to that level.

How much oil anyone fills their gearbox with is up to them and what they feel is suitable.

At the end of the day I know I feel comfortable knowing where my levels are and not having to rely on guesswork or having to resort to dismantling drive shafts and flanges just to see if there is enough oil.

A gearbox oil change should be a simple easy procedure not one that requires dismantling of components.

Dimi

[Craig White]

Dimi, I agree, it's fantastic what you have done. I feel that you might have got the wrong idea from my posts.

It's just that 5lt is a lot more than the 3.5lt that quite a few of us have been using when these boxes have been inverted.

So just wanted to confirm levels.

I've got to change my oil soon, so will be interesting to see how much I drain out of it. I've got a G50/03.

[Dimi]

Originally Posted by CraigW

Dimi, just grabbed this info that Lynn L posted some time back.

"It seems that best way to get it at the right level, is to pull (or loosen) one of the output flanges and fill until the oil leaks out of the opening. (retorque to 19-22 ft.lbs. for '72+) This will get enough oil in the gearbox to adequately oil the diff gears/clutches (the ring gear will dip into the oil and spray the pinion at much lower levels.)"

It looks like your level is higher than that from the photo.

Not sure of the consequences of this.

Craig
Even going by the above quote from Lynn L if the box is filled up to the level Lynn suggests this would mean the box is holding 5 Litres as shown by the sight tube.
Remembering that the flange shaft where it enters the box is higher than the bottom edge of the flange that the driveshaft is bolted to.
Dimi

[Big-Foot]

Nice work!

I just hope that the tubing you used is up to the constant abuse of heat as the gearbox oil can reach a constant state of 300* F.

[Russ Noble]

Good work Dimi,

That now gives everyone a reference point.

The interesting point now is what is the RIGHT level. We all know the effects of having insufficient lubrication can be rather severe, but at what level is that likely to occur?

IMHO you have to remember that in use the the gears are spraying oil everywhere inside the housing and oil will be draining back into the bearings and giving them plenty of lubrication anyway. And this will occur with a lot less oil than most people currently use.

Are there any experts there who know the effects of running too much oil in a transaxle? Wanni has alluded to the effects of hydraulic pitting when gears are sprayed direct into the tooth mesh. IMHO with a high oil level and the fact with the flippped trans that the ring gear carries the oil almost immediately into the mesh, rather than going through 3/4 of a turn first as in the original configuration I feel there is a similar scenario for hydraulic pitting.

What other effects are likely with excess oil? Heat build up? Frothing? Discharge from the breather? Let's hear from some experts on this.

IMHO you need the minimum oil level to provide adequate lubrication and cooling, whatever that is. In this case I don't necessarily feel that "more is better".

Let the discussion begin.......

Cheers

[Bill Musarra]

Russ,
I posed this very question to "our" expert Porsche mechanic. His answer to me was to fill it to the sight plug and it would be fine. Not knowing how much that is, makes it kind of interesting. Will contact my other guy and pose the question to him. He has an inverted 930 also.


Dimi,
What type/weight oil are you using? I can/t say I have ever heard of clear trans oil(I am assuming you mean transparent). But hey, the only trans I knew about before the 40 was a Muncie 4 speed. On the advice of my experts, they use only Swepco 201 which is 80/90 oil which is made for high performance, heavy use transmissions and differentials. According to him, one should only use an oil made for LSDs in an LSD setup. I would gather that the LSDs have a higher level of friction/requirement with the clutches. Then it also depends on how you have them setup, as some are 80/20, others 50/50 etc.
Swepco 201 is blue by the way, and smells worse than a 4 day old baby's diaper.

Bill

[Dimi]

Hi Bill

OK Hear it is direct from Dr Porsche himself.

The certified oil for the porsche box is Mobilube SHC fully synthetic 75w-95 transmission oil as required for warranty on porsche boxes.

The factory fluid quantity for a porsche transmission in normal orientation is
3 Litres standard and 3.5 Litres with oil cooler.

The above is from the official Porsche factory workshop manual.

In the normal orientation the crown gear and shift forks are immersed in oil and due to the rotation of the gearsets the oil is thrown in a specific direction to effectively lubricate required parts.

In the inverted situation these gearsets etc are now out of the oil pool and are relying only on the thrown oil for lubrication and as the oil is now being thrown by the opposite gearset it is now also being thrown in a different direction to which it was originally intended providing a different amount and path to the areas that require lubrication.

To compensate a greater amount of oil in the box would be beneficial but just how much is not known.

Given that at any one moment in time while the car is being driven and the gearsets are turning a substantial amount of the total oil in the box will not be at the bottom of the box but in motion either flying around in the space in the box or running down the sides of the box there would be no detrimental effects unless the box were totally overfilled.

The unofficial estimates and opinions suggest up to a third of the available space in the box could be filled with oil without any detrimental effects after that the gearsets would be trying to turn while totally permanently submerged which could create problems such as overheating, frothing,etc.

Due to the gearbox being inverted when draining the oil very little would remain in the box as the lowest point in the box is now at the top and this allows the box to fully drain so the amount of oil that is put into the box should be exactly what comes out allowing accurate measurement of oil quantities.

The measured amounts done on my gearbox with the sight tube now gives us some very accurate reference points to work with and it leaves it up to us to do whatever we are comfortable with.

No one from any official Porsche source would be drawn to comment as what we are doing with these boxes is not a condoned use of the box or what it was designed for.

The thoughts and opinions expressed above are from several qualified and highly experienced Porsche factory mechanics that I managed to talk to and as close to an official answer that we could expect to get.

Some food for thought.
Dimi

[EGLITOM]

For the oil discussion this thread will probably help. lengthy discussed with one solution ( almost:-)):
Porsche G50 Info

Dimi,

thanks is now more clear for me

Russ;

would be great to explore the oil level question a little more. Also the question if one plans on using an oil cooler ( like me ,because i will have > 500 hp going into a G50/05 with a Quaife ATB Diff and a billet sideplate) where to direkt the return line to. Into the lower " sump" or onto the Crown wheel, or onto the diffhousing ? Working as a food engineer i have seen the destroing effects of cavitation, so want to avoid this definitely. But there should be a lot of experience already on this forum. May be a scetch or picture of oiling systems also.

TOM

[BruceLambo]

I am sure there has to be a happy medium between too much and too little.
I would think that too much oil in the box would be detrimental with power hogging and syncro sleeve operation. Remember though that when the gearbox is operating the level drops due to having the oil splashed around the gearbox internals - there will be no part left untouched by the oil. I dont believe there will have to be an 'exact' amount of oil. How many of you have heard of box failures due to either low oil or excessive oil?

Ive just checked a Renault box and see that the filler hole is about half an inch above the output shaft centre line. So what ever level this turns out to be (about 4 litres I think from last measurement) would be a good compromise between too much and too little.

I would like to hear Wannis take on this oil level thing, as I have seen him chat about such issues in the past. Mind you where is he? I havent seen him around here lately?

[Kalun D]

I found in my notes that to get to the bottom of the side seal edge it takes 5 qts, that's what I'm running with no problems yet but it does seem like a lot of oil.

I also am running 1 oil temp gauge on the dash switched to 2 senders, 1 on the engine and 1 on the trans, (but haven't hooked up the trans sender yet) so we'll see. If it doesn't run hot might just leave 5 qts.

[kenny]

Hi Craig.

I too have a G50/03. Can you tell me what high torque starter motor you used on your car please?

Regards,

Ken

[Big-Foot]

Originally Posted by kenpile

Hi Craig.

I too have a G50/03. Can you tell me what high torque starter motor you used on your car please?

Regards,

Ken

Ken - Check my build site and you'll see what I am doing to fit a high-torque starter..