Gear drive oil pump will not prime?

[BioBa]

After my gear drive rebuild I have noticed that there is no oil being returned via the top oil line. Is there a trick how to prime the pumpto get it going. I thought about overfilling the gear drive so the lower oil line will fill up the the height of the oil pump, put the car in gear to get it going and then draining it to the correct level. I am sure there is a "correct" way to do this. Any help would be apreciated.

[Ron V]

Jack up the rear end and get a buddy to help you turn the wheels over really really fast.

Not sure if it will work but it was my first thought.

Ron

[Ron V]

Overfilling it will be fine too. Just let it sit for a while after you have the system full and primed and then pull the side plug. All the excess oil will just drain out the side until you reach the proper level.

Ron

[BioBa]

Ron V said:

Jack up the rear end and get a buddy to help you turn the wheels over really really fast.

Not sure if it will work but it was my first thought.

Ron

Tried that but did not work. I even ran the car at a short three lap sprint, still did not work.

[Ron V]

Hmmmmm. How do you know it is not working? I would assume that it being a mechanical system as soon as you have some fluid in it and start driving around it should be working.

Pull the top line on the cooler. Fill it up with the bottom line to the cooler plugged. It should be full minus a bit of air.

Fill the rear end to the prescribed level.

Button it all up everything should be working fine.

No?

Ron

[BioBa]

Ron V said:

Hmmmmm. How do you know it is not working? I would assume that it being a mechanical system as soon as you have some fluid in it and start driving around it should be working.

Pull the top line on the cooler. Fill it up with the bottom line to the cooler plugged. It should be full minus a bit of air.

Fill the rear end to the prescribed level.

Button it all up everything should be working fine.

No?

Ron

I have done exactly what you suggested. The problem, as I see it, is that the larger diameter tube supplying oil to the pump from the low point of the gear drive contains air. Having oil in the lines and cooler exciting the pump does not solve the problem.
The only way to remove the air in the line supplying oil to the pump is to overfill the gear drive so that the internal oil level is at the height of the oil pump (the pump sits quite a bit ABOVE the recommended oil level).
Once the oil is at the pump level turning the wheels would allow it to suck in oil instead of air. Once the air has been removed and the system starts to operate correctly the excess oil would need to be drained to reach the correct level.
I am surprised that no one else has come across this problem when replacing the gear oil. Maybe many others have the same problem but are not aware of it as they have never checked if oil is being returned to the gear drive via the top oil line?

[BertBert]

It's not a subject that I know a great deal about...but if the pump is above the normal oil level, won't the oil drain away back to the normal level leaving air in the feed line to the pump when the car is standing?
Bert

[Ron V]

I am thinking that the Big R wants the pump to grab whatever oil is dragged up to the inlet when set on kill.

Bert Bert is right.........as soon as the car rests the oil will creep back out of the pump.

Fill her up, button it up. Go to the track. Make a run and temp the rear end.

Anyone got any figures for how hot a diff should run under normal conditions? I have never temped mine.......

Ron

[BioBa]

BertBert said:

It's not a subject that I know a great deal about...but if the pump is above the normal oil level, won't the oil drain away back to the normal level leaving air in the feed line to the pump when the car is standing?
Bert

Good point and I had thought about it myself. If the seals on the pump are tight the oil should not drain back as no air can enter to allow it to drain back. At least that is what I think but I might be wrong.

I have heard that some do not even run an oil-cooler on the gear drive? I am also interested in the maximum temp recommendations for the gear drive.

[austurbine]

My car has the same issue and has never worked, despite assurances from a Radical technical person, that it will function when running.
I have tried to run my car on the jacks in sixth gear with the return into a bucket with zero flow, even tried to fill the suction with oil above the pump without any luck.
I can only assume that the pump in my car has worn internals or the design is poor and ineffective.
My suggestion would be to monitor the case temperature and if it's over a 100 degrees C then fit an electric or tow the car to Melbourne and drive Phillip Island, the weathers always cooler in VIctoria!!!!!

[BioBa]

Overfilled to reach pump level. Turned wheels for several turns and it started pumping.
In my excitement I drained oil to correct level and put everything back together, but forgot to test if it still pumps with the oil at the correct level!
Will update if it works at the next track day.