Time to inspect my GDU pump and gears.
First, what is the easiest way to verify that the GDU cooler pump is working properly? While the GDU was full of fluid, I removed the line from the top of the GDU (where we fill the GDU at), and, with the wheels off the ground, rotated them for several minutes. At no point did any fluid come out of GDU oil cooler return line. I'm assuming this means that pump is bupkus?
Second, I need to remove the case to inspect the gears. I planned to use this ( https://www.pistonheads.com/gassing/topic.asp?t=1318222) as a guide. I planned to:
- Place the car on the lift.
- Remove the diffuser.
- Drain the GDU oil and remove the hose.
- Remove the top upright bolt on the driver side to gain space to remove the drive shaft.
- Remove the eight bolts for the cover plate and remove.
Are any of the other steps I have removed from the linked guide necessary?
Hi Garrett (@gwt561324). The test you did is a good one and you should be getting oil returning out of that hose when you spin the wheels. I would do a little more trouble shooting before removing the GDU. The next test I would do is to remove the pressure line from the pump and and rotate the wheels to see if the pump is pumping without having to go through the lines or radiator. This will help eliminate a clogged line or blocked radiator. If it still doesn't pump fluid I would remove the pump from the GDU to see if the drive is rotating the pump. if it is then you can dig into the pump or replace it. If the GDU is not driving the pump you will need to dig into the GDU. When you pull the drain plug from the GDU are there any metal shavings or splinters on the magnet? This is a good sign that you are getting gear wear.
Here is the GDU Service guide that should be helpful in understanding and trouble shooting the GDU.
Charley
@charleyh,
Thanks for the excellent info!
What is the life expectancy of the GDU pump? My GDU was rebuilt along with a pump replacement over the previous winter. During my last event of 2020 I suspected that the pump may again not be working properly.
I change the fluid nearly every event. I didn't have anything in the way of metal accumulation on the magnet plug until the second to last event. Event that was relatively minor. I put about 1200 miles on the unit this year.
@gwt561324, I am not sure what the pump life is, but if you just had it replaced it shouldn’t need to be done again already. I would reach out to the dealership that rebuilt the GDU and talk with them about it.
Charley
The pump is bad. There are some obvious signs that metal has gone through it.
Outside of changing the fluid between events, what other actions can I take to reduce wear on the gear box? I'm not relishing the idea of rebuilding it every year.
@gwt561324, I reached out to one of my friends at a Radical dealer and he said that it is fairly unusual for GDU pumps to fail, and it definitely shouldn’t have failed in one season. He said that possibly your car had a GDU failure in the past and the cooler wasn’t changed. After a GDU failure it is important to replace the cooler because it is impossible to get all of the metal shavings out.
Charley
What would you classify as a failure? The pump had failed last year because of metal shavings. I know the cooler was not replaced.
@gwt561324, Any wear that is extensive enough to send significant amounts of metal through the system. Gear wear shouldn't be enough to cause the issue, but if the bearings failed or there was part failure it is a good idea to change the cooler. It sounds like you have just had regular GDU overhauls during your ownership so the initial issue may have started before you got it? If you had enough metal in the system to fail the pump twice it is likely that there is metal coming out of the cooler. I am sure there are other possibilities but you shouldn't have two pump failures in a year, so something else is going on. How many hours / miles did you put on your car since the last GDU overhaul, and how much was changed when the did the overhaul?
Charley
These parts were replaced/used according to my invoice:
- Drive pegs
- Gear drive service unit kit
- Forward gear (synchro)
- GDU spacer
- Crownwheel gear drive unit
- Gear drive oil pump
As you can see the cooler is not in the list of items replaced last winter.
The pump I just took out has significant scarring inside it. Of the 8 drive pegs, 5 of them are broken as well (not sure if this is significant).
As far as usage, I did 1072 miles this year over about 16 hours of moving time. Total run time was about 35 hours.
At no point did any fluid come out of GDU oil cooler return line.
I read that lengthy procedure at Pistonheads on removing and replacing an SR3 GDU. Everything sounds pretty straightforward except the part where he needed to prime the GDU pump to get the pump to work. Is this as complicated as it sounds? The procedure mentioned overfilling the GDU with oil, and attaching a vacuum pump which sounds messy and tedious. Is this necessary?
This is the the paragraph about priming the pump:
The procedure is described here
Priming of gear drive oil pump: I found that after refilling oil into the gear drive, the oil the pump needed to be primed to start working. The only way I managed to do this was by overfilling the gear drive to reach the level of the oil pump. I then turned the wheel to see if any oil is beeing pumped. At one stage even this would not work and I needed to use a vacuum pump to suck oil out from the line exiting the oil cooler. Once the pump is pumping I drained the excess oil to the correct level.
I just spun the rear wheels on mine - eventually we got fluid. It did take quite a while though.
Thanks Garrett. I plan to swap my GDU, and begin in the same way you did -- before removing the current GDU, make sure that I can get oil from the return line when I spin the wheels. My current GDU has only 21 hours load and functions well, however it has been leaking oil out of the right side case ever since I can remember.
I dont know how to attach an old thread "Need help: GDU pump issue??" on this website, but I had issues with pump priming earlier and posted the following:
SOLVED:
I talked to a Radical race team in the UK, explained the issues. They had an interesting take. They had experienced similar issue trying to get flow for some unknown reason in the past. The pump moves extremely slow, and can loose prime. When/if a car is running on track sloshing and going thru the gears, the pump gets primed naturally. When simply on car lift, can be difficult to get pump primed when only spinning wheel or running the car slowly in 1st or 2nd gear. Even after several attempts. They said to actually run the car up thru the gears into 5th and 6th gear which would spin the pump much faster at 2,000 rpm. Boom - worked perfect.
They also had interesting comment about the factory. When building and assembling the car, they simply put fluid in GDU, close it up, and dont actually get flow themselves before sending to clients.
So, all my worries averted, have flow, closed up and ready for next event. BTW: I did all this because I installed a Tim Gray filter system to help preserve the GDU long term.
Thank you very much for this timely post Dan which answers several of my questions. I too could not get oil to flow by spinning the rear wheels by hand and after five minutes of trying I gave up on the idea.
