Hi @davidf and any others interested, Happy New Year!
I have been having some of the same issues with my GDU which was fully rebuilt before I drove my car for the first time in ager early last year.
I purchased a relatively cheap borescope online and have been using that between each event since I first noticed wear on the 24 tooth ‘forward drive gear’. I've talked to several people who have all indicated that this is fairly 'normal' ... although I suspect my wear happened earlier than what others might have experienced??
I’ve tried two different oils – Motul ‘Gear Competition’ 75w140 and Neo-Synth 75w90 RHD although given I have only driven my Radical less than 5 or 6 hours on track (total engine run time of ~8 hours) I’m absolutely sure I haven’t got anywhere near enough empirical evidence yet to judge between either of them. I know people on this Forum have good things to say about the Neo-Synth, so I'm trying that at the moment. (and I also know that the wear I'm seeing can only get worse... no oil can fix that!)
I’m also concerned that after filling my rebuilt GDU for the first time that the oil pump to the cooler might not have ‘primed’.... and I suspect that this might be main reason why I might be experiencing premature wear.
The reason for saying this, is that after using it for the first ~3.5 hours I drained the oil (original fill was Motul 75w140) and used my new borescope to see what things looked like. That’s when I first found the ‘forward drive gear’ had the damaged tooth faces.
The video below shows the damage now after a few more hours racing (now roughly 6 hours). The worn areas on the gear face are about 20-30% larger than when I first took a video at 3.5 hours.
- …. Sorry about the focus – it’s as good as I can get it
- Note that the video starts at an area of the gear where there is limited wear, and then the wear gets worse… This video only shows part of a full rotation (video size limited here), but when you watch the full rotation its almost like the gear is 'out of round' with the wear noticeably worse on one side than the other
As a result I decided to do two things;
- First I installed a magnetic filter (Magnom Mini) into the suction side of the oiling system to at least try and stop any metal particles going around and around doing more and more damage than necessary. This worked extremely well for the last event I did. There was definitely some really small metal particles captured by the magnets (almost like a 'paste' - nothing large). This material would most obviously have been from the worn areas in the video above.
- Secondly as mentioned above I also changed to the Neo-Synth RHD (suspecting the oil wasn’t working as well as it should)
… but when I’d refilled the GDU I also decided to check the oil flow to the cooler (Which really underscores the value to someone like me of being active on this Forum.... this is where I first heard of the GDU pump prime being a potential issue)
That’s when I discovered there wasn’t any flow. At first I was turning the rear wheels by hand, but when that didn’t give me any flow, I removed the rear wheels (to reduce the chance of inertia damaging the gearbox if it started to get any driveline chatter) started the car and ran it up in 2nd and 3rd gear – probably only to 3,000 rpm, but still no flow…..
I have no way of actually telling if there was or wasn’t flow before I drained the oil, so I’m not 100% sure… but there is a chance that there may not have been any flow during that first 3.5 hour run period…?
I don't have access to a vacuum pump as suggested earlier in this thread, so I used a large syringe I have in my workshop to suck oil up through the cooling system until it arrived at the return fitting into the top of the GDU. It took a few 'strokes' of the syringe, but it worked well in the end. Once I had done that the oil flowed freely when the car was in 1st gear and the pump seemed to retain a ‘prime’ (I waited a few hours and tried again and all was OK)
I’ve since built a better "test tool" for this and I think I will check the oil flow before each event while warming the car up at the track… just to be sure!
Does anyone have any other suggestions?
Does anyone have any insights into how much worse the wear shown in the video can get before it needs changing/rebuilding?
In the meantime I’ve used my Christmas bonus to splurge on a spare GDU (and oil pump which is sold separately FFS!)…. So at least I have one here I can swap straight in... when the time comes.
@rjbender, when I got my first SR3 it had 13 hours on the engine and the time on the GDU was unknown. I was told by the seller that it likely had similar hours to the engine. At my first GDU oil change I found some slivers of gear material in the magnet so I started to suspect that the GDU had higher hours on it. At 40 hours I had the engine and GDU overhauled and the gears were well worn (see picture). But despite the wear the GDU operated flawlessly. A couple of years ago I had the GDU overhauled from a 1340 that I had and the wear wasn’t anywhere near that bad. The engine on that car had 80 hours and the GDU was believed to have similar hours.
Regarding gear oil, I have been told by experts at the factory that they have tested many different oils and that the Neo is superior. A few weeks ago I was having a conversation with Phil Abbott about his new Revolution cars and he said that they use the Neo in those cars also because of how well it performs.
@charleyhradicalsportscarregistry-com … great to hear from you Charley. HNY!
… thanks for the post and especially the photo…. Now I’ve got something to aim for!… 🤣
interesting the area of wear on both gear sets is the same side of the gear…
For another ‘reference’…here’s another pic of what others have experienced. Interesting on this one that it seems to be limited to only a few gear faces
Just to make sure I am following the above correctly, especially with OP thread initiated on GDU priming. It is my understanding that the GDU pump is simply to force fluid circulation for cooling. Thus, in theory, if fluid did not get too hot, it would not have any effect on lubrication. I think the gears are lubricated from vehicle sloshing and gears throwing up oil on themselves (similar to a traditional rear end differential). The only reason that I say this, seems as though discussion on bad gears is unrelated to pump priming/flow when considering lubrication.
@raider89 - His Dan,
Your understanding is correct re the GDU pumps function relating to the cooling circuit, rather than any 'forced' oil feed into the gearbox itself... but your assumption that the gear wear is unrealted to temperature is fundamentally wrong. Oil temperature is in fact a key characteristic that is taken into account in the design of any motorsport gearbox, and particularly in the selection of the correct oil for the application.
It may well be this characteristic that makes the Neo-Synth a preferred oil, as it may well cope with higher temperatures better. Many people are using the Motul 75w140 to try and provide better film stability at higher temperatures, but it may be that the Neo Synth 75w91 RHD actually performs better in these GDU's (at least based on empirical evidence from many dealers who service a lot of GDU's - they have a lot of real life experience)
The reason that I started thinking about whether my GDU oil cooling pump might not have been working correctly was after I first put my hand on the GDU after removing the rear bodywork immediately after a race in June last year. It was EXTREMELY HOT. I wished I had the foresight to have taken an IR measurement of the outside of the gear casing (and should have thought to do the same in November at the last race meeting too!) I think I'll do that next time I use the car, at least to get a baseline. Maybe others could do the same and report what they find here?
Anyway Dan, I hope I have understood your concern in the post above properly, but if I have then I can assure you that temperature is always a key factor in determining the efficiency of any lubricant... hence the (potential) relationship between 'GDU prime' and 'GDU wear'
@raider89 I would say "yes", the priming topic is separate from gear wear and GDU lubrication. In fact, there is a thread on this forum somewhere with a Radical that does not have an oil cooler or pump.
Another observation on wear: I pulled my 21/37 hours load/run time GDU because it is seeping oil out of the right side cover which is the side that has the paper gasket. The ratio gears have no pitting or observable wear. There were just a couple tiny pieces of metal on the magnets. Car has been driven hard.
@davidf .... out of interest, what's the 24 tooth 'forward drive' gear look like David?
(How old is the chassis without the oil cooling circuit? I'm happy to be corrected but I don't think Radical sell any SR3's anymore without the oil cooler - it's certainly not shown on their 'options' list... I suspect that might be because they are needed to prevent/minimise these wear issues??)
I did not open up the GDU beyond the left cover, and I won't refresh this myself, but I will ask the tech and then report back. I was quite surprised that the ratio gears look like new, and I hope that there is not much going on besides the oil leak.
I am sure you are correct about the importance of the oil cooler; My answer to Dan was posted almost simultaneously with your post. My belief/understanding is that the GDU is lubricated by splash, not pressure circulation, but perhaps the return line helps to distribute oil?
I believe the SR3 I referenced which did not have an oil cooler was made in 2008. I think it is this one:
@davidf … yes, I reckon the oil return being above the main section of the gear train would help distribution, but only because it cascades over the rotating gears. The gears wouldn’t require that though as the bottom half of the gear train is submerged in oil at normal fill level.
I look forward to hearing how your 21 ‘load’ hour gear train looks like. I guess you are using the Neo-Synth oil?
Rod, I have been using the Motul 90PA oil, however I may switch to something lighter to reduce drag this year -- a performance vs mechanical wear tradeoff. I just remembered that not all of my 21 hours load is on these 3.07 ratio gears. During a race event at Barber we used a 3.235 set.
Just a couple of points to add. Yes some of the early SR3’s were available without GDU oil pumps but it was a problem. A pump and circulation is essential to GDU longevity.
the other point is that the gears that get the most wear are inside the GDU and can’t be easily seen. The wear on the ratio gears is not a good indication of GDU wear. If you see slivers or chunks of metal on the magnet it almost certainly is coming from the small forward gear inside the GDU (part 6 in the attached drawing).
@charleyhradicalsportscarregistry-com - Thanks.
In case it wasn’t clear, the ‘forward gear’ with 24 teeth is the gear I’m showing in the video I posted. I took it using a borescope down though the threaded port where the oil cooler return line attaches in the top of the GDU case. Once you’ve got the oil drained it only takes a couple of minutes to do the inspection. I’m going to video it to track progress - probably every cop of hours running when I change the oil. Hopefully I can at least track the wear, if not try and determine what causes the wear to happen/accelerate.
What is becoming quite common in the UK is super finishing the gears. It’s certainly not a “fix”, but it should improve the life of the gears. Having said that I have heard of a bad batch of forward gears, maybe the case hardening quality varies quite a bit.
out of interest, what's the 24 tooth 'forward drive' gear look like David?
21 hour load time: Two small pits in the forward gear. No other significant wear throughout the GDU.
The technician I spoke with today does a mini refresh, like I am doing, at 20 hours run time to replace the forward gear and often the crown wheel. He said that at 20 hours, there are sometimes extensive damage to the forward gear, sometimes minor.
