el_freddo Posted February 19, 2023 Share Posted February 19, 2023 Sam try running the front half of the shaft only, drop the rear section. That’s one of the beauties of the L series two piece shaft. The only other things I can think of are: - broken/worn engine or gearbox mounts - modified gearbox mounts aren’t sitting true/have changed driveline angles - rear output shaft bearings are toast in the gearbox, but this is usually accompanied with a leaking rear output shaft seal too (been there done that) Other thoughts point towards a drive shaft issue, and it could be any of them! I know you’re down and out on this one, keep at it though, you’ll work it out. I doubt an EJ conversion will solve anything - but with that said, do you have all cylinders running at 100%? Theory on this: if the vibration happens in 4th but disappears by dropping to 3rd or it changes significantly, it could be an engine issue. 4th ratio is just over a 1:1 engine speed to tailshaft speed. If there’s something in the engine that’s not operating as it should it could be manifesting as this vibration. One of the reasons I say engine issue is because we had an old family bus Holden WB Statesman series II with the 308. One day towing it developed a MASSIVE vibration under load to the point it was almost undrivable - we limped it home. The issue turned out to be one fed spark plug and a failing spark lead. For a V8 that was substantial and surprising that it was just that simple. Does this vibration come on strong/quickly straight up when you start driving or does it work itself up to the vibration at set cruise speeds? Cheers Bennie Quote Link to comment Share on other sites More sharing options...
Silverbull3t Posted February 20, 2023 Author Share Posted February 20, 2023 Thanks for the suggestions Bennie, let's see if I can address them all And yes I've been driving around with the rear half of the shaft out up until I got those new uni joints in the post. The vibe is gone with that out of the picture. Guess I can keep it in the back of the car when I'm en route to a destination then install it for the 4WDing part - broken/worn engine or gearbox mounts They were all brand new when I installed them, I did check the gearbox mounts at least withtin the last 6 months and they are fine/intact. Engine mounts, I will check. - modified gearbox mounts aren’t sitting true/have changed driveline angles They're the stock MY/Brumby mounts, bolted onto the L series brackets if I remember right which I filed the holes out oval shaped where they bolt to the sides of the gearbox. This is what Steve Rising sun (certified old subie guru) told me to do. Using the standard MY X-member. I never was 100% happy with this setup though. - rear output shaft bearings are toast in the gearbox, but this is usually accompanied with a leaking rear output shaft seal too (been there done that) I do suspect this gearbox (and diff for that matter) are trash, you could be onto something. The rear main seal isn't leaking though. (selector shaft seal is, dripping) There is another un-related weird low frequency wobble even in 2WD with the tailshaft removed, happens when I let off the throttle at around 80km/h or so. A bent internal shaft in the gearbox has crossed my mind. Amazingly that wobble went away with the tailshaft installed I'll be glad to get that new 3.9 box in there to compare. Does this vibration come on strong/quickly straight up when you start driving or does it work itself up to the vibration at set cruise speeds? It's weird is all I can say. Today I could feel it at 60km/h, then at 80 it was less severe but definitely still there. At 100 it is like a butt massage, get's worse from there. 3rd, 4th, 5th gear it seems pretty uniform. As for engine health, I should hope it's not that but it's not out of the question I suppose. Been meaning to do a compression test on it, it just feels too gutless (big wheels don't help) Maybe I didn't break the engine in properly? But it doesn't burn a drop of oil. Spark plugs I replaced a few months ago, old ones looked clean, good combustion signs. Can't understand that either, how it could be not running rich with the amount of fuel those twin carbies drink It might even be slightly lean as it pops/crackles on deceleration. Quote Link to comment Share on other sites More sharing options...
Silverbull3t Posted February 20, 2023 Author Share Posted February 20, 2023 On 2/19/2023 at 7:22 AM, Steptoe's photos said: and convert to c clip - what is done to make the grooves for c clips in correct position? You do it or pay some engineering shop? The new bearing caps have the C clip grooves in them. The original yoke has a flat area on the inside faces which I cleaned up with a hand file, the C clip sits up against this face on the inside of the joint, 4 places. Quote Link to comment Share on other sites More sharing options...
el_freddo Posted February 21, 2023 Share Posted February 21, 2023 Did you ever swap out that rear diff? I can’t remember if you ran without the diff fitted to see what happens… I’m keen to get to the bottom of this one with you! Tyre condition and pressures? Cheers Bennie 1 Quote Link to comment Share on other sites More sharing options...
el_freddo Posted February 26, 2023 Share Posted February 26, 2023 Talking to a mate over the weekend and he had an issue where it was the wheel nuts not clamping the wheel to the hub properly, effectively the weight of the vehicle was only on the hub centric ring thingy-bit. Weird hub setup with the studs as though. Anyway, it got me thinking, what stud pattern are you running as I remember some mention of redrilled hubs - is this correct? Is it possible these modified hubs are not done well and could be causing the vibration issue? Could be clutching at straws but thought I’d ask. Cheers Bennie Quote Link to comment Share on other sites More sharing options...
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