Strange vibrations

[Mad_Max 231]

So I swapped the auto out for a manual, all went well...

Thursday I had to travel from Invers to Cromwell for business, got up there not a worry. On the way back, even quicker trip (yes gave the car death as I do lol), all was well until I hit Invercargill and stopped for fuel. Once back in the car, there was a strange vibration, wasn't there the rest of the time.

I'ts a Getrag box, everything has been swapped over for a couple of weeks now and working fine, first time I've ever noticed this problem. Vibrations start at about 2k rpm and go through to around 3, maybe 3500. Happen in every gear, worse under load but still present while cruising/engine braking. No vibrations while in neutral, so I'm thinking definitely drivetrain.

Possible thoughts, it's the guibo/flex disc on the tailshaft or centre support bush is gone, allowing the driveshaft to vibrate. Or, one of the output shafts. Or maybe even a uni joint in the tailshaft.

Has anyone experienced anything like this? Any ideas, ways to test without dropping the exhaust, heat shield etc? Car still drives fine (apart from the vibration), still has plenty of power etc, and balancing weights still on the wheels so that rules the obvious wheel balance out.

[zero 1162]

Over tightened gearbox mounts can cause a vibration at the rpms you specified.

The torque settings for the mounts is very low.

Also, if the guibo is installed backwards it will destroy itself pretty quick.

[Mad_Max 231]

Over tightened gearbox mounts can cause a vibration at the rpms you specified.

The torque settings for the mounts is very low.

Also, if the guibo is installed backwards it will destroy itself pretty quick.

Interesting.... I shall look for the torque specs and retorque the mounts, see if that helps.

I'm assuming it's installed correctly as it was still on the front half of the tailshaft, I didn't remove it. Is there an easy way to check?

[e30ftw 410]

Did you put the whole driveshaft or just front half into your existing one?

Did you pre-load the center hanger bearing?

[Mad_Max 231]

Did you put the whole driveshaft or just front half into your existing one?

Did you pre-load the center hanger bearing?

Just the front half, undid it at the joint and slipped the manual half onto the auto rear.

Yes, did all that.

Think I discovered the problem last night, a bolt has come loose from the joint, one that passes through the guibo and onto the output flange on the box. So suspect that's the cause of it. So will hunt down a replacement bolt, check all the others and see if that fixes it. Strange that it came loose and disappeared, so will be putting loctite on the rest for extra insurance.

[e30ftw 410]

Bolt should be fine, it's the lock nuts that's need replacing. Did you phase the u joints correctly?

[Mad_Max 231]

Sorry, when I said "come loose" I meant "come loose and fallen out completely" lol so only has two out of 3 bolts holding it together

[*Glenn* 854]

There should be 6 bolts

[Mad_Max 231]

There should be 6 bolts

Correct, 3 from the tailshaft to the guibo and 3 from the guibo to the output flange. One of the guibo to output flange bolts was missing. I've managed to put another bolt in there for now, see if that fixes it while tracking down the correct bolts for it.

Kind of suspect it didn't like the absolute hiding I gave the car lol. Will know next time I take the car out if that was the problem or if I need to look further, next on the list will be hanger bearing and just work my way backwards.

[zero 1162]

Make sure the bolts go in the direction of the little arrows on the guibo.

If they don't the guibo will self destruct reasonably quickly.

[Mad_Max 231]

Make sure the bolts go in the direction of the little arrows on the guibo.

If they don't the guibo will self destruct reasonably quickly.

Yes, made sure of that when I was putting it together, it's funny how the strangest little things can make a big difference lol.

Thanks all for the input, just come back from a test drive, no more vibrations. It was the missing bolt after all, so glad to report all is well. Will track down a set of new bolts and replace them all to stop it happening again. So back to terrorising the streets and putting boy racers back in their place for me hehehe.