105 GT Junior driveline vibration

[Roo504]

Good morning all,

My 105 has developed a nasty vibration at speeds over 80kph. It happened suddenly and at the same time the speedo stopped working.
I put the car up and had a look underneath:
- The uni joints are fine;
- The donut looks as though it's in reasonable condition (no cracks etc.);
- The rubber for the centre driveshaft bearing is a bit tired and I will probably replace this;
- I can move the driveshaft backwards and forwards approx. 10mm (possibly slightly more). This has the effect of moving the centre driveshaft bearing out of its position slightly. The movement can be seen at the output shaft of the gearbox - the three bolt flange which sits on the output shaft (this connects to the donut) moves back and forth, and I also can see what looks like a pilot bearing in the extension housing being able to move back and forth when I pull the driveshaft backwards and forwards.

I'd love to know what has gone wrong with the car. I hope it's something simple, but I'm thinking it might be a nut inside the gearbox which holds the output shaft in place has come off and will mean the gearbox needs to come out? I suppose this would also explain why the speedo stopped working as I imagine the speedo drive must run off the output shaft.

Appreciate your help,
Andrew

[CarterHendricks]

The output flange nut is loose, which has allowed the
speedo drive gear to move rearward and out of engagement,
and the loose mess will cause a lot of vibration.  If the
threads on the output flange are not damaged it might
be able to be tightened up.  But everything, including the
donut and the end of the output shaft and the bushing in
the center of the front section of the driveshaft--all of it
should be closely inspected.  There is a tab washer that
is supposed to secure the nut on the output flange but
I've gone to loctite, no washer...

--Carter [in St Louis!]

[Roo504]

Hi Carter,
Thanks for the info. Can you tell me where the output flange nut is located (inside or outside the gearbox)? This will help me work out whether I will do the work myself or whether I'll take the car to get fixed by someone else.

Kind regards,
Andrew

[AikenDrum105]

Hi Andrew, 

It's on the outside.    The 3 bolt flange/yoke  fits onto the spline of the output shaft, and is held on by the large nut.  You'll need a deep socket (forgotten the size again... )  to tighten it - and the front driveshaft / giubo  will need to be  undone from the flange/yoke   to get to it    The nut can't escape while the driveshaft is on,  so it's still in there      Getting the Giubo off can be tricky - a couple of large/heavy hose clamps linked together and strapped around it to hold it compressed makes it easier to feed the yoke and driveshaft bolts through.

If the speedo drive has been badly damaged by the yoke moving around - you can replace them cheaply enough from a wrecker etc - but the yoke/speedo drive are a matched pair to go with the ratio of your differential,  so make sure you get one from a car with the same diff     The drive's easy to remove from the side of the box,  check it out while you're there maybe - if a couple of teeth are just burred on the end facing the yoke,  just clean them up with a file and chuck it back in   It's a bronze gear I think.

The loctite Carter recommends is a great idea.  I use the basic pink 222 grade,  stops things vibrating off, but doesn't cement them on so you can't get them off later.

Hope that helps a little,

Cheers,

[bonkfrog]

Andrew

Don't forget that your diff is the 2000 LSD. I'll call you later.

[Roo504]

Thanks for the replies,

I'll bring the car home on the weekend, pull the donut off from the flange and have a look at the splines and speedo drive. Hopefully all will be well (speedo works when I push the driveshaft back into place) and there won't be any problems with the gearbox.

I'll let you know how I go.

Kind regards,
Andrew

[Roo504]

So I pulled the propshaft off from the gearbox flange back to the first uni joint. As I did this the nut for the output flange fell out! Thanks for the heads up Aiken and Carter!
I replaced the centre support bearing rubber as well as the donut (both were a bit tired), and put it all back together. Went for a drive this morning and all the vibration has gone and the car is driving well again.
I had to file the output shaft gear as it was slightly chewed up - but was still in very good shape, just needed cleaning up. Speedo still works!

Thanks very much for the advice.

Cheers,
Andrew