Play between driveshaft and gearbox
 

I've got a bit of a backlash in the drivetrain on my NA, extensive searching told me that it was most likely the front diff mount, but I've got the rear jacked up and had a good push on the front of the diff without any movement.

So by rotating the driveshaft by hand I seem to have a tiny bit of play at the diff end, and quite a bit of play where it enters the rear of the gearbox.

Obviously its a fairly major job dropping the driveshaft and box, is there anything else I'm missing, or is it just a case of bite the bullet and drop it out?

There is a normal backlash at the diff, in fact, it must be set when putting one together. The trans side could be worn slip yoke splines or worn slip yoke bushing. Or, it could just be the normal clearance you're feeling.

If we're speaking of rotational, the shaft can't have more movement at the trans end when compared to the diff as it's a solid shaft.
Most like, especially if there is excessive movement at the diff, I'd say excessive backlash.
Our '89 TII has had excessive backlash since new, no problems.

I think its more than the normal back lash I'm feeling.

If any of you ride motorbikes, you know when the chain is too slack, it feels like that. When switching between acceleration and deceleration there's a delay and then a clunk as the driveline tightens up.

Turbonut, what I mean by play is, when I rotate the shaft by hand I get a bit of free movement each way, at the diff end I can see there is very little play when turning the shaft, turning it immediately turns the rear wheels, whereas at the gearbox end there is noticeable play when changing directions.

Sounds like I've got either worn splines or a worn gearbox end.

how about a worn U joint?

I guess its possible, I actually have a spare driveshaft from my donor car, so it might be worth my while fitting it to see if it makes a difference.

normal play may seem excessive to most who have never felt it, but 1/16-1/8 full rotation of the shaft is perfectly normal. while that doesn't sound like much on paper, it feels like a lot when you are turning the driveshaft by hand.

you can't really compare this slack to slack in the chain of a motorcycle.

I didn't say it was slack like a motorbike chain, just that the feeling whilst driving the car was like the feeling of a motorbike with a poorly adjusted chain, which means there is a lot of lash in the drive train.

In stop start and slow moving traffic its very bad as every time I get on and off the throttle, no matter how gently there is a shock between acceleration and deceleration.

I don't know if the play is normal, but after checking if I could push up the front of the diff (which was rock solid) I checked the shaft and i feels like there is excessive play.

Mark the diff housing and yoke, turn and you'll see how far it moves.

Its dark now, but I'll try that tomorrow.

Diff backlash is easily felt by hand when in spec.

Slip yoke play/backlash between the trans output shaft and the yoke on the driveshaft should not be perceptable by hand, but what you may be feeling is in the trans itself so it's hard to know if you have excessive wear.

sure its not the engine bucking? mine does it all the time if your not perfect with it, really any clutch type vehicle can do it

The engine does buck, which definitely doesn't help the situation, at neutral throttle it seems to want to buck quite a lot.

However I've had a good few cars, many of them RWD and there's definitely excessive play in the drive line somewhere, its just working out exactly where.
I have another driveshaft so it might be worth me fitting it, thought it might be worth me posting here first though before I get stuck in.

if you can lift the diff nose then your diff mount is broken and is your problem, not driveline slack. if the play is only in the driveshaft then it's u-joints, if there is play between the diff yoke and your differential case then your pinion bearings are shot.

Sounds like its the universal joints then as the diff feels rock solid and there is no play at the diff yoke end.

I have a spare driveshaft, so I'll swap that in next week and see if it improves matters. Unfortunately I've not had time to look at it this last few days as I've been working late.

if your getting alot of bucking I'd adjust the TPS also. I know thats what mine is, just haven't adjusted it yet

Will do.

I'd lent out my multi-meter, but got it back today so I'll follow the FC3SPro guide and hopefully that will improve things.

I did this and its transformed the car, no more bucking and bouncing at light throttle.
I found the throttle cable was ever so slightly still engaged even with the pedal fully up, so the throttle never quite fully closed.
Also the TPS was way out.

I still have the backlash and clunking, but its a lot more manageable now the car isn't bucking.