Triumph Repair: Differential Play, tr4a irs, spider gears

Question
Hi Howard,

I have a 1966 TR4A IRS with overdrive transmission.  I have isolated the play in the rear driveline to inside the differential itself (i.e. it is not coming from the u-joints, splines, diff mounts, etc.).  I am trying to determine what is considered an acceptable amount of play inside "factory service tolerances".

There is 1" to 1.5" inches rotational play in the wheels before the differential acts on the driveshaft.  Likewise, there is 3/4" rotational play in the driveshaft before the differential acts on the wheels.

Engaging 1st gear after being in reverse results in a reasonable clunk. But, otherwise, I am generally able to slip the clutch to avoid any major clunking.

So, based on what I have described, would you say this is a near-term service item?  If so, any idea if this would necessitate a complete rebuild of the diff or would perhaps shimming up the spiders be sufficient to remove the play?

Thanks Howard,

Bob

Answer
Hi Bob,
It does sound like spider gear play. There is only about .005" inch free play of a ring gear to the pinion gear and if that were excessive you would have a very loud wine. Spline free play can not get that great but spider gears can. When you said 1 to 1.5 inch wheel, are you talking about at the tire tread? If so that is not bad but 3/4 inch at the drive shaft is a little excessive. Keep in mind that the drive shaft is the pinion and it is hypoid gear and makes a swiping motion to move the ring gear so you will not get that very tight especially when all the play in the spider gears had to be taken up to move a axle.
In my opinion you may take some of your play out by attending to play in the spider gears. You will never take it all out.

You may inspect the clutch release system too and idle speed. Also there is free play in the gear box that you are contending with when going from reverse to first. Try this, set at idle in neutral and depress the clutch and put it in second gear and then go all the way to first. Note if there is any noise, then put it in neutral and then shift to first. Then shift into neutral and sit with the clutch down for 10 seconds and then shift to first and note any noise. Keep it at idle all this time and clutch down.

When you are in reverse and clutch down you still have some amount of drive backwards from the pilot bearing, flywheel, pressure plate trying to rotate the first motion shaft in a forward motion and inside the gear box ALL the gears are held stationary by reverse and even in thin oil there is still a slight drive being applied backwards. And if you are using gear oil there is a lot of torque applied. This takes up all the free play in everything in the differential. So when you shift to first all of the free play is reversed to the opposite direction even though the clutch is still depressed.

What I am saying is you may be chasing a ghost on a 32 year old car.

If this is a nice example of that car and you want to go into the differential you can easily see and feel the spider gears to see if some of the free play can be removed. So you don't have to completely disassemble the diff to check it.

Howard