Sprint water cover bolt size and axle shims.

[cleverusername]

Having sheared one of the water pump housing bolts, then broken a screw extractor init, I have only just drilled it out. The thread needs repair, so I wondered if anyone knows the correct thread for these bolts? Might have to helicoid it.

And I am a bit baffled by the axle shims behind the brake backplate. I put it together with no shims and have no play. I thought the point of shims was to remove movement, not add it?

[Flyfisherman]

Having sheared one of the water pump housing bolts, then broken a screw extractor init, I have only just drilled it out. The thread needs repair, so I wondered if anyone knows the correct thread for these bolts? Might have to helicoid it.

And I am a bit baffled by the axle shims behind the brake backplate. I put it together with no shims and have no play. I thought the point of shims was to remove movement, not add it?

water pump cover bolts are 5/16" UNF x 3/4"

Paul

[gmsclassics]

The water pump cover bolts are 5/16 UNF.

You do need a small amount of movement in the rear axle half shaft (end float) to allow for the metal to expand and contract. The correct amount is 4 to 6 thou total so the process is put shims in equally at both end of the axle tube, measure the end float with a dial gauge and adjust as necessary, again equally at both ends. It does take time and a few goes but once done you shouldn't need to repeat it for years. You do need enough shims in the first place so you have end float to measure. You can't start with none.

Geoff

[SprintMWU773V]

Also don't forget that you need to fit and tighten both half shafts, you cannot do one side at a time. When I did mine I fitted both sides without shims to give an idea of the play and then that gave me a starting point for my shims. It actually took me ages to get it right, then I changed my back plates for my final assembly and had to do it again! The good news is though that I was able to get the end float even more spot on.

As said, you will need a dial gauge and appropriate base and arm. You should be able to mount the base on the back plate if you have removed the wheel cylinders.

Oh and don't forget to bend over the lock tabs when done. My top tip is to slight bend them on a vice before fitting them as it makes it easier to bend over the tabs when they are fitted to the axle.

[cleverusername]

Also don't forget that you need to fit and tighten both half shafts, you cannot do one side at a time. When I did mine I fitted both sides without shims to give an idea of the play and then that gave me a starting point for my shims. It actually took me ages to get it right, then I changed my back plates for my final assembly and had to do it again! The good news is though that I was able to get the end float even more spot on.

As said, you will need a dial gauge and appropriate base and arm. You should be able to mount the base on the back plate if you have removed the wheel cylinders.

Oh and don't forget to bend over the lock tabs when done. My top tip is to slight bend them on a vice before fitting them as it makes it easier to bend over the tabs when they are fitted to the axle.

Yep i did one side, then the other. I do have a dial gauge and the axle is on the garage floor, so access is excellent. Looks like I have to take it all apart and start again, Which is a pain.

[tony g]

I don't understand why both shafts need to be in? How does one shaft affect the other?

Tony

[tony g]

No ideas on this?

Tony

[gmsclassics]

The halfshafts do mate up with parts of the centre diff and can put undue pressure on that if the end float isn't both correct and equal. Can't show you the parts on a standard diff but my original LSD was damaged when it was installed by 'a professional' who shimmed the axles unevenly. You can see from the following photo how the parts of the centre diff where the end of the halfshaft contacted were worn (on one side where there were no shims!). This was only part of the damage as there are taper bearings on each side of the diff head which can wear if undue force is applied if the end float is large. One of the reasons I try to do as much of the work on my racecar as I possibly can and only let a couple of people I have complete trust in near it (or any other car I own come to that).

diff centre.JPG (52.33 KiB) Viewed 1186 times

Geoff

[tony g]

Cheers Geoff, I have one to set up that's out of the car so I'll take the rear cover off and investigate.

Tony

[SprintMWU773V]

Not sure about the Dolly diff but I know in some of the ones we have here in the workshop the halfshafts push against a sliding pin in the middle part of the diff. If you don't put both in then you'll end up with too much or too little gap on each side.

Sometimes you'll find you can't get the end float equal, it might be worth tapping the shaft in slightly to push it home and this should solve the problem.