Castor correction thoughts.

[Andy]

Can check tomorrow, think I’ve got a spare in the workshop I can measure, I know they were a fine thread high tensile, got them from a local fixings
supplier

 

[stumog]

Andy that would be amazing thabks

 

[Andy]

 

[Andy]

 

[stumog]

Cheers Andy.

So that would it a m18 x100 metric fine by the looks of it. Off to the shop tomorrow.

 

[stumog]

So I have fitted the drop boxes and now seem to have some prop vibration at 40 to 50mph. Has anyone solved this?

 

[Shayne]

This is one of my fears about going to high on suspension alone Stu so i read all i could find on the subject and i reckon first and foremost (cheapest and simplest possibility) i'd try swapping the prop .

 

[Chris]

Stu, I have spent a lifetime on this and not sure I really found the answer. But, on a std 80 the front prop UJs are an odd thing. The T box end is at an angle but the diff end goes in straight so effectively there is only one UJ working on the front prop. Even on bumps etc it does very little. OK when you lift the truck you introduce much more offset in the prop and even with castor correction, I saw the input and output angles of the prop change. Therefore it's essential that your prop is phased correctly. I've looked at a lot of std 80s that have never been touched and the front prop phasing has been seemingly random. I did the maths and with the spline angles there are only 2 symmetrical phasings you can have 0 and 180. You can't have 90 or 45 etc. So do look at your ujs and see how they are aligned. That's the first thing.

Also as you lift, the prop slide joint will extend. That means less is engaged. Grab the prop and see if you can flex it on the joint. I've just had a whole new prop built because I had too much play in mine.

 

[Chris]

Also remember that UJs are a very crude rotating joint and even if the diff end goes in perfectly in line to the companion flange, if the T box end is at a hard angle it won't spin without some binding.
Always worth dropping the prop and see if it goes away.

 

[stumog]

Thanks chaps that was my thinking of first to try.

I just find it odd that it's been lifted for ages without caster correction and it's been fine, now I have vibes ones I fitted the drop boxes.

It's running OME heavies so is around a 3 to 4 inch lift at the moment I would guess

 

[Shayne]

Might these help https://shop.snakeracing.com.au/sj80-tailshaft-spacers-13mm/

 

[stumog]

Thanks Shayne

I think I found my issue

Will know 100% tomorrow.

 

[frank rabbets]

Stu. I have not read the whole thread recently but have you removed your castor correction bushes before you fitted the drop boxes? Just a thought.

 

[stumog]

Hi Frank

Never had bushes fitted.

So I sorted this I had a uj that had gone. Couldn't tell until you removed the prop. Also rephased the prop so I expect it was both causing the issue.