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9" backlash


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#1 neglectedtorana

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Posted 04 February 2024 - 02:15 PM

Hi,

 

I notice some drive line clunking at times when changing gears or coasting then accelerating and I am wondering if I have too much backlash in the diff.

 

I have taken a crude measurement at the yoke, I tried to measure directly on the circumference. it is about 1.8-2mm when rotating.

I know its not a perfect measurement but is it too much?

If it is I will take the centre out and it can go to a diff shop to be checked/set but would be nice to know how much backlash there should be before I go that far.

 

The info I have found online measures the backlash at the crown wheel so I can't do that in place. When I grab the tail shaft and rotate it feels like a lot of play but without something to compare it to its a guess.

 

Any thoughts?

Pic shows where I have set up the dial indicator.

 

Cheers, Tom

 

Attached File  P1140406.JPG   156.53K   2 downloads



#2 neglectedtorana

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Posted 04 February 2024 - 02:31 PM

Here's a video.

It does have a TruTrac centre.

 



#3 Bigfella237

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Posted 04 February 2024 - 02:49 PM

Here's a video.


YT vids don't show up on the forum any more, you have to link them instead...

 

https://www.youtube....h?v=Ex0oxWtPvW8



#4 neglectedtorana

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Posted 04 February 2024 - 05:26 PM

Thanks Andrew,



#5 Bigfella237

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Posted 04 February 2024 - 06:15 PM

Tom, in a perfect world we want zero backlash. Zero backlash means the teeth on the crownwheel and on the pinion are achieving the best mesh possible, and the best mesh means the most strength (and the least NVH, and the longest lifespan).

 

But most things expand as they heat up, so the idea of having backlash is to allow for this thermal expansion.

 

It's normal to have a little backlash when everything's stone cold, but the trick is having the least amount that you can get away with, without things binding when they get hot.

 

Different components, made from different materials, with a different mass, all expand at different rates, which is why manufacturers specify different backlash settings for different diffs.

 

The other thing to consider is the cause... Was it originally setup with that much backlash, or has something worn, or has somebody over-tightened the yoke and crushed the crush-tube between the pinion bearings?

 

It's usually no big deal the setup the diff centre again, the only parts involved should be a pinion seal, the gasket and the oil, and maybe a shim here or there, but labour ain't cheap these days if you can't do it yourself.



#6 76lxhatch

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Posted 04 February 2024 - 06:21 PM

Some diff centres use deliberate backlash movement too, e.g. mechanical lockers can cause a 1/4 turn of the driveshaft. There's a small amount even in normal spider gears, not to mention axle slop if the splines are not a snug fit (too much of this can be a problem as it causes more wear). As you say you're not just measuring crownwheel backlash.

 

Sounds like it's fairly minimal at 2mm though, I wouldn't worry about it if the diff isn't noisy. There's probably more movement at the transmission end?



#7 dron

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Posted 04 February 2024 - 08:01 PM

May be a good idear to leve it alone if it is not noisey and the bearings are ok.

 

      If you change the back lash you will move the contact point of the gearset and it will be noisey!  If it has ford factory gears it will have a lot of back lash. Aftermarket gearsets normaly have a smaller back lash spec than the factory gear sets. With used gears it is normal to do a tooth mark up and back lash meshorment before striping a diff and use that to set it up again after the rebuild. Never a good idear to move the contact point on a used gearset if it can be avoided.


Edited by dron, 04 February 2024 - 08:05 PM.


#8 neglectedtorana

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Posted 05 February 2024 - 06:48 PM

Thanks for the replies gents, 

I am hoping to leave it alone. Ideally I will get the car to the diff builder and get his opinion, unfortunately I now live a lot further away than when I had it built.

 

It has always had the same noise and hasn't gotten louder so it could be the way the Tru Trac is meant to be setup.

 

Cheers, Tom



#9 neglectedtorana

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Posted 09 February 2024 - 01:23 PM

I spoke to the diff builder and he thinks its not uncommon to have some noise similar to what I have in a car with stiffer suspension etc. and after driving the Hilux I borrowed for this weekend which has a similar noise but louder the noise I was hearing in the Torana doesn't seem a big deal.

 

Not going to do anymore about it.



#10 ozyozyozy

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Posted 13 February 2024 - 10:02 PM

9 inch are suppose to have about 7 to 12 thou backlash from memory, which is a bit more than a lot of other diffs out there, eg borg warner is about 7 on the wide side. The tooth mesh reading tends dictate that measurement to some degree.
Larger diffs normally have more.

#11 Heath

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Posted 14 February 2024 - 09:35 AM

^ Measured at the crownwheel tooth obviously.
 

Tom, keep in mind you're testing the mechanical lash including the splines of the axle plus the gear system in the differential itself. Not just the crown wheel & pinion backlash which is what you test when you set up the centre.

That looks like a fair bit of back-lash but not absurd, I think? I have never measured mine from that point.






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