Issues with Primitive Diff Guard

[Dave Hansford]

Hi Folks:

I wondered if anybody on here has fitted Primitive Racing's old-style R160 differential bash plate? I did, a while back, and since then, I've noticed a whine from the rear that's sensitive to accelerator. To fit this bash plate, you literally have to use the biggest pry bar you can fit under there to prise the rear diff carrier crossmember sufficiently clear of the back of the diff to slide the rear plate of the guard in between them. When you release the pry bar, it's essentially jammed tight in there. It's five millimetres thick, and while that doesn't sound like much, I'm starting to wonder if it's actually a good idea.

I guess my concern comes from the fact that, to install this plate, you have to use considerable force to move something from where it naturally wants to sit, then jam something in there that ensures it can’t return to that position. In other words, you permanently displace the diff and/or crossmember and in doing so, pre-load those units with considerable tension that wasn’t there before.

I don't understand enough about the internal workings of diffs to know for sure, but it seems possible that this bash plate could actually exert a load on pinions etc...

What I do know is that after I took the bash plate off, the whining appears to have stopped. I note with great interest that Primitive Racing has since developed a new bash plate that does away with the "jam it in there" installation, using instead a bracket that's secured by the rear diff cover bolts. I contacted Primitive about this experience, and they were friendly and helpful, but naturally enough, rejected the idea that the earlier-style bash plate might actually cause damage to the very unit it was supposed to be protecting.

Anyway, I thought I'd ask whether anyone else might have had the same experience?

 

[Kevin]

Interesting and of course they would deny any issues.
(I've never seen any need to protect the rear diff as it is probably the strongest part of the vehicle)

 

[SquiresSquire]

Subaxtreme now have 4EAT and R160 Guards available as well

 

[Dave Hansford]

Subaxtreme now have 4EAT and R160 Guards available as well

I see their diff guard mounts the same way - if anything, it looks thicker than the Primitive one... 6mm?

 

[El_Freddo]

Interesting and of course they would deny any issues.
(I've never seen any need to protect the rear diff as it is probably the strongest part of the vehicle)

If reversing and you hit a rock you can shatter the alloy rear cover plate. I’ve seen it done once on the internet. Not exactly a common issue, but a possibility that would see you stuck on the track.

@Dave Hansford - you won’t effect the pinion shaft settings in the diff by moving this 5mm. I doubt you’d wear out any bearings quicker either.

What it might do though is allow the diff to contact something to transfer the internal noises of the diff into the body. Or a Bush is being compressed to do the same.

End of the day, if you’re not happy with it it’s best to do something about it until you are satisfied. Did the bash plate you have come from an older model second hand, or is it a new unit but not the latest design?

Cheers

Bennie

 

[ABFoz]

I will check where my rear diff guard sits but mine is a genuine one from the USA and is only 3mm thick max.

When I installed mine, though, I didn't pry but removed the whole diff and installed everything back without needing to pry or force anything.

 

[Dave Hansford]

What it might do though is allow the diff to contact something to transfer the internal noises of the diff into the body. Or a Bush is being compressed to do the same

Thanks Bennie:
your theory is entirely possible, because the diff guard plate is in direct contact with the diff carrier bolts, and of course with the crossmember too, so I think noise, or some weird harmonic, could be getting transferred...

 

[Dave Hansford]

I will check where my rear diff guard sits but mine is a genuine one from the USA and is only 3mm thick max.

When I installed mine, though, I didn't pry but removed the whole diff and installed everything back without needing to pry or force anything.

Thanks ABFoz:

I came lazy out of the womb, so if it comes to that, I probably won’t put the diff guard back on. we don’t go that hard off-road anyway... it’s only there because, this being the South Island, we end up on a lot of rocky river banks.

 

[ABFoz]

Thanks ABFoz:

Welcome.

Here is the photo of the diff guard I took just a while ago.

It's also wedged between the bushes and the diff bolts but it moves together with the diff. There is still a considerable amount of movement. The diff guard is only 3mm but made of mild steel.

Are your diff bushes in good shape? Cheers.

 

[idw]

Had a crossbred rear diff guard when I still had the SF, i force it into place, used it as a jack point, and beat it on all kinds of stuff for almost a decade. probably not gonna be an issue

 

[Dave Hansford]

Welcome.

Here is the photo of the diff guard I took just a while ago.

Yup: that’s the same design, pretty much, as the Primitive one - except for the section width. The bushes are top notch... the car hasn’t yet done 80k, and I recently added those Whiteline inserts..

 

[ABFoz]

Did the sound/whining start after the installation of the inserts? The black Whiteline polybushes are usually rated at 70A on the Shore A durometer scale. It is just slightly stiffer than worn-out rubber bushes at 69A. Cheers.

 

[Dave Hansford]

Thanks ABFoz:

Yes, the noise did begin after I inserted those bushes, but I also fitted the diff guard at the same time. But since I took the diff guard off, the noise appears to have stopped, even though the bush inserts are still in there.

 

[ABFoz]

Good to know. You may be right. There is a chance that some NVH are translated to the body through harmonics. Cheers.