E36: Feedback on 14 mm diff bolt vs. stock 12 mm

[FredK]

I have a Bimmerworld diff bushing kit that uses a 12 mm through hole for the diff bolt bushing.

Is a 14 mm bolt a "must-have" for reliability purposes? I don't really want to be swapping out diff bolts because they've fractured. I doubt I will ever break one since I drive like grandma but I'm curious.

[olemiss540]

Not required in my opinion. Have never had a diff bolt issue once I upgraded the bushing. The 12mm bolt works fine as long as the bushing stays intact IMO.

[AJLM34A]

Both of the diffs in my E36s are using bushings, one was built 6 years ago and the other 2 years ago and have not had any problems.

[pbonsalb]

With a stiff front bushing, stock should be fine. With an inexpensive Maximum Psi weld on diff brace (welding part requires some knowledge), the longer stock diameter bolt supplied with the brace held launching on the dragstrip with drag radials that broke driveshafts, ZF320 transmissions and M3 diff output stubs.

[FredK]

With a stiff front bushing, stock should be fine. With an inexpensive Maximum Psi weld on diff brace (welding part requires some knowledge), the longer stock diameter bolt supplied with the brace held launching on the dragstrip with drag radials that broke driveshafts, ZF320 transmissions and M3 diff output stubs.

That's great to hear, especially because you are way above stock power levels!

[aeronaut]

Poly or spherical everywhere, random infrequent off-road use, curbing groomer. 12mm no issues.

I am using an extended 12.9 bolt so that if it did break, there would be some of the bolt extended past the through-hole so that it'd be easy to remove.

[pbonsalb]

Maybe slot the rear end in case it bends when it breaks and can’t be unscrewed out the back. The rear end stiffer bushings help reduce the movement that breaks the bolt.

[NeilM]

I have a Bimmerworld diff bushing kit that uses a 12 mm through hole for the diff bolt bushing.

[...] I doubt I will ever break one since I drive like grandma but I'm curious.

The little old lady from Pasadena
(Go granny, go granny, go granny, go)
Has a pretty little flowerbed of white gardenias
(Go granny, go granny, go granny, go)
But parked in a rickety old garage
There's a brand new shiny red super stock Dodge

And everybody's sayin' that there's nobody meaner than
The little old lady from Pasadena
She drives real fast and she drives real hard
She's the terror of Colorado boulevard
It's the little old lady from Pasadena

If you see her on the strip, don't try to choose her
(Go granny, go granny, go granny, go)
You might drive a go-er, but you'll never lose her
(Go granny, go granny, go granny, go)
Well, she's gonna get a ticket now, sooner or later
'Cause she can't keep her foot off the accelerator

"Little Old Lady From Pasadena"
Jan & Dean, 1964
https://www.youtube.com/watch?v=D7f9hsFrKUY

[FredK]

Poly or spherical everywhere, random infrequent off-road use, curbing groomer. 12mm no issues.

I am using an extended 12.9 bolt so that if it did break, there would be some of the bolt extended past the through-hole so that it'd be easy to remove.

thanks for the feedback!

Maybe slot the rear end in case it bends when it breaks and can’t be unscrewed out the back. The rear end stiffer bushings help reduce the movement that breaks the bolt.

Ah, that sounds like a good idea. It'd be a lot harder to slot it on the car by necessity!

The little old lady from Pasadena
(Go granny, go granny, go granny, go)
...

[golgo13]

I'm on the OEM 12mm 12.9 and never had a problem (knock on wood) in six years of track driving. I did have the bolt come loose once and back out when at the track which was easy to put back in and retorque while I was there.

[jayjaya29]

Only upgrade to 14mm if your 12mm breaks and you have to drill it out of the differential.