Incorrect Arrow Directions on Flex discs from Doorman (maybe other brands, too?)

[samtheman48]

I wanted to warn those of you who are replacing or have replaced a flex disc recently with one not made by Febi/BMW. I completed by manual swap 4 months ago. I replaced all wear components with new, mostly OEM BMW or OEM supplier parts. The one exception was the flex disc. I bought an Doorman flex disc from Rockauto. Admittedly, I should've compared the part with the good-condition BMW part I pulled off the car (130k miles). I didn't and I installed the flex disc following the directional arrows on the unit. Fast forward 4 months and 5,000 miles, and I went under the car to inspect everything. I was shocked to notice significant cracks in the disc. My first thought, was that I had installed the arrows backwards, meaning that the thinner (compression) portion was taking the tensile loads. Turns out, I had installed according to the arrows, but my intuition about the crack propagation turned out to be correct. The arrows on the Doorman part are OPPOSITE the arrows on the BMW part. If you install the Doorman part "correctly" it will fail. I made sure the part number I received was the same as I ordered. I have some photos of the original BMW flex disc (left) next to the Doorman (right).
IMG_1516.jpgIMG_1523.jpg
Clearly, the relation of the arrows to the thinner and thicker portion are different. BMW disc is on top. If you rotate the disc, then you can clearly see the arrows line up.
IMG_1527.jpgIMG_1530.jpg

[geargrinder]

Yeah. Looks bogus.

TBH while officially the guibo does have a 'direction', I don't think it's 'direction' that is most important really. The arrows aren't 'front/back' directional, they point to where the bolts go for each yoke, but, that's of course depending on it being oriented a specific way. Because of the alternating nature of the holes vs the yokes etc. you could absolutely install it backwards fine, as long as you get the pairings right. For each pair of holes for each 'thick' section, you want the tranny on the 'leading' hole and the driveshaft on the trailing hole... As long as you did that flipped the stresses should be the same I think.

But that's all academic, agreed the markings are clearly reversed on the cheapo Dorman part.

[pshovest]

Another quirk about guibo installation is that you're not supposed to tighten the nut/bolt head that rests on the guibo. You only tighten the nut/bolt head that rests on the steel DS or trans flange. Tightening the nut/bolt head on the guibo puts torsion into the metal sleeve, which in turn puts stresses in the rubber. With photo's showing every other guibo bolt sleeve cracked, I wonder if this is the real cause of the failure.

[philly98540]

^this

[samtheman48]

Another quirk about guibo installation is that you're not supposed to tighten the nut/bolt head that rests on the guibo. You only tighten the nut/bolt head that rests on the steel DS or trans flange. Tightening the nut/bolt head on the guibo puts torsion into the metal sleeve, which in turn puts stresses in the rubber. With photo's showing every other guibo bolt sleeve cracked, I wonder if this is the real cause of the failure.

Hmm. Could be possible. One thing I didn't mention in the initial post was that the cheaper part seemed to have a much lower elastic modulus. It is probably about 60-70% as stiff as the BMW part. This could have lead to an expedited failure, too.