Do you need to index your bell?
SHORT ANSWER. YES. We have seen that even on our precision machined aluminum bells, which we keep within a tight .002-.003 variance, that the Toyota blocks are not as tight in tolerance or consistency. For example, if i took 10 of my bells, and put all of them on the same block, the runout would be very consistent across all 10 bells, ensuring our machining is consistent. BUT, if I would take 10 JZ blocks, and check one bell against all those blocks, my variance would be all over the place. This tells me that the Toyota machining tolerances are not as consistent.
What are your odds of being out of index?
While it is a smaller percentage (about 15-20%) that have shown an out of index condition, so I think it is better to play it safe and just check these to be sure. Out of index can cause premature failure of the input bearing as well as uneven wear and heat in the input gear. A tell-tale sign of an out of index bell can be a lot of rollover noise coming from the transmission. This is due to a side-loading condition on the input which over time can cause transmission issues.
TREMEC requires you to index your bellhousing to keep your factory warranty in check. TREMEC specifications are .005" (5 thousandths) or under.
The quickest and easiest way to ensure a trouble free transmission is to buy an index plate and check your runout.
TECH TIP:
To remove your stock dowels, i recommend soaking them in a penetrating oil and let them sit overnight. Use a pair of heavy duty vice grips and slowly work them back and forth. If the get tight, heat applied to the block around the dowel may be needed
Here is a quick video I did on indexing and offset dowel install:
