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Drive Belt tensioning method ?


New Member
Nov 18, 2020
Country Flag
Hello all

I need to tighten the dual drive belts (alternator) but the process is too simple for anyone to have documented it for a fool.

The Toyota maintenance manual does nt even mention it. So as per the diagram - do first loosen the lower alternator nut (highlighted in yellow) then turn the horizontal adjustment bolt at the top?

And without the SST drive belt deflection tool, what’s the best way to get the tension as close as possible to spec?



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if I remember correctly, there is a lock nut on the horizontal bolt. Don't forget to loosen that one when you try to adjust the horizontal one.
Don't loosen the bolts too much. The alternator just needs enough play to be movable.
The best way to get the tension right: It's a bit of gut feeling. Try to get the feeling on another cars' belt. It's very simple.
Thanks for your reply Firewout. Just to confirm- I still need to slacken that lower pivot bolt first, then the lock nut as you suggest…
Yep, slacken the one you have marked in yellow, tighten using the horizontal bolt, then retighten the pivot bolt.

Don't over tighten as this can cause damage to the bearings. I seem to remember the Haynes manual saying is should deflect 1cm with 10 newtons applied to it, whatever the **** that means..... As long as you can move it with a bit of a yank its all good.
Regarding the tension: my mechanic taught me that the belts should be tight enough so that you can twist them just one quarter turn.
If tightening the V-type drive belts doesn't help, it might be that the belts are bottoming out, and then you can tighten until something breaks and still not get a good grip. The belts have to contact on the sides only. When they wear, they creep further down into the groove. When they touch bottom, they loose traction. One trick commonly used is to use a slightly wider belt, like 1 to 1.5 mm wider than standard, then you have more belt to wear. You might have to compensate with a slightly longer belt as well, as it rides a bit further out. I know some use 11.9 mm when the spec says 9.5.
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