Drive line critical speed.

Transmission to Rear-end

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Re: Drive line critical speed.

Post by Supershafts » Thu Nov 20, 2014 9:19 pm

BUT when someone says they have a ceiling of 7k rpm and are using ______ transmission it's better to know exactly what they mean, or design it that at 7k in that transmissions top gear the shaft can or can not handle it.

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Re: Drive line critical speed.

Post by jacksoni » Tue May 31, 2016 3:58 pm

Older thread but I have a question about my set up and its safety/trans output shaft issue. LSR car, Richmond 5 sp (1:1 5th). Last time down the track went through the lights at 9750 rpm. The shaft is 3" x 41.75" mild steel. Balance has been rechecked couple of times. Rear is fixed with IRS so it doesn't move. I have had problem with burning up the bearing on the tailshaft and pushing out the seal. As far as I can see there is no real lubrication to the output shaft seal. I modified the tailshaft housing to take a roller bearing and rigged a small pump to lubricate the bearing. Though I feel no vibration it pushed/vibrated/whatever the bearing/seal out again. I now have retainers on those. I checked the alignment of the shafts- front was about 1.5* tailshaft to driveshaft and rear 0*. I recognize this is not optimum but pretty close. I have shimmed the nose of the differential so the trans and pinion shaft are parallel to within 0.1-0.2* and with 1.2-1.3* angle to the driveshaft which I understand is pretty good.

Two questions:
I see driveshaft critical speeds for this at about 11300rpm or so (various calculators). Is my shaft safe? (more or less) or should I go up in diameter? RPm's may increase.

Any ideas on why it tends to push out the seal, and sometimes the bearing as well. The bearings both stock and now roller are slight press fit, not super tight.


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