Gearbox friction

[Eric Parham]

Is internal friction really much less for 4th gear versus 5th (or lower versus higher) gears? What effect on friction if the R&P is adjusted so that the overall ratio stays the same?

[Tak]

That is somewhat of a loaded question. It depends highly on the gearbox.
Many traditional front engine rear drive cars have a 4th gear that is 1:1 (and not transmitted through gears). In theory, there will be slightly less drive line loss in 4th gear in such a box. Do note that even though it's 1:1, in a modern synchromesh tranny, all the gears are still engaged and turning (1 gear of each pair is disconnected from it's shaft), so the parasitic losses are unchanged. Also note that virtually every front drive trans-axle has 4 or 5 true gear ratios--no 1:1 ratio. Lastly, the state of shaft and bearing alignment can have more impact on drag than the actual gear train. If a bearing gets sloppy, or the tranny is mis-bored or mis-aligned at the assembly, the gears become mis-aligned and drag can become significant. I've seen a bent transmission consume 40 hp (in a car with with 130 to start with!)! This is why transmission blue printing has become popular in some circles...
At the end of the day, total driveline losses are typically in the 10-15% range, with most of it coming from the (Hypoid) ring and pinion. Consider spending your time and dollars in a well functioning, well aligned, well adjusted R&P (If you have one!)
My $.02 worth

Tak
# 29 ITA
SFR SCCA

[leawil]

Interesting...

Any way to determine amount of power loss in diff other than comparison of dyno runs with different diff's?

[billf]

<_< Love to have the experts&#39; answer to this.

I&#39;ve always wondered about the method of transmission to the drive axle (rear) when, say: an under driven 5th drives thru a super high numerical ring and Pinion, compared to a 1:1 final drive thru a lower numerical ring and pinion to achieve the same overall ratio.

I&#39;ve always thought that the loss thru the underdriven 5th, coupled with the losses of high numerical R/P would be greater. A one to one anything would have to be the ideal minimal loss device.

Anyone from the industry to answer this?

Good racing.

Bill :024:

[msogren]

Textbook theory; The closer the gear sizes are to each other, the less the gear drag. Impact angles and uneven bearing loads, etc. Bigger gears spin easier, but take more to get them moving, of course. Tiny gears get very hot and have a lot of drag, from the impact angles.
Real world, the bigger gear moves more oil and the most transverse gearboxes spin all of the gears, all the time.
Other than taking out the gears you arnt using . Some FV boxes remove the syncro rings to reduce the oil drag, and the SSC guys run ATF, synthetic.
The only place I could envision reducing gear drag would be an oil scrapper on the upper two gears. Maybe with oil relief slots ground in the gears.
The other is to use straight cut gears.
From the above, the same overall gear ratio would make abit more power in 4th. All of the gears are closer together, size wise. And 4th gear might have a straighter cut. My guess is 2-3hp at 125hp crank.might be more..
IMHo the textbooks should give apretty good idea, But they need the gear angles, sizes, speed, etc.
MM