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Pinion bearing making noise.
https://slantsix.org/forum/viewtopic.php?t=54719		 Page 2 of 2
Author:  Joshie225 [ Fri Mar 14, 2014 8:45 am ]
Post subject: 
I've never seen 2.71 in an 8.25 myself nor do I recall seeing it on later (F-body) option sheets, but it helps explain why the Sure-Grip didn't fit.

I've owned 2.45 (V8 car), 3.21 (OD 6cyl car) and 3.55 (D100) geared 8.25s. 2.45 makes for rather relaxed highway cruising with a 318, but the overall 6:1 starting ratio makes for rather relaxed launches too. More modern transmissions are so much nicer. My current daily driver is a 5-speed auto with 3.67, 2.00, 1.41, 1.00, and .74 ratios combined with a
3.38 differential. That gives 12.4:1 in low and 2.50:1 in OD. It scoots off the line and cruises at low RPM.

Ring and pinion work is tricky and getting the pinion depth spot-on is the most labor intensive part. If the noise is fairly mild I would probably leave it alone. New 2.71s are available, but I'd be tempted to go with 2.94s and use the Sure-Grip.
Author:  DusterIdiot [ Fri Mar 14, 2014 6:07 pm ]
Post subject:  Stock...
Quote:
I've never seen 2.71 in an 8.25 myself nor do I recall seeing it on later (F-body) option sheets, but it helps explain why the Sure-Grip didn't fit.
2.71 is the early 8.25 2.76 ratio...you can find it in the early 70's to 1974 B and C-Body diffs mostly...(I had a 1973 Fury 2 400-2v and a 1974 Satellite 318-2v that had the 2.71 open diff under them).
Quote:
I'd be tempted to go with 2.94s and use the Sure-Grip.
I would x2 that as the best mileage and passable performance in a mild to moderate build 225, very nice on the highway in direct.

-D.Idiot
Author:  Joshie225 [ Fri Mar 14, 2014 7:21 pm ]
Post subject: 
DI,

Now that you mention where those gears were used I'm thinking that might have been what I had in my '74 Satellite behind the 318 and 904.
Author:  DusterIdiot [ Fri Mar 14, 2014 10:00 pm ]
Post subject:  Yep...
Quote:
Now that you mention where those gears were used I'm thinking that might have been what I had in my '74 Satellite behind the 318 and 904.
It's that fine line when doing the rear diff shuffle...the 3.23 or the 3.21 if 7 1/4 or 8 3/4 or 8 1/4... the 3.54 vs. 3.55 ratios (or in the very early 60's 8 3/4" the 3.58...)...just subtle differences due to ring gear size and tooth counts.

:wink:
Author:  Sam Powell [ Mon Mar 17, 2014 3:21 pm ]
Post subject: 
Thanks for the great feedback. So is it the pinion depth that makes for the whine? It is not too loud, but is definitely there but only at 36-37 mph and then goes away. Is there any way to adjust that without tearing the rear down again? That is unfortunately a very common speed to drive in these parts. Above 38 mph or so it is actually quieter than my BMW, which has a subtle, whine most of the time.

It does seem to drive nicely now. Here is what the plan is currently. I will drive it this way, without the OD for this season, and test the gas mileage and performance. If it is above 20 mpg on the highway, I may just leave it alone. I think I would have to put quieter mufflers on for that to be pleasant on the highway.

If I make a change, the plan is to get 3.23 gears, or whatever fits this rear in this range, and then get the Gear Vendors OD. That would result in a 2.58 OD ratio. This would uyield slightly better highway milege, and maybe better town mileage owing to the better ratios for acceleration in first and second gear. This engine pulled the 5th gear nicely at highway speeds before, and that was 2.14.

If I thought the posi would fit a 2.94 I would go with that and the sure grip with the OD. That would give a final drive of 2.35,which would fall between the current 2.71 and the OD drive ratio of 2.14 with the T-5.

Lou has always been an advocate of spinning up higher RPM's on the highway, but then he has always run bigger cams than this engine has.

Sam
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