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Author
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Topic: Rebuilt rear end questions
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jay67fast
Journeyman Posts: 87
From: Boca Raton, Florida,U.S.A.
Registered: Nov 2004
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posted 12-14-2005 04:02 PM
  
I just bought a 2.47, 9", open rear pumpkin for my 67, 289, C4 fastback from a rear end rebuilder. He used a 2.47 ring and pinion from a Lincoln and rebuilt the rest of the unit. I have two questions:
1) Does this rear end have to be ��broken in�� in any way, and if so, what��s the procedure?
2) What rear end oil should be used? 85/ 90 or 85/160. What��s the difference between them? It��s my understanding that the first number is the actual weight of the oil, and the second number is the equivalent protection of the oil, that is, the oil will protect to the same degree as the weight oil of the second number. For example, 85/90 oil is the viscosity of 85 weight oil, but affords the protection of 90 viscosity (weight) oil, whereas 85/160 oil is the viscosity (weight) of 85 oil, but affords the protection of 160 viscosity (weight) oil. If this is correct, then it follows that 85/160 oil should be better to lube the rear end than 85/160 oil.
This all sounds perfectly logical, but I��m not sure it��s correct!!! Can anyone out there set me straight on this?
Thanks
Jay67fast
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jay67fast
Journeyman Posts: 87
From: Boca Raton, Florida,U.S.A.
Registered: Nov 2004
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posted 12-14-2005 04:14 PM
Whoops! Slippsies!
Third line from bottom should read "oil should be better to lube the rear end than 85/90 oil".
Sorry!
Jay67fast
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Ryan Wilke
Gearhead Posts: 2714
From: Stanton, Michigan, zip 48888
Registered: Oct 2000
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posted 12-14-2005 06:04 PM
Jay:
A 2.47 ratio ring & pinion?
Really?
Wow, you must plan to do lots of freeway cruising or do some "cannonball racing"?
If not, I'd re-think installing it. Sure it'll keep the rpms low at highway + speeds, but it will be pretty boggy off the line compared to a numerically higher gear ratio. It all depending on your application; but for simple all-around cruising, you may be better served to run a set of 3.00 gears or such.Question #1: No. Especially since you said it's a used gear from a Lincoln, no "break-in" required. Question #2: Guessing at your application, I'd recommend you stick with a quality-grade (Valvoline, Shell, etc.) 85/90 weight gear lube. That 85/160 wgt. stuff is overkill as would synthetic stuff for your setup. Just my 2 cents,,,,,,,, Ryan 
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jay67fast
Journeyman Posts: 87
From: Boca Raton, Florida,U.S.A.
Registered: Nov 2004
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posted 12-14-2005 06:58 PM
Ryan,
You hit the nail on the head. I live in Southeast Florida, and believe me, all the highways (and most of the main streets and avenues) are raceways!!! The speed limit is 70 on the interstates and thruway and that's just a recommendation! LOL! With my current 3.25 lim. slip I was turning 3500 rpm just to keep from being run off the roads! Between the high rpm's and the flowmasters, I feel like I'm going to be picking the pistons off the road! I need to bring the rpm's down, and since I don't EVER race the car, off the line speed isn't a priority.
Thanks for your reply.
Jay67fast
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Fastymz
Moderator Posts: 21741
From: Reno Nv USA M&M#1240
Registered: Apr 2001
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posted 12-14-2005 07:01 PM
Jay, with 25" tall tires and 3.40 gears and a C-4. I'm only at 3000rpm at 70mph. I'd go to taller tires before changing the gears. Get some 28" tall tires on the rear of the car.
Going from 26" tall tires to 28" tires will drop the rpm about 200-300rpm. Going to 30" tall tires would drop it about 400-500rpm.
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oddly obsessed with big scoops on little MustangsHOOD HACKERS DELIGHT!
My Pics [This message has been edited by Fastymz (edited 12-14-2005).]
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