Gearing/differential question - Vintage Mustang Forums
 
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Old 06-26-2019, 05:08 PM Thread Starter
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Gearing/differential question

I'm chasing down various bad noises coming from my rear end. My car's, not my own. Get your head outta the gutter.


It first started with the groaning/grinding noise on acceleration, then whining on decel chimed in - when it was warmed up. Took it to a local diff shop who basically told me I couldn't/shouldn't drive it home (20 miles). Towed it home.



Pulled the axles and discovered the right axle bearing was grinding - the exact noise I was hearing. YAY! Except...the whining? I'm suspecting the pinion might be going bad. SO...tonight we're putting the axles with their new bearings in, and driving it to see if all the noise is gone. If it isn't, I'll be doing an entire diff rebuild. This will be the second time it was rebuilt.



Currently the car is a C4 auto w/ 3.23 gears. I have a T5 to go in it...eventually. And since this is a track car, I was thinking 3.80 gears but MAN that would make it whine until I can get that T5 in. So do 3.55s sound good? Any thoughts on this whole mess?


1966 Restomod/track car, 1973 Q-code Mach 1, 1997 F250 diesel, 2000 VW Beetle Rallycross car, 2010 Crown Vic (ex-City of Lakewood PD), 2015 Focus ST-2
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Old 06-26-2019, 05:15 PM
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3.55's is as steep as I would go on a C4 for sure. But man, 3.73's are glorious behind a T5. What's the hold up to row your own? (besides time, money and everything else, lol)

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Old 06-26-2019, 05:26 PM
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depends on the T-5 3.35 or 2.95


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Old 06-26-2019, 06:51 PM Thread Starter
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Quote:
Originally Posted by BlakeTX View Post
3.55's is as steep as I would go on a C4 for sure. But man, 3.73's are glorious behind a T5. What's the hold up to row your own? (besides time, money and everything else, lol)

Money for parts, time to put them in. Soooo basically money lol. I have everything but the hydraulic system & the pedals.


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Originally Posted by 2nd 66 View Post
depends on the T-5 3.35 or 2.95

The T5 I have is a WC out of a '91. 5th gear is .68. Is that what you mean?


1966 Restomod/track car, 1973 Q-code Mach 1, 1997 F250 diesel, 2000 VW Beetle Rallycross car, 2010 Crown Vic (ex-City of Lakewood PD), 2015 Focus ST-2
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Old 06-26-2019, 07:03 PM
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Quote:
Originally Posted by Sparky66 View Post
Money for parts, time to put them in. Soooo basically money lol. I have everything but the hydraulic system & the pedals.





The T5 I have is a WC out of a '91. 5th gear is .68. Is that what you mean?
T-5's come in 2 basic flavors as stock v8 gear sets go
1st gear being 3.35/.68
or
1st gear being 2.95/.63
I have the 3.35/.68 as it sounds you do , I have a 3.40 tracloc much more than that and 1st gear is useless
with a 2.95 1st 3.55 would probably be nice or 3.73 as Blake mentioned


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Old 06-26-2019, 07:30 PM
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Too bad you can't do the T5 1st to gain a more scientific perspective of the changes. you might be happy with what you have with a sufficiently torquey engine.
What you have now 2.46x3.23=7.95 ...with T5 3.35x3.23=10.82 That is already a 36% better take off ratio not to mention the gain from the manual opposed to the slush box. Think of the old geezers that would brag about their 4:11 gears with their C4s (or even 4spds)which equals 10.11 drive ratio in 1st.


Decide if you want to shred tires or actually accelerate through 1st gear and 2nd. My 3:00 rear wouldn't be horrible to keep except that the 1-2 or 2-1 drop in the generic T5 is awfully wide.

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Old 06-26-2019, 08:39 PM
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Quote:
Originally Posted by 1ofAMillion+ View Post
Too bad you can't do the T5 1st to gain a more scientific perspective of the changes. you might be happy with what you have with a sufficiently torquey engine.
What you have now 2.46x3.23=7.95 ...with T5 3.35x3.23=10.82 That is already a 36% better take off ratio not to mention the gain from the manual opposed to the slush box. Think of the old geezers that would brag about their 4:11 gears with their C4s (or even 4spds)which equals 10.11 drive ratio in 1st.


Decide if you want to shred tires or actually accelerate through 1st gear and 2nd. My 3:00 rear wouldn't be horrible to keep except that the 1-2 or 2-1 drop in the generic T5 is awfully wide.
What you have to remember is that due to the torque multiplication of the automatic transmission you don't need as deep an overall ratio.

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Old 06-27-2019, 11:34 AM Thread Starter
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My old '89 GT had 3.55s behind a T5, so I'm familiar with the gearing "feel".
I'm not concerned about off the line speed - more about engine RPM at high speeds (120+). Track days with the C4 are numbered, and I can just keep the rpms down if I do go out, so I'm thinking more towards the future when I do drop the T5 in. I do know I'll be rowing a bit through the turns, so with manual steering I'd like to keep the rowing to a minimum lol.

According to some calculators, 3.55 is more engine/rpm "friendly" at higher speeds. If the rear wasn't making so much noise (it's better with the new axle bearings, but I have my doubts it's actually fixed, especially since the noise *completely* went away when turning around to the left. Thinking a side gear is worn out.) I'd keep the 3.23s.


1966 Restomod/track car, 1973 Q-code Mach 1, 1997 F250 diesel, 2000 VW Beetle Rallycross car, 2010 Crown Vic (ex-City of Lakewood PD), 2015 Focus ST-2
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Old 06-27-2019, 11:38 AM Thread Starter
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It's early, sorry for the rambling...but want to add that I'll spend the majority of track time in 3rd & 4th, with short stints in 5th. I'm thinking (again, it's early...) that the bigger "drop" between 3rd and 4th might be an advantage? I dunno...


1966 Restomod/track car, 1973 Q-code Mach 1, 1997 F250 diesel, 2000 VW Beetle Rallycross car, 2010 Crown Vic (ex-City of Lakewood PD), 2015 Focus ST-2
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