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fastricky

5 speed + 3.45?

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(edited)

Hi all, I've got the stock diff in my tii and wondered about installing a 3.45 to bring the revs down further. Currently with my 5 speed and 3.64 at 80 mph the rpm is roughly 3750, at 90 mph 4000 rpm. If I did the math right, the 3.45 should reduce the revs by @ 250 rpm at those speeds. I find the current 1st gear a bit too low & stump puller-ish for my taste (requires quick shifts) so the taller differential would be welcome in that regard too I think... any flaws to my thinking?

Edited by fastricky

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If you live in a place where you do mostly highway driving, I think you're spot on. If you're in a place like the SF Bay Area and can't seem to get out of 2nd gear, maybe not the best ratio. But hey I'm just peeved that I'm in stop and go havoc as we speak, ugh.

Jeff

Sent from my SM-G973U using Tapatalk

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You’ll give up some acceleration, but if most of your driving is above 80 mph, go for it!

 

Regards,

 

Steve

 

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5 minutes ago, Conserv said:

You’ll give up some acceleration, but if most of your driving is above 80 mph, go for it!

 

Regards,

 

Steve

 

 

That's all the confirmation I needed, thanks Steve!

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1 hour ago, fastricky said:

Currently with my 5 speed and 3.64 at 80 mph the rpm is roughly 3750, at 90 mph 4000 rpm.

Dunno whether it's my tach or your math, but with that same setup (OD 5 speed from an E21) 3200 rpm is about 70, and 4000 rpm is +/- 80...

 

The trick is gonna be finding a 3.45 in the USA...

 

mike

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(edited)

that's what I run in my tii. 3:45 lsd / 245... i love to get out on the freeway and buzz along at  80..85

 

I'll never go back to the 3:64.

 

I'll just work on making my tii faster

Edited by iinca
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(edited)
1 hour ago, mike said:

Dunno whether it's my tach or your math, but with that same setup (OD 5 speed from an E21) 3200 rpm is about 70, and 4000 rpm is +/- 80...

 

The trick is gonna be finding a 3.45 in the USA...

 

mike

I agree, my E21 5 speed with 14" wheels but lower profile tires than the original 13" wheels gives me much less RPM than OP states. My speedo registers real close to cell phone speed apps.

Edited by 7502

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1 hour ago, iinca said:

I'll never go back to the 3:64.

 

I'm still 4speed and enjoying the reman 3.45 LSD.  My speedo is spot-on to GPS.  First time in 29 years.

 

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Found one with limited slip to boot... wasn't cheap but I was looking for awhile. I'll post my findings when it's installed, thanks all!

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2 hours ago, PaulTWinterton said:

I'm still 4speed and enjoying the reman 3.45 LSD.  My speedo is spot-on to GPS.  First time in 29 years.

 

I'm still 4 speed and enjoying the original 3.90 slipperydiff.  My speedo is spot-off, according to Conserv.  For all of it's 43 years. 

 

 

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If you currently have a 3.64 diff and an OD 5 speed, your rpms at 80mph in 5th gear should be about 3,400rpm. And that is with tires at or near stock diameter. Your RPM reading is way too high. If you had a 3.90, you would be turning 3.660rpms in 5th at 80, which is nearer to your reading. With a 4.10 diff and an OD 5 speed you'll be turning about 3850 rpm at 80 mph. Are you sure you have a 3.64 diff ? It sounds like you have a 3.90 or possibly 4.10.

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6 hours ago, Slavs said:

If you currently have a 3.64 diff and an OD 5 speed, your rpms at 80mph in 5th gear should be about 3,400rpm. And that is with tires at or near stock diameter. Your RPM reading is way too high. If you had a 3.90, you would be turning 3.660rpms in 5th at 80, which is nearer to your reading. With a 4.10 diff and an OD 5 speed you'll be turning about 3850 rpm at 80 mph. Are you sure you have a 3.64 diff ? It sounds like you have a 3.90 or possibly 4.10.

 

I'll get confirmation today thanks

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7 minutes ago, Squid's 02 said:

I found this to be useful during my decision making process:

 

 

 

Thanks! It's similar to the chart on the FAQ which is what I went by to get my info...

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