Rear Diff Gear Change- Help please
Thread Starter
Instructor
Joined: May 2017
Posts: 102
Likes: 2
From: Temecula CA
Rear Diff Gear Change- Help please
Hey guys, I have an 89 with the ZF 6-speed. I have the build sheet on my car and it appears to have 3;33 gear ratio. I think the other option was 3:54 ratio. I was thinking of maybe changing my gears to the 3:54s. Is this a very hard thing to have done? Also where would I get the gears? Any input is appreciated. Thank you in advance.
Race Director
Joined: Oct 2008
Posts: 17,982
Likes: 1,074
From: Lansing MI
Its not particularly difficult if you have done it before, but there's a pretty steep learning curve if you haven't.
Im sure Jegs or Summit can sell you the gears and the other required parts.
Im sure Jegs or Summit can sell you the gears and the other required parts.
Thread Starter
Instructor
Joined: May 2017
Posts: 102
Likes: 2
From: Temecula CA
Planning on having it done by my regular mechanic. I will go search out what Summit has for gears and parts recommended.
Team Owner
Joined: Sep 2003
Posts: 25,393
Likes: 2,741
If it is a 3.33 it would be a very desirable gear for some. I'd consider maybe a purchase of another rear in whichever ratio you desired and a sale of your 3.33 assembly. I won't offer up any ratio that you should consider but I know that if it were me I'd be selling yours as a complete unit. I'd think you could (of course based on condition) break 'even' or perhaps make a little on the change. If you found someone with a 3.73 or 3.54 that was interested in the 3.33 that you could drive to confirm condition it would be to your advantage.
Yours drives so you don't need to be in a RUSH!!
Yours drives so you don't need to be in a RUSH!!
Team Owner
Joined: Sep 2001
Posts: 62,153
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
D44 3.33 is a rare enough factory gearing that I would never change it, and even if I did I wouldnt go with 3.54, not enough change to be worthwhile.
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Thread Starter
Instructor
Joined: May 2017
Posts: 102
Likes: 2
From: Temecula CA
Le Mans Master
Joined: Sep 2004
Posts: 6,019
Likes: 568
From: Conroe Texas
when corvette came out with the zf 6-speed, they used the 3.54 gears till about nov - dec 88'. then they started using the 3.33 gear for the rest of the year. there were more 3.33's out there than the 3.54's. then in the 90' year they started using 3.45, i believe, until the end of the c4 run.
Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
Nobody has ever wished they would have stayed with a higher gear (numerically smaller). I had a 3.55 in a Mustang and was on the fence between 3.90 and 4.10. I received this advice and went witht he 4.10. Absolutely loved it and that was with a 5-speed. With the 6-speed, go ahead and go lower. You won't regret it.
What I found with the 4.10 was I actually got better gas mileage in town as I was in a higher gear in the transmission and actually turning less RPMs at 35-45mph. Yes highway suffered a bit, but nothing as bad as some may paint it. I know a lot of LT1/LS1 guys go 4.11 with their 6speeds. I highly recommend you go this route to. Not sure what Dana offers in the range, but it will feel like you gained 50hp.
What I found with the 4.10 was I actually got better gas mileage in town as I was in a higher gear in the transmission and actually turning less RPMs at 35-45mph. Yes highway suffered a bit, but nothing as bad as some may paint it. I know a lot of LT1/LS1 guys go 4.11 with their 6speeds. I highly recommend you go this route to. Not sure what Dana offers in the range, but it will feel like you gained 50hp.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
The stock L98 isn't a high revver...only good to about 4500. If you have the stock TPI intake you might not want to change gears and do something with the intake first...Accel TPI, Superram, Mini Ram, Stealth Ram ...etc .
Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
Diesels aren't high rev motors either, the tow package still comes with a 4.XX gear.
Racer
Joined: Jul 2015
Posts: 313
Likes: 15
From: Modesto Ca
I put a set of 3.73 gears into an 85 d44 vette .I got the gears from ebay.They came out of a jeep grand Cherokee.the d44 is actually a dana 44s that is the same diff in a Viper.I had to grind above and below the ring gear because the ring gear would not fit into the case.If you want to save money pull the diff at home and take it to a shop for the actual gear work.
Melting Slicks
Joined: Aug 2003
Posts: 3,399
Likes: 394
From: Lakeville MI
Here's a handy gear calculator that has been rehashed and updated from the old f-body.org calculator with some new functionality added by the author:
http://www.pszweb.com/car/gears.htm
I would suggest using 811 revs/mile for standard tires (275/40R17). 3.33 appears to be about the optimum ratio for a ZF6 L98.
FWIW: I run a 3.73 gear with a 769 revs/mile tires in my own 4+3 car...but it still makes good power beyond 6500 rpm.
http://www.pszweb.com/car/gears.htm
I would suggest using 811 revs/mile for standard tires (275/40R17). 3.33 appears to be about the optimum ratio for a ZF6 L98.
FWIW: I run a 3.73 gear with a 769 revs/mile tires in my own 4+3 car...but it still makes good power beyond 6500 rpm.