I was planning on putting some 3.73's in and wanted to know what I would have to do to correct my speedometer. I know that there is a gear to change in the tranny, but after reading the FAQ I was confused as to if there was another gear to change at the speedo itself and if so what combo of gears (tranny/speedo) to use for this swap ?

 

The only gears you'll need to change are in the transmission. Manual or automatic?

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1984 Camaro Z28 Astral Silver w/ 2 1/2" cowl induction hood
Engine: Decked 385 cid 4 bolt w/ oil cooler, 9.6:1 compression, ARP fasteners, 600 cfm Performer carburetor, Torker II intake, Performer RPM Heads, XE268H cam, Magnum roller tip rockers, MSD6AL ignition, Blaster2 coil, recurved HEI distributor
Exhaust: Terminator headers, Custom 3" TIG welded stainless exhaust, Twister muffler
Transmission: 4L60 w/ Corvette servo, .500 boost valve, TransGo 7-CS clutch springs, 700 PKH pump rings, 700-2 reprogramming kit, Borg-Warner High-Energy frictions & bands, 2400 RPM lockup torque converter
Drivetrain: 2.73:1 limited-slip Dana 44 w/ disc brakes
Tires: Front P225/50VR15 Rear P265/50VR15 Eagles

Because you can always sleep in your car, but you can't drive your house.

 

Automatic 700r4

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86 TPI 305 Iroc-Z
700R4 (rebuilt)
Accel HEI SuperCoil
Flowmaster
K&N Filters
Comp Cams H268 218@.050 454/454

 

What size tires?

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1989 IROC-Z 5.7L

 

I've got some 265/50/15 on the stock 15x8 rims.

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86 TPI 305 Iroc-Z
700R4 (rebuilt)
Accel HEI SuperCoil
Flowmaster
K&N Filters
Comp Cams H268 218@.050 454/454

 

You need:

15T Gray Drive 8642620
45T Lt Blue Driven 9775187

And possibly a new sleeve.

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1989 IROC-Z 5.7L

 

Hey Guys I did the same swap on my 1991 GTA. I still haven't fixed the speedometer yet because I was a little confused also. I had 323s and went to 373s. I have a 4L60 automatic. Could someone please tell me which gear(s) in the tranny I will have to replace I have the stock size tires on 245/50/16. Thanks in advance
Darrell
1991 GTA
Canada

 

8642620 - 15T Gray Drive Gear

25513052 - 45T Lt Blue Driven Gear

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1989 IROC-Z 5.7L

 

Just to let you all know that GM has external ratio boxes for our trannys. For example I went from 3.08s to 3.73s. Put your new ratio in the numerator and put the old ratio in the denominator. For me that would be 3.73 divided by 3.08, which is about 1.211. This means my speedo is reading 21.1% higher than it should. GM makes a ratio box that is 1.21 ratio, you just plug it into the speedo cable hole on the tranny and then plug the speedo cable into the box. These cost about $50, call to see if the ratio you need is available.

Apparently not everybody knows about this, I was told GM didn't make the right speedo gears for my car when I put the 3.73s in, and I was not told about the ratio box.

Hope this helps,

Jason

 

Hi,

I'm going from 2.73's to 3.42's, what speedo gears do I need?

Thanks in advance.

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1997 Chevrolet Camaro SS # 379
1992 Pontiac Firebird Formula
1973 Chevrolet Camaro RS/Z28
1969 Chevrolet Camaro SS 350

I'm old enough to know better, but too young to care!

 

Assuming you have a 700R4 with 245/50/16 tires, you need:

8642620 - 15T Gray Drive
25513052 - 45T Lt Blue Driven

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1989 IROC-Z 5.7L

 

Omar, dont the 3.42 gears need a 41 tooth driven gear, not 45?

 

Thanks Omar and Kevin91Z. I'm a friggin' idiot. I meant to add that I have a 700 R4 and P245 50 ZR16's.

I appreciate your help. Thanks.

 

Thanks, Kevin. You are right. I dont know how I made that error. I think i was looking at someone else's specs.

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1989 IROC-Z 5.7L

 

Omar, how do you figure out the speedo gears needed?

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82 z28 350cid, vortec heads, comp 262h cam, Holley 600cfm carb, 2in twice pipes, MSD ignition, turbo 350 trans, 3.73 posi, manly b&m megashifter