Gears

[fredk]

I am planning on changing my gears from 2.59 to 3.54. Does the computer have to be modified after this gear change or will it shift as before ?

Thanks
Fred

 

[Ken]

No modifications to the computer are necessary.

 

[fredk]

Thanks Ken !!

 

[Vettefan87]

But you will have to modify the speedometer? Which can be done through the Prom correct? So kind of you do, but not really I know I will get yelled at for that, but to my knowledge you have to reprogram it for the speedometer to display the correct speed.

 

[Hrtbeat1]

Not sure. The 700R4 uses a throttle valve cable for line pressure, the 4L60E does not. The 4L60E uses solenoids to control the shift points, which are controlled by the computer. Most likely it will shift as normal due to the computer that you already have (it controls everything like it should now.)

I changed my rear end from a Dana 36 with 2.59 gears to a Dana 44 with 3.45 gears. Everything works like it should (still using the TV cable.) My only problem is the little idiot shift light comes on even when I'm in 4th gear. I have to change the Memcal to one from a standard tranny (the only ones that had such a high gear ratio) one from a 3.07 geared auto may work but have yet to swap them out.

Hope this helps

 

[Hrtbeat1]

Actually he would have to change the speedo gears in the tranny for the speedo to read correctly. The shift light I was refering to is part of the Network resistor pack that is on the Memcal, its not actually in the Prom itself.

 

[Vettefan87]

Ah, I stand corrected. Thanks. How hard are the gears to change for the speedo?

 

[Hrtbeat1]

There are actually two. The driven gear and the Drive gear.


The Drive gear has from 15 to 19 teeth (each tooth size has its own color ... red, green, ect) and is on the output shaft of the tranny. It is a real PITA to get to because you have to take off the tailshaft housing ... the part that attaches to the C-Beam. It has a strange little clip that keeps it in place.

The driven gear is a snap. One 10mm bolt holds the clamp to the tranny case (outside) remove it and the clamp then slide the speed sensor out the drivers side. The driven gear is on the end of the speed sensor. They are color coded also ranging from 34 - 45 teeth.

When I did mine I was rebuilding the tranny and had it toatally disassembled which made it easier. I ordered the new speed sensor with the two gears and just reassembled everything when I was done with the rebuild. IIRC there are two speed sensors depending on the number of teeth the driven gear has.

 

[brock71]

88 automatic Dana 36 gear ratio change

I need some advice before I swap rear end ratios on my 88 with auto transmission.

It's a stock L98 with exhaust and intake as the only mods. The present rear end is a 2.59. I want to go to either a 3.08 or even further to something a 3.54.

My questions:

Is the 3.54 too low for the low reving L98? Has anyone gone there that would share the experience?

Can I get spedo gears that would correct for a 3.54 in the auto transmission?

Thanks for the help,
John

 

[TedC]

I really like the 3.07 in my stock 1989 automatic. I had a 2.59 in my 1988 and it was not the best match for the L98 and auto gear ratios. When I purchased my next vette it had to have the G92 performance gear (3.07). The difference is night and day. I feel the 3.54 is a better gear ratio for the 6 speeds. Traction can be an issue for me, so I need to keep the tank full. Even with 2 people on board, burning a dual 20-25 foot patch is not hard, and I get a strong 1st to 2nd gear chirp. I also find it didn't impact MPG that much vs. my 1988.

 

[vetteoz]

My questions:
Is the 3.54 too low for the low reving L98? Has anyone gone there that would share the experience?

I agree with Ted C
Unless you have some mods that let the engine rev out more the 3.07's are a great all round ratio.The 3.5's will work and the O/d gets you some fuel economy back but you have short legs running up to the TPI limited 4500rpm

My questions:
Can I get spedo gears that would correct for a 3.54 in the auto transmission?

Can get gears for stock ratios from dealer or trans shop
For 2.59 to 3.07 swap you don't have to change the drive gear inside the trans.You just pull out the VSS unit and swap the stock 35 tooth driven gear ( orange ) for a 42 tooth one ( green )
3.54 requires removal of the tailshaft housing to change the drive gear as well as changing driven gear on VSS

Cable drive T700 shown but setup the same with VSS.

 

[brock71]

88 gear swap

Thaks for the advice on ratios. I think the 3.08 is the way to go.

One more question came up today. With the L98, auto transmission, and a switch form 2.59 to 3.08....what about a different torque converter? I'm not sure what came stock from the factory. Would a higher stall work better?

John

 

[vetteoz]

Higher stall ( within reason ) gives a good kick in the pants
Stock IIRC 1500 -1800 rpm

 

[TedC]

Thaks for the advice on ratios. I think the 3.08 is the way to go.

One more question came up today. With the L98, auto transmission, and a switch form 2.59 to 3.08....what about a different torque converter? I'm not sure what came stock from the factory. Would a higher stall work better?

John

Change the rear axle gearing first. You may find out you don't need a different torque converter.