I've been reading and banging my head trying to understand this stuff.

I have a '91 LB9 and I'm doing a 5 speed conversion.
I have a T5 from a '92 LO3

I ideally wanted the LB9 T5 and 3.42 gears,but this T5 kinda fell on my lap.

My goal is to make a peppy daily driver with the rare race against a friend or something.
I'm not trying to get 1/4 mile times and I'm keeping my 305, so please keep that in mind.


I'm beginning to consider a 3.23 as I'm have a LOT of trouble finding the 90-92 3.42.
I realize 3.23 came factory on autos and 3.42 as an option for 5 speeds.


I edited this list to show only what applies to me. In bold is what I have and above it is what would've been mated up factory.


Model Yr...Engine(s).Input....Speedo.......Ratio........Model # (BWA)

1992 1/2..LB9 5.0L...26............7..............T5U.73......1352-212(wc)
1992 1/2..LO3 5.0L...26............9..............T5U.63......1352-213(wc)


Speedo info
7=Purple Speedo
9=Red Speedo

Ratio........1st.............2nd.........3rd.........4th............Rev.......5th

T5U..........2.95...........1.94.......1.34........1.1............2.76


This is what I'm talking about:

Theres First/Fifth:
LB9 2.95/.73
LO3, LB9 2.95/.63

Understanding how the rear end gears manipulate the power to the wheels is understandable, but when I start seeing different T5 ratios coming into the mix it starts getting confusing. Not to mention I'm not using the T5 that was meant for my engine!


I bought the car with 2.73 drums and an automatic that was toast, so any advice will help me get behind the wheel of my first american muscle car by the time summer hits.


Will my setup be just fine with either 3.23 or 3.42?

How will a LO3 T5 change things vs. if I had a LB9 T5?

Do they use the same drive & driven gears?

Which rear end gears would you use with this setup?



Thanks in advance guys. These forums have been very helpful...

-Shawn

 

You did a lot of research (bravo!) but missed a little data for 5th gear on your copy pasta.

the 1352-212 has a .73 fifth gear (which is less ideal on the highway in my opinion)
The 1352-213 has a .63 fifth gear (which works out pretty nice with 3.73s in my experience and would probably be nice w/ 3.42 also.)

That's the only difference.

There's no "designed for my engine" really at this point. You're dealing with decades-old parts that may have their original gearsets and speedo drive gear and they may not. Plus, some of the ID no. lookups have erroneous information for the T5 anyway like the 2.74 first gear someone alluded to in a recent thread.

You could remove the tailhousing and change the 5th gear ratio and speedo gear pretty easily.

If I was trying to get 3.42 gears, I'd consider shopping the fourth-gen stuff and swapping those into the third-gen housing w/ the late third-gen 28 spline axles (assuming you want stock-width rear housing.) Sometimes, the carrier and it's shims and the pinion with it's shims swap easily into another housing with minimal setup trouble.

 

Thanks for the rapid reply and advice.

So the the M39 & MK6 would use the same drive/driven gears for the speedo, since the 5th gear difference works in front of the output?

I'm wanting to switch to disc brakes also. Looking hard for a third gen disc rear is the goal so rims, tires, spacers, etc.. don't have to be purchased this year. (I don't like the wide rear look)

Is swapping out the fifth gear pretty straight forward and where would I get this piece?

Do you think 3.23's would do okay in 5th gear with my current setup?

Thanks for helping me!

-Shawn

 

You're welcome.

It depends on the rear axle. It's pretty easy to look inside and see a red 9 tooth or purple 7 tooth. Don't assume by colour, but those are the stock ones as you noted.

I'm a fan of the Torsen (standard in 99-02) for street driving and lots of work on using the 4th gen discs has been done so visit the brake board and look for a 99-02 six-speed rear if those are your desired parts. IMO.

Check out the svc. manual for the T5 on Tremec's site. If you're familiar with the use of gear pullers and can find access to them, you can do it.

Compared to higher gears, it would make first a little less tractable and fifth wouldn't be useful until a higher mph. I'd aim for 3.42 personally. 3.73s don't do much for the LB9.

 

Is there a difference between 99-02 V8 vs. V6 rear?

I don't need the traction control anyways. I ask because people say V8 has bigger brakes, but if I call up Advance or Auto Zone they say the V6 rotors are 12 in. diameter.

If V6 is the same, it would help me by having a broader range to search.

 

Is there a difference between 99-02 V8 vs. V6 rear?

I don't need the traction control anyways. I ask because people say V8 has bigger brakes, but if I call up Advance or Auto Zone they say the V6 rotors are 12 in. diameter.

If V6 is the same, it would help me by having a broader range to search.

 

I don't know what gear ratios or limited slip availability was in V6s those years.