What transmission do you suggest?

[1971Stepside]

I just purchase an LQ4 for my rebuild and I am excited about my decision. I had planned on a 454 with a 700R4, but the appeal of the newer motors is really there when it comes to dollars vs. HP.

I have a 3.73 posi installed in the 12 bolt and plan to run 18" wheels on the truck. The 4L60e is the obvious choice, but I hear it isn't very strong (I plan to swap heads/cam/and intake to get around 450 hp). The 4L80e is heavy and more expensive and sounds like a lot of extra work.

For those that have done this, what are your opinions? I'll post pics next week after I pick up the engine. The donor comes in next Wednesday and I asked to hear it run before they pulled it.

[greentruck]

I would suggest going with the 4L80E. I don't think the 4L60E could take the HP that you're after for very long. It would be far less expensive to move your trans cross member back and shorten your drive shaft than to replace the 4L60E. That's what I did.

[jessemthompson]

4L80E is the trans you want. You’ll need a high hump for it, but it’s worth it’s weight. I would not put a 4L60E behind it. It won’t last long.

[Mike C]

Since you have the motor already, it's moot I guess. But if I were doing an LS swap and keeping the electronics I would be looking for a donor vehicle with either the 6 speed setup or 8 speed. Getting a transmission built is $$$ that it makes sense to get a donor with compatible trans in running condition.

[1971Stepside]

It is hard to find an LQ4 around here that isn't in a 4WD donor. I had to buy the 6.0 and the transmission from two different donors. I looked at the 6/8 speeds and from what I read on-line is that they are not the best for "hot rod" applications due to difficulty in programming. Not sure if that is true, but I read it with enough frequency that I narrowed it down to the 60 or 80.

[jessemthompson]

I have a 60 In my 5.3 swap and I’m afraid to do too much to the engine as I’m fearful the trans won’t last. I definitely wouldn’t have one behind a 6.0. A stock 80 will hold up to the abuse you throw at it.

[57taskforce]

Originally Posted by jessemthompson

I have a 60 In my 5.3 swap and I’m afraid to do too much to the engine as I’m fearful the trans won’t last. I definitely wouldn’t have one behind a 6.0. A stock 80 will hold up to the abuse you throw at it.

This.
Keep in mind gm put the 85 which is just a slightly beefed up 80, behind the 8.1 in the 3/4 ton avalanche and suburban. I’m sure everyone is well aware how much of a torque monster the 8.1 is. I’ve got an 80 and an 85 both with over 200,000 behind factory big blocks. The 80 has been pushing 35s around for over 100,000 of those miles. Neither have ever been out or touched other than fluid and filter changes. They are quite reliable and plenty strong.

[RustyBucket]

Just for info, I've had an '02 GMC 4dr. 1500HD since it was new. 6.0 eng., 8 lug wheels. I think, but I'm not sure that it has a 4L60E transmission. 200,000+mi. and it's towed a lot, boats, campers, open & enclosed car trailers and KNOCK ON WOOD it seems to be fine. Good shift, fluid looks & smells good. Has a trans. temp gauge which I watch but it's never run hot even towing heavy stuff.

[ZEKE68]

4L80E fit in my truck behind a big block on stock mounts with a low hump. I am not sure if the LS engine position will work with the low however.

[weq92f]

Thank you Sir.

Originally Posted by ZEKE68

4L80E fit in my truck behind a big block on stock mounts with a low hump. I am not sure if the LS engine position will work with the low however.

-klb

[1971Stepside]

I bought a 4L80e. Cab is already a high hump. May change out the transmission cross bar. I pick up the 6.0 and trans this Friday. Thank you all for the advice.

[davepl]

I have the 4L80E. They're big (like a TH400 that our trucks came with though) and heavy like a (TH400) but they're strong as heck and have a great overdrive.

I made sure to get a STOCK rebuild with a STOCK converter as I'm not racing it.

You have to solve the speedo issue as there is only electronic. You can get a box that drives your speed cable electronically for about $600, but you can get an aftermarket tail stock with the speedo output cast into it for $695, and as brutal as that is, that's how I'd go.

Then's its just your standard swap - need a controller, length will be a little different, etc.

[1971Stepside]

Can I run a modern speedo since I am building this thing from the ground up anyway. I wasn't planning to run the stock gauges.