I am right in the middle of gathering parts to finish my GS, and one of the items I am thinking about doing is putting OD on my car. The gear vendors solution seems awfully high for a TH400, and a built 4L80E seems like a cheaper solution than the TH400. The advantages I see in the 4L80E is (if purchased setup correctly) is slightly cheaper, and has bigger first and second gear ratios, that I can't get with the TH400. However, I don't know how well they fit to a Buick 455, and what floor/firewall modifications are needed to make this thing fit. I am not sure how I feel about the brain box, and the tunability of the trans. Do they make 4 pattern shifters? (1,2,3,4) Can you make the 4L80E shift fast, and how does the wide ratio affect shifting RPMS. Talk to me, I need to either be talked into it or talked out of it, I am on the fence between the two trannys! JP
The 4L80E has a chevy bolt pattern and requires a computer to control it. Otherwise, I like it a lot! FAST (the same people that make the fuel injection controller) sells one - http://www.fuelairspark.com/Information/Catalog/FS2001/14.pdf -Bob Cunningham
I put a 4L80E into the 1968 Firebird convertible that I had. It was powered by a Pontiac 455 so I simply used this adapter. The TCI TCU system provides great tunability. See here for some software screen shots. You mentioned ratios. The 4L80E has the same ratios as the TH400; 2.48, 1.48, 1.00 with the addition of a .75 overdrive. So, that doesn't present any issues. I'd imagine that a GS has more tunnel room then a 1st generation F-body and I had little difficulty getting the transmission installed. The rear mount was the biggest challenge there since the ragtop F-bodies have a stiffening x-brace underneath. A TH400 crossmember and mount should suffice. Here are transmission dimensions for reference purposes. As far as a shifter goes, you don't really need to mess with your original if you don't want to. I used the original two-speed shifter in my 'Bird. I was able to manually select Park thru manual 2nd with it and that was fine. If you want to be able to manually select all forward gears, I believe that there may be aftermarket gate modifacations available to convert OEM shifters to OD units.
4l80 E Trans I have also read several times about a kit available that will make the trans so you can get overdrive in all foreward gears. like a six speed. just an additional thought. Bernie Steffen..zstef@mchsi.com
they make 4 pattern shifters for automatic buicks at 'shiftworks'.. They even got a replacement console insert for the 68-69 buicks...
The gear vendors set up is not cheap at all. But, it can handle 1200 horses out of the box, lets you get overdrive in any gear (making it a six speed) and a replacment unit is only like $650 with exchange. I replaced mine in the Suburban last year at about 125,000 mi. I had already done the trans (th400) two years earlier. There are different 1st gear sets availible for the th400, you can get something around a 2.75:1. This would cause a greater rpm drop between 1st and 2nd gears when shifting, but if using the GV overdrive, you can split the gears. They both have good/bad points. If I had the cash, I would chose the GV set up. Plus, it can be converted to many other trans with a front housing/input shaft change availible seperately.
I use the 2004R in several of my conversions and I like it a lot! :TU: Has dual bolt pattern on bellhousing and almost the same size as a TH400/350/St300 same drive shaft ( cept yoke on 400). They have a better gear ratio's in my opnion and can be built to handle the power. they fit excellent and I plan to convert at least 6 of mine to 2004R's with in the next 3 years as money permits and the wife don;t watch ( even my RX7 with a V8 uses one ) ou: ken
There are different 1st gear sets availible for the th400 really? joe, could you point me to a vendor for these? i'm looking for a closer 1st/2nd ratio. maybe even a custom 2nd gear set?
TA sells gearsets- last I understood they offered a 2.75:1 and a 3:1 first gear ratio to replace the standard 2.48:1. I use their 2.75:1 kit. (And it is unavoidable that whenver you change the first gear ratio, you also change the 2nd gear ratio by a proportional amount, so a 2nd gear change can only follow a 1st gear change) -Bob Cunningham
