trans upgrade

Of course the 7427 ECM can also be retrofitted for fuel injection down the road as well. It is a very well documented ECM, and a big favorite amongst ThirdGen owners. (ThirdGen is one of 2 primary sources on the net for ECM customizing. The guy who wrote TunerPro is a Third Gen Camaro owner, and initially wrote the software for himself. It has since evolved into the best tuning software out there.)

One big thing that the 7427 ECM does is monitor slip between the input and output shafts. As the slip increases as a result of wear, the ECM automatically increase the pump pressure to compensate. This means that for the full life of the trans, it will always shift like it did when new. This also reduces the wear, as the trans gets closer to the end of its life. One other feature is the variable TC lockup. GM designed a special clutch inside the TC, which is porous. This allows fluid to work its way through the clutch to cool it. Based on conditions, the clutch pressure is varied to intentionally allowing slip. This keeps the engine RPM up when needed for power. They also begin to engage the TC in as low as second gear to improve mileage throughout the upshifts. TC engagement is soft, so you hardly feel it. I would be very surprised if any after market controller uses this scheme. OF course the other side of this is, that one must use a GM TC. Any after market rebuilders must buy the TC clutch from GM. Otherwise it will not hold up. GM has a patent on the clutch design, so it is exclusive to them.

Thanks Dave, that is another great option. I've also read of a standalone GM 4L80e controller used on early '90s diesel p/u's that can be retrofitted fairly easily. I like the Megashift since it can be integrated into a DIY Megasquirt EFI system later down the road. Plus there is a lot of developer support on the web. Just cool stuff to think about!

-Tom.

If you are that level of DIY and cheap is your goal, you could consider this option:
http://mattw.dyndns.org/4L80E/
Probably run you around 35 bucks for the ECM from a bone yard, another 80 bucks for the chip burner, and a small sum for the harness from a bone yard. That will give you all the protection of the original design. You can program it with TunerPro.

I plan to use the DIY Megashift controller, its cheap enough to have a spare, around $300. Not sure what to do if the TCI controller went out on the road. That is also another reason not to use a modified 700R4, I'd rather have a basically stock 4L85E away from home in case of problems. Depending on how much paid for a core tranny, probably could get the swap done for around $1G.

http://www.diyautotune.com/catalog/gpio-basic-kit-black-case-p-417.html

Stim wrote:
I had to have two 700R4's rebuilt in 100,000 miles in a 1989 1500 Silverado and I am a conservative driver.
First one slipped, second one quit coming down an interstate ramp. (planetary gear broke)
Yours is a tough call. Not sure why you are going so slow? I had a 1983 Winne 454 and had it up to 85mph getting away from a trucker that kept passing then slowing down on hills.

I think mine is very choked with emission junk, needs headers, emission garbage gone and maybe a intake and a carb rebuild or a Holly. Bottom end power is fine, get's right up to 55 mph very well, even loaded. I can push it maybe to 75 but sure wouldn't hold it there for long

Stim wrote:
.......I am a conservative driver.........I had a 1983 Winne 454 and had it up to 85mph getting away from a trucker that kept passing then slowing down on hills.

:h LOL

I had to have two 700R4's rebuilt in 100,000 miles in a 1989 1500 Silverado and I am a conservative driver.
First one slipped, second one quit coming down an interstate ramp. (planetary gear broke)
Yours is a tough call. Not sure why you are going so slow? I had a 1983 Winne 454 and had it up to 85mph getting away from a trucker that kept passing then slowing down on hills.

Daveinet wrote:
Lift one rear wheel off the ground and count how many times the drive shaft goes around for one turn of the wheel. Then double that number, because you are only turning one wheel instead of both. That will tell you your diff ratio.

The other way to come up with the correct answer is what RPM are you turning at 60 mph?

BTW: The 4L85e will be a little nicer at .75 overdrive, than .7 overdrive of the 700R4.

And just so you know what the designations stand for, the 700R4/4L60E the "60" means it was originally designed for vehicles with a combined weight rating of 6000 LBS, the 4L80E was originally designed to support vehicles with a combined weight rating of 8000 lbs. The 4L85E - the "5" designation stands for 5 planetary gears instead of the standard 3, and is rated for vehicles up to 16,000 lbs. Hmm, which one do you want in your motorhome?

The TH700, built properly by someone who will guarantee it to 800+HP!

Jagtech wrote:
With your differential ratios, running an O/D tranny will require more throttle opening at cruising speed, which will reduce your MPG. Something to consider.

No...low RPM and more throttle is more efficient that higher RPM's and less throttle.

Daveinet wrote:
Two things, First, I would not consider a 700R4 in a motorhome. Even though you can build it, it is a light duty trans and just not designed to take the load. Guys that build them for race, build them to last for a limited number of runs, not a constant heavy load. The one big thing everyone forgets about racers - they break stuff. The see breaking things as the normal cost of doing business.

A properly-built 700 WILL hold up in a motorhome. I have seen it, including one behind a crate 502 in a huge tag-axle Pace Arrow, pulling a ~6000lb trailer. In the trailer was a Super Bee, running a TH700 behind its EFI 426 Hemi. IIRC, that 2-ton car ran 11's.

The 4L80E is the same load rating, and uses many of the same parts as the TH400 did, which has been proven to have long term reliability. The only disadvantage of the 4L80E is weight - but it has to be heavy to be tough.

Actually, the biggest disadvantage is that it requires a standalone electronic controller...big bucks.

As far as Gear Vendors vs 4 speed, my big concern with Gear Vendors is torque converter stall speed. If you get the engine spinning too slow, the TC slips, and you loose efficiency. Before I installed the 4L85E, I was running 3.53 gears and a step up 1:1.1 chain case. Unless I was traveling 70 mph, the TC would slip, so it was impossible to save fuel by driving slower. You have to look at your gearing and figure out what your typical operating RPM will be. You need it to be above 2500 RPM, and really should be above 2700 RPM at moderate cruising speeds. Otherwise you won't gain anything.

One other idea to consider would be to change your rear end ratio, and then put different gears in 1st and 2nd for your TH400. You can buy different ratios, which will allow you to still get off the line with a taller diff ratio.

Many ways to skin a cat.

That would probably cost as much as a 4L80E swap...