Transmission change needed...looking for input - Fuel Economy, Hypermiling, EcoModding News and Forum

Nevyn · 10-12-2009, 01:23 PM

My wife's 1999 Pontiac Grand Prix SE is in need of a new transmission. Yes, I'd love to replace the car; Yes, I know there are other relatively cheap alternatives out there.

I don't know if it has a 4T60-E (I think so), or the 4T65-E.

I have found that the final drive ratio came in different values. Does anyone know which car had the lowest one? From what I found, it was available down to 2.97, or up as high as 3.74. I don't want to replace it with a short one - I want longer for MPG.

The problem with this is, I've also seen that getting a different FDR requires an ECM change. Any thoughts on this being very bad/causing troubles?

Christ · 10-12-2009, 02:04 PM

Input - the thing that the torque converter acts upon to create a phase change in the transmission's internal parts resulting in the transfer of kinetic energy from the engine to the planetary gear set, and eventually driving the wheels.

You'll find it once you pull the transmission and remove the torque converter.

Alternatively, you can look at a this: 3100 or 3400 with a stick shift? - Page 2 - Grand Am Owners Club Forums, or this: How do you determine 4T60E final ratio (2.73, 2.97, 3.33)? - Cadillac Owners Group to get some ideas.

Seems that you can use a 5 speed from the Quad-4 4 cylinder if you change the front half of the transmission case, don't know if that's an option for you, but it has a nice FDR.

If it's not an option, you might look into learning to rebuild an Auto tranny for the longer gears.

The PCM thing is just a matter of taking the chip from the PCM of the car you took the transmission from, or having someone flash yours. The longer FD will make the PCM think that it's not shifting properly.

I'm sure if you wanted to build a tranny from the case up, you could make an interesting combo of gears and FD to make a great tranny for both city and highway driving.

Nevyn · 10-12-2009, 03:59 PM

I see what you did there.

Acutally, I saw that thread on the Caddy forums when I was searching. I was wondering if anybody here could say anything like "The Grand Prix GXP's had the short gears, and the long gear set with the lowest final drive was put on Buick Centurys," or whatever the ACTUAL models are.

Manual is not an option at this time.

Christ · 10-12-2009, 09:00 PM

I think the best thing you'll find is to learn the serial designations for each type of transmission.

The gears are identifiable by the serial number on the transmission. Of course, you'll need a cross reference for the serial numbers so you know what you're looking at, as well.

jkp1187 · 10-12-2009, 10:33 PM

Quote:

Originally Posted by Nevyn

I see what you did there.

Acutally, I saw that thread on the Caddy forums when I was searching. I was wondering if anybody here could say anything like "The Grand Prix GXP's had the short gears, and the long gear set with the lowest final drive was put on Buick Centurys," or whatever the ACTUAL models are.

Manual is not an option at this time.

I don't know for sure (I think you're right about the 4T60-E. You have the 3.1L, right?) Clubgp.com might be a good place to start, though.

Nevyn · 10-13-2009, 10:24 AM

I found some good info there - thank you. It's looking like we may try to push the car through the winter and replace it altogether at tax time. There seems to be little point in putting $300-$400 into it when we paid $900 for the car...

jkp1187 · 10-13-2009, 10:55 AM

Quote:

Originally Posted by Nevyn

I found some good info there - thank you. It's looking like we may try to push the car through the winter and replace it altogether at tax time. There seems to be little point in putting $300-$400 into it when we paid $900 for the car...

Hmm.

Cars are an expense, not an investment. It doesn't matter that it's only worth $900 (or less) now, instead consider that for the price of maybe $300, you could have a car that keeps going all through next year - far cheaper than a down payment + payments on a new vehicle.

I'm not saying don't buy a new car - by all means, if you think you'll be ready to do so and won't need to rely on the GP in the intervening months (b/c you can take public transportation or drive another car,) then go for it!

I'm just saying, there's a tendency among Americans to assume that cars are an investment and it isn't "worth" fixing a car that has a low Blue Book value. I think that's a fallacy. If you're just looking strictly at finances, it's almost always better (cheaper) to fix an old car than buy a new one.

Christ · 10-13-2009, 12:21 PM

Quote:

Originally Posted by jkp1187

Hmm.

Cars are an expense, not an investment. It doesn't matter that it's only worth $900 (or less) now, instead consider that for the price of maybe $300, you could have a car that keeps going all through next year - far cheaper than a down payment + payments on a new vehicle.

I'm not saying don't buy a new car - by all means, if you think you'll be ready to do so and won't need to rely on the GP in the intervening months (b/c you can take public transportation or drive another car,) then go for it!

I'm just saying, there's a tendency among Americans to assume that cars are an investment and it isn't "worth" fixing a car that has a low Blue Book value. I think that's a fallacy. If you're just looking strictly at finances, it's almost always better (cheaper) to fix an old car than buy a new one.

Which is why I'm so happy to buy a "junker" for $250, fix it up, drive it for a year, and then sell it for 2-3x what I paid for it.

Nevyn · 10-13-2009, 01:44 PM

Wife won't let me get cars at the $200-300 mark and fix them...she doesn't want "unfinished projects" to 'lay around.'

You folks are right, though, too. I'm not having an easy time with it, but maybe you folks can help me shove the pill down my throat (sideways if need be), it's tough to swallow. I/we don't NEED a different car. I don't say new, because whatever is purchased would be used. We NEED a working car, capable of 2 adults + 2 (sometimes 3) car seats/kids.

I'd like to do it myself, but it seems a little daunting to do it LIVE on the only tranny I have.

Thanks for the advice and encouragement. I'll admit I'm kind of scared, but I'm also willing to do it scared.

Too bad that I can't get one of the DeVille trannys with the 2.73 for low, LOW cruising. Lowest available is 2.89 for my model/year.

Christ · 10-13-2009, 03:27 PM

Quote:

Originally Posted by Nevyn

Wife won't let me get cars at the $200-300 mark and fix them...she doesn't want "unfinished projects" to 'lay around.'

You folks are right, though, too. I'm not having an easy time with it, but maybe you folks can help me shove the pill down my throat (sideways if need be), it's tough to swallow. I/we don't NEED a different car. I don't say new, because whatever is purchased would be used. We NEED a working car, capable of 2 adults + 2 (sometimes 3) car seats/kids.

I'd like to do it myself, but it seems a little daunting to do it LIVE on the only tranny I have.

Thanks for the advice and encouragement. I'll admit I'm kind of scared, but I'm also willing to do it scared.

Too bad that I can't get one of the DeVille trannys with the 2.73 for low, LOW cruising. Lowest available is 2.89 for my model/year.

Got a junkyard or a car club locally? Maybe you can get someone to check out the gear sets for you and see if they'll fit in a case like yours.

If it were me, I'd weigh the options of finding the correct transmission used and putting it in, or seeing if I could just put one together and tune the PCM afterward. The tuning software is often free, and an OBD-II/Serial cable isn't usually too expensive either. This also gives you the option of later on, tuning for more power or more economy, checking your CEL's without a code scanner, and resetting your ECU for "quick learn", etc.

You could get a "junk" tranny with a good case and rebuild it for a couple hundred bucks, and a learning experience. You don't need any special tools, usually, just a working knowledge of hand tools and a shop manual.