4T80E 3.11 to 3.71 swap

[AJxtcman]

Bert AKA Highline Cady Ordered the parts today.
Now we can see what I have done to a DHS for less than $1000 Total. That would include the exhaust and intake also. Full cat back system.

[Highline Cady]

Hey just wanted to thank everyone for their input on this, especially AJ. I'm looking forward to the swap. I've driven many, many DTS's and STS's and personally think that the gears (3.71) make a big difference with how the car acts from a dead stop. I just want a little more go off the line and figure that this will help, it can't hurt. Except mileage, but I figure it'll only be 2-4 mpg. We'll see, I'll let you all know after I get it done and run it around for a little while. Parts are already ordered.

[jadcock]

I prefer the better torque of the LD8 engine (like what's in the SLS, DeVille, DHS, etc). But the 3.71 final drive vs. the 3.11 final drive should make a nice difference as well. Can't wait to hear how this turns out.

[eldorado1]

Honestly I couldn't really notice a difference in acceleration. Maybe 1/2 sec faster 0-60. Maybe. Maybe not. The highway RPMs were a lot higher. My gas mileage probably went down.

[AJxtcman]

Originally Posted by eldorado1

Honestly I couldn't really notice a difference in acceleration. Maybe 1/2 sec faster 0-60. Maybe. Maybe not. The highway RPMs were a lot higher. My gas mileage probably went down.

We ran a 15.09 in the 1/4 on a hot humid day with the traction control on

[Highline Cady]

Edlo1,
A 1/2 secound 0-60 would make it worth my money. I hope your guesstimate is right. Thanks for the info.

[jadcock]

I suspect that it's not going to make THAT big of a difference. The SLS cars (3.11) run 0-60 in the 6.7-7.0 second range. The new Buick Lucerne (same powertrain) does it in the mid-to-high 6 second range. Virtually the same.

I loved the highway rpm of the 3.11 ratio. I could run 75 mph and still be under 2000 rpm. In the STS, I'm already at 2000 rpm by 60 mph.

[Highline Cady]

Jadcock,
I hear what you are saying about the change in RPM's (SLS vs STS) especially relating it to gas mileage, I'm assuming. I personally don't care about that. I figure it'll help a little with acceleration, and you just made me think, that'll let the pipes rattle a little more also (I have aftermarket exhaust), plus it should keep me right in the powerband also. Anyway, I'll post my impressions when it gets done. I appreciate everyones input on this so, Thanks again everyone.

[AJxtcman]

Originally Posted by jadcock

I suspect that it's not going to make THAT big of a difference. The SLS cars (3.11) run 0-60 in the 6.7-7.0 second range. The new Buick Lucerne (same powertrain) does it in the mid-to-high 6 second range. Virtually the same.

I loved the highway rpm of the 3.11 ratio. I could run 75 mph and still be under 2000 rpm. In the STS, I'm already at 2000 rpm by 60 mph.

You must have missed the 0 to 60 time with the 3.11 gears. 5.88 seconds
That is one slick program I have. VIN Y motor WOW

[94greencaddysls]

Could this swap be done with from 3.11 to 3.71 without a computer modification? I have a 94 so I OBDI, I'm just thinking an inline resistor of some sort could modulate the signal to the computer and fool it, though I really dont know how the signal works. I have my trans apart and the differential at hand, I'm just not sure how I could get the computer to co-op with me. Any ideas? or electronics wizards?

[AJxtcman]

2000 to 2005 Devilles and Sevilles.
Case Extension Replacement
Tools Required
• J 8001 Dial Indicator Set

• J 25025-7A Dial Indicator Mounting Post

• J 28585 Snap Ring Remover

Removal Procedure

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle .
2. Support the vehicle with safety stands.
3. Remove the right drive axle. Refer to Wheel Drive Shaft Replacement .
4. Remove the wiring harness.
5. Remove the vehicle speed sensor. Refer to Vehicle Speed Sensor Replacement .
6. Remove the right transmission to engine brace. Refer to Transaxle Brace Replacement .
7. Remove the ground wire from the case.
8. 
   
   FIG #1
9. Remove the following parts from the case extension:
10. • Five 13 mm bolts (128, 129)
    
11. • One 15 mm stud (127)
    
12. Remove the case extension (134) and the seal (126).
13. Remove the roller thrust bearing (132) and the selective washer (133).
14. 
    FIG #2
    
15. Remove the 8 mm scavenge tube bolt.
16. Remove the scavenge tube by prying on the differential.
17. Remove the scavenge tube seal.

.
.
Final Drive Assembly Replacement
Removal Procedure

1. Remove the case extension. Refer to Case Extension Replacement .
2. 
   
   FIG #3
3. Rotate the manual shaft (16) counterclockwise in order to place the transaxle in Park (P) and prevent the differential from rotating.
4. 
   FIG #4
   
5. Remove the 4 bolts (119) from the differential housing to transaxle case.
6. Remove the differential carrier.
7. 
   FIG #5
   
8. Push on the output shaft in order to expose the left side differential gear snap ring. Remove the left side differential gear to output shaft snap ring (56).
9. Remove the differential side gear (118) and thrust washer (117).
10. 
    FIG #6
    
11. Remove the final drive carrier (100) and the thrust bearing.
12. Remove the final drive sun gear (121).

Installation Procedure

FIG #7

1. Install the sun gear (121) with the bushing and the seal side facing differential.
2. Install the final drive carrier (100). Turn the unit until it meshes with the sun gear and the internal gear teeth.
3. 
   FIG #8
   
4. Install the left thrush washer (117).
5. Install the left differential side gear (118).
6. Install the snap ring (56).
7. 
   FIG #9
   
8. Use the manual shaft to place the transaxle in park.
9. This will lock up the final drive unit. The actuator rod will move up.
   
10. Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
    
11. Install the differential housing and the four bolts (119). Hand tighten, using a star pattern.
12. Tighten
13. Tighten the bolts to 76 N·m (56 lb ft).
    
14. Install the case extension. Refer to Case Extension Replacement .

[jadcock]

Originally Posted by AJxtcman

You must have missed the 0 to 60 time with the 3.11 gears. 5.88 seconds
That is one slick program I have. VIN Y motor WOW

That's a whole different discussion. I didn't say your computer tune didn't work. I said that there's not a big difference in performance between identical 3.11 and 3.71 cars, using the "same" (LD8) Northstar tune.

If your 3.11 car does 5.88 seconds NOW, and that drops to 5.22 seconds with the 3.71 gears, THEN I'll be impressed!

[Highline Cady]

Hell, I'd be happy with a 1/2 second drop in the 1/4. LOL

[AJxtcman]

I got the gears out and on the bench. I started on Friday about 10 after 5. I had all my tool put away and was clocked out just before 6pm. I would say about 30 to 40 minutes on the way out.
I had to find the wheel lock key.
Wheel lock keys are a pain. Have you ever looked for one in a car that is not yours?
My Service manager wanted to race me in Bert's DHS against his DTS. I really wanted no part of a hot trans to work on.
The way I look at it Monday morning it will be done.
I think of this as the ultimate N/A tune.
.
Hey Bert how much are you in to you Tune total?
Exhaust + Intake + PCM Tune + Gear set + Time slip = ??? $$
I mean the cost not the replacement cost.

[Highline Cady]

Originally Posted by AJxtcman

I got the gears out and on the bench. I started on Friday about 10 after 5. I had all my tool put away and was clocked out just before 6pm. I would say about 30 to 40 minutes on the way out.
I had to find the wheel lock key.
Wheel lock keys are a pain. Have you ever looked for one in a car that is not yours?
My Service manager wanted to race me in Bert's DHS against his DTS. I really wanted no part of a hot trans to work on.
The way I look at it Monday morning it will be done.
I think of this as the ultimate N/A tune.
.
Hey Bert how much are you in to you Tune total?
Exhaust + Intake + PCM Tune + Gear set + Time slip = ??? $$
I mean the cost not the replacement cost.

Sorry AJ, didn't notice that anyone had posted on this thread for a while. To answer your question, I'm not really sure AJ, not as bad as some might think, the exhaust was free, well it was a swap with my factory pipes so all I payed for was the gasket, the intake was a birthday present, tune and gears well you know, find out on the gears this week, be gentle, LOL and the time slip, I think it's $37 on the weekend and $30 during the weekdays. Find out for sure this weekend have to get the Cady down there for giggles.