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droppointalpha
04-07-2012, 02:17 PM
To make a long story short, the rear end took a bad hit. Thankfully, I carry full coverage.

Pretty much, the entire rear axle was replaced. After, getting the car back from the shop, I carefully drive it round to ensure everything was good. Long story time... You probably ought to go grab a beer real quick.

Well, around 35 with just enough gas to barely accelerate, I get this feeling like the transmission is alternating between full lock up and not or between two gears (not sure I'm explaining it right). Acceleration still feels good and I know the feeling occasionally happened before the event. I read around and reread that the vehicle had some hunting around (reading lido's prefab tune page). But once the bug is there, worry is tough to ignore.

But now I'm thinking. The shop guy was surprised the marauder had unique rear diff compared to I don't know what. He was expecting it to be the rear from the interceptor. I told him I knew out had a unique final ratio in the 3 range but couldn't recall the number off the top of my head. Now, I'm perusing the internet to learn what I can about the rear diff and find the ratio wasn't unique except that it hasn't been seen in the platform before hand. First response on google is an OLD post on here. A guy needed to replace his but no one had the full assembly, if I read correctly.

That was 2009. Now I'm worrying. The CV LX Sport used a 3.27 and the CVPI used the same and offered the 3.55 in 2006; both could be fitted with a LSD; I identify these vehicles as I didn't notice a tremendous difference that should have come from a 2.72 or perhaps a 3.08 rear end. I have also read how to ID the diff externally by reading the tag 3 55 & 3 L 55 being the tags for an open and LSD respectively. But, my worry attacks upon the ship, ergo I cannot satisfy my fear nor curiosity. However, I can post here some questions and perhaps spark some interesting exchange of knowledge in the process.

1. Would a post 2006 CVPI 3.55 LSD even be able to fit/function with the ole MM? Number splines and such? I ask because the old thread was from 09 but the CVPI was never more than suggested as a source of parts. (link here http://www.mercurymarauder.net/forums/showthread.php?t=53347 )

2. Assuming the answer to the above is yes, would I be right in assuming an open diff is not going to harm the car, only reduce rear end performance? Was there a quality or performance difference between the MM and the CVPI/LX Sport diffs? (out side of whether it was open or limited slip)

3. Would a 3.27 gear do damage or cause problems? (other than an incorrect speedometer reading)

4. What was the stock MM's top speed if you removed the limit? Does the engine put out enough power to reach higher speeds if the 3.27 final gear was in place? If the 4.10 gives better grunt at the sacrifice of a higher engine rpm per given speed (an thus higher fuel consumption), would the 3.27 give a similar but opposite effect? (sorry, curiosity ruining wild now)

5. Has anyone ever done a 3.27 swap for higher top end speed (stand alone our in conjunction with other mods)?

6. (back to earth) Is it worth while to pay to change back to a 3.55 gear from 3.27 assuming the wrong one was in fact installed?

Finally, I ask some forbearance as I am typing this from the phone. It doth not like the search bar and thus I cannot use it to search the forum for additional answers.

Fond regards.

RF Overlord
04-07-2012, 04:02 PM
I'll try to answer what I can.
1. Would a post 2006 CVPI 3.55 LSD even be able to fit/function with the ole MM? Number splines and such? 2005+ used 31-spline axles.

2. Assuming the answer to the above is yes, would I be right in assuming an open diff is not going to harm the car, Correct. Was there a quality or performance difference between the MM and the CVPI/LX Sport diffs? No.

3. Would a 3.27 gear do damage or cause problems? (other than an incorrect speedometer reading) No.

6. (back to earth) Is it worth while to pay to change back to a 3.55 gear from 3.27 assuming the wrong one was in fact installed? Only you can answer that. You may notices a slight reduction in acceleration and/or a slight improvement in fuel economy, depending on your driving habits.

droppointalpha
04-09-2012, 09:03 PM
Good to know.

Thanx

Mote
04-10-2012, 12:12 AM
6. (back to earth) Is it worth while to pay to change back to a 3.55 gear from 3.27 assuming the wrong one was in fact installed?


If driveability is fine in your opinion it may not be worth it. However

0. I think you do need to determine what ration is actually in there.

1. Your odometer must be showing fewer miles than it actual has. That will be an issue when you sell it, and it is altering maintenance intervals if that matters to you.

2. If by chance the ratio is not 3.55 and you do want to change it, consider changing to 4.10 or 4.30 if of course a performance boost is desirable. You will need a way to correct the tune on the car to take care however.

droppointalpha
04-12-2012, 03:56 AM
If driveability is fine in your opinion it may not be worth it. However

0. I think you do need to determine what ration is actually in there.

1. Your odometer must be showing fewer miles than it actual has. That will be an issue when you sell it, and it is altering maintenance intervals if that matters to you.

2. If by chance the ratio is not 3.55 and you do want to change it, consider changing to 4.10 or 4.30 if of course a performance boost is desirable. You will need a way to correct the tune on the car to take care however.


1. Good point. Forgot about that. Haven't driven very far with it so any descrepancy is minor now.
2. What is the usual mpg efficiency loss going to a 4.10 gear from a 3.55? I was getting a good 26 on the highway.

RF Overlord
04-12-2012, 05:12 AM
2. What is the usual mpg efficiency loss going to a 4.10 gear from a 3.55? I was getting a good 26 on the highway.Lots of variables here, but in general those of us who switched to 4.10s saw a roughly 2-3 MPG hit on the highway, but many saw a slight improvement around town, due to not needing as much pedal to launch the car, so the average MPG hit was more like 1-2 overall.

droppointalpha
04-12-2012, 10:30 PM
Interesting... Not what I expected at all.

droppointalpha
04-27-2012, 08:37 AM
OK, update. A speed run test second day home reveals a non-linear speed error, starting at around 1mph difference at ~35mph and getting up to 5mph at 65mph (readings from the speedometer compared to true off a GPS unit).

So the shop got sent the wrong unit by the Ford dealership they ordered from. As they are making good by replacing the diff completely, I'm trying to help out too by running down as much info as I can regarding the correct specs and markings the unit should have.

So, if someone whose search-foo is better than mine or who knows by experience can correct me

3.55 Traction Lok LSD (28 spline 8.8" correct?)
Markings should be " 3 L 55 88 " on the second line