Rear End Questions Need Help.

[05moneypit]

Am I the only one on this forum going with a 3.90 Motive gear?
I finally decided to order it a couple weeks ago...UPS delivered it Friday.

Anyway, what's the deal with the 3.90?

I've been running a 3.90 Motive pro gear for 5 years. It's the right ratio for my application. No issues with the gears.

 

[BadPiggy]

3.90 gears have a bad rep for noise. It has to do with the tooth count on the ring and pinion not being ideal in spacing.

Trutrac needs mineral oil. No synthetic. I'm using Valvoline 80w-90 and haven't had any problems.

Of all the noisy gears in the world, there are none noisier than a Harley Davidson transmission. The Redline shuts them the F up, which is why I was going to use it.

 

[AutoXRacer]

Most of the autocross guys that run TruTracs, use Shockproof!!!

My only concern is using straight heavy especially during the winter.

 

[panama]

I had 3.90s. They were unbelievably noisy, sounded like I had a set of mud tires. The guy tried to set them up a few different times but it was a no go. I really loved the gear though performance wise, I tried different oils and weights to try to make them work. My 4.10s just feel short sometimes. 4th gear at 100 mph is turning around six grand even with my tall tires 275/40-19. Off the line it is a beast though.

 

[BruceH]

I had 3.90s. They were unbelievably noisy, sounded like I had a set of mud tires. The guy tried to set them up a few different times but it was a no go. I really loved the gear though performance wise, I tried different oils and weights to try to make them work. My 4.10s just feel short sometimes. 4th gear at 100 mph is turning around six grand even with my tall tires 275/40-19. Off the line it is a beast though.

You should be at 120 with that combo at 6k. Something's off.

http://www.wallaceracing.com/calcmph.php

 

[Mattr89]

I was thinking about going with 3.73 gears. I make 500 rwhp and I am sitting at 2600 Rpms @ 70mph.

I have 285/40/18 tires now and going to get 285/45/18 in a few weeks.

Any thoughts on the gears?

Also as far as the spider gears how do I know if they are worn? Mine don't have any damage that I can see.

Suspension is next for me. I have a 2.2 60 foot time and even with that I can still run a 12.2 @ 124mph.

I have stock shocks with h&r super sports. So I am now wondering what is a good shock to get? I was thinking the blisten or koni yellows as they are fair priced. Relocation braces and possibly ford racing Lca's at the same time.


Also on a side note to whomever might think it can't be done. I have removed the spider gears numerous times with the rear in tact. I take the pan cover off and drain the fluid, then I push the retainer c clip out and then push on the tires to remove the retainer clips on the axles. Then work on getting them out.

 

[Mattr89]

I also forgot to ask a couple questions. I am running 75w140 should I run that in the rear some people are saying 75/90.

Second question is my engine makes a pronounced tick and when the engine is cold it's somewhat loud and is best heard between 1200-1900 rpms. Once I'm past 2k it's starts to go away. Once the car is warm it isn't as noticeable but can clearly be heard still.

If I hold the car at 1600 rpms or drive down the road at that rpm I can hear it like tick.........tick.tick............tick.


Like once every 2 or 3 seconds. It's not like a fast tick or complete and constant tick.

 

[panama]

I'll have to go for a run soon and re-check that mph vs rpm. I only drive it maybe once a week and usually around town.

My motor has some pretty pronounced ticks at low rpm, sounds like a sewing machine. My v twin on my motorcycle though always has a new noise but it's completely normal somehow. That drove me nuts for a while

 

[TexasBlownV8]

I also forgot to ask a couple questions. I am running 75w140 should I run that in the rear some people are saying 75/90.

I use the 140; 75w90 was the spec'd fluid for 2005/2006 v6 7.5 rears.

I use 373's and turn around 2500 rpm at 70-ish, stock-height tires. When I used 331's for a brief period, rpms at highway speed dropped maybe 200 rpms or so.

And ticking can come from many places, including injectors, timing components, exhaust, etc.

 

[BruceH]

I was thinking about going with 3.73 gears. I make 500 rwhp and I am sitting at 2600 Rpms @ 70mph.

I have 285/40/18 tires now and going to get 285/45/18 in a few weeks.

Any thoughts on the gears?

Also as far as the spider gears how do I know if they are worn? Mine don't have any damage that I can see.

Suspension is next for me. I have a 2.2 60 foot time and even with that I can still run a 12.2 @ 124mph.

I have stock shocks with h&r super sports. So I am now wondering what is a good shock to get? I was thinking the blisten or koni yellows as they are fair priced. Relocation braces and possibly ford racing Lca's at the same time.


Also on a side note to whomever might think it can't be done. I have removed the spider gears numerous times with the rear in tact. I take the pan cover off and drain the fluid, then I push the retainer c clip out and then push on the tires to remove the retainer clips on the axles. Then work on getting them out.

Think ahead a little. Is a t56 magnum or 6060 in your future? If so go 4.10 minimum.

 

[Mattr89]

I use the 140; 75w90 was the spec'd fluid for 2005/2006 v6 7.5 rears.

I use 373's and turn around 2500 rpm at 70-ish, stock-height tires. When I used 331's for a brief period, rpms at highway speed dropped maybe 200 rpms or so.

And ticking can come from many places, including injectors, timing components, exhaust, etc.

Mine had 3.55 rear with 17's originally and turned 2200 rpms at 65-70.

Think ahead a little. Is a t56 magnum or 6060 in your future? If so go 4.10 minimum.

Yea I agree that that 6060 with 3.73's would be great for a high top speed.

Anyone know If I can keep my same clutch and flywheel as well as driveshaft if I go with the 6060?

Is it geared better for acceleration than the 3650?

 

[BruceH]

Mine had 3.55 rear with 17's originally and turned 2200 rpms at 65-70.



Yea I agree that that 6060 with 3.73's would be great for a high top speed.

Anyone know If I can keep my same clutch and flywheel as well as driveshaft if I go with the 6060?

Is it geared better for acceleration than the 3650?

You will need a 26 spline hubbed clutch disk with a 6060. You can have your current clutch rehubbed and use it. I was able to use my dynotech 3650 driveshaft with the 6060. A stock GT shaft won't work though. I'm currently running a GT500 shaft that was $125 on ebay.

You would never be able to reach the 228mph @ 6.5k speed that is possible with 27.7" tires, 3.73 gears and the .63 ratio of 6th that was used on the 2007 and 2008 6060. Even with 4.10 the top speed would be 207 and require a lot of power. From 2009 on the 5/6th gears are .74 and .5. The earlier ones are .8 and .63.

A 6060 with 4.10 gears behaves more like a 3650 with 3.55 from 1-3 gears. I've had 3.55, 4.10, and 4.56 with the 6060 and would say don't consider anything below 4.10 unless you have 650+ rwhp and even then I stayed with 4.10. I went from 4.10 to 3.55 to 4.56 to 4.10. I may still swap back to 4.56 or even 4.30 in the future. It depends on how strong the new motor is going to be.

Here's the calculator. http://www.wallaceracing.com/calcmph.php

 

[19COBRA93]

This is what worn side/spider gears look like:

 

[Mattr89]

I just inspected my old discs with the tabs and dont seemed warn out, Yet when one tire got stuck in the grass and was spinning the other tire was on the driveway and wouldnt turn why is this? Is it because royal purple is too slippery?

I am thinking about using Ford Convention 75w90 the stuff that comes with the mustang gt from the factory.

Any thoughts?

 

[chaoscentral]

These cars come with 75w140 synthetic from the factory, older cars came with 75w90 conventional

 

[19COBRA93]

I just inspected my old discs with the tabs and dont seemed warn out, Yet when one tire got stuck in the grass and was spinning the other tire was on the driveway and wouldnt turn why is this? Is it because royal purple is too slippery?

The factory limited slip diff isn't designed for that. The clutches are only there to assist. That's it. Power will always go to the wheel with the least amount of grip. That's why diffs like the Trutrac and Torsen work so well. They actually send power to the wheel with the most grip. Big difference.

My advice is to ditch the factory slipper diff and go with something that actually works in your favor.

 

[05RedDevil]

I trashed the gears in my diff. I went with a Detroit Tru Trac and am quite pleased with the upgrade. Just my $0.02

 

[Sprayer84]

This title......LOLZ