The 5.29 Mega Thread!!

That is more of my drive to get 5.29's, even just running 33s, sliders and underside armor...it certainly seems like an upgrade in driveability while towing, even empty utility trailer the stock setup just doesn't want to get out of 4th!

 

So that’s 2600 for the front and rear already built? If so it’s not bad, right around what you’ll spend anyways. How do you purchase it? I couldn’t find it built, just the kit.

 

You can see the options and prices here

I paid $2500 for both front and rear (after the $1500 core refund) with the REM polishing and ARB air locker, Then $725 to get it installed.

 

Thank you for the link!

 

It seems like there is some uncertainty regarding the speed limitation with 5.29s. I have a 2018 OR and can confirm that my truck will NOT allow me to get to 84mph in 6th gear. When I am in 5th, it allows me to over 90. Based off some of the feedback on here, it seems like it may only be certain years that its an issue.

 

This statement makes no sense.

 

What part doesn’t make sense? The speed governor kicks in at 83 in 6th. In 5th I can go over 90. Fuel cut occurs earlier in 6th gear.

If I leave the truck in 5th it’s no issue maintaining 90. The moment the truck shifts into 6th, it hits fuel cut off and doesn’t resume until it’s down to 83 mph.


I believe it’s due to a certain calculations in the ecu. The ecu is calculating vehicle speed off of rpm times gear. In 6th at 2800(est.) rpm the truck would be going over the factory speed limitation. I’m not exactly sure why it can’t make the same calculation in 5th.

Edit: Auto trans if that was part of any of the confusion.

 

Confirming the fuel cut at ~85mph on the speedo in 6th. Not sure about 5th though.

 

What size tires are you running. Two guys have two different years with two different engines and drivetrains.

It doesn’t make sense because the speed is calculated at the ABS sensor. If the truck calculated vehicle speed off RPM and gear then you would constantly have fuel shutoff in 4-lo at 20 mph.

Stock gears between 6th and 5th at 90 is 2200 and 2600 respectively. With 5.29s it’s 3000 and 3600.

If rpm and gears were used for speed limitation the trucks top speed with 5.29s would be 67 mph. Conversely, trucks with large tires reduce rpms and and have a 14% higher speed than reported on uncorrected speedometers; meaning someone with large tires is essentially bypassing the speed limiter.

Obviously, there is no evidence to support this which is why your statement makes no sense.

 

It's $1500 front and rear already built. $1100 ($550 per core) core charge. I did the install myself so I saved on labor.

https://eastcoastgearsupply.com/c-62270-assembled-3rds-clamshells.html

 

Does anyone have a gear chart for a 2nd gen 6MT? found it
1st = 4.17
2nd = 2.19
3rd - 1.49
4th = 1.19
5th = 1
6th = .85
r = 3.73

With the higher ratios that the 2nd gen 6mt has am i better off going with 4.88's?


Ill be regearing within the next month or two and have been considering going with 5.29's over 4.88's

 

The guys that installed mine said don’t use synthetic gear oil. Any ideas why not?

 

Maybe the reason why the governor is coming on doesn’t make sense. I can assure you I know what fuel cut is and I know when a governor is kicking in.
Regarding 4 low, if the ecu knows the truck is in 4 low I would assume it would bypass the speed limiter.

It seems like this truck does use strange logic to control things, so I couldn’t tell you specifically why it’s happening. @OVTune might better at explaining this than I am.

I am running 285/70-17 tires. Indicated 83mph is closer to 87 true speed for me.

Regardless of whether people believe me or not, this post was to confirm that on some trucks speed is limited to lower than stock speeds with 5.29 gears. I am not here to argue or debate if this is happening or not on my truck.

 

I’m here because I want 5.29s for my 6MT and need someone to tell me it’s dumb.

Don’t all line up at once.

 

I can confirm my truck acts the same way. The cut off is very soft but it’s there. 2018 34’s 5.29’s AT.

The speedo uses the the abs sensor to calc speed. The ECU can calculate speed knowing your gear and rpm. This is pretty well documented in the OVtune thread.

@JoeCOVA Because the truck knows what gear it’s in this isn’t an issue in low range.

Stock gearing and tires 6th gear AT 2600 rpm is 104.7mph

34’s 5.29 6th AT 2600 is 85
34’s 5.29 5th AT 3000 82.7

These are corrected mph estimates. Part of the problem is the speedo indicated speeds that some maybe or may not be reporting are going to vary with tire size. Leading to do discrepancies.

The speed indicated or actual at which you hit cut off will be variable depending on your tires and r&p ratio. The rpm and gear should be consistent between trucks.

 

But the ECU doesnt know your gearing..The ECU can only assume stock but the rpms do not correlate

You guys are shooting in the dark and there is no consistency

Using your stock numbers of 6th gear AT 2600 is 104mph and that is the limit
A truck with stock tires and 5.29s AT 2600 rpm is about 77 mph, we can all confirm that you are not limited

 

What makes you think the ecu doesn’t know what gear you’re in? The ecu doesn’t know rear end gearing, which is why I mentioned “indicated” mph vs Gps. I fully acknowledge that I am in fact going faster than 83mph due to my tire size. But again the ecu doesn’t know what size tires you have.


How are you so certain that our trucks aren’t being limited? Do you have a 2018 AT?

You keep bringing up tire size, why? While tire size definitely effects true speed, it doesn’t have anything to do with what the ecu sees.


For what it’s worth, when I’m at an indicated 83 in 6th I’m at “about” 2500-2600 rpm, which is where fuel cut off happens (which lines up with your factory math, just looking at rpm)


I will get a video of it. Not to appease you, but to hopefully help others who had the same questions.

 

Your first sentence speaks for itself, I never mentioned transmission gears, I was referring to the dif gears which you agree the ECU doesnt know. Meh, I was curious to find an answer but now I don't care.

My truck isn't limited and most others aren't. Your problem, good luck.