I was downshifting why comin up to a light and when i downshifted
into 1st why doing about 25-30mph the rearend just took a crap...

5.4 4r70w 8.8

now im never rebuilding a 8.8 again but do you think its shot ??


it dont spin at all....
tires dont move...
driveshaft spins...

Do you think i broke a axle ?
wheels did not come off on the tow home... about 6miles doing 25-30

O HEY this will be my 3ed 8.8 just rebuilt it less then 15k miles ago....

 

Any reason you are not using the 9.75" rear end prescribed for the 5.4?
And you said you "down shifted". So you have a 5spd in the truck? Sounds like you have done some mods. WHy did the rearend go last time? Where did it break?

 

truck came with a 4.6 and i did a 5.4 swap

you can downshift a auto trans
still got the 4r70w


the last rearend
i put 50k miles on or more...
pulled a huge dump trailer...
mudded....
power braked....
I put beat it bretty bad...
But it showed signs of it about to go....
makeing sounds and ex.....

But this rearend i did not beat on and i dident tow any thing big...
and it showed no signs of wear it just broke...
i have yet to look inside but im wondering if a axle snaped or something

 

how do you know if the rear end you have is an 8.8 or a 9.4 and also what do those numbers mean

 

Each number refers to the diameter of the ring gear in the rear end. 4.2 and 4.6 used the 8.8" rear end while the 5.4 got the 9.75".

SSJ4Shane:
I know you can downshift and auto, it was just an unusual statement and action for an auto unless you are towing or going down hill. It is not good regular practice for any automatic to do so.
If the drive shaft is spinning than you may have lost the pinion gear or it's pin to the drive shaft.
Sounds ****.

 

You could either broke the pinion, or more likely blew your spider gears/LS carrier up.

Time to take it apart and see whats up with it. Definately post up some pics and let us know.

As you found out, you don't downshift automatics. No reason. They do it all on their own. If going down a hill, and wanting to use your gearing and a means of braking, then I'd suggest going a whole heck of a lot slower then 25mph. I slow down to either a stop, or damn near crawl before downshifting into 1st, and still can feel it.

I'd highly suggest going with the 9.75" rear. Maybe a custom 9" ? Or a rear dana 60. Those would help cut down on breakage.

 

ill be looking into it soon... i gota work and what not but...

its just ****ty how much less i put stress wise into this rearend compared
to the last 2 and this one lasted 1/4 of the time....

 

what did you replace the last rear end with? internal wise? and whats the gear ratio?

 

X's 2

refer to the above

 

powerbrakeing and other things like lunches do way more stress...

you cant tell that the compresson from the motor puts more stress on the
rear then other things...

i beat my rearends... this is nothing compared to the past

yukon install kit
fordracing limited slip
and some off brand gears....

yes i know the gears might be the weak link but they made no noise....

i dont know yet ill get a look at it soon...
theres a ****ty part with that to because i towed my truck home...
whole rearend smoked i bet...

 

4.56's this will be my 3ed set


and this will be the first time it broke at once...
last 2 rebuilds they started chipping teeth and took time... never just
broke and stoped working....

im saying they took days and days... lil noise to loud pop's and stuff

i took my time braking in this rearend to.....

 

Dude, it broke all at once cuz you frickin shifted from drive to 1st, going 25 mph Say what you want, but more times then not that will lead to "catastrophic failure". Don't downshift your auto's, period.

Also, if this is your 3rd 8.8" rear end... well then my sympathy level is next to none. If you keep breaking it, why do you replace it with the same thing ? Expecting different results ? Defination of insane: Doing the same thing over and over again, expecting a different result.

UPGRADE. Time to start looking into a complete swap. Go with something bigger, stronger, more reliable, and stop beating on your truck. No downshifting, if you are going to use 1st, get down around 2-5 MPH MAX.

 

Exactly, that will do it. - Why did he purposely break his rear end, I can't find it ?

 

ok wait im stupid i forgot there was warning signs....

no noise but my brakes started acting up a day befor it broke....

my truck only has rear abs and it seemed like the abs was acting up....


what could brake in the rearend that would effect the abs and then take out the rearend?

 

IMHO, I believe what happened was two completely different things, just happened around the same time. I would bet your ABS acted up, for whatever reason.

What destroyed the rearend was the downshift.

Its hard to be certain, being over the internet and all, and not being able to get my hands on it and see whats going on. I just can't think of anything related to the ABS system that could posibly damage your rear, let alone make it grenade on ya.

You taken it apart yet ? See what happened ? Or are you bringing it somewhere ??