Destructive forces inside the rear differential
Destructive forces inside the rear differential Can we have some discussion about the destructive forces, and modes of failure within a rearend differential. Sketches would also help out too. Could we limit our discussion to "weak" sections of a rearend, which tend to fail/flex/move/whatever and ultimately lead to catastrophic failure. The 10 bolt would be a great example for pointing out weaknesses? Perhaps someone could develop a failure tree of the rearend and walk us through how the torque from the input shaft eventually leads to failure.
CTSmechanic is correct, the Ford 9" is massive so to speak especially compared to the 7.5 in the F-bodys. Honestly You have the same size gear and differential in an S10/Blazer that you have in a 320+ft lb tq car that will be abused. A very big limiting factor. Increase the Size, Increase the Strength. Like she always says guys bigger is better 
I for one would like to see some actual discussion on this. There are far too many pat answers stating that it is a waste of time to build a 7.5". Everyone agrees that a Ford 9" is huge and strong. Let's not waste time on that argument. Besides, it has a huge hypoid distance causing it to waste a lot of energy
I would like to hear more about case flex. It seems unlikely that the gears themselves are to blame. If they are inadequately held in place and are allowed to separate under load they will lose teeth. Furthermore, who is blowing up their rear ends, is it people with stock gears (ie set up by GM) or people with replaced gears (ie aftermarket set up the gears, possibly incorrectly). Lack of carrier preload (most people give little credence to needing to take a lot of care or measurement of it) could be killing a few of them.
I would like to hear more about case flex. It seems unlikely that the gears themselves are to blame. If they are inadequately held in place and are allowed to separate under load they will lose teeth. Furthermore, who is blowing up their rear ends, is it people with stock gears (ie set up by GM) or people with replaced gears (ie aftermarket set up the gears, possibly incorrectly). Lack of carrier preload (most people give little credence to needing to take a lot of care or measurement of it) could be killing a few of them.
Also, there are people who live with the 3:42 stock gears just fine, even under the stress of 400+ ft/lbs. of torque. I built mine in 2002 with a T2R differential and solid race pinion, TA cover with preload bolts. 1.91 60 fts. and numerous HARD gear changes from 1-2 and 2-3. I've been to the 1320' probably 75 times on this combo and numerous autox. It lives.
I also know (or read on this board) of others who break them leaving a parking lot.
For me, I think the T2R diff made the difference.
I also know (or read on this board) of others who break them leaving a parking lot.
For me, I think the T2R diff made the difference.
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Originally Posted by BJM
I for one would like to see some actual discussion on this. There are far too many pat answers stating that it is a waste of time to build a 7.5". Everyone agrees that a Ford 9" is huge and strong. Let's not waste time on that argument. Besides, it has a huge hypoid distance causing it to waste a lot of energy
I would like to hear more about case flex. It seems unlikely that the gears themselves are to blame. If they are inadequately held in place and are allowed to separate under load they will lose teeth.
I would like to hear more about case flex. It seems unlikely that the gears themselves are to blame. If they are inadequately held in place and are allowed to separate under load they will lose teeth.
1. For the pinion we have possible deflection in the pinion shaft and pinion support-->housing
2. For the ring gear we have deflection in the ring gear, carrier, main-caps, and housing
Does anyone have specs on the pinion shaft diameter between the 10 bolt and 12 bolt? I'll bet the weakness of the 10 bolt is in the housing itself as stated before and its ability to resist deflection under high torque loads. If this is the case I believe a great deal of strength could be added to the housing by adding truss supports. Many off road truck owners with with big tires and ultra low final drive ratios in the order of [(70-100):1] truss their axles (then there problem becomes breaking axle shafts!)
Spider Gears Are Too Small And Wear Out Quick.. Also The Ring And Pinion It Self Are Also Small...anyone Wo Has Actually Looked At A 7.5 Inch Diff Then Looked At Any Other Diff Can Quickly See The Thing Is Way Way To Weak.. I Dont Think Most People Have Problems With The 28 Spline Axles Or The Housing, As A 10 Bolt With A Spool Is Plenty Strong For Most 11-10 Sec Cars.. But With The Limited Space You Cant Pack Enough Material In Side That SMall Diff To Allow For Much Reliablity
Most of the 10-bolts that I saw get destroyed while I lived in Florida were due to the Posi blowing...I think I also recall someone breaking some 3.73s in an A4 leaving the line on nitrous. Not sure what happened there, but I don't think it was posi-related in that case. Seems like there are a few too many variables in this one...
My gears from GM came set up noisy as hell, and it took them 4 times to set them up right. Unfortunately, there is now a great deal of play between the ring and pinion - you can turn it about 5 degrees or so before one contacts the other (might be exaggerating, but it is a lot more than I think it should be). This rear has held up to my sticky clutches, but I've never run sticky tires. The rear is now starting to make some more noise (whining, clicking, etc), but is still holding in there.
My gears from GM came set up noisy as hell, and it took them 4 times to set them up right. Unfortunately, there is now a great deal of play between the ring and pinion - you can turn it about 5 degrees or so before one contacts the other (might be exaggerating, but it is a lot more than I think it should be). This rear has held up to my sticky clutches, but I've never run sticky tires. The rear is now starting to make some more noise (whining, clicking, etc), but is still holding in there.
When GM drew up the 7.5 they did it for as cheap as they could... They didnt even worry about folks like us beating the hell out of them....Unless your going to have pay the money and have some custom parts made or or go to any other lengths to try save the 7.5 your wasting your time in my opinion.You have to know when to hold'em and when to fold'em....Like everyone knows there are many many options avalible.People on this site worry about some stupid stuff.. who cares how much power a 9 inch takes.... or how much a Dana 60 weighs... if they'll let you get down the track faster and more consistent then its a gain.
my old 10bolt lasted for a little less then 2 years before the posi split. it cracked in the middle & sheered 2 of the 4 bolt heads off that bolt it together. my dad is an ASE mastertech & built it for me with a set of OEM 3.73's. it was built right & never made a noise of any kind. i ran redline lightweight shockproof fluid in it also.
i had the stock cover too. i know it had a minimum of 250+ track passes with 1.52-1.80 60's on it, i launched it off the transbrake on the kit more times then i can remember. when it broke i had just had the 370 tuned on the kit which did 510rwhp through the th400. after it broke i sold the ring & pinion and axles which were still in good shape.
a lot of the failures i have seen are with aftermarket gears. i've seen 2 of them with 4.10's that broke & i know they were not installed correctly and sounded like a 2 yearold screaming.
i had the stock cover too. i know it had a minimum of 250+ track passes with 1.52-1.80 60's on it, i launched it off the transbrake on the kit more times then i can remember. when it broke i had just had the 370 tuned on the kit which did 510rwhp through the th400. after it broke i sold the ring & pinion and axles which were still in good shape.
a lot of the failures i have seen are with aftermarket gears. i've seen 2 of them with 4.10's that broke & i know they were not installed correctly and sounded like a 2 yearold screaming.
On The Tree
Joined: Sep 2006
Posts: 163
Likes: 0
From: Warsaw, IN
Any body ever tried an 8.5" GM 10 bolt? I'm tryin to decide on building mine, or droppin two and a half G's on a 9" I don't see a half inch difference (1/4 inch each direction) bein worth that much.
Has anyone got a CAD drawing of one of these axles? Preferably an IGES or STEP file. I would make a finite element model of it for fun to see where all the loads go and what distorts the most.
Launching!
Joined: Dec 2005
Posts: 207
Likes: 0
I put my 4.10s and ZT in myself
I didnt know the pinion nut was supposed to be 150ft/lbs which is a bit.
After a year later it slowly gave away (I knew it was cause of the screaming)
then I took a turn and it all fell apart. shattered teeth and cut up my ZT.
Now I put the 3.42s back in and its going good
I didnt know the pinion nut was supposed to be 150ft/lbs which is a bit.
After a year later it slowly gave away (I knew it was cause of the screaming)
then I took a turn and it all fell apart. shattered teeth and cut up my ZT.
Now I put the 3.42s back in and its going good
TECH Fanatic
Joined: Mar 2004
Posts: 1,017
Likes: 0
From: Laguna Niguel, CA
Originally Posted by BJM
Has anyone got a CAD drawing of one of these axles? Preferably an IGES or STEP file. I would make a finite element model of it for fun to see where all the loads go and what distorts the most.
And do you know why is is called Finite Element models?
