I think my 8 ¾ housing is toast.

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flyfish

flyfish

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I put CalTracs on my car a few weeks back, took it to the track and ran it. When I got the car home I was looking it over and my pinion angle had changed…it was 3° down, now it is 2° up. I checked the spring perches and it looks like they have moved. The passenger side spring perch has actually dented in the axle tube quite a bit…and that axle is now leaking from the end of the housing (by the wheel).

So, is the housing toast, or is this something that I could fix? Or maybe a better question would be, should I just switch to a dana since this one is breaking, before there are no good parts of the 8 ¾ to sell?

FWIW, this is behind a 540 hp small block, foot break car, 3200#’s.
 
Using a back brace on the back of the 8.75 makes them pretty strong, but in you case the rear is done. I'd go Dana and sell all the remaining good parts I have for the 8.75 to help fund the new rear.
 
Was there not another housing for sale on here? Get that one and add a brace! However, you kind of scaring me into getting a brace. hmmm
 
Hey FlyFish,the exact same thing happened to me(perches moving)I got them rewelded on(using wet rag for cooling)A couple months later I pulled an axel to check splines for twisting(again)Yes the splines were twisted again.:banghead:I already had plans for peicing together a Dana 60.Upon removal of my narrowed 8 3/4 I noticed the driver,s side perch collappsing and the housing twisting(no brace).So I put my narrowed Dana in with the mono,s/Caltracs.I also decided to improve my driveshaft to a chromemoly one with the 1350 u-joints and 904 yoke(Mancini,s)She,s bullit proof now.Maybe you can find another housing and brace it?Mine was a C-body rear narrowed that I paid $100 complete with .489 case and 2.76,s.Couple pics of damaged rear..
View attachment 66 Dart project Nov2010 360.jpg

View attachment 66 Dart project Nov2010 215.jpg
 
pettybludart said:
Hey FlyFish,the exact same thing happened to me(perches moving)I got them rewelded on(using wet rag for cooling)A couple months later I pulled an axel to check splines for twisting(again)Yes the splines were twisted again.:banghead:I already had plans for peicing together a Dana 60.Upon removal of my narrowed 8 3/4 I noticed the driver,s side perch collappsing and the housing twisting(no brace).So I put my narrowed Dana in with the mono,s/Caltracs.I also decided to improve my driveshaft to a chromemoly one with the 1350 u-joints and 904 yoke(Mancini,s)She,s bullit proof now.Maybe you can find another housing and brace it?Mine was a C-body rear narrowed that I paid $100 complete with .489 case and 2.76,s.Couple pics of damaged rear..
View attachment 1714504849

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Is it just me or... it looks like you axle is actually bent???
 
flyfish said:
FWIW, this is behind a 540 hp small block, foot break car, 3200#’s.
Click to expand...

It really needs to be back braced for sure. I did it on my street car before I put the rear in. Bending at the perches is a common issue when you hit them hard.

FWIW a buddy of mine has an 8 3/4 in his Dart, 620 HP and hits it at 3400 off of the trans brake. His holds up just fine. It is shortened some with the brace and after market axles.
 
When you put the back brace on, does it need to be in anything special or just place and weld?
 
I've been running at or near this power level for a lot of years, but it looks like the extra umph of the Caltracs found the week link in the suspension...Can I use my 35 spline axles from the 8 3/4 in a dana?
 
flyfish said:
I've been running at or near this power level for a lot of years, but it looks like the extra umph of the Caltracs found the week link in the suspension...Can I use my 35 spline axles from the 8 3/4 in a dana?
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If the housing isn't bent then you might save it. I saw a thread on here a while back where someone had the same problem and they came up with a way to actually brace the perches.
 
No I don't believe Dana and 8.750 axles interchange.
 
Well they do interchange as long as its 35 spline. Im using 8 3/4 axles that I bought from Pettybludart. As long as the housing ends are mopar no problem. Even the backing plates and brakes work. Bolt in deal.
 
72ScampTramp said:
Well they do interchange as long as its 35 spline. Im using 8 3/4 axles that I bought from Pettybludart. As long as the housing ends are mopar no problem. Even the backing plates and brakes work. Bolt in deal.
Click to expand...

Wow, learned somethin' new.
 
Mine are 30 spline units from Moser I bought off a member that was using them in a 8 3/4. As long as the housing ends are 8 3/4 your good.
 
flyfish said:
I put CalTracs on my car a few weeks back, took it to the track and ran it. When I got the car home I was looking it over and my pinion angle had changed…it was 3° down, now it is 2° up. I checked the spring perches and it looks like they have moved. The passenger side spring perch has actually dented in the axle tube quite a bit…and that axle is now leaking from the end of the housing (by the wheel).

So, is the housing toast, or is this something that I could fix? Or maybe a better question would be, should I just switch to a dana since this one is breaking, before there are no good parts of the 8 ¾ to sell?

FWIW, this is behind a 540 hp small block, foot break car, 3200#’s.
Click to expand...
8.75s have the same size axle tubes as a Dana. Same thing will happen. A back brace will keep you from twisting the tube in the banjo. There are cars out there with a lot more hp than you running these rears. When you weld a housing (when relocating the perches) you weaken the metal around the area. Also the metal tolerances vary between axle housings. When switching to a cal trac you are putting stress on the perches that used to be taken up by the pinion snubber. So reinforcement of the perch is necessary. Plating the perch will make it better, also buying a MO875 is a good cost alternative and will be much stronger and cheaper than a D60.
 
Also, there are after market perches that have front and rear flanges for a full perimeter weld. Dr. Diff is one place that sells them.
 
flyfish said:
I've been running at or near this power level for a lot of years, but it looks like the extra umph of the Caltracs found the week link in the suspension...Can I use my 35 spline axles from the 8 3/4 in a dana?
Click to expand...
Are those the stk perches? and what rpm do you leave at?
 
I had the same problems with running the caltracs with 8.75. I went to the Moser MO875 and it fixed that problem. It is a very nice piece, but if you start making over 550 rear wheel HP it will create another problem.(Then you are going to start breaking the gears and the transmission). Been there and done that. I run low 10s so I went to a DANA.
 
I would think your axles are twisted like pettyblu's pictures. You already have the center section. The cheapest way out for you is the MO875 Like Turbodart68 is recommending.

http://www.moserengineering.com/com...5m-housing-axle-package-inch-part-number.html

This is another alternative for you........

I am in the middle of building a Ford 9" for mine and Triangulated 4 Link. I am swapping out the 8 3/4 with basically the same set up.

Labor to shorten etc is my own.
Paid $160.00 for the complete 9" rear end.
$60.00 for new big ford housing ends
$45.00 Back Brace
$45.00 Large Aluminum fill & Drain Plug assy
$80.00 for sheet of .250 Chromoly

Total to shorten with new tabs built by me...... $390.00

$1000.00 for New Nodular Drop out with 35 Spline Spool, 3.50 Gears, 1350 Billet Pinion Yoke, Daytona Pinion Support.
New 35 Spline Axles $350.00

This set up is good for 1200+HP.

Here is what I started with and where it is as of today.

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