Posted By: 1x59rr
8 1/4 to 8 3/4 - 02/28/11 03:46 PM
I am going from a 8 1/4 to an 8 3/4 in my dart. Are the backing plates and drums the same. if they are not, will any 8 3/4 set work or do they have to be a body specific
Posted By: Kern Dog
Re: 8 1/4 to 8 3/4 - 02/28/11 04:39 PM
The brakes will swap over. The 8 1/4 only used 4 of the bolts, the 8 3/4 used all 5. The driveshaft may still work too. The 8 3/4 is about 3/4" longer.
Posted By: JohnRR
Re: 8 1/4 to 8 3/4 - 02/28/11 04:59 PM
Need more info before making any recommendations...
Does the 8 3/4 have large bolt pattern axles , if so are they new axles with the big car brake offset or redrilled small bolt pattern axles ?
As far as the driveshaft , if the 8.75 is longer than the 8.25 how can anyone say it's onk to to use a draveshaft that is obviously too long ?
Posted By: Kern Dog
Re: 8 1/4 to 8 3/4 - 02/28/11 05:37 PM
Many of the stock driveshafts that I have seen sit with the yoke over an inch and a half OUT of the trans with the vehicle at rest. All of my cars sit at or below stock ride height, and the suspension travel is less as well. Less suspension travel means less fore/aft slide of the yoke. If you have 3/4" to one inch of yoke out of the trans with a driveshaft in a zero angle straight line into the trans, wheres the problem? I am certain that in a truck or a vehicle with lots of suspension travel things would be different. Sorry if I was unclear. I sometimes forget that My methods can be unusual!
Posted By: Kern Dog
Re: 8 1/4 to 8 3/4 - 02/28/11 06:05 PM
You are in need of a vacation. Relax. This forum is for help and suggestions, right? I take help from people here but I still have my own brain. If some anonymous guy says a Nova fender would fit my Dart, I'm not going to try it. I ask more questions and do more research. What are we doing to people? What happened to personal responsibility? We cant just do stupid things and then blame other people. Remember when the town idiot was ridiculed instead of protected? Nowadays we make excuses for why the town idiot makes mistakes...
He was led astray
He trusted the wrong people
It wasn't HIS fault.
This forum isnt an owners manual and it isnt the bible. Its chock full of a wide range of people with a full spectrum of answers from the dead on accurate to the absurd. Sometimes my responses are at one end or the other. John, I usually respect your posts. I'll just figure that you are having a bad day but I look forward to your posts in the future. You are one of the smarter ones here.
Posted By: vandude
Re: 8 1/4 to 8 3/4 - 02/28/11 06:18 PM
On an 8 1/4" rear, the axle centerline to pinion yoke centerline measures 11.69".
On an 8 3/4 rear, the same measurement is 12.35
That's a little over 5/8". If the suspension travel on my B200 can tolerate that same swap I bet a Road Runner would be fine too.
'course the RR is worth at least 10 times as much as Junkyard Jitters, my ratty old '77 Tradesman, so the decision is still yours.
I would measure for driveshaft length just to be sure. After you have the rear in with the cars weight on the tires so you achieve ride height, measure from the end of the tail stock (not the shaft)to the flat surface where you're u joint clips bolt on. That will give you the length. If you need to shorten it take it to a reputable shop and have them shorten it and balance. You may also want to call your local shop and ask them how they want you to measure. If there's a minimal difference then you might be ok.
Unless someone wants to take the trouble of checking the full suspension travel to see if the driveshaft stubs itself into the transmission there's no way you should take this for granted.
Do it right for $90 or run the risk of tearing up a driveshaft, trans, floorpan and/or rear yoke.
I did a similar but way different swap from an 8.2" GM rear end assembly to a 8.5". Driveshaft wouldn't even go in. Ran the car for many years prior to that.
Posted By: forphorty
Re: 8 1/4 to 8 3/4 - 03/01/11 02:00 AM
On my duster, since i was running a larger diameter tire, i made some shims and put them between the body and the front spring hangars. This centered the wheel in the wheel opening. Prior to this , the tire was pretty close to the leading edge of the wheel opening. I can't remember how much i moved the rearend back, seems like about 3/8. This might help with you driveshft issue, plus will give you more tire clearance at the front if you need it.