Using 8 3/4 with /6

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Greenmachine225 said:
Unfortunately I didn't build this myself and I have limited information on the engine specs but I do have this link, Mopar 225 Cam & Kit 268 Mechanical this is the set up that the guy told me is in it, it was converted to big bolt pattern, and I believe what I said, "it can't put the power down", isnt the right thing to say which is what some people are confused by it but what I mean is that if I give it full throttle from a stop it is obnoxiously slow and think this is due to the rear end which is why I am looking to swap it. Please correct me if I'm wrong on any of this because I'm still learning.
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That combination is going to need something between 3:23 and 3:91 to have any get up and go. Considering he swapped in a BBP 7.25, there is a good chance you are dealing with a gear set in the 2:4 range right now.
Also, and EXTREMELY important...you need a converter. Something in the 3500 to 4000 rpm range.
Lastly, I have found that most 4 barrel carbs are factory jetted way too fat for the Slant.
Pull your plugs and give them a look over, then consult the experts here.
We'll work with you, man. Patience and you'll get it all sorted out
 
Killer6 said:
OK, too much missing info to help You effectively, "a rear suspension kit" tells us nothing that we can use other than the kit apparently has 3" axle tube clamps instead of 2.5".
Putting the power down means having enough traction, IS that the issue? If so SureGrip anything will fix that for most slantys w/decent rubber, and I'm guessing it's an open
diff. at present? Which bolt pattern do you have,4" or 4.5", and do you plan on keeping it that way? Keeping the same rollers & what are they(size/type)? As far as slow out of
the hole goes, a better torque converter is the cure, not gears.....assuming an auto. I tried to make out kickdown rod or dipstick, don't see a clutch rod/bellcrank either, so I'm
going w/auto. Anyways, welcome to FABO! That is a awesome looking greenmachine indeed!
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So the suspension is something I'll worry about in the future, but what I said, "can't put the power down", I think was the wrong thing to say, what I mean is when I give it full throttle from a stop it is ridiculously slow, I believe that is because of the rear end. It is the big bolt pattern(4.5), and I'm not sure about the rollers. And yes it is a 904 3 speed automatic
 
whitepunkonnitro said:
That combination is going to need something between 3:23 and 3:91 to have any get up and go. Considering he swapped in a BBP 7.25, there is a good chance you are dealing with a gear set in the 2:4 range right now.
Also, and EXTREMELY important...you need a converter. Something in the 3500 to 4000 rpm range.
Lastly, I have found that most 4 barrel carbs are factory jetted way too fat for the Slant.
Pull your plugs and give them a look over, then consult the experts here.
We'll work with you, man. Patience and you'll get it all sorted out
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Thank you very much, I appreciate it.
 
Just for the record. ...beautiful

downloadfile-36.jpg
 
Greenmachine225 said:
So the suspension is something I'll worry about in the future, but what I said, "can't put the power down", I think was the wrong thing to say, what I mean is when I give it full throttle from a stop it is ridiculously slow, I believe that is because of the rear end. It is the big bolt pattern(4.5), and I'm not sure about the rollers. And yes it is a 904 3 speed automatic
Click to expand...

well, that can be one of two things
either there is no power to put down (it is a slanty afterall)
or, all the power is made at the top of the RPM range and the engine needs to work through the lower, weaker RPMs to get to the higher powerful RPM
a high stall torque converter will cure that, if that is the issue (a different rear end will NOT)

it s comparable to dropping the clutch at say 3400 RPM on a stick shift
 
Ok now we are on the same page.
So what you really need is a TC and probably gears.(as others have stated)
Or to swap out that cam.

IDK what gears are available for the 7.25, but I'll wager yours has 2.76s which are nice hi-way gears. Your slant does not need a bigger rear end like the 8.75, nor the 8.25. However if one fell into your lap with the appropriate gears and a SureGrip,for a good deal; then of course you should jump on it.But there is no other reason to ditch the 7.25.
But above all, you will probably need a higher stall TC.

I couldn't find specs on that cam in the link you sent; but it is titled as a 268. If 268 is the intake duration on that cam, then that is a pretty big cam, and unless the engine was well engineered around it, it will certainly be soggy on the take-off. So before you spend any money at all, you need to do 3 things.
1) do a compression test and print the cylinder pressures here.
2) do a stall-test
3) determine the current rear gears.
From the results of those we can see where you are at,why it is soggy, and what to do about it.
 
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Greenmachine225 said:
Unfortunately I didn't build this myself and I have limited information on the engine specs but I do have this link, Mopar 225 Cam & Kit 268 Mechanical this is the set up that the guy told me is in it, it was converted to big bolt pattern, and I believe what I said, "it can't put the power down", isnt the right thing to say which is what some people are confused by it but what I mean is that if I give it full throttle from a stop it is obnoxiously slow and think this is due to the rear end which is why I am looking to swap it. Please correct me if I'm wrong on any of this because I'm still learning.
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You need some gears. AKA, more gear, higher numbers. (I'd still go for the 8-1/4)
 
A cam and tall gears are going to make it sluggish off the line. What size are your rear tires? A taller rear tire only makes things worse as it changes the overall gear ratio.
 
I see you live in San Jose. There are two pick n pulls in town as well as one in Newark and one in Moss Landing. I have had good luck over the years finding bits and pieces for A bodies. You may want to sign up for "Row 52" that advertises on the pick n pull sites. It may help you find a donor car for an 8 1/4 rear end. It is possible to find an 8 3/4 in a yard but rare. Keep your eye on cars that may be wider than an A body. As others mentioned sometimes a wider rear end can be made to fit but my reason for looking at them is the center section. You can find an 8 1/4 sure grip in the high performance versions of the volare as well as 8 3/4 center section in trucks or grocery getter grandma cars.

There are other ways and places to get an 8 1/4 or 8 3/4 but they usually involve more cash than the flat rate pricing from pick n pull. I learned a lot about cars by spending a lot of time in high school with a buddy at our local wrecking yards. Be careful if you go out yarding. Even though they place cars on those welded together rims as make shift jack stands a car can still fall on you. Bringing a friend is always a good idea.

I don't have the information on hand with me at work but you can look up the model year cars that have the parts you are looking for and use it for reference when looking online or if you go to a junk yard. BTW, if you find a rear end and you put it in the trunk of that pretty car of yours make sure it does not slide in the trunk and make dimples on the sheet metal of your trunk.

Good luck and enjoy that car.

Mike
 
There is a member on .org with a set of Mopar 3.55's for the 7.25, in LA I believe, find a looser converter & she'll take off much better w/that combo.
 
I looked on summit and ebay; Motive and a couple other mfrs still sell ring and pinion sets for them (3.55, 3.90, 4.10)...kinda surprised actually. They are a little pricey though--about $250-$300. Also saw a set of NOS 3.91 gears on eBay for $175. And I have seen SG units in the classifieds, but they come and go quickly.
 
the 7 1/4 is strong i have it behind my slant six 4 speed 3.23 gears in the rain in the dirt in normal weather dumping the clutch no problems at all i did this as well to a 318 4 speed with 3.55 out back people have told me there weak i could'nt break it till this day, not unless you have a 340 360 383 then that's another case and to add these rear ends have never been rebuilt. both 4 speeds have 3.09 first gear. the only benefit i would see is the swapping of gears for long highway drives.
 
I ran a 3.91 SG 7 1/4 rear for years in a low 13 second drag car on slicks. The 7 1/4 SG rears are actually pretty strong. That said, getting parts for the SG units (if you can find a sure grip) is almost impossible. I have not seen any clutch kits for several years, and most any 7 1/4 SG will need clutches. Also new spider gears and axle end gears are hard to find, cross shafts are impossible. So just be aware of the parts availability situation.
 
Charrlie_S said:
I ran a 3.91 SG 7 1/4 rear for years in a low 13 second drag car on slicks. The 7 1/4 SG rears are actually pretty strong. That said, getting parts for the SG units (if you can find a sure grip) is almost impossible. I have not seen any clutch kits for several years, and most any 7 1/4 SG will need clutches. Also new spider gears and axle end gears are hard to find, cross shafts are impossible. So just be aware of the parts availability situation.
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....or, you can just weld up the spiders. Just sayin
 
Slantsix64 said:
welding them how long would a 7 1/4 last ?was thinking of doing that myself would this effect over all mileage? i would think it wouldnt just maybe it would'nt handle corners that well?
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If you live in an area with a lot of curvy roads, you will definitely see a hit in gas mileage.. And you want to go real easy on the rain.
How long will it last? How well can you weld?
 
Welcome to the site and that is a very nice Duster. I have a 7 1/4 Sure-Grip in my 66 Valiant and have no issues with it. Yes the car is slow, but I don't care about how fast it is. I just have fun driving it. I think that you should keep the 7 1/4 and just gear it up to 3.23's or 3.55's. It would wake it up a bit.
 
Welding up the spiders will make the back handle like a spool.With 325s in the back, I hated that thing.
With the tire size your slanty needs, it will be fine. Obviously the inside tire will have to slip on every single turn.So try to make as many lefts as rights, or you will be buying tires one atta time,lol.
But like I said I hated that spool out back. One time I shimmed my cone-type a little too tight, and I hated that too.Then I made a tool, so I could measure the tightness BEFORE I installed it.lol. After that I set all my "posi's" the same.But I suppose that might be a lil too tight for skinnier than 295 tires,lol,again. I would have to learn all over.
Bottom line is this; I hated full lock-up in the back, with fat tires.That doesn't mean you will.

Yes your engine will use a bit more fuel around town, cuz,on every turn,you will have to gas it to maintain cornering speed.
On the hiway, it should make as good as zero difference in fuel useage.
But hey, If you put fat enough tires on the back, that the slanty cannot even spin one of them,problem solved,lol! I did that once; N50-15s. Or maybe it was L60s, not sure. But no matter,with a 2800TC, my slanty had no where near enough oats to do little more than chirp just one of those fat-boys.
I don't recall the size codes for Ls or Ns, but they were huge. Ls mightabin 9.25. And Ns mightabin 10.25. These,back in the day, were actual tread-widths, not section-widths like the metrics we now have.If I had to guesstimate, I'd say the 9.25s were 275s and the 10.25s were 295s. They were pretty tall too, requiring a bit of a lift out back,lol, to keep the body off the tires, cuz they were sticking out pretty far.
That's how we rolled in the 70s; I was 22ish. Sheesh, that's over 40 years ago :(
 
Very nice car!

and OH MY GAWD. Let the kid run whatever rear end he wants to. Will an 8 3/4 take more power to turn? Yeah. Are you runnin for money and points in a drag race? Probably not. That 8 3/4 will last virtually forever behind a slant. Unless you want something to eventually BREAK, I don't recommend welding spider gears. It's a stupid thing to do for everything except going in a straight line, IMO.

As I said.....NICE car. Good luck!
 
I don't reccommend welding spiders on any rear except a demo derby car. It totally sucks on wet or slipery roads. If you really want a limited slip, do it right, and replace the complete rear with a unit that has readily available parts. Several options, from low dollar to big bucks. Chose your poison.

PS: Greenmachine225, Please install a proper battery hold down. That car is too nice, to have a battery short or acid meltdown.
 
For the record Greenmachine225, Mopar recommended a 10"dual-purpose bracket converter w/that cam, I wouldn't use anything less. I picked up a BBP 7.25 and put it in
my '64GT, came from a '76 vali sdn., has open 2.76's in it. I would check the tune on the mill 1st, asWhitepunk stated, then put the correct stall converter 2nd before any
fooling around w/the rear end.
 
A few years back the 7-1/4 in 70 Challenger which has the /6, A904 decided to die due to bad spider gears. Needing a rear end for a d/d up jumped an 8-3/4, 742 one legger w/ 3:23's for an E-body. Paid a kings ransom $50.00 drum to drum (11x2-1/2). Fit up under no probs, shortened, rebalanced drive shaft new u-joints drove away with no apparent problems. Handled as it did before. Nothing like a little over kill, but hey, I won't twist axels and won't blow it up. 10 years down the road still driving it.
 
Nice!,but I wouldn't lay odds on Greenmachine225 scoring an A body 8.75" rear for anything remotely close to that these days, not to mention having to get LBP axles, not
cheap either!
 
Killer6, yeah guess your right on that one. The Mopar gods were really smiling down upon me when in my frantic search for a rear end caused me to trip across the one I found and for the price and I was only out of my d/d Dodge 3 days. I threw it in with no pomp and circumstance and drove off. I hope green machine can line something up without a great lot of expense.
 
rumblefish360 said:
Poor & pathetic notation. This statement is misleading but true. Read more below.
Dude hell yeah im thinking of doing the same thing to my 1965 dodge dart and that helped out alot hahahah and you sugesting cam hmm i want to hit clifford performance eventually i have the smaller slant six and how about tire diamater i know that takes play into driving down the freeway and making sure your rpm is not screeming at like 60 miles per our


(Insignificant, amounts that total squat.)



My favorite words above, "I can not tell you."
An insignificant amount.

You would NEVER EVER know the difference when driving it.
You will NEVER EVER know the difference in your wallet thickness when paying for gas.
The drag strip will show the difference more so in driver error.
The dyno is the only place where you can (sadly and pathetically) point the finger and claim (like a brat teenager) that your right.

GREENMACHINE

The 8-3/4 rear can be swapped in easy.
You will need to find an "A" body 8-3/4. The expense of cutting down another rear is crazy and stupid to do unless your doing a custom or drag racing.

The rear will also need the normal 3 inch U bolts and shock plates. The 7-1/4 uses a odd smaller 2-1/2.

The big expense after the rear end purchase is shortening the driveshaft to fit.
(Or fixing the worn out brakes.)
The 8-3/4's nose, where the driveshaft bolts to is slightly more forward or longer. The driveshaft needs to be cut down to fit.

As mentioned before, a 8-1/4 is MUCH cheaper and still very strong. But not available with the small wheel pattern.

Excellent gas mileage? Look for a 2.76 ratio, about the most common ratio there is. A 3.23 & 3.55 offer somewhat of street performance. But they drive up the RPM's and will consume more fuel.

I did indeed notice your engine. Can you post up some specs on the engine? I would like to specifically know about your cam specs. The duration @ .050 would be a BIG/HUGE help in suggesting a rear gear ratio.

I also get being 16. You have a lack of funds to do things much less do them twice! Frack that!

(Edited, added a ",".
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