Rear End Swap 7-1/4" to 8-1/4"

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I Did the same but I am Having a problem that the brake pads that I ordered are too big. I dont know what is happening. The pads and the Drums are of 2 1/2 in. Does yours take the same or are they 2". This Is driving me crazy. I got a diff that only had the back plates and I guess that is why I am having the problem of finding the right ones.I ordered the same for a 1973 Dodge Dart Sport and Advance says that the 2 1/2 in are the right ones. Help
 
67limecrazy said:
I Did the same but I am Having a problem that the brake pads that I ordered are too big. I dont know what is happening. The pads and the Drums are of 2 1/2 in. Does yours take the same or are they 2". This Is driving me crazy. I got a diff that only had the back plates and I guess that is why I am having the problem of finding the right ones.I ordered the same for a 1973 Dodge Dart Sport and Advance says that the 2 1/2 in are the right ones. Help
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If it's an 8-1/4 it's most likely 10X2-1/2" which would take shoes 2-1/2" wide. Take a measurement to check the shoe width, if it is 2-1/2" wide chances are it's the right one. Also set it inside the drum and see if the arc of the shoe matches your 10" drum. When my duster ran drums on all four corners it was always a hassle to get brakes, the shoes were the wrong width or the wheel cylinders were the wrong size. Are you sure they did not stick you with 7-1/4" back plates, they may bolt up but are only good for the smaller brakes. Check the air gap between the back plate and the drum, if it's a big gap chances are they are the wrong backing plates. Getting mopar parts can be a royal pain...

Never heard of an 8-1/4" with anything smaller than 10X2-1/2" drums. If anyone knows different please chime in.
 
Well, I filled her up with lube this morning and let it run in gear for several minutes and warm up while still on the stands. Everything sounded really good, no weird vibrations or bad noises. The driveshaft guy knew where to put the weights. Shaft looked like it spun pretty true.

I took it off the stands and drove it about 4 miles at speeds between 35 AND 55mph. I have to say I am impressed, the motive gears while a tad touchy to set up are about as quiet as the factory rear end was. I did use a heavy gear lube which was rated for limited slips. Not even a chatter or growl from the new trak-lok carrier.

She is still sitting a bit higher than I want it to. Will drive it around this way for a couple of months. Ride is perfect though, not harsh at all, just no more wallowing. I can take the family for a ride now without riding on the bump stops:)

It was cold down here this morning, was probably 60 degrees for it's maiden voyage, probably perfect for breaking in new gears, they got warm but not hot. I proceeded to take it on one more jaunt before parking it this afternoon. Ran about the same loop. Could not get it to whine during accel or decel.

Here are the before and after shots:

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LeftCoastJeff said:
Keep us posted, as I'm about to do a transplant myself.

Problems, busted hardware or knuckels etc.

I just wish I was making the upgrade, not enough frequent driver miles yet!:toothy10:

Lcjeff
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Well Jeff, the only casualty was a broken ujoint grease fitting, forgot to remove it before pressing out the old joint. Not a tradgedy though, the seals were as hard as ceramic. They had also cracked and allowed most of the grease to escape, left a nice rustproofing on the trans tunnel.

I replaced them with neapco brute force joints. They do not have grease fittings so the center section is not hollowed making them stronger. Spicer makes a similar one but none were to be had at Advance Auto but for $14.00 each I am not complaining. I simply dropped them off with the shaft when it was cut and balanced. They have to take them out anyway so it's best to bring them in loose.

Ps, I love your handle Leftcoastjeff, classic:)

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I used Valvoline 85w140, it gets pretty warm down here and it is a high performance dino based lube. I have used this stuff in my 5.0 stang and the limited slip has never complained.

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The final piece of the puzzle arrived in the mail today:
The red 36 tooth speedometer gear, which with 26" tall tires should yield the correct speedo calibration with my 3:55's. So back under the car again this weekend, at least my back isn't sore anymore.

I bought this part online as used for $23.50 including freight. I have seen this dopey gear priced as high as $77.00. Don't even think of calling the dealer for this one. Part was in 100% useable condition as advertised.

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Got underneath the car this evening and swapped out the speedo gear, while no 36yr old mopar is ever finished at least this rear end swap is completed. Notice how much larger the red 36 tooth gear is compared to the black 29 tooth one for the 2:76 rear. Gives you an idea of the tremendous difference in gear reduction there is compared to the 3:55's it has now.

Note how there are a range of numbers listed on each quadrant of the speedo adapter, just line up the quadrant line on the adapter that matches your gear with the dot on the trans. I believe the worm gear on the tailshaft works with all possible speedo gear combinations. Boy this was easy. On my early GM stuff this would have required pulling the tailshaft housing and swapping out the worm gear on a gear spread this large.

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I pulled the cover and inspected the gears. Everything looked pretty good. The motive gears I used showed quite a bit of tool marks after that black coating(phosphorous?) was worn off of gears during run in. This is probably what separates lower cost aftermarket gears from OEM quality gears. Pattern looked pretty good, kind of hard to tell from pics. The blackish color on the pinion is where some coating is still left, it highlighted the cross hatch pattern from finish lapping at the factory.

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The run in process turns the gear lube pretty dark. I don't think it would have hurt to run it like this for the next 40,000 miles but fluid is cheap insurance.

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I went ahead and pulled the axles so I could use my new tool to check carrier adjuster torque as I had done it the stumblebum way with an elbow screwdriver and a hammer. I started on the driver side first and worked my way over to the other side which did take an 1/8 of a turn. I checked backlash before and after adjustment, kept it at .008", same as when I set them up before run in.

You can make the adjustment with the axle bearings and seals in place but it is tight. I torqued them to 90ft lbs as they had already been run in. I have seen recomendations for this range from 100-150ftlbs. This should generate about 15inch pounds of drag on the carrier bearings.

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Took it for a drive yesterday to see how it behaved with some additional preload on the carrier bearings. Noticeably quieter. Still some slight noise on decel that was probably there from day one but is quieter on float and accel. Loose carrier bearings do make noise. I think this set will last a long time now.
 
thanks for taking the time & posting this, this should be made into a sticky for easy access in the future. Or post it in the tech articles. Lawrence
 
I have a 8 1/4 waiting in my garage to get put it. I still have no back plates at all so that is the only thing I am curious about. I was told I could go to any junkyard and get a set of 10x2.5 drums pretty easy. Did you just use sandpaper to strip down the rear end before painting it becuase I am working on mine now and the paper is wearing me out.
 
doogievlg said:
I have a 8 1/4 waiting in my garage to get put it. I still have no back plates at all so that is the only thing I am curious about. I was told I could go to any junkyard and get a set of 10x2.5 drums pretty easy. Did you just use sandpaper to strip down the rear end before painting it becuase I am working on mine now and the paper is wearing me out.
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Hi Doogievlg, glad you found this old thread. As far as I know, the back plates are the same for all of the 8-1/4 if they are 10X2.5". I am by no means an expert on mopar driveaxles so there may be a 10X2" set up too. If the donor rearend has 2.5" wide drums you should be ok grabbing the backing plates. Wheel cylinders and drums were still pretty reasonable when I assembled mine three years ago, would only go the junkyard route for the back plates and hardware. The brake bars are getting hard to come by new so make sure you get those with the back plates. All the spring hardware and retainers are cheap, make sure you use new stuff there too. If this rear is being run as is, no new guts, I would at the very least remove and inspect axles and replace the axle bearings and seals.

As far as cosmetic prep, I used a sandblaster to clean mine down to bare metal before hitting it with epoxy based primer,then a real nice coat of dupli color flat black for that factory/aged look. My rear axle was really cruddy, sandpaper would not have worked out as easily but it would work.
 
I actually got the rear end from a guy who had just taken it out of his scamp so everything should be good to go. I'll check anyways when I pull the axels to do the breaks. I went out and got a wire wheel and it has done a real good job so far. Ill snap a few pics tonight as soon as it cools off enough for me to get to the garage.
 
doogievlg said:
I actually got the rear end from a guy who had just taken it out of his scamp so everything should be good to go. I'll check anyways when I pull the axels to do the breaks. I went out and got a wire wheel and it has done a real good job so far. Ill snap a few pics tonight as soon as it cools off enough for me to get to the garage.
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FYI:

In case you got the driveshaft from this guy as part of the swap a scamp shaft will be longer than a Duster or standard Valiant shaft. Scamps had a longer wheelbase.
 
Wake this great old thread up :glasses7:
There is some real good info in here I have been looking for.
I am going to say my 8 1/4 will be 10" Drums with 2 1/2" wide brake shoes.

A big thanks go out to goldduster360 for the work he put into this thread :color:
 
Yeah, I also used this thread last month when I did the 7 1/4 to 8 1/4 swap. I chose 75W90 Valvoline oil and even though it claimed to have the limited-slip additive, I had some chatter in my "new" sure-grip differential until I added a bottle of Mopar friction modifier. I should have read post #14 again before putting the car back down on the ground, as one of my rear shackles got flipped upward into the trunk when I set the car down.
 
Hello all. I would like to do a 7 1/4 to 8 1/4 swap as well. Were is a good place to look for an 8 1/4 rear end for my 66' Dart ? I have found none here in Az.
 
66'GTRob said:
Hello all. I would like to do a 7 1/4 to 8 1/4 swap as well. Were is a good place to look for an 8 1/4 rear end for my 66' Dart ? I have found none here in Az.
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Best places to look are craigslist, ebay, contact a local salvage yard that specializes in old mopars. I have used Texas Acres to locate parts in the past if you don't mind paying freight. I have also scored parts through making connections at swap meats, auto auctions, flea markets, where sometimes you get a call weeks or months later from somebody who has located your part.

FYI, if memory serves the only factory correct width 8-1/4 comes from an A-body so it is important to know the origin of the rear axle if not in the donor car and even then you should measure to be sure.

Also, you will have to switch to large bolt pattern wheels on that 66' Dart if you swap in an 8-1/4 with stock axles/drums. Then you will be swapping front drums to disks with the larger pattern up front:)
 
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