7.5 to 8.25 swap findings

[MoparBrit]

As you can see I'm a really new poster, but thought others might be interested in the swap and what I came across.

Car the 7.5, 2.76 rear is coming out of is a '71 Dart Swinger, made and sold in California, slant 6, 904 auto.

I'm putting in an 8.25, 3.21 I found at the local self serve auto wrecker. Rear came out of a '75 Scamp. Has the large bolt pattern lug pattern that I wanted and of course the upgrade in strength for the later planned V8 swap.

Everything I'd read (not just here) said it was a straight bolt in job. I got the rear home, rebuilt the brakes with all new, pulled the cover and inspected the inside, changed the gear lube in it and cleaned it up and painted it.

I took the rear out of the '71 and that is where I noticed the first difference (yes, should have noticed long before, but there you go). The emergency brake cables are different. On the '71 the cable comes down the driver side and goes into a plate with a single bolt adjuster on it. Both of the rear cables hook into this and you adjust the tension with the single bolt. This means you have a short emergency brake cable off the driver side and a REALLY long one off the passenger side. On the 7.5 the passenger side cable was clipped to the rear end axle tube and then goes up and has a bolt clip that bolts to the floor of the car before it turns and connects to the adjuster.

On the Scamp the emergency brake system was different in that it had two shortish cables coming off the rear end one either side. These cables went straight forward on their respective sides and hooked into a C type clip on each side. In other words, the driver side had a C clip hook on that side and the passenger side had a C clip hook on that side. Each side of the car also had a tension adjuster that the other end of the C clip was hooked to by another cable.

So, and here is where I hope I can make this work, I had to remove my just built brakes (oh, 10" drums on the 8.25 by the way) and squeeze the clips in on the emergency brake cable from the inside to release them so that I could pull out the emergency brake cable from the backing plate. I also had to do the same thing on the 7.5 rear so I could get the cables out of that rear. I've now swapped the emergency brake cables over from the old rear to the new 8.25 one and have my fingers crossed that by doing so that I will be able to hook up the emergency brake cable system as it was on the '71 and get it to work.

For those that might be interested I'll post again to let you know how it works.

Also, a note on the rear brake hose or centre hose as it is called in parts books. Looks like the '71 and the '75 list different hoses. Appears the brass block at the end that bolts to the rear is the main difference although there could be a length difference, but I did not note what it was. For the correct hose for the rear it seems as though I remember that the length was somewhere around 14 to 15 inches from info from the parts books. The brass block on the end of the hose that bolts down to the axle tube has the brake lines to each side bolted to it. Looks like the lines come in at different angles between the two hose types. In my rush to pull the 8.25 I just cut the hose thinking I could bolt the other on that works great on the '71. Had been a long day by that time anyway.

So, I'm going to have a look today and see if the existing hose from the '71 can be bolted onto the axle and the brake lines from each side made to bolt in it. If not I'll be getting a hose to match.

On the plus side, I measured the cup area of the yoke from one side to the other of the yoke where the U joint from the drive shaft would bolt in. On both rears the yoke measured the same so I should be able to get the drive shaft shortened by 1.6 inches (thanks again for the answer to my previous post on how much to shorten the driveshaft by) and bolt it right in.

As they say, results may vary, but that is my experiences with a 7.5 to 8.25 swap so far. Hope it is of interest and that others doing the job may get a tip on what to check when sourcing the pieces. If I'd been more observant I'd have noticed from the start, but then when you are walking around the salvage yard and all of a sudden notice a new A body and it turns out it has the 8.25 your have been looking for ages for................. well you get a bit excited to say the least.

Cheers

 

[H22A4]

Great post!!! :thumbup: Good find!

I will be doing the 7.25 to 8.25 swap this Fall. I've already got the 8.25 rear end but first priority will be putting the car back together which should be done by mid summer. Are you putting new leaf springs in as well?

Keep updating us as you install it!

 

[MoparBrit]

Hi, Thanks. Just about to go back out there and get cracking on putting the rear in.

At the moment I'm going to keep the '71 springs as they were pretty new on the car when I got it. I'll probably end up upgrading though when I get into the V8 swap. Maybe some super stocks, but not sure as yet.

On another note, I forgot to mention that I have limited space to do the swap. At the salvage yard I unbolted everything and pulled the rear end out from the side of the car. Plenty of room there.

At home no such luxury. So, what I did after getting the 7.5 unbolted all the way was to take the tension off the springs by jacking the rear up a bit and then take the two bolts out that hold the rear spring perches in place. I'm not talking about the side bolts where the spring slides on, but rather the two bolts that bolt straight back that hold the whole perch on. The whole spring then drops down and out of the way so I could roll the rear end out from under the car. Worked really well for the removal of the old one. Had the car high enough on jack stands placed in front of the axle on the frame of course. That way the old axle could slide right out the back.

I then bolted the old rear wheels back on the old one so I could roll it around and out of the way easily. On the new rear I have the wheels bolted on so I can get it rolled easily in place behind the car. I'll then jack the rear up a bit and take the wheels off as the car is not high enough for me to just roll it all the way in place. Once the wheels are off again I then plan to lower the rear enough to clear, roll it in place, pivot the front up a bit using a block of wood so that the springs can be pivoted up on the front mount and align with the perch holes straight. I'll then bolt the U bolts and shock plates in place on each side to attach to the spring and then jack the rear up so that the whole assembly pivots on the spring front mounts and allows me to align the rear spring mount plates and bolt them in. Hope that makes sense.

From there it is just reattaching the shocks, brake line, emergency brake cables and putting the wheels back on and should be done apart from bleeding the brakes.

I'll post how I get on. Need to get out there and do it!

Cheers

 

[H22A4]

It makes sense. Are you installing new brake fluid lines (metal lines that spans the rear end, goes over the top of the differential and into the backing plates) or using the ones that came on the 8.25?

Did you pick up a new yoke already?

 

[dgc333]

Here are some tips from when I did the 7.25 to the 8.25 swap on my 68 Barracuda;

1. I used the e-brake cables that were on the car. The simplest way to get the cable out of the backing plate is to use a small hose clamp to compress the fingers. Those cables fit the 8.25 rear drums with no issues.

2. The rubber hose from the axle to the body was replaced with a new one. I ordered one for the 68 and the block bolted to the 8.25 with no issues.

3. I got generic u-bolts to clamp the 8.25 to the springs from NAPA. I also just elongated the holes on the shock plates to accept the larger u-bolt (3" inside spacing compared to 2.5" on the 7.25 rear, also went up to the next size on the bolt diameter 7/16"??).

4. I had my driveshaft shortened 1.5" and balnced.

I considered this swap to be a very straight forward and easy swap.

 

[MoparBrit]

Back in for a quick break. Swap is going pretty straight forward. I'm doing it myself so things go a bit slow, but then I'm pretty slow as it is.

Rolled the rear behind the car on the wheels. Lifted each side one at a time and put it on a jack stand. Removed the wheel and then lifted the rear down on the floor. Did that both sides. I then rolled the rear end under the car with the jack. Had to lift it a bit and balance the centre on the jack to stop it falling forward and to miss the spring arch the further it went in. Once jostled around in place I pivoted the front up to match the spring angle (remember that I had the rear spring perches taken off the car with the two bolts so the spring would swing down at the back) and put the U bolts and shock plates on. I reused the shock plates and U bolts that originally were on the Scamp. I got those in the price of the rear end from the salvage yard. Just cleaned them up, painted them and chased the threads. I tightened the U bolts/plates on each side back and forth to make sure all was in straight and all the pins (spring to rear perch and plate to spring bottom pin were aligned and correct.

What worked for me was to get the U bolts started good with the plates under them. I then jacked up the rear end and jiggled the plate etc. around until all the pins were aligned. I then tightened this down a bit and continued to jack the rear up until the rear spring perches aligned with the body/frame holes. I popped the two bolts in either side and tighened them down just as planned.

I then torqued down the spring shock plates/U bolts in place all the way. All is in and very nice.

I've run the emergency brake cables over and hooked them into the factory plate that is on the driver side of the car. I still need to hook the adjuster plate onto them and adjust them down.

On the brake hose, I'll have to get one. The '71 Slant 6 hose might work with some more surgery to the hard lines that run along the rear, but as it is the long line will bolt in as factory, but the shorter (driver side) line wants to bolt in where this '71 line has no hole. The hole is around the other side so no go and I don't want to rebend my nice new line to try and rig it so I'll order a hose. Sounds like most places around here it is going to take 2-3 days to get one in to fit a '75 Scamp.

To answer some of the others who were kind enough to post on this. I went ahead and put new hard lines on the rear while doing the brake rebuild. Was just too cheap not to. I think the short line cost about $1.50 and the other was maybe $2.50. Just got the old tubing bender out and matched the old route of the old lines.

Good tip on the hose clamp for removing the emergency brake cables. I used a pair of needle nose vise grips and a flat blade screw driver. They came out without too much bother. I was more bothered about not noticing that the cable systems were different and I'd just put all the new drum brake shoes, springs and wheel cylinders together on them. To take the old cable off and put the new on I had to dismantle my just completed work.

I also have used a deep socket to get emergency brake cables off. Just slid them over the cable end and had them so that they were just big enough to slide on the retainer at the backplate and push the retainer pins in.

As far as the yoke goes I don't believe I have to get a new yoke???

I measured the yoke from side to side where the u-joint fits in on both rears and the measurement was the same. I'm going to double check it, but I thought there were only two u-joints and one would measure longer than the other? I'll look on the car, but I think the driveshaft u-joint end will bolt right in what I have. I just need to get the shaft shortened. Just called and looks like $85 plus tax to shorten and dynamically balance.

Well, back out to finish off the job apart from the brake hose. I have to agree. Apart from the surprise of the emergency brake cables and the brake hose alignment to the lines being different it has been pretty straight forward and bolt in.

 

[MoparBrit]

Another new day. Finished the job on swapping the rear yesterday. Only things I don't have done are the brake hose swap to one that has a block that aligns with my hard lines on the rear end and I need to take the drive shaft down to get it shortened by the 1.5 inches that was posted on this forum.

It still looks like the u-joint on the driveshaft will bolt onto the rear end yoke. I popped one of the caps off of the u-joint and it clicked right into the yoke cup. Anyone confirm the differences? Would the cap sizes be different between the two joints or is it just a length issue?

On another note, looked at my '73 Dart parts car. It came with a 318 and a large bolt pattern 7.5 2.76 rear in the back of it. The emergency brake cable routing is the same as what was on the '75 Scamp I got the rear end out of. One short cable off the rear end each side, into a C clip and then on to an adjuster on each side. Would have been a true bolt on with this car if doing the swap as I had it. Anyway, just found it interesting.

 

[MoparBrit]

Been very busy, but wanted to finish up on this post so that perhaps it would help someone else doing the same swap.

I ordered a brake hose for the '75 Scamp the rear end came out of. Installed it today. Got all the fittings hand started with the bolt that holds the hose block to the rear just a few threads in. This gave me enough room to get everything to align and start without cross threading. I then tightened everything down.

For a brief moment I thought there was something wrong with the brake hose clip where it clips the hose and metal line through the body bracket. The clip just did not want to seem to align and start. I then realized that the bracket on the '71 where the line goes through has a very specific hole in it. The hole is designed to allow the hose to go in and if you lightly twist it a bit the hose will align with the hole and seat all the way. The clip slid in fine then.

Don't know if I mentioned, but the emergency brake cables hooked in on the driver side no problem. Well, I did have to pull the long passenger cable back out from the adjuster as I'd run it the wrong side of the exhaust pipe for it to be able to bolt back to the body as it did before. The long cable has a bolt that goes through a clip that bolts it to the body above the rear end.

I then realized that I was having such a hard time getting the cables to go in the adjuster because the cables have different size balls on the end of them. The adjuster has a large and a small hole to fit them. Just a matter of getting them the right way around in they went.

Got the driveshaft back today. I'd been looking at the MP rear end guide and saw that they listed the difference in length for a 7.5 rear and an 8.25 as 1.6 inches. The length I'm talking about is the yoke will stick out further towards the front of the car 1.6 inches. I took out the digital caliper and ran it to 1.6 and then held the caliper part over a tape measure. I came out really close to 1 5/8 inches. Looks like to me that for my car the 1 1/2 inch or 1 5/8 inch driveshaft sorten would work fine. Decided to go with the 1 5/8 inches derrived from the MP books. Bolts in no problem and the shaft on the trans end is sitting right where it did with the old rear end in it.

All that is left now is to bleed the brakes, but I'm holding off on that until I get the front end discs swapped for the larger bolt pattern ones. Then I'll do the lot at once.

So, swap was pretty easy. Few curves that I didn't realize with the cable differences etc., but nothing that could not be overcome.

Hope the post helps someone doing theirs.

Cheers