With most peoples' opinion on this forum about the 7 1/4" rear end, if they have an opinion, as it being something to change out to a heftier unit if possible, I have to put forth the following thoughts: One of the main shortcomings of the Hotchkiss drive rear end is the sheer weight of the unit. More precisely, the ratio of sprung to unsprung weight is not conducive to the best handling, especially when cornering on washboard roads and similar situations. This is why Chrysler made it as light as possible, and only upgraded it if really necessary over the years, if the upgrade added weight, to save every pound possible. So wouldn't the 7 1/4" unit be the most desirable one if it did the job without breaking? The point I am getting at here concerns the optional (early) sure-grip unit. The early sure-grip had four differential side gears instead of the standard two, didn't it? I'm almost certain the one I saw apart had four side gears. And this is the part that usually breaks with hard usage. The rest of the rear end, the ring & pinion, the bearings, the axles etc. seems up to the job. And if the sure-grip clutch plates wear out, which they do as often as every 20,000 miles I am told, it reverts to a standard differential anyway. So wouldn't it make sense to build a 7 1/4" rear end using an early sure-grip unit if you can find one and just delete the clutch plates, and in so doing have the advantage of the lightest weight rear end with extra strength in the area where it needs it? If so, why didn't Chrysler do something like this at the factory, just use four side gears instead of two, instead of going to the all around heavier 8 1/4 or 8 3/4 units?

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1964 Dart 225 1966 Valiant 225
1966 Dart 273 1966 Barracuda 273
1969 Dart 225
'64-170 engine '66-170 engine
(two) 198 crank/rod sets in custom-fitted wooden boxes

wooden motor scooter with hybrid-electric drive

..........mebbe they did.....

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Yeah....Im the one who destroyed this rare, vintage automobile.....

First, 7 1/4 sure grip units, don't grow on trees. If you happen to have one, it doesn't make any sense to make it an unsure grip. Also, they don't wear out that quickly. I have been running the same 7 1/4 SG rear since 1974. It has been in 5 different cars. It is now in my 66 Valiant (13.64 @ 92 mph.).

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Are you, uh, sure?


(...how 'bout a Reasonably-Certain-But-Don't-Quote-Me-On-It-Grip?)

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Well, maybe I'm swimming counter to the popular current but I intend to use an early suregrip carrier, with the clutches intact, in a late ( '74 ) 7.25 rear axle. To me it just seems like the reasonable way to go. since I already have everything for it except the the later style R&P in the desired 3.23 ratio.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

You are referring to the spider gears as side gears. Side gears are the ones that slip onto the axle splines.
The early Sure Grip has 4 spider gears and 2 side (axle) gears, open style 'peg leggers' and cone type Sure Grips have 2 spider and 2 side gears.

If there was a source for the early SG, I'd run the '73-'76 LBP 7.25 A body rear. I want weight off the car and would sacrafice a bit of durability for it. I think Lou reported the 7.25 is 115-120lbs lighter than the 8.75.

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Slant Cecil

Yep, a 7¼" weighs a lot less than an 8¾". When I replaced the 7¼" with an 8¾" in my '65, weight distribution improved noticeably and the back of the car wasn't as prone to breaking loose (more weight over the drive wheels). But, I wasn't racing that car, I was driving it on public roads, so weight distribution and handling were more important than weight reduction.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I have no problem running a 7 1/4 SG rear on a 14.00 or slower automatic car. Runnig 13's is a little risky. Once into the 12's would definatly go for something stronger.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Good discussion and observations on the 7 1/4 rear.
As noted, the weakest part of the assembly are the spider gears.

I had the "honor" of working with a bunch of 7 1/4 rears when I was first starting in the Mopar hobby and learning about automotive mechanics... said another way, I spent way to much time trying to get a 7 1/4 to last, because I did not know any better.
(I honestly did not even know what a 8 3/4 was. )

I had a 63 Dart station wagon at the time, I swapped out the 170 SL6, 3 on the tree for a 340 six-pack, 4-speed setup out of a crashed AAR Cuda. (Man.. I should have bought the whole car but what did I know back in 1976)

Anyway, I found out quick that a hard shift or a clutch "dump" would break the 7 1/4 rear end, usually the spider gears would have teeth knocked off or they would be split in half.

The good news, these rear ends were easy to find, lots of them in the JY's and a 'want ad" in the local paper would make my phone ring.

After blowing up a few, I started patching units back together. I found out that shimming the spider gears as tight a possible make them last longer... and then you could get some straight line posi action out of the unit.
Again, a hard shock to the unit... even bad wheel hop, would blow it up.

More used rear ends, more wrenching showed me that there were some differences in the later 7 1/4s that made them stronger. I put one unit together that actually lasted a few months... it broke on a 1st to 2nd gear speed shift and split the gear carrier in half, right where the spider gear cross shaft went through the casting.

More used units... and BINGO... I got one with a clutch type posi in it.
It worked great and did not blow up when speed shifting. One night I did one of those roll backwards, stick it in first and dump the clutch starts and BAM... Whop, Whopp Whoppp... broke the yoke right off the pinion shaft.

Stupid high school kid hot rodder... (me) I swapped the posi unit into one of the other blown spider gear rears, (a 3.23) and get back on the road.
For my next "trick"... snap goes an axle shaft while doing doughnuts, I fixed that but getting the splined axle "stub" out of the posi's smired-up side gear spline was a real pain.

The posi unit goes into yet another 7 1/4 assembly and then it happened... Crunch,...crunch... knocked teeth off the 4 spiders in the posi.

OK, now I am a self appointed 7 1/4 "expert" and I start calling around looking for another posi unit. I talk to a Mopar mechanic who basically says: "Why are you screwing around with those 7 1/4's ?? Use this rear-end and you won't have any more problems". He sells me my first A-Body 8 3/4, a 3.23 "cone" posi. setup. I blew the posi out of that unit after a month and go on to learned about the differences between the clutch and the cone style posi units.

So the short version, if you fix one weak point in a 7 1/4, it will just lead you to the next weak point.
As Charlie said, a good working 7 1/4 sure grip in a 14 second or slower
automatic trans car works well.
When built "right", the thing I hate the most about a 7 1/4 are the cheap ball bearing axle shaft bearings. The 73 - 76 LBP assemblies have the biggest axle bearings but they still suck because they are ball bearings with no ability to adjust the end play.
DD

And there are people who go out of their way and spend a fair amount of cash to "upgrade" (...?) to nonadjustable ball bearings in their 8 3/4" rear axles — the so-called "Green bearings" (Green is/was a bearing manufacturer; "Green bearings" are a brand, not a type).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I like the observation of unsprung weight and multiclutch packs. The only real problem is that such observations are made in what I call "theory" some people call it bench racing. Something we say as engineers is "Do you know the difference between practice and theory?" I call it our Semper Fi. It means that everything seems to work in theory.
All I know is the 7 1/4 is the only rear end I've managed to go through two sets of bearings, enough metal shavings to rebuild the effiel tower, and blow out seals. The 7 1/4 is just simply a set of weak link chains and will not handle anything above stock. Not to say give up on it right off the bat, but especially for the slant six any easy way to make it faster is to swap out for a stronger better geared rear.

One thing I've not seen mentioned: fluid capacity. One of my beefs with the 7.25, other than strength in the non-SG version, is that it holds less than half the fluid of the other rears. Less fluid means less cooling capacity. Probably not that big a deal, but something to consider.

Truth be told, all of the rear ends Chrysler used are pretty decent. I've got an 8.25 with nearly 450,000 miles on it under my '73 Satellite. Its one of the few parts of the car that has literally never been opened. I've sucked the fluid out and replaced it maybe twice. NOTHING else, not even a seal.

The 8.75 in my Polara is the same story, only it only had about 270,000 trouble-free miles when I changed pigs from a 2.76 to a 2.93 just for grins. And I re-packed the wheel bearings while I had the axles hangin' out. I did have a *really* noisy 8.75 pig with 3.23 gears in my R/T when I got it, but that whole thing had been royally screwed up by some previous owner. The axle end play was way off and lots of other things were set squirelly, so I can't blame the pig itself. The 8.75 holds up well behind big-blocks with automatics. 4-speeds and a twitchy clutch leg can shock-load it enough that the pinion shaft flexes and the ring gear carrier flexes, which together let the pinion partially disengage, which can kill it instantly. That's the one strength that the Ford 9" has over it- the pinion is supported by bearings on both sides. Chrysler just threw mass at the problem by putting the Dana 60 in big-block 4-speed B-bodies

I hear stories about the 9.25 liking to eat bearings more than some of the others, but I've never actually owned one so I can't testify one way or the other.

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how much HP would you say a SG and non-SG would be able to take?

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1976 Plymouth Feather Duster
2002 Dodge Dakota 4.7l v8

hi sages- read the thread on this. back in 65 i think dumping the clutchwas called popping the clutch which meant letting the pedal up fast in one stroke with the rpm bumped up instead of letting it up in two stages, first to the friction point then after a split second pause , all the way. am i right? clearly popping/dumping puts heavy stress on the cushion springs in the disk, 1st gear and the differential parts.can only justify that if track racing or outrunning bad guys. never had a problem with the 71/4 2.93 with od in the feather, but then again never raced it. have had to pop the clutch occassionally on a downshift to quickly get out of the way of a road hazard and have cruised it at 80 on the interstate. it has 260k. the 81/4 3.23 in my two f bodies seems a lot tougher and heavier. in an old ssn issue i think the doctor said the 81/4 was not much better than the 71/4. sure looks bigger and heavier. only had to put end axle shaft wheel bearings in one 81/4 after 360k. had to use a puller and crow bar to get them out and a pipe nipple and mallet to get new ones in. that must make one hell of a noise when the rear blows up under load. regards bf

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