Best gears for a /6 ??

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Princess Valiant

Princess Valiant

A.K.A. Rainy Day Auto
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just looking for some input based on experience.

I am on the bubble between 3.55 and 3.91

The car: 1963 Plymouth valiant wagon

The engine: 1970 225 slant six with a shaved head (.080) Clifford header and aluminum 4 bbl. intake. 4bbl. 390 cfm Holley. (unknown cam)

Trans: 1964 4 speed with 3.09 low gear (it's a ball and trunion)

rear end: 7.25 with undetermined gears ( the point of this discussion)

The application: fishing wagon, cruiser, for sure not a race car. A car with some very good "pickup" on the highway and feels like a very "torquey" tire fryer

Other factor: I DO NOT care about gas mileage. I believe gas is very cheap in America and I will pay to have fun, so gas mileage is not a concern. However I don't really want to be blasting 6k on the highway at 65 MPH either

what are some ideas?
 
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With that engine and that list of wants, you ought to be choosing between 3.23 and 3.55, depending on tire size.

In something other than a 7-1/4" rear axle, which you're fixin' to spit out in pieces all over the road.
 
slantsixdan said:
With that engine and that list of wants, you ought to be choosing between 3.23 and 3.55, depending on tire size.

In something other than a 7-1/4" rear axle, which you're fixin' to spit out in pieces all over the road.
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hi ya Dan - I have tech-mik-eel question about /6 stuff and have been told you may be the man with an answer - can you PM me?
 
someone has already put an 8 1/4 in the car but I had in mind to go back to a 7.25 because I wanted to stay SBP.

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is a 7.25 really that bad....they were put in millions of vehicles and seemed ok
 
Rainy Day Auto said:
is a 7.25 really that bad....they were put in millions of vehicles and seemed ok
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No, it isn't bad, but it's not the greatest if it's an open diff. & You're beatin' on it w/a stick & bootleg burnouts! My personal experience with an open 7.25 failure
was behind a cammed 318 in My '69 Dart, and I can tell You I left many huge clouds of tire smoke w/it before the diff spit the spiders out & left 'em in the
bottom of the housing. It was an auto at that time, but upon inspection it also wasn't exactly full of lube, thus encouraging the galling & heating that leads
to spider gear oblivion :rolleyes:, that part was on Me. That engine ran well enough to get My Dart just over 94MPH thru the traps when I ran it, and I can honestly
say I couldn't remember how many burnouts before it let go, but it was in the dozens..............probably over 40.
That said, since You're already converted, there are those who have switched their 8.25 to small pattern, the drums & axles need drilled, and the drum
meter/register/hub section needs turned down. Not that difficult to do for any competent machine shop.
Ratio? The 3.55's.............................
 
Rainy Day Auto said:
is a 7.25 really that bad....they were put in millions of vehicles and seemed ok
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If you plan on doing hi power clutch dumps, then yes your 7.25 will eventually grenade.
But if you drive it respecfully, you can make it last. But in reality, you will be taking 2 steps back, with the 7.25. Plus you more than likely will need a new driveshaft, u joints, ect. You might also be messing with a ball an trunion u joint.Just some things to take into consideration.

You might be better off with a big bolt disc upgrade on the front.
 
Rainy Day Auto said:
someone has already put an 8 1/4 in the car but I had in mind to go back to a 7.25 because I wanted to stay SBP.

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If you HAVE to stay SBP it might be much cheaper (and better in the long run) to just get new axles in SBP for the 8 1/4. They must exist. The upgrade to the 8 1/4 is definitely worth it.

For city/highway gears. 3.23 or 3.55. In my mind 3.55 has always kind of been the ultimate "compromise" gears. It works good on the street and highway.
 
You all are really helping me push away from the 7.25 ....(Shame too because i have a pile of like 7 of them and one with Bbp)

I am actually thinking ford 8.8 or maybe an 8.25 from a Dakota??? I am not sure of the width of a dakota it Durango rear end.

There are some ford options that are almost dead on A body width with very good parts and "posi" unit availability.

I am already into a custom made driveshaft because of the ball and trunion, so the other end can be made to turn just about anything.

As far as the sbp vs. Bbp thing......i was being lazy and keeping my drums all around. But with BBP i might as well upgrade to disk fronts. To my surprise, there are a ton of disk upgrade kits on the market now a days....way more than last time i looked into it, several years ago.
 
Rainy Day Auto said:
someone has already put an 8 1/4 in the car but I had in mind to go back to a 7.25 because I wanted to stay SBP.
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I'm sorry, but now I'm confused Rainy...............
1) If it is already an 8.25, why would You consider changing anything except the gears?
2) No, Dakota rears are way too wide & the spring seats would need cut & moved.
3) Are any of Your 7.25 rears Sure Grip? If so, they can handle what You're planning on.
4) If You have a SG 7.25 I'd purchase it & You can fund your gears, :thumbsup: ! My '64 GT's an auto, so I'm staying 7.25 SG.
5) There's really no shortage of affordable 8.25's from A-bodies out there if Yours is missing???
6) The cost to switch to front discs will be worth it if You would consider the savings not paying to convert the 8.25 to SBP.
 
I would just convert the front to BBP front discs and keep the 8 1/4 in it now with some 3:55s.
To me, this is the easiest way with the bonus of the better brakes and BBP all around instead of the crappy SBP set up.
Easier, better, and cheaper in the long run.
Just my 2 cents..............
Tom.
 
Rainy Day Auto said:
You all are really helping me push away from the 7.25 ....(Shame too because i have a pile of like 7 of them and one with Bbp)

I am actually thinking ford 8.8 or maybe an 8.25 from a Dakota??? I am not sure of the width of a dakota it Durango rear end.

There are some ford options that are almost dead on A body width with very good parts and "posi" unit availability.

I am already into a custom made driveshaft because of the ball and trunion, so the other end can be made to turn just about anything.

As far as the sbp vs. Bbp thing......i was being lazy and keeping my drums all around. But with BBP i might as well upgrade to disk fronts. To my surprise, there are a ton of disk upgrade kits on the market now a days....way more than last time i looked into it, several years ago.
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If you're thinking of going BBP. Just pull a 73+ k member out of a car. They are all BBP with disc brakes (at least to my knowledge). If you find a donor car with it all. It's a super easy swap. In goes the K member, the master cylinder and brake lines. Get new rear axles in BBP. Done. Can probably find a donor car for cheap. Lots of guys getting rid of 76 a bodies for more "desirable" 72 and lower.
 
In the baby 7.25's defense, I would hardly call that looking at it. Lol
 
Johnny Dart said:
In the baby 7.25's defense, I would hardly call that looking at it. Lol
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I was being sarcastic. If you build one right, they will take a lot.
Mine has 4:10 gears, welded spiders, crush collar eliminated and larger cap bolts.
I LOVE the 7.25. Lightest, least power robbing rear in the Mopar universe.
 
whitepunkonnitro said:
I was being sarcastic. If you build one right, they will take a lot.
Mine has 4:10 gears, welded spiders, crush collar eliminated and larger cap bolts.
I LOVE the 7.25. Lightest, least power robbing rear in the Mopar universe.
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to the original poster(Rani), just get it running and sell it to me , I`LL finish it !
 
What size tires?Are you still running 13s?Or short 14s like 25.5 tall?
Then 3.23s and that 3.09 make a nice 9.98 starter gear, that cruises at 65=2768; Not so bad for the straight six.

FWIW
I peglegged a 7.25 behind a 340 and 904 for about 2 years. The tranny gave up first.
But not just any 340. This hi-compression one had all the 2bbl teener top end, and cam, and with fenderwell headers. So basically it was big-bore teener. Torque? You better believe it.
 
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Lustle said:
If you're thinking of going BBP. Just pull a 73+ k member out of a car. They are all BBP with disc brakes (at least to my knowledge). If you find a donor car with it all. It's a super easy swap. In goes the K member, the master cylinder and brake lines. Get new rear axles in BBP. Done. Can probably find a donor car for cheap. Lots of guys getting rid of 76 a bodies for more "desirable" 72 and lower.
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The k-member won't fit in her car from a newer one, and not all '73 and up a-bodies were bbp disc brakes.
 
I was forced into rebuilding the 225 in my 64 because it was locked up and needed it. .04 overbore, head cut .08, pocket ported and gasket matched, Oregon regrind around .440 lift. Still has the BBS and stock exhaust manifold. 3 speed stick with 3.23 7-1/4 rear, 10" clutch, 185x13 tires around 24.5 diameter. GPS tells me my speedo is dead accurate so the radials are pretty well matched to the original tire size.

Sometimes I accidentally "peel out" from stops so it has plenty of power down low. Not intentionally, it just happens sometimes. Burnouts, like a certain brand of cereal are for kids.

I have almost 500 miles on it. I have a mini tach around here somewhere but haven't installed it yet so I don't know what the cruising rpm is. I've probably only had it up to 55 but I wish it had a taller gear. I don't think I'd like a 3.91 but this is a driver and it's going to Carlisle this summer.

Not sure what a fishing wagon entails (around here every old wagon seems to have surfboards strapped to the roof with Ron-Jon stickers in the windows) but my advice to you is just drive it around for awhile and make your determination after that. The car will tell you the answer.
 
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