1951 Plymouth Cranbrook motor swap...

Hey Gang - This is very premature - but just hoping to get some initial info and insight from the vast knowledge on this board.

I bought a 51 plymouth cranbrook about a year ago. It has the original flathead 6 in it. I actually really like having the original motor – I love driving the car - she’s clean and runs like a clock and I LOVE the ‘three on the tree’…. But I just got back from the Syracuse Nationals and I’m starting to give thought to swapping it out for something with a little more kick and dependability on long trips.

So that being said – I’m completely a newbie! So please bear with me. I don’t plan to undertake this project alone and have some family that could help me out. But I’m hoping to get a better understanding of what goes into swapping out the motor and what else needs to be replaced. I’m pretty sure I’m looking at motor, transmission, drive shaft, brakes and suspension, covert to 12 volt. So that being said – am I missing anything else and does anyone have any suggestions on what direction on should go here as far as a motor and everything else on the list that would need to be changed?
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Thanks in advance everyone – this forum is a lifesaver! <O></O>

 

I would consider rebuilding the stock front suspension and adding disc brakes to it.

As for motorvation, I would find a Dodge pickup or van with a 360 and A-518 automatic overdrive to drop in your Plymouth, and find an 8 3/4" rear out of a 66-71 b-body, 10" or 11" drum brakes included.

You can build a nice torquey street motor out of a 360, pretty damn good in stock form as well.

My $0.02

 

Dependable? What could be MORE dependable than a Chrysler/DeSoto or Plymouth/Dodge flathead inline six cylinder engine?
They were used from the 30s-late 50s in cars and pickups, and by industry in various machinery as forklifts, welders, generators, airport tugs, and on and on for many more years after being discontinued in cars and pickups.

 

There's a number of threads on putting a 318/904 in 46-50s Mopars.

 

I agree with both replies above. You can do the late V8 with all the nice stuff (that's what I'm doing with my '40), or you can build up another flatty with better breathing and compression, add a 5 speed and modern rear, upgrade the brakes and have a great driver. My '47 is staying flatty. Do the research, save up the bills, and either way you can't lose!

 

Like George says, lots-o-threads on the subject. Keep in mind that for alot of folks, the trans is the central issue and overdrive is a must if you want to keep the 218 and drive the freeways or drive long haul. You can change to a late trans but that also requires a rear axle swap. Now you are at a point where including a 318-360 or even a B series makes some sense. Steering column clearance is a common problem.
The front suspension is good, just PM Olddaddy for a disc brake kit.
Highly recommend a wire kit and change to 12 volt. Hard to trust wire that has been in the car for the last 58 years. This is a must if you change to a late v-8.

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Great stuff so far! Thanks so much!

That's a good point - The reality is that it's not the motor so much I have a problem with... the transmission just won't allow for anything over 55-60 miles and hour and I'm not sure how safe the current brakes and suspension would be at anything over that anyway.

AJ Mopar - suggested the A-518 transmission... would that be a major deal to fit into the body? Just curious how much modifications are required with various transmission selections.... Also, would I need something that beefy with a 318 or was that a specific recco if I'm going with the 360?

As far as putting in a 5 speed with either a 318 or a 360 - what would that entail and what would be some options? I'd love to keep it standard if possible...

Sorry again guys if these are basic questions - new to the game but I'm thrilled to be learning as much as I can!

 

Try this site the best for this kinda info.

http://www430.pair.com/p15d24/mopar_forum/

 

not sure what the room is like in the trans tunnel on those - might need some floor surgery to fit the 518, but it would be worth it.

Keisler makes a nice 5 speed conversion for mopars, how much money do you want to spend?

http://www.keislerauto.com/index.php?initState=mopar

 

I put a nova subframe with 307 chevy in my 50 ply. If I had to do it again, I would go with S10 subframe.

 

why sub it at all, the stock with disc and relocated shocks works fine.

 

There are numerous disc brake kits available as well as rack and pinion kits. As stated above OldDaddy can hook you up with both. You should also consider a shock relocation for the front end. Other than that just a stock rebuild and your front suspension is set and adequate for either the flatty or a small block Mopar.

As for transmissions if you go with a small block Mopar the suggested A-518 would be a great way to go. If you keep the flatty, look for a Borg Warner R10 Overdrive. It is a direct bolt in swap and requires no driveshaft modification. I put one from a 53 Plymouth behind the 218 in my 48 Coupe and it made it a totally different car. Can cruise at 70 mph with no problem at all. Another option with the flatty is a T5 from a Chevy S-10. There are kits available for this install. It moves the shift to the floor but is a fairly straight forward swap.

If you can't find an R10 or don't want to go through the T5 swap look for the previously mentioned 8 3/4 from the B-Body or the rear from an 89-90 Dakota. The available higher numeric gear ratios will get your cruising speed up as well. Both of these are fairly easy swaps and would require you to basically move the spring perches and then address the rear U-Joint connection to be back on the road.

As mentioned earlier the Mopar flatty is a very reliable power plant. Not going to win many (any) drag races but will get you where you want to go and is something different in the sea of V8's. There is also performance parts available for the flatty (see pictures of mine below) that will kick up the HP some mainly by opening up the breathing. You can also get a cheap boost in power by simply having the head milled about 0.50 to bump compression.

Again check out the P15-D24 site http://www430.pair.com/p15d24/mopar_forum/index.php?referrerid=1152 there is a wealth of knowledge there on the 40's-50's Mopars, including all the modificaitons I mentioned above.

 

Sounds like you just need more highway friendly gears to me. Either with an OD trans or a rearend swap, or both. Which the latter is a good idea anyways just to get away from that Mopar tapered axle deal.

 

I run my 46 with it's 4.11 rear end on long distance runs quite a bit. Did add some 225 75 15 tires which relaxed it quite a bit. The engines sound busy compared to what we have become used to but with most set ups 60 is about 3K rpms. Alot of the noise it the fan. I run indicated 65, which is 63 on my gps. Easies way to deal with it is throw in a mopar rear from a B body or get a uit out of a 2wd Jeep cherokee. (usually 3.55 with limited slip in a lot of cases) Yes you will need to modify the driveshaft but the rest is nearly bolt in. You can even do that if you still intend to put in a v8 down the road. But if all you are looking for is more relaxed cruising, that is the easiest way to deal with it. You can also look into putting in a A 833 chrylser OD trans. Came in Volare Aspen in the early 80 and in /6 powered vans an pickups, Chevy and GMC also used them in light vans and pu's. They aare a 4 speed with an .70 OD gear.

 

keep the flathead and update it with hei and newer carb. i drove a 51' and a 54' plym. and the 54' had a rod knocking and the new owner dropped the pan slid in new bearing and away he went. i would opt for overdrive and disc brakes. post some pic's of your car.

 

Ihave the flat 6 in my 50 plymouth, All stock, Taller rear tires, i keep up with interstate traffic just fine. I drive it 4 hours to indy, no problems. Purrs right along. Planning on upgrading to front disc, and maybe a rear swap. Keeping it simple.

 

If you decide to keep the original motor, you definitely need an OD tranny.

A not-so-currently-politically-correct-to-many-on-the-HAMB-these-days solution is (gasp) a SBC. Slips right in; I installed one in my 1950 Plymouth when I was 16.

Regardless of the motor you select, you will be facing a rear end swap for two reasons: (1) the Plymouth has the e-brake on the tranny, and you shoiuld have an e-brake and (2) the goofball u-joints these cars use. Many rears bolt right in; the one I have experience with is a first-generation ('67-ish) Camaro rear - either ten or twelve bolt - these bolt right up to youe stock rear springs and all you will need is custom u-bolts and shock mounts.

Regardless of what you decide motor-wise, I would suggest relocating the upper end of the front shocks from the upper a-arm to the frame. There are kits for this. This one change makes the most profound change in the cars handling. Do this forst, and again regardless of what motor you decide to use, and from there you can consider front disks, etc. depending on how you drive and what you want out of the car.

 

ok - you know that whole 'there's no such thing as dumb question' saying - well that's a load of shit but I'm going to go ahead and ask anyway ;o) what's an SBC?

 

Ok, you let the cat outa the sack, so I'll say what Ive seen done that will work better than a sbc. SBF works better because it is narrower across the exhaust manifolds and an early ('62-'67) left exhaust manifold curves inward and around the steering box. There are also no fuel pump or oil pan issues. A '60-'64 Ford rear is a bolt in with pickup truck or other longer u-bolts. Just another option from another camp, if you're going to build a bastard child.

 

Small Block Chev

 

If you stay with the flat 6 you do not want the A-518, it absorbs way too much power. The A-500 is a better choice and it is a wee bit smaller. Floor surgery will still be required.
There are a couple of options for a manual OD, (in addition to the ubiquitous t-5) including the Mopar A-833, and one of the Dakota 5-spd.
Seems that most OD units run a reduction around 0.7 so you can run a fairly deep rear gear and have spirited around town driving as well as be comfy on the freeway. I am not sure that I would keep a flat 6 at 3000rpm for any extended period of time as that is well above the peak torque. Use this calculator to play with the numbers: http://ctny.audiworld.com/mark/s4/gears/gear_calc.html

In terms of dollars, it will be alot cheaper to put a manual trans behind a 360 than putting a manual OD behind a flat 6. The 360 is a great torquer, fits without major issues and a 66-67 Dart (?) driver side exhaust manifold clears the steering column. A 360 makes enough torque that it will happily live with any final gear between 2.76 and 3.9 without OD and up to 4.88 with an OD.
If you make any changes that include a 12 volt starter then you need to make appropriate changes in that area which could be as simple as 2-6v batts in series or a complete re-wire (check with rebelwire on that) depending on what direction you go.


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you say you love driving it and it runs fine, you really enjoy the car. the thing is you are lucky to have a old car that is still usable and drives well. Thats unusual nowadays, but its a good thing, and there are things that you can do to it to make it more drivable. Seems basically you could use a taller rear gear, or some kind of overdrive. Mopars of that era had OD,s and would probably bolt in. You could adapt a T5 tranny and it would work good with your rear gear ratio, plus you have an open driveline. one of the neatest mopar a friend had was a 39 plymouth with a 38 chrysler
OD and a 50,s chrysler flathead 6. Also I believe the old Dodge, Desoto, and Chryslers flathead 6,s would bolt in pretty easy, and have more cu inches. I know its not fun when ya can,t keep up with them V8,s an such but just driving an old car is a ball. When you start building it up with big V8, automatic, etc etc. its a whole different ball game. Just playing around with a stocker is fun, however the one thing that I do recommend on any oldie is disc brakes. just my cents worth, ask around to the mopar guys you can get specifics on fixin her up.

 

If this has not been answered already: SBC = small block chevy. 265, 283, 302, 327, 350, 383.

BBC = big block chevy. 396, 427, 454

SBF = small block ford. 289, 302, 351, whatever (not much of a Ford guy) :0

 

The Ford motor might indeed fit well as you have stated. I did not have any distributor or oil pan issues with the 283 I put in. I used a 55 Chevy left exhaust manifold and that cleared the steering box just fine.

 

The advice from the other folks on using MoPar or Ford engines is all fine, as are their observations about the different trannys you can use.

However let me again emphasize something very important: ONLY with a stock manual transmission (regular or overdrive) can you keep the stock rear end.

Reason #1: Old MoPars had the emergency brakes on the tailshaft of the transmission. Very few if any modern trannys - certainly anything you would normally find behind a later model V8 - has this. The e-brakes are on the rear end.

Reason #2: Old MoPars used slim shady u-joints and it will be somewhat of a cobble to use a conventional open u-joint on one end and the MoPar unit on the other. I did it initially when I dropped in my 283 and Super T-10, but I quickly realized the error of my ways and I replaced the rear (and got me some e-brakes) by swapping in a 67 Camaro rear.

Low-cost approach for your rod: Keep the original 6, get a 52 Plymouth OD tranny, add a PCV system and paper air filter element to the 6, relocate the upper shock mounts to the frame (there are kits), and if you really want to get crazy, front disc brakes. The result is a car you can drive anywhere. Note I did not add dual carbs or split exhausts to the list - these are mostly eye-candy and not required to have a car you can enjoy.

If you need to be able to accelerate more quickly, corner better and stop in a shorter distance, get a Harley (in addition to your Meadowbrook).

 

You'd have to hunt for a rear sump pan for the Ford.

 

Why? Almost every 302 built since 1980 comes with one attached. Actually, the first ones were used in the V-8 Fairmonts and Zephyr in '78. I just posted what I had seen done to an early '50's Plymouth because the Chevy guys stuck their 2c in. If the car was mine, I would keep it all Mopar except for the 9 inch Ford rear, and if there is a later Mopar rear that would bolt up like the Ford does, I would use that too.

 

The newer 302/5.0s are double sump, not sure what clearance might be on the front hump. 71-3 Mustang/Cougar fit with relocated spring perches.

 

Just how much power do you think a flat-6 makes ?


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I forgot to mention that, you are right. A front sump motor will interfere with the tie rods in an old MoPar.

But I also just learned something, that late model Fords have rear sumps. Didn't know that.