Which K frame would you use, given the choice?

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Dohc Rocks

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I'm in the process of building a Duster 340 from a complete, numbers matching car that's rotten out and two rolling chassis. I have both the 70-72 and 73+ K frames to use.

All things being equal (I'm using BBP spindles, upper arms and lower BJs either way), would you run the older biscuit style K frame of the later spool type?
 
I have only ever worked with the earlier style biscuit mounts and I'm not going to say they were "difficult" to work with but just by the LOOKS of the spool type, I would figure that the spool type would be easier to get the motor in and out. That being said, how often do you really plan on pulling the engine? As far as numbers matching goes, if everything else is going to be original or original looking then pick the K-member that matches your year for the picky onlookers at shows since that will still be visible under the hood.
 
Biscuit mounts are easier to install. But the later k Frame has the pass through sway bar. So a tighter package....
 
Biscuit mounts are easier to install. But the later k Frame has the pass through sway bar. So a tighter package....

70-72 K frames were made better and the biscuit mounts take less room. But, I do like the pass through sway bar. What lower control arms and front sway bars do you have? But since you are using BBP spindles, upper arms and lower BJs either way, That would change my mind to the 73+ style. Just have it welded and strengthened up while it is out.
 
What year is the car ? I would use that year K-Member.
 
To answer all the questions.... I have 3 cars:

1) 1971 340 4 speed. Complete numbers matching Hammtrack-built car but quite rotted;

2) 1970 340 4 speed. LA-built rolling chassis. California car. Solid car apart from lower quarters, trunk pan and left inner fender battery damage. Original K frame with Kelsey Hayes discs;

3) 1970 340 4 speed. Windsor-built rolling chassis. Came into my possession with 73+ K frame with slider front discs and 8.25 rear installed.

My goal is to take the best of all three cars and make one excellent vehicle. I'm just wondering is either K-frame design is fundamentally superior to the other. Shy of grafting the VIN stampings from the complete car onto one of the rollers (likely the Cali car) this will not be a numbers matching car, and I'm totally cool with that. I'm building this for the missus and myself and not the purists.

It may be sacrilege, but I plan to shelf the thermoquad in favour of EFI.
 
How good is the #3 car body?

Pictures or it never happened.
 
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The spool type mounts are called fail safe. When the biscuit mount fails the fan eats the shroud. I've heard drag racing stories of engines torqued far enough that the automatic trans changed gears.
 
To answer all the questions.... I have 3 cars:

1) 1971 340 4 speed. Complete numbers matching Hammtrack-built car but quite rotted;

2) 1970 340 4 speed. LA-built rolling chassis. California car. Solid car apart from lower quarters, trunk pan and left inner fender battery damage. Original K frame with Kelsey Hayes discs;

3) 1970 340 4 speed. Windsor-built rolling chassis. Came into my possession with 73+ K frame with slider front discs and 8.25 rear installed.

My goal is to take the best of all three cars and make one excellent vehicle. I'm just wondering is either K-frame design is fundamentally superior to the other. Shy of grafting the VIN stampings from the complete car onto one of the rollers (likely the Cali car) this will not be a numbers matching car, and I'm totally cool with that. I'm building this for the missus and myself and not the purists.

It may be sacrilege, but I plan to shelf the thermoquad in favour of EFI.

I'd keep #2 as is and work from there, nothing wrong with Kelsey Hayes discs, and I'm sure it has an 8 3/4 rear to boot. Just get everything up to snuff. Spend your time and money elsewhere. Same for the EFI. But it is your car, time, and money. Good luck.
 
I e worked on both types of motor mounts. While the biscuit is easier to work with, the spool isn’t hard ether. It just has a narrower window of drop in. The bolt that secures the fail safe mount is a little harder to install than a nut from under the car to the biscuit. But not much harder.

Honestly It’s splitting hairs on the install. The biscuit wins by a hair. However with that said, I myself would use the fail safe and not worry about it ever. I’ve ripped the biscuit mounts in half before with my small block 4spd Cuda really easy. The fan does indeed eat a shroud for lunch.

So if there is any power in the engine, the fail safe wins big. And that’s what I would use.

How the sway bar runs is the least of any concern and doesn’t hit my radar at all.
 
How good is the #3 car body?

Pictures or it never happened.

#3 left, #2 right
#1.jpg


#1 up front, #2 in the rear.
#2.jpg


#3 looks really good but there's a lot of bondo hiding a lot of sins. #2, the California car is the best build candidate with excellent frame, rockers (inner and outer).
 
Too bad about number one. I would use what parts I could on number two and get it going.
Number three is one I might put on a rotisserie and take my time repairing it.
 
I e worked on both types of motor mounts. While the biscuit is easier to work with, the spool isn’t hard ether. It just has a narrower window of drop in. The bolt that secures the fail safe mount is a little harder to install than a nut from under the car to the biscuit. But not much harder.

Honestly It’s splitting hairs on the install. The biscuit wins by a hair. However with that said, I myself would use the fail safe and not worry about it ever. I’ve ripped the biscuit mounts in half before with my small block 4spd Cuda really easy. The fan does indeed eat a shroud for lunch...

Either "mounting system" you should add a torque strap, preferably to a head boss.
 
the early sway bar mounts are wider and it should provide an advantage for roll control. I think you will have to keep the struts with the K frame but could be wrong.Just go with the cleanest rust free pieces.
 
73+ with spool mounts every time. Better engine mounting design, no chance of the engine shifting forward with an engine mount failure. Much less chance of an engine mount failure to begin with, unlike the biscuit style mounts that are notorious for failing. Better sway bar design routed through the K frame, increasing ground clearance and moving the sway bar mounting tabs further in, allowing for wider front tires and removing the interference issue you get with the 73+ calipers and the 67-72 sway bar design.

And the 67-72 K frames weren't made any better. I've seen examples of both styles that had great welding, and examples of both styles that had horrendous welding. It wasn't a production year thing, just plain old 70's mopar quality control.
 
the early sway bar mounts are wider and it should provide an advantage for roll control. I think you will have to keep the struts with the K frame but could be wrong.Just go with the cleanest rust free pieces.
There is only a slight difference in the length, but the rule of thumb is coarse thread on the LCA side is 73 and up, fine thread is everything before 1973
 
There is only a slight difference in the length, but the rule of thumb is coarse thread on the LCA side is 73 and up, fine thread is everything before 1973

There is no difference in effective length. The difference in the strut rods is due to the change in the design of the strut rod bushings from the single piece bushings to the split, 2 piece bushings. It doesn't matter what year strut rods you use as long as you keep them paired with the strut rods bushings for the model year of the strut rods. They can be used with any K.
 
I like spool mounts.


I drilled my biscuit mount and used a counter sink allen bolt, you can't see it and it wont break. My AAR was a 4 speed and I would drop the hammer with 4.88 gears and 9.00 x 29.5 slicks, never broke a mount. With a fiberglass hood and the AAR air cleaner if I broke a mount it would be bad.

91253A591L.GIF
 
I drilled my biscuit mount and used a counter sink allen bolt, you can't see it and it wont break. My AAR was a 4 speed and I would drop the hammer with 4.88 gears and 9.00 x 29.5 slicks, never broke a mount. With a fiberglass hood and the AAR air cleaner if I broke a mount it would be bad.

View attachment 1715766379

I JUST recommended doing that in another thread either yesterday or the day before. I think it went in one ear and out the other. It's a good mod.
 
I JUST recommended doing that in another thread either yesterday or the day before. I think it went in one ear and out the other. It's a good mod.

It worked good for me for many years, and if you are going to change K-Member for a mount that wont break I would do this first.
 
73+ Spool Mount is the better of the two for sure, along with the rest of the front suspension. It's common knowledge.
 
66fs- No there's a big difference. A- body front suspension was revised in 73 and it is better.
 
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