1973 Road Runner K Frame Body Mount/Bushing Swap

[zombezoo]

Planning to help Dad swap his subframe bushings for fathers day. 1973 340 Road Runner.

Im looking to keep this as simple as possible, have to do this outside on the ground with hand tools, jacks, and jack stands...

Im thinking of the following:
1) Get some longer bolts for the K Frame or perhaps some threaded rod.
2) Swap one by one to the longer bolts
3) Lower (equally) all 4 sides to get clearance enough to get the bushings out of their locating holes
4) Remove one long bolt at a time to swap the bushing at each point
5) Tighten back up and swap back to the original fastners

I expect I will need to remove the upper control arms from the K frame to get enough drop clearance. I'm hoping this strategy will keep everything aligned so we dont need anything else. I dont have an engine hoist where the car is so Im looking to avoid using one. Im thinking a jack on the K frame can assist with the raise and lower of the assembly.

Am I kidding myself here?
Does anyone know the thread size/pitch of the 73+ bolts for the isolated K frames? I have seen a few different sizes listed.

 

[Darter6]

I expect I will need to remove the upper control arms from the K frame to get enough drop clearance.

I did this on a 79 Cordoba. Did not have to remove the upper A arms.
I loosened all 4 including the trans cross member (changed those bushings too)
I like the idea of longer bolts as I fought quite a bit to get the old ones out. Hope you don't have to deal with too much rust.
I can't help with the thread size of the bolts.I posted photos on here.it was about 6 or so years ago. Maybe do a search.

 

[Vaanth]

Planning to help Dad swap his subframe bushings for fathers day. 1973 340 Road Runner.

Im looking to keep this as simple as possible, have to do this outside on the ground with hand tools, jacks, and jack stands...

Im thinking of the following:
1) Get some longer bolts for the K Frame or perhaps some threaded rod.
2) Swap one by one to the longer bolts
3) Lower (equally) all 4 sides to get clearance enough to get the bushings out of their locating holes
4) Remove one long bolt at a time to swap the bushing at each point
5) Tighten back up and swap back to the original fastners

I expect I will need to remove the upper control arms from the K frame to get enough drop clearance. I'm hoping this strategy will keep everything aligned so we dont need anything else. I dont have an engine hoist where the car is so Im looking to avoid using one. Im thinking a jack on the K frame can assist with the raise and lower of the assembly.

Am I kidding myself here?
Does anyone know the thread size/pitch of the 73+ bolts for the isolated K frames? I have seen a few different sizes listed.

I have done this on two of my vehicles in 1995 using the Chrysler 4419942 cast iron bushing kit. I installed the kit on my 1977 Fury (B-body) and 1979 Newport (R-body) police package cars while I was rebuilding the front end on both. The upper control arms are attached to the K-member structure on these cars, so control arm removal is not required. Back off on the torsion bars to remove the tension of the bar to replace the torsion bar rear cross member bushings. I replaced the torsion bar rear cross member bushings with new Chrysler 3817172 and 3817173. If I was doing the swap now, I would use urethane bushings for the rear cross member such as Energy Suspension 5.4110G.

Support the car chassis separately and the K-member assembly with or without engine and transmission can be lowered and raised with a floor jack, or two. watch for any conflicting areas such as fan to shroud. Not much lowering is needed for the swap. A small access hole is on the side of the frame rail on the cars I have done where penetrating oil can be sprayed on the bolt threads. As noted, rust cleanup from the area of the old rubber bushings might be required. I

I have not used aftermarket bushing kits, but the Chrysler cast iron bushings are self aligning in the oval K-member holes. Aftermarket polyurethane or aluminum kits might differ. Front suspension re-alignment is not required with the Chrysler kits. Some cars might have left or right alignment shims. Re-use these as needed.

The procedure for stock bushing replacement is in the service manuals, although early manuals do not specifically cover individual isolator (bushing) replacement for B-bodies, later manuals do, and refer to the K-member as H-member in these cars.

Diagram showing the isolators:

The bolts used to mount the K-member assembly are 5/8"-11. The following images show an original bolt:

The following images show the P5249550 Mopar Performance kit contents and instruction sheet which replaced 4419942. Although listed for F/M-bodies, the kit also works for B/R-bodies as noted in the instruction sheet. The bolts are shorter than stock because the lower bushing is eliminated.

 

[zombezoo]

I did this on a 79 Cordoba. Did not have to remove the upper A arms.
I loosened all 4 including the trans cross member (changed those bushings too)
I like the idea of longer bolts as I fought quite a bit to get the old ones out. Hope you don't have to deal with too much rust.
I can't help with the thread size of the bolts.I posted photos on here.it was about 6 or so years ago. Maybe do a search.

Good to know, I just did my 73 satellite (his parts car gifted to me in the 90s) and had to remove the uppers to get the k frame to drop completely out. Wasn't sure if there was enough clearance to swap the bushings. Will try that first.

 

[zombezoo]

I have done this on two of my vehicles in 1995 using the Chrysler 4419942 cast iron bushing kit. I installed the kit on my 1977 Fury (B-body) and 1979 Newport (R-body) police package cars while I was rebuilding the front end on both. The upper control arms are attached to the K-member structure on these cars, so control arm removal is not required. Back off on the torsion bars to remove the tension of the bar to replace the torsion bar rear cross member bushings. I replaced the torsion bar rear cross member bushings with new Chrysler 3817172 and 3817173. If I was doing the swap now, I would use urethane bushings for the rear cross member such as Energy Suspension 5.4110G.

Support the car chassis separately and the K-member assembly with or without engine and transmission can be lowered and raised with a floor jack, or two. watch for any conflicting areas such as fan to shroud. Not much lowering is needed for the swap. A small access hole is on the side of the frame rail on the cars I have done where penetrating oil can be sprayed on the bolt threads. As noted, rust cleanup from the area of the old rubber bushings might be required. I

I have not used aftermarket bushing kits, but the Chrysler cast iron bushings are self aligning in the oval K-member holes. Aftermarket polyurethane or aluminum kits might differ. Front suspension re-alignment is not required with the Chrysler kits. Some cars might have left or right alignment shims. Re-use these as needed.

The procedure for stock bushing replacement is in the service manuals, although early manuals do not specifically cover individual isolator (bushing) replacement for B-bodies, later manuals do, and refer to the K-member as H-member in these cars.
View attachment 1864038

Diagram showing the isolators:

View attachment 1864039



The bolts used to mount the K-member assembly are 5/8"-11. The following images show an original bolt:
View attachment 1864007
View attachment 1864006

The following images show the P5249550 Mopar Performance kit contents and instruction sheet which replaced 4419942. Although listed for F/M-bodies, the kit also works for B/R-bodies as noted in the instruction sheet. The bolts are shorter than stock because the lower bushing is eliminated.
View attachment 1864010
View attachment 1864008
View attachment 1864005
View attachment 1864009
View attachment 1864011

Thanks for all the details! This is very helpful

 

[440 PHIXX]

The only rubber bushing subframe Mopar I owned was an ‘81 Mirada. I only had it for a few months and gave it to my brother. I do remember Herb Adams of GM (Pontiac) when he started his own company VSE offering a sintered iron bushing replacement kit for GM F bodies and X bodies. He was able to get his Fire Am and Cheverra to handle better than a Porsche 930 Turbo. I’m sure it would help Mopars with that squishy crap as well.

 

[Darter6]

I’m sure it would help Mopars with that squishy crap as well.

Yeah, the 79 Cordoba wandered all over before. I used the Prothane kit.Night and Day difference. Sold the car before installing the rear axle kit.