The Stovebolt Site Forums The Shop Area Paint and Body Shop Doors Replaced cab mounts, doors won't close...

I was crawing around under the 58 a little while back and noticed that the bolts for the rear cab mounts were both snapped off. The passenger mount was just gone, nothing between the cab and the frame at all. The driver side still had the upper half of the mount, but it was pretry collapsed.

I got a new set of cab mounts and put them in today, and that process went fine except the the doors don't shut anymore.

The driver door is not visibly different, but it takes a pretty hard slam to close now. It was always a little stiff, but I was waiting to adjust it until I got some other thinga done. I don't see any binding anywhere, but it is just hard to close.

The passenger door opened and closed like butter before. Now the latch on the door side hits the mechanism on the cab side a good 1/8" low. Getting the door to latch requires lifting from the handle and slamming it home.

The hinges are mounted to the cab as well, so I feel like this shouldn't have happened.

Maybe I could shim the front mounts up and that would help? I don't really know where to go from here.

I could take the new rubber mounts out and just bolt it back together the way it was, but I feel like the right answer is to adjust something else.

Probably a symptom of a bigger problem, possibility the flexibility of the cab. I don't think it should be that flexible that changing the cab mounts would throw the doors out of alignment. How are the joints between the rockers and A and B pillars.

The door latches are adjustable at the "B" pillar. I would remove the striker from the "B" pillar and close the door to check for any interference. If the door fits the opening and the gaps are decent all around the opening, adjust the striker to latch the door. If the door can't swing full open to full closed with the striker removed, you have hinge issues or the cab is twisted.

Truck was in a wreck that knocked the cab off the frame and broke/bent all those mounts. The frame may be twisted and by putting the cab back on the new mounts made it conform to the twisted frame, thus twisting the cab.

I did some thinking about where the stresses would have changed with the proper rear mounts and decided the problem was likely the front mount shims.

I shimmed the front up proportionally to extra thickness on the back and the doors work again.

Yay!

Good work, Jason!

My original assumption was that it should just rotate about the front mounts, but upon further reflection, I think that the fenders and front mounts were making a box and the rear mounts made it deform.

The thickness I added at the front mounts was what I added at the back times the ratio of the distance between the two cab mounts and the front cab/core support mounts.

Just in case that info is helpful to anyone else.

That;s awesome. So the door frame was slightly racked out of square

Jason;
I am trying to develop a picture of the actions taken to solve the problem... when you say "times the ratio of the distance..." are you really meaning "plus the average of the difference..." Forgive me if I am nit-picking, just trying to learn from what has turned out to be a nifty solution.

Thanks

I guess it cannot be "average" becaause that would be too big of a number... I will keep noodling, Sorry.

I didn't write down the measurements because I ran the numbers while I was doing it, but the math goes like this:

The cab is mounted with two mounts on each side (front and back). The fenders are mounted to the cab and the core support (which has one mount on each side.

Distance from the core support mount (front of fender ) to the front cab mount: 42"

Distance from the front cab mount to the rear cab mount: 23"

Height added to the rear mount: 3/8"

The front mount is 42/65 (64.6%) of the way between the core support mount and the rear cab mount. So I needed to add 64.6% of 3/8" in the middle to put the three mounts back in line. That works out to just under 1/4" according to these measurements.

The drawing below is not to scale, but it hopefully illustrates the problem. The initial change (just raising the back) caused the cab to deform in the door openings enough to be a problem.

I did check in the FAM and those three points *should* be a straight line.

Jason;

your solution is of great interest to me as I have yet to face the issue of aligning all of the pieces of metal for optimal fit (my cab and front end are all separated from the frame) and I understand that this can be a complicated exercise. Thank you for taking the time to explain what you did to solve the problem of your doors fitting properly after replacing cab mounts.

Do you know if this FAM rule appplies to the AD trucks as well as your 58?


Many thanks for helping this old man anticipate an issue that he knows is coming his way.

I don't have an AD FAM, so I don't know.

I will add one additional note here relaative to Gib70's comment.

The FAM says that the mounts should be in a line. That does *not* mean that the shims should necessarily be the same or proportional if you are doing a new/clean assembly.

In my case, the cab was aligned such that everything worked with variable thickness shims at all of the mounts. I could only use the math to figure out the correct new shim because I was changing an existing (notionally) correct setup.

The shims exist to correct small cab-to-cab and frame-to-frame variances, so proper shimming using traditional methods will be neccesary to get that baseline.

Theoretically a person could measure the locations of all the mounts on the frame and all the mounts on the cab/fenders and calculate the necessary shims for that particular combination of parts, but given the flexibility of the parts and the complicated geometry, I do not believe it would be any faster or more accurate than determining it experimentally.

I think the most valuable bottom line takeaway from my experience here is that improperly shimming the front of the cab can cause door frame deformation that prevents the doors from closing properly.