Replacement of rear cab mounts on a 1991 Chevy K1500 short bed pickup

I would highly recommend several days of soaking the bolts with a good rust buster like PB Blaster to try and loosen them from the weld nuts. I would even drill 1/8" or 3/16" holes above the weld nuts to get the penetrant in there if needed. This is what we have to do on our Jeep tubs to try and avoid the weld nuts from just spinning out.

I live in the rust belt and had to change all my mounts also and I used loctite on all mine. This was back in 2000 and all my bolts are still clean and I am able to easily loosen them off to adjust my body or in the case right now, take them off to replace my terminally rotted frame.

Loctite is a rust preventer and works way better than grease. If you want a slippery connection for things you expect to take apart, antiseize compound also works very well and is permanent unlike grease. I use that on all my brake parts and hub parts.

If you are adding a 1/2" lift to the rear mounts, you should do that at the front and sides also or the torque twist on the front mounts will likely cause a failure down the road. Having the mounts all level is also very important for keeping the door openings the right shape and any rain gutters still running downhill. I have seen door openings kink even from having uneven mounts. I even recommend stainless shims to make up for rust divots if new frames aren't used, but that is on open top cabs where the fit of the hardtop and doors is more critical.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:

Thanks for your feedback Mike,

Spraying the bolts with a rust buster is a good idea. There are two small holes in the bottom of the round steel retainer that goes under the lower rubber cab mounts, I think I will spray a some type of good penetrating oil into the holes as I think it should reach the weld nut. I don't want to take the seat or carpet out of the cab, so I have no way to get to the top side of the weld nut from the inside of the cab to spray it with penetrating oil.

When the truck was new, I sprayed silicone grease into the same holes, trying to preserve the rubber cab mount bushings. Since then, years later, I have sprayed cavity wax rust inhibitor into into the same holes. The cavity wax may prevent the penetrating oil from reaching the weld nuts and/or not allow the penetrating oil to really soak in. On the other hand, perhaps spraying the silicone and cavity wax also prevented the bolts from rusting to the weld nuts.

I had >If you are adding a 1/2" lift to the rear mounts, you should do that at

Presently, the rear of the cab is sunk down, (rubber mounts sunk through the steel brackets that are welded to the frame) so that the cab tilts down from the front of the cab to the rear, you can see the space between the rear of the cab and the bed is larger at the bottom.

Would the fact that the bed is tilted down in the rear also cause the torque twist you mention ? I'm not 100% clear on what you mean by torque twist as it applies here.

I'm only adding a 1/4" thick plate on top of the existing steel bracket that the rubber cab mounts go through, to bring the rear of the cab back up to it's original height. I am also adding a 1/4" thick steel plate on the bottom of the existing steel brackets that the rubber cab mounts go through simply because this will keep the rear cab mounts from "lifting up" from the steel brackets. However, the lower 1/4" thick steel plate has no effect on the height of the cab.

I would appreciate any other feedback or thoughts you may have.

Thanks John

I got the rear cab mounts replaced along with the steel brackets I made and everything went fine for the most part. The cab mount bolts did not have a bit of rust on them where they entered the weld nuts (I was very surprised).

I centered the round steel retainer under the lower rubber bushing as best as possible, then I torqued the bolt down to 55 foot pounds just like the GM service manual said, however, it seemed to smash the lower bushing much thinner than the original bushing. Other than the fact that it seemed at least half as thin as the original bushing, everything looked fine, the right side looked perfect and the left side lower bushing had a 10 or 15 degree portion of the rubber that seemed to slip or walk out from under the retainer, but nothing serious. The upper mounts seemed perfect, cab at correct height, etc..

After driving, there was no change to the left side, but the right side of the lower bushing had a fair portion that seemed to slip or walk out from under the steel retainer. As long as it does not get any worse any time soon, I think it will be OK, it did not slip all the way out, I can't see inside of the bushing or anything, but it does have a portion (probably at least 45 degrees) where the retainer either cut into the bushing or that part of the bushing just walked out or "bulged out" from under the retainer. Probably more likely that the retainer cut into the bushing since I can't see inside of the bushing, if a portion of the bushing walked out, I could probably see inside of the bushing. Perhaps a little cutting of the retainer and a little walking of the bushing occurred.

I wonder if I either was sold the wrong GM lower bushing by the dealer, or if the GM part changed a little over time and is no longer an exact replacement (I had that happen with the connectors of a coolant temperature sensor in the past), a NAPA aftermarket was a better fit and better choice.

I doubt GM makes a heavy duty bushing. If it gets worse I will have to check into an aftermarket replacement or perhaps a Urethane aftermarket bushing since those are tougher than rubber.

After everything was torqued down, I did spray some valugard rust inhibitor on the parts, the stuff does penetrate, but I can't believe that it could get between the steel retainer and the lower bushing (after it had been torqued to 55 foot pounds) and then cause a portion of the bushing to slip out. A 12 mm OD cab bolt torqued to 55 foot pounds is exerting a fair amount of force, as evidenced by how much it smashed the rubber bushing.

Any ideas why this may have happened ? If it becomes necessary to replace, any suggestions for a quality aftermarket replacement for the lower bushing ?

Thanks John

Did your old bushings not have a steel anti-crush sleeve inside of them to prevent blow out? This way the torque on the bolt comes up hard to the tube so the rubber is sandwiched at a certain compression factor.

I know there is a large issue with some aftermarket bushings for Jeeps that don't come with the center tubes. They are crap and they do blow out, especially if the Jeep sees any off road stresses.

The ones I got for mine, (Daystar if I remember right) came with the anti-crush tubes so I was fine. Folks report it is a real problem trying to cut what is left of the stock tubes out of the old bushings to re-use or to try and find the right sized ones for the new bushings.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > I got the rear cab mounts replaced along with the steel brackets I

Hi Mike,

Thanks for your message.

I got all the replacement bushings right from a GM dealership, the upper bushings or cushions have an integral steel piece that is part of the bushing, but the lower bushings did not have any type of steel sleeve associated with them, nor did I see a sleeve in the original lower bushings when I removed them. Unless the anti-crush sleeve totally rusted to dust, I don't think it was in there originally, however, even the upper steel sleeve or tube that extends down from the upper bushing was rusted to crumbs so perhaps the lower sleeve totatly rusted away :-).

I can't believe the mounts rusted this way, I mean, the steel sleeve on the upper bushing is basically "inside" and protected from the elements once everything is torqued down. I guess water and salt got in there somehow. I even sprayed some silicone lube on the bushings when the truck was new to try to preserve them, that stuff was supposed to help prevent rust, but it did not seem to do much good here.

The upper bushings look very stiff (there is no bulge on them, they look the same with the weight of the cab and the force of the bolt on them as they did right out of the factory package). But the lower bushings just smashed down like a pancake when I torqued the cab bolts down to 55 foot pounds.

If there were a steel tube or sleeve in the lower bushings, then as the cab mount bolt is tightened, as soon as the lower round retainer hit the end of the sleeve, the lower rubber bushing could no longer compress and any further compression would need to come from the upper bushing, or if the upper bushing would not compress then there would be no signiifcant compression from that point forward. Is that how it's supposed to work ?

I have a GM factory service manual and I did not see any sleeve mentioned, nor did I see a sleeve mentioned in a Chilton repair manual I have. Actually, if there's going to be a steel sleeve inside the lower bushing, I don't see the point of the rubber bushing, you may as well just put the steel sleeve in and torque it down, as soon as the retainer bottoms out on the steel sleeve, the rubber bushing would not really be able to absorb shock at that point, it would be basically steel on steel, with a compressed bushing around the tube or sleeve. The lower bushing could still act somewhat like a damper or shock absorber though, if one side of the cab were to go down (due to flex in the upper bushing and a rough or bouncy road), the cab bolt and retainer might pull away from the end of the sleeve a little, and the lower bushing would act like a damper when the bolt & retainer came back up to make contact with the sleeve.

Do you ever get any noise with those sleeves in there, ?

I have driven the truck about 25 miles or so and the condition of the lower bushings did not seem to get an worse. If it gets worse I guess I will try to find a Urethane replacement for the lower bushing.

It looks to me like the GM replacement bushings were simply not as tough and/or as tall as the original lower bushings that came with the truck. That's a major drag because you go to a dealership parts department to get exact replacement parts that will install, fit, and perform just like the original parts.

I wish they would just make all vehicles out of Aluminum or some type of material that does not rust. At the very least, they should coat all steel parts, frame, body, everything that can rust, with some type of tough coating (maybe epoxy or something) to prevent rust. The zinc coatings they use don't cut it in the long run, and they don't even coat the frame with the zinc, if they did, perhaps the cab mount frame brackets would not have rusted out.

Heck, I had a brake line rust out on this thing at 6 years old, replaced it, and it rusted out again in the same place a few years later, replaced it again, coated with rust inhibitor, no problems yet. It was rusting where a plastic clip was holding in moisture. In my opinion, brake lines, fuel lines and fuel tanks should never rust through, just as a matter of safety. They can either make them from materials that won't rust (preferably), or coat them so they don't.

At least I got the job done, I've had the parts sitting on a shelf for about 1.5 years avoiding the job, and it was not quite as easy as it looked. I did not realize how far the one side of the cab had dropped down, and I had to raise the cab up much higher on that side than I had anticipated.

Thanks John

That sounds correct then. The upper bushing has the sleeve and the lower is the compression bushing. I would only expect to see one bushing in there. Mine just wouldn't over tighten because the sleeve fit down through the bottom bushing. My sleeves stuck out below the top bushing, but I have a Jeep that has different stresses than a pickup cab so it is also bushed for the 'upward' stress.

Oh do I hear you on the rust! I put all new brake and gas lines in 8 years ago and they are now due for replacement with one already popped.

I went fiberglass for a body tub 8 years ago and now need to replace my frame that has terminal rot. Welding patches on patches....

Mike

John2005 wrote:

Mike,

do you rent your services out inexpensively? My dad has a '76 Scout II that has a solid frame and drivetrain, and neither one of us is ambitious enough to attempt to really fix it...

nate

Hi Mike,

I just thought of something, is the steel sleeve or tube that extends down from the underside of the top rubber bushing actually *supposed* to bottom out on the round steel retainer under the lower bushing when you torque the cab mount bolts down ?

In my case, I added a 1/4" thick plate under the top bushing and a

1/4" thick plate under the bottom bushing (between the bushing an the steel frame bracket). Because of this, it is *as if* the the sleeve or tube in the top bushing is 1/2 inch shorter than it really is, which would make the lower bushing flatten out 1/2" more than it would have if I had not put the two 1/4" support plates in there, which as mentioned in my previous posts, I did because the original steel frame support brackets rusted through.

However, if the sleeve of the upper bushing is not designed to bottom out on the retainer under the lower bushing after the cab mount bolt is torqued down, then the addition of the two 1/4" thick plates would have no effect, and it's probably due to the replacement bushings not matching the originals or being made from inferior material.

If the upper bushing sleeve is designed to bottom out on the lower bushing retainer, then I could take it apart and make a 1/2" spacer to go between the lower bushing retainer and the bottom of the upper bushing sleeve, or I could perhaps stack some washers in there. I'm not crazy about fooling with it any more unless I have to though.

Thanks John

My bushings are two donuts of 'rubber' with a steel sleeve inside their hole and a large thin fender washer on top and bottom. The frame mount is sandwiched between the rubber donuts. When torqued down, the fender washers hit the steel sleeve so the rubber donuts can only be compressed so much. They then act as a unit buffering both the downward movement and the upward movement with the frame mount sandwiched.

It sounds like you have the correct understanding of why your lower donuts tried to over compress. You 'may' want to back off the torque a bit and use a Loctite product on the threads so the nuts won't back off, well you really should do this actually or at least get the thread locker on there (it should soak in from the outside if you don't want to wrench them) because your bushings, as set up, are likely going to 'work' some which normally loosens off the nuts. I see them fall apart lots if not done exactly right.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > Hi Mike,

Old beasties take a lot of TLC, that's for sure. I used to help folks get their rigs together, but don't have the mobility these days to even keep my poor old CJ7 on the road. (well the needed frame swap is a big job, have started picking away at it) I got banged up as a passenger in a passenger side T-bone hit and am not moving well.

What part of the continent are you in?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:

Hi Mike,

Actually, I used some blue removable Loctite (#2440) on the threads when I torqued the cab bolts, I also used a grade 8 split loc washer under the head. I guess I could back off the bolt as you suggest, then re loc tite it. I was not sure how important the 55 foot pound torque specs of the bolt were.

I think I i will leave it alone unless the bushings get too torn up, if that happens, I will replace with the best bushing I can find, probably polyurrethane. I may also add a spacer in there, or just not torque the bolt down so far as you suggest.

Thanks again for your help. John