Replacement of rear cab mounts on a 1991 Chevy K1500 short bed pickup
John2005
I have a 1991 Chevy K1500 short bed pickup. I'm replacing the rear cab
mounts (rubber bushings). I have a Chilton and it looks like a fairly
straight forward job, but I have never replaced cab mounts before.
Does anyone have any tips or suggestions before I do the job that
might make it go smoother ?
I purchased the new cab mounts from the dealer, along with two new cab
mount bolts. The steel brackets that the rear cab mounts are bolted to
have rusted through, (rubber cab mount bushings are falling through
the steel brackets) and I will be putting a 1/4" inch thick steel
plate on the top and bottom of the existing steel brackets.
I purchased two 10.9 class 12 mm bolts that are 1/2 inch longer than
the stock cab mount bolts, in case the stock cab mount bolts are no
longer long enough, since I added 1/2" inch to the stack-up with the
two 1/4" thick plates.
One thing I noticed about the stock cab mount bolts (GM part #
15704266) is that they have what looks like a yellow nylon patch on
about a 1 inch long portion of the threads about 1/2" from the end of
the bolt, which I assume is to prevent back-out of the bolts once
their torqued down.
The very end of the stock cab bolts also have some small grooves
running axially through the first three threads. There are 4 or 5
grooves evenly spaced radially around the bolt. The very end of the
bolt almost looks like it's supposed to clean the threads of the weld
nut on the cab floor, almost like a thread chaser.
If I have to use the longer bolts that I purchased, can I just put
some blue removable loc-tite on the end of the bolt to prevent back-
out ? I also have two 10.9 class split lock washers, along with some
regular round washers, I could use under the heads of the bolts as
well.
The main thing that worries me is that when I go to take the existing
cab mount bolts out, they may be rusted to the weld nut on the cab
floor and either strip or break off the weld nut.
When I go to put the new cab bolts in, I had considered putting some
grease on them to keep the threads from rusting to the weld nut on the
cab floor, however, that would seem to defeat the purpose of the nylon
patch on the stock bolts, and if I use the new longer bolts that I
purchased, I could not use loc-tite on the threads if I use grease,
although the loc-tite itself could possibly prevent rust.
Depending on which bolts I use, do I have any options for preventing
rust where the bolts thread into the weld nuts on the cab floor ? Do I
need to worry about it ?
The rest of the truck is in great shape, and the funny thing is, the
front cab mounts are almost in perfect condition. I'm not sure why the
rear cab mount brackets rusted through, especially since they are
located further from the road (less salt) than the front cab mounts.
Why do these cab mounts rust through, the metal is fairly thick just
like the frame ? Do the rubber mounts hold in moisture and/or salt ? I
have always tired to keep the salt hosed off the undercarriage in the
winter. There were times I drove through some deep water, but if that
was the problem it did not effect the front cab mounts.
In addition to any feedback you may have on my questions, I would
appreciate any general advice that may make the job go easier and/or
come out better.
Thanks
John
Mike Romain
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: http://mikeromainjeeptrips.shutterfly.com
John2005
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 one person suggest to back the bolts off, then tighten them
down, then if or when the bolts get tight, tighten them back down a
little than then try to work it back an forth. That seems pretty
shady, if it seems too tight when taking the cab bolts out, It's
probably best to stop, and then I will have to see if I can go through
the carpet and get some penetrating oil to the top side of the weld
nut (something I would rather not have to get into).
Mike wrote:
>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.
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
John2005
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
Mike Romain
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 in '00
'New' frame in the works for '08. Some Canadian Bush Trip and Build
Photos: http://mikeromainjeeptrips.shutterfly.com
John2005
Thanks for your message.
>Did your old bushings not have a steel anti-crush sleeve inside of them
>to prevent blow out?
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
Mike Romain
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
Nate Nagel
> 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
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
--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel
John2005
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
Mike Romain
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 in '00
'New' frame in the works for '08. Some Canadian Bush Trip and Build
Photos: http://mikeromainjeeptrips.shutterfly.com
Mike Romain
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?
John2005
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