Hi everyone,

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

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).

After replacing the upper and lower rubber bushings, 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 new 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