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Engine and Transmission Mounts  Rating:  Rating
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 Posted: 03-31-2005 01:23 am
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Mark Rosenbaum
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My car's motor mounts and transmission mounts have been in dubious condition for the close to five years I've owned the car, and after months of gazing longingly at JHPS advertisements and Delta's catalog, I finally decided to replace the parts. As Delta Motorsports and I are both in Arizona, if I order through the JHPS I may pay a bit more in shipping and handling, but avoid paying any state's sales tax.

After I placed my order, Greg Fletcher of the JHPS sent me an email advising that the original style transmission mounts were still back ordered, but that Delta had a "replacement" that supposedly would fit as long as the buyer elongated the mounting holes. This seemed a simple enough modification -- even I can operate a file -- so I told Greg I'd take a chance. The parts arrived a few days later.

Others have noted that the new motor mounts use metric threads rather than the SAE threads of the original parts. At least one owner has complained that he had to go out and buy new nuts for his mounts, but the ones I received were furnished with nuts -- though these were plain hex nuts (17 mm across flats) rather than lock nuts like the original part.

The new mount is 2.25" diameter, with a donut section some 1.3" thick, and an M10 x 1.5 mm pitch x 21 mm long stud on either end. There were no markings on the part.

The original mount is also 2.25" diameter, with a donut section some 1.5" thick, and 3/8"-24 x 0.75" long stud on one end, and a 3/8"-24 x 1.38" long stud on the other. Cast into the rubber donuts were "Metalastik" and "31/302."

Curiously, although my engine had an original style mount on the intake side, on the exhaust side was a metric mount identical to the ones I received from Delta. Both have been on the car as long as I've owned it, but the metric mount was in near-new condition while the original style mount was unserviceable.

Installation was pretty simple, and involved removing the motor mount hardware, raising the engine with a jack, prying out the old mounts, and slipping in the new ones. For both removal and installation, the intake side upper nut is best accessed from above, but the remainder should be approached from beneath the car. Both upper nuts are awkward, and using a stubby combination wrench, perhaps with an internal ratchet, would speed things up tremendously. One also needs a thick flat washer on each lower nut that's large enough to cover the triangular hole in the suspension crossmember.

The exhaust side mount may also need one or more 'packers' to raise the engine slightly so that the header will clear the steering shaft. These 'packers' are 2.25" diameter flat washers with a bolt-wide slot cut all the way from center to rim. The one on my car was 0.13" thick and apparently made of aluminum alloy.

So much for the easy part.

IMHO, installing Delta's non-original 'replacement' transmission mount is not something a novice mechanic should attempt at all, and I think the average JH owner would find its installation very difficult. OTOH, those with Bridgeport milling machines in their garages probably won't have any problems.

The new mount's upper holes are 7/16" diameter on 3.75" centers, while the threaded holes in the transmission are 5/16" diameter on 4.0" centers. The new mount's holes need to be filed out about 1/8" on either side, so that one can install the original bolts into the transmission. This is tedious, but is not a real difficulty.

Unfortunately, this is not the only change required. The new mount's lower holes are oriented in a straight line left-right on 1.5" centers, while the original mount uses studs located on the opposite corners of a 1.25" x 0.75" rectangle. Next, the new mount's lower holes are threaded for 3/8" USS bolts (which Delta kindly provides) while the original mount uses 5/16" SAE studs. This means that one must do a LOT of filing, at odd angles, on the mounting bracket's holes, and due to the lack of studs must lever the transmission around during installation until everything lines up. This takes a tremendous amount of physical brute force applied at awkward angles while under the car.

Next, at 1.95" thick, the new mount is a bit shorter than the 2.63" of the original mount and its intermediate bracket -- and I don't think ANYONE will attempt filing the intermediate bracket so that it, too, will fit. This may be an advantage as it gives a bit more clearance between the floorboards and exhaust system. It could conceivably exacerbate any clearance problem between header and steering, but I did not observe this in my car.

In its favor, the new mount is far more rigid than the original design, is very unlikely to suffer catastrophic failure of any sort, and will probably have a service life several times longer.

Naturally, I had to take the car out for a test drive after cleaning up, putting tools away, and bandaging several minor wounds. I noticed several improvements. First, the car no longer jerked at light throttle and low engine rpm under load -- e.g when driving at 20-25 mph in 2nd or 3rd gear. Second, an exhaust rattle related to engine vibration seems to have disappeared. Third, the gear shift lever no longer wobbles around -- it's now so predictable that one could use a metal shift gate like a Ferrari. My JH is now a much better-mannered car.

In conclusion, then, the motor mounts were easy, and worth the effort. The transmission mount was a real PITA -- but I grudgingly admit that it was worth it.





UPDATE: I must be getting old.  When transcribing my notes, I mis-read the diameter of the motor mounts, new and old.  The correct diameter is 2.25" not 2.5".  The body of the text has been corrected.

 

Last edited on 04-02-2005 07:20 pm by Mark Rosenbaum

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 Posted: 04-18-2005 08:06 pm
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Mark Rosenbaum
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Followup.

I guess even a transmission mount as stiff as the make-do provided by Delta will settle a bit in the first couple of weeks after installation.  I now find that when shifting to reverse the shift lever just barely impacts against the cigar lighter and the upper front corner of the central part of the transmission console (MkII).  I suppose I'll have to get under the car one of these days and stick a couple of shims between the transmission mount and the crossmember.

Sigh.  It's always something....

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 Posted: 05-05-2005 10:23 pm
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kneff
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My shifter impacts the console when shifted into 2nd. Is that a transmission mount-related issue? How can I tell?

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 Posted: 05-05-2005 11:38 pm
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Mark Rosenbaum
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Assuming that your transmission console sits at the normal height, then yes, most likely your car's transmission mount is at fault.  The rubber in the stock mount is fairly soft when new, and becomes softer still with age and long-term exposure to oil.  Usually the first warning of a too-soft transmission mount is when you start hearing thumps, clumps, or clonks from the middle or middle-rear of the car when making high-acceleration starts or shifts.  I'd think that contact with the transmission console suggests that softening has progressed past this point.

To evaluate your transmission mount, put the car on jack stands, support the tranny with a small jack, remove the transmission crossmember and spacer, and finally unbolt the mount from the transmission itself.  All this should take less than 15 minutes or so.

Moving the upper part of the mount by hand, with respect to the lower part, should be difficult.  If the rubber is badly cracked or eroded, if it feels soft, if the threads on the studs are damaged, or if there are any cracks in the metal, the part must be replaced.  This is a safety matter, as a sudden gross failure of the mount could conceivably shift the engine so much that the headers would contact the steering shaft and jam the steering.

Once the transmission mount is reinstalled or replaced, check for interference problems with (a) the exhaust header and the steering shaft/U-joint assembly, (b) the exhaust system and the floor of the car, and (c) the shift lever and the transmission console.  Take a look at the motor mounts, too, just to make sure they're all right.  When satisfied, the car can be lowered back to the ground.

 

Attachment: 4 spd trans mount.gif (Downloaded 333 times)

Last edited on 05-05-2005 11:38 pm by Mark Rosenbaum

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 Posted: 05-06-2005 04:10 pm
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Brett Gibson JH5 20497
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if you have a 5 speed it could also be a shifter bushing issue.

Brett.

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 Posted: 05-07-2005 01:33 am
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kneff
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I put the rear of the car up on jack stands, and this is what I found:

1) The transmission mount is visibly toast. The rubber is visibly deteriorated, almost split in two.
2) When I fire the car up, put it in gear and let the clutch out, it makes a horrible continuous clunking noise. I had my wife repeat the process while I observed from below (to the side), and it looks like the front driveshaft u-joint is banging against the u-shaped metal plate that surrounds it.

Obviously, I need a new transmission mount. Is Delta the best source?

I'm hoping that's all that is wrong (with that specific issue :-)). Should I be looking at anything else?

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 Posted: 05-07-2005 03:14 pm
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Mark Rosenbaum
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First, apologies for not making it completely clear that my transmission mount comments apply to 4-speed cars.  I'm slowly realizing that I have a tremendous blind spot in this area.

For the 4-speed tranny mount, a horizontal gap between the upper and lower rubber sections is normal.  This is what I tried to indicate with the color added to the line drawing in my earlier post.

There's very little clearance between the driveshaft front U-joint and the chassis stiffener plate, and under extreme conditions with some parts combinations the U-joint yoke may graze the plate.  This is more a minor design flaw than anything else.  But in Kneff's case, where the driveshaft repeatedly impacts the plate, it's pretty clear that something has gone wrong.

I'd certainly take a look at the motor mounts.  These do age, and unless they're in good shape, I'd replace them too.  Additionally, I'd look very closely at the transmission crossmember, the chassis stiffener plate, and their various mounting bolts (all of which go through the floorboards and appear to be welded in place).  Any significant damage to any of these parts would probably justify replacement.  Delta should have the the two sheet metal parts in stock.

AFAIK the transmission mount itself was used on the JH, probably various Sunbeams, and perhaps a few other Chrysler UK cars.  As for sources, in addition to Delta Motorsports and the JHPS (which here is Delta's sales agent), you could try the various Sunbeam spares sources.  Judging from the long backorder times, the UK supplier is of the 'we can start mining the ore for those sometime in the fall' sort, so I wouldn't think a direct overseas order would have much hope of success.  Finally, as I understand it, there are one or two companies that remanufacture such parts by casting new rubber on the metal bits, which I suspect would be rather expensive.

I'll close here by noting that although Delta's substitute tranny mount is a real PITA to modify and install (I'm guessing it's at least a 3 on Greg's Vino Scale), it does allow a JH to remain safely operational until the correct parts are again available.

 

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 Posted: 05-12-2005 02:46 am
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Paul Koehler
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Mark,

Have you put in the shims or a bushing around each mounting bolt yet? I think this would give you the correct hight, and not cause clearance issues with the shifter shaft. Calculations indicate a 0.5in. bush might just about be right. Also the bolts supplied by Delta would not be long enough, and have to be replaced by a set, a half inch longer.

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 Posted: 05-12-2005 04:51 pm
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Mark Rosenbaum
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Paul,

I'm lazy, the driving weather where I live is wonderful at the moment, and thus I have not yet shimmed up the new transmission mount I installed.  Did I mention that I'm lazy?  :^}

As you observe, the rear end of the transmission needs to be raised about 1/2".  Depending on the approach chosen, spacer(s) could be installed between the transmission and the mount, between the mount and transmission crossmember, or both.

According to my notes, the mounting holes in the transmission's aluminum tailshaft are on 4.0" centers and are threaded 5/16"-24 SAE.  One normally uses a coarse thread with aluminum, however, so my notes may be wrong.  It'd be easy enough to check from under the car.

The lower mounting holes in the new tranny mount are on 1.5" centers and are threaded 3/8"-16 USS.  The bolts provided by Delta to fit these holes were 3/4" long.

Local hardware stores usually carry 1/8" thick aluminum strip in a variety of widths and lengths.  This material is generally very soft and is readily cut, smoothed, and drilled by tools likely to be available to the average owner.  Obviously, one would require four thicknesses of this material to obtain the desired 1/2" spacing.  Aluminum plate would be preferable but is generally harder to come by.

For spacers to fit between transmission and mount, I'd use strips 1+1/2" wide and 4+3/4" long.  For spacers to fit between mount and crossmember, I'd use strips 2+1/4" wide and 3" long, so that there would be a proper footing for the mount.  For either approach, as you've noted, bolts about 1/2" longer than the originals would be required.  Grade 5 hardware would be entirely satisfactory.

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 Posted: 05-14-2005 03:02 am
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kneff
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Mark,

Is the transmission mount working OK without being shimmed? I just took my old one off, and I have a new replacement (from Delta). I was planning on modifying and installing it tomorrow. Without being shimmed, do you not have clearance problems with the chassis stiffener plate?


Thanks,
Ken

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 Posted: 05-14-2005 02:27 pm
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Mark Rosenbaum
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Ken,

In my particular case, I have not noticed any interference problems with the stiffener plate at the rear of the transmission tunnel even after some moderately ambitious driving.  However, there is tremendous variability in the stiffener plates Jensen used (not to mention, in the cars themselves!) so in many cases there may well be interference.  It would be prudent to make up some shims, just in case, and install them if they proved necessary.  With the aluminum strip shims I described in a previous post, this involves only a moderate expense and a little extra work.  There may well be better methods of shimming things, of course, but if so they currently escape me.

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 Posted: 05-23-2005 11:00 pm
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kneff
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I installed the Delta mount the weekend before last, and everything went so smoothly that I couldn't believe it! Many, many thanks, Mark, for your description of the required modifications!

I spent about 2 hours between modifying the transmission mount and the crossmember. For the mount, I used a combination of a round file and a Dremel. For the crossmember, I ended up using my drill press and a little creativity. A Bridgeport would have been better, but I managed with what I had.

I ended up making 1/8" shims out of bar stock. I used 2 above the mount and two below. For the ones above, I cut two 1.5" x 4.75" (1/8" thick) pieces and drilled 3/8" holes on 4" centers to match the holes in the transmission. For the ones below, I cut two 2" x 3" (1/8" thick) pieces and drilled 3/8" holes on 1.5" centers to match the holes in the crossmember.

I ended up buying new upper and lower mounting bolts, each 1/4" longer than the originals (or, in the case of the upper bolts, the ones supplied by Delta). I also purchased oversized washers to compensate for the large holes in the replacement transmission mount.

When I jacked the car up to reinstall, it took me no more than 20 minutes to install, align and bolt everything up! It was just too easy! The advantage to using a total of 4 x 1/8" shims is that I could easily remove 1 or 2 if I had a problem with header or steering column clearance. I didn't need to, but I like the flexibility.

Of course, I now have a problem with the exhaust pipes impacting the rear suspension bump stop, but I'm missing an exhaust mount so that problem might be easy to resolve.

All in all, I'm thrilled with how simple it was, once I reviewed Mark's notes and took careful measurements.

Ken

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 Posted: 06-02-2005 12:18 am
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Mark Rosenbaum
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Yet Another Followup.

As I noted in an earlier post, ever since my new transmission mount settled in, my car's shift lever hits the cigar lighter when shifting to reverse.  The town I live in is oddly lacking in aluminum vendors with a wide assortment of stock, so rather than spend an hour on the road to visit the nearest provider, I instead ordered a 2-foot length of 1+1/2" wide 6061T6 aluminum from 'Aircraft Spruce'.  As they did not have 1/8" thick bars in this width and material, I bought a 1/4" thick bar instead.  Usual disclaimers, but their price was surprisingly low and shipping charges were reasonable.

Using 1/4" rather than 1/8" stock, but otherwise following the plan that Ken Neff has followed through on, I fabricated a simple spacer -- cut to length, two slightly oversize holes, and deburring -- to fit atop the transmission mount.  Installation was easy enough, and the car's shift lever now just avoids contact with the cigar lighter when shifting to reverse.  Another 1/4" spacer, either top or bottom, would restore things to essentially their original orientation, and I may try that eventually.

I'll mention here that the bolts holding the upper side of the transmission mount to the transmission do in fact use a coarse thread rather than the fine thread my notes erroneously stated.  Well, I was suspicious about that.  In any event, the original bolt, Jensen P/N 65157, is fully identified as 5/16"-18 tpi x 3/4" long, Grade 5.  Mine were the same UK brand (GKN) used almost everywhere on my car, and initially had a black oxide surface.

Naturally, when a 1/4" thick spacer is added between transmission and mount, a somewhat longer bolt will be required if full engagement of the threads in the transmission foot is to be guaranteed (a highly desirable condition).  Fortunately, the holes in the foot go all the way through, so one can use a bolt quite a bit longer than necessary, if desired. I ended up using 1+1/4" long bolts as they were what I had to hand and I won't need new hardware if I should ever install an additional spacer at the top.

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 Posted: 06-02-2005 02:44 pm
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Ron Earp
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If you need some metals:

http://http://www.onlinemetals.com

Good stuff, delivered, and if you provide dimensions or drawings will make anything you want. Another good one is:

http://www.emachineshop.com/

Make anything you need with drawings/cad that you supply.  We use both of these a lot over on http://www.gt40s.com and they work well.  I have nothing to do with either one, just thought I post since Mark said he didn't have a lot of choices for metal working or metal suppliers.

Ron

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 Posted: 06-02-2005 03:02 pm
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kneff
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Last weekend I attempted to replace the engine mounts. I say "attempted" because I only succeeded in replacing the right (intake side) mount. I did not see any easy way to remove the upper nut on the left (exhaust side) mount.

The mount on the exhaust side looks fine, so what's driving me is really more an obsession with thoroughness than anything else. I'll admit that I didn't try too hard, as it was a holiday weekend and I had family visiting. I would like to complete the job, though.

Any words of wisdom on techniques, tools, etc. for reaching the upper nut on the left (exhaust side) engine mount? I'm hoping there's some non-obvious but clever way to get this nut off. Unlikely, I know.

BTW, on my car the mount I did replace seemed to be original ("Metalastic" on the donuts, etc.) but they are exactly the same thickness as the replacement mounts I purchased from Delta. I was very happy to discover this, as it obviated (love that word) the need for additional spacers. There was one spacer on the intake side, but none on the exhaust side.


Ken

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 Posted: 06-02-2005 03:52 pm
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Sander
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Common issue.  Take the tire off, remove the lower bolt on the engine mount, jack the engine as needed to access the upper engine mount bolt.  You'll need an assortment of open end wrenches and you'll find making the bolt rotate 1/16 to 1/8 of a turn a wonderful task for a few turns.  Try some PB Blaster or other lubricant.  As always use your head when jacking and placing stands.  Do not trust a 15 cent O ring on a hydralic jack, use good quality jackstands and give the car a good test shake before you try to get near/under it.

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 Posted: 06-02-2005 04:25 pm
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Mark Rosenbaum
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Ken, attached is a photo of the new exhaust side mount on my car.  It's hard to get to, and one needs to approach from underneath.  IIRC I used a standard-length Craftsman combination wrench to hold the nut in place while I turned the mount by hand (lower nut removed first, of course).  As mentioned in my initial post, I thought that a stubby wrench would be the best tool for the job as it would be much easier to maneuver it so you could gain access to the nut.

Sander's comments are entirely sensible, though in my case I didn't find it necessary to remove tires.  I've had both hydraulic and mechanical jacks fail on me, and I ALWAYS use jack stands nowadays if I'm going under a car that's been lifted off its wheels.  Being slowly crushed by a car is no fun at all.

Ron, many thanks for the pointers to
http://www.onlinemetals.com  and  
http://www.emachineshop.com/  .
I've heard of both but have not yet used either one.

Attachment: exh mount.jpg (Downloaded 142 times)

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 Posted: 06-02-2005 05:16 pm
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kneff
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See- I knew someone would have a clever answer! Putting a wrench on the top nut and then rotating the mount hadn't occurred to me. Of course, tightening up the new top nut won't be as simple. I think I'll go buy the stubbiest wrench I can find.

Where do you place jack stands in the front? I assume I will jack from the center of the front subframe (directly under the engine) but are there reinforced points for jack stands?

Thanks,
Ken

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 Posted: 06-02-2005 06:19 pm
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Mark Rosenbaum
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These mounts aren't intended to be torqued down all that much.  I'd think that 5 ft-lb would be adequate, which is basically what you can get if you have strong hands.  You might be able to get the nut a bit tighter with a stubby wrench or a socket on a flex handle, or you could try holding the nut and turning the mount with a strap wrench -- whatever works for you is fine.  For my car, I'm planning on re-checking things after a few months, but won't worry unless the nut has somehow worked loose.

I put the jack stands where I think they'll do the job and be out of the way.  For the front end this is generally beneath the inner pivot points of the lower suspension arms, though I've occasionally used the flat center part of the crossmember.  I've used the frame rails a couple of times, but I'm not really comfortable with doing that.  I don't use the sills at all -- a PO did, and consequently there are a number of bends in the sheet metal lip down there.  At the rear, I favor the rearward pivot points of the lower arms, or under the axle tubes just inboard of the brakes or suspension pickup points, depending on what I'm doing.

 

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