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| Joined: | 03-12-2005 |
| Location: | Kingman, Arizona USA |
| Posts: | 532 |
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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 08:20 pm by Mark Rosenbaum