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Design Flaw Rusts Rear Mounts

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Rob Spiegel
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Re: Design flaws and rusted motor mounts.
Rob Spiegel   2/3/2012 3:40:30 PM
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The 1970s were rough years for the automotive industry. The workers on the line were an angry bunch. There was plenty of worker sabotage going on. Not a happy time in Detroit.

At the time, I worked for Celanese Coatings. They produced much of the paint for Chrysler. In the lab, we tested paint against multiple environments. The salt spray was the worst. At the time there was no way to protect paint against salt. Cars in Detroit started to rot through the floorboards after five or six years.

David12345
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Re: Design flaws and rusted motor mounts.
David12345   2/3/2012 4:17:55 PM
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William K.:

In the mid-1970's I built-up a V8 Chevy muscle car and Chevrolet had recently come out with "safety mounts" that had interlocking steel T and slot features to limit travel even when the rubber failed.  This was popular with performance oriented applications; although, serious racers also went to either a back-up movement limiter (chain or steel cables), or else solid steel mounts (which transmitted unacceptable engine vibration for all but the most hard-core race-only cars, even rattling your vision).

What I only learned recently was that this "Safety Motor Mount" was precipitated by an investigation in 1971 of 127 Chevrolet motor mount failures resulting in 63 accidents and a few fatalities.  The result of this National Highway Safety Transportation Board investigation was the motor mount redesign, and a recall where a steel limiting cable was installed (presumably cheaper than retrofitting new motor mounts).  What made this type of failure a greater problem leading to the investigation was the cascading problems from the motor mount failures.  The lifting engine pulled the throttle linkage "on" further lifting the engine even more. The engine movement also locked-up the transmission linkage preventing a shift into neutral, and the engine movement sometimes ripped loose hoses to the power brakes and power steering making steering and braking MUCH more difficult.  Hmmmm, sounds like an accident waiting to happen similar to the more recent drive by wire Toyota throttle issues. 

I guess Chrysler anticipated this problem better, or experienced it sooner with their monster 429 Hemis.

I know the GM and Ford sub-frame module constructions, such as in the Ford Taurus and GM X body cars, did allow for better road vibration isolation in a unibody car construction as well as provided a convenient module for efficient assembly.  I don't think the concept is flawed, but it does need to executed properly, and reliably, or things can become very unglued in an ugly way.

David12345
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Re: Design flaws and rusted motor mounts.
David12345   2/3/2012 5:15:19 PM
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Information Correction:

The National Highway Traffic Safety Administration (NHTSA) Case IR 162 correspondance with GM between December 1970 and January 1971 indicated 172 reports of failed motor mounts, with 63 accidents and 18 injuries. There were NO reported fatalities.

I apologize for my misinformation from my inaccurate memory of the report.

Ann R. Thryft
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Re: Another engine mount nightmare
Ann R. Thryft   2/6/2012 12:53:09 PM
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Thanks for your story, David. The Northern California mechanic who told me about the 2 destroyed engine mount gaskets looked at my like I was crazy for driving it like that for so long. This was the first time I'd taken my car to him, and it was for a once over checkup. When he explained the situation, I must have turned pretty pale, and assured him I was not in the habit of driving my car in such a dangerous condition. Maybe he also thought I'd been hot-rodding it, although that was pretty unlikely by that time in my life. I can say I've since never taken any unusual car sounds for granted, especially those that occur at 65 mph.

I like the safety motor mount idea!


Rob Spiegel
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Re: Design flaws and rusted motor mounts.
Rob Spiegel   2/6/2012 3:34:40 PM
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Thanks for the look-up on the statistics, David. That certainly helps with clarity.

David12345
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Re: Another engine mount nightmare
David12345   2/7/2012 8:51:16 AM
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In most cases, (as in my parent's 1964 Oldsmobile) I believe the engine mounts usually fail due to petroleum products (usually engine oil, or power steering fluid leaks) deteriorating/weakening the bonded rubber vibration isolation engine mounts. "Hot rodding" can be the straw-that-broke-the-camels-back. Alternatively of course, with a very stout engine being raced hard, even a new mount can be broken (also a frame can be bent by a racing engine without sub-frame connectors and a robust roll-cage.).

In the case of the Oldsmobile, I believe (based upon examination of the worn failure surface) the "hot rodding" just identified a problem that was already there for some time, but undetected.  I do not feel I broke their mounts, but the identification of the problem also pointed-out that I was "hot-rodding". Even though this action was somewhat mild, it was contrary to their boundaries.

As a point of interest, to address the root cause on my parent's car, I also replaced the leaking power steering hoses, and valve cover gaskets, to get rid of all the fluid leaks.  That particular car was still going strong at 199,000 miles when I sold it to a friend. He still had no problems with it by 230,000 miles when I last saw him in 1984!

streetrodder
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Re: Another engine mount nightmare
streetrodder   2/7/2012 10:51:47 AM
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By my tag, you can guess my hobby.

This was a well known issue with Chevrolet V8s a long time back.

Along with my 1940 Chevy street rod, I have a 69 chevy pickup.  The pickup has a cable on the driver's side of the engine - it bolts to the exhaust manifold, runs through a hook in the frame and back up to the mainfold.  It's only needed on the driver's side because the engine torque lifts the driver's side and compresses the passenger side.  The angle of the mounts limits the 'spin' factor and act as pivot points.

Aftermarket motor mounts have interlocking steel plates that eliminate this problem.

Ann R. Thryft
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Blogger
Re: Another engine mount nightmare
Ann R. Thryft   2/7/2012 12:31:56 PM
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The fluid that destroyed my engine mount gaskets was transmission oil, so that fits. I made sure my new mechanic fixed the hose leaks that had caused the problem, and also checked all other hoses and gaskets. I've been pretty proactive about doing so on all my cars since then.


David12345
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Re: Another engine mount nightmare
David12345   2/7/2012 2:13:34 PM
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Streetrodder,

From what I read about the 1971 National Highway Traffic Safety Administration (NHTSA) report to GM, the drivers side cable you mentioned may have been a dealer installed recall fix to the 1969 Chevrolet V8 engine mount prior to the "Safety Mounts" from the factory with interlocking steel plates starting around 1972.

Another example: The rear mount on the flat 6 Corvairs had interlocking steel backup structure from the start.  When these rubber parts failed the T steel would drop onto the sides of the steel channel slot.  This would then transmit much more engine and road vibration to the passengers until replaced, but without the steel backup the engine would have fallen onto the road.  To check, we would lay a straight edge across the rear mount. It should rest on the center steel T without touching the mount side rails.  If it touches the side rails the rubber had failed and the center T has dropped. I didn't use this information much because my last Corvair had a 327 cid SB Chevy V8 in a mid-engine configuration, but this was relevant for several friends with Corvair engines, (e.g. - street Corvair with modified 60 over 172 cid, big valve heads, big turbo and water injection putting-out 250+ hp, and the most radical one was a drag-track VW bug "Snoopy" with a Corvair engine  custom twin-turbo putting-out over 600 dyno-horsepower at 12,000 rpm and around 30 psi boost for short time periods between blowing it or the transmission up).

RICKZ28
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Platinum
Rust on cars
RICKZ28   2/10/2012 4:43:33 PM
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1 saves
I lived in Maryland during the early 1980's.  All cars tended to have rust problems after a few years, due to the salt used on the winter roads.  The Honda cars seem to be the worst, frequently with rust through the body side-panels.  My 1975 Chevrolet Monza had its fair share of rust around the rear wheel wells.

I now live in Southern California, enjoy the wonderful weather.  My 13-year old 1998 Chevrolet Camaro Z28 looks just about brand new underneath...not one spec of rust.  It's rare to see rust on any car in SoCal, even close to the Pacific (salty air). 

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