[valiant67]

Part of the reason is they'd been building the same basic car since the 1976 Aspen and Volare, only with different trim.
The design has a few basic weaknesses.
First is the front suspension. The transverse torsion bar setup did not hold up well as the cars aged, but in a babied Fifth Avenue it may be OK. Otherwise, wear is often associated with chronic inside edge tire wear.
Next is the drivetrain. The plastic timing chain gear, lockup torque converter in the transmission and 7.25" rear axle are all weak spots. Timing chain is an easy fix, torque converter not so easy. The rear axle can be fixed with a swap to an 8.25" axle and some even had this better axle from the factory. The complex computerized ignition and feedback carb can have problems, but it's not really that difficult to make work right or swap out.
Last, the cars are not efficient. Lack of fuel injection and no overdrive in the transmission meant a 2.2 gear in the rear axle. The car lugs in town and does OK on the highway. But it's far form easy on gas for the size it is.

With reasonable care, they are pretty durable though I'm sure many are junked for transmission or reaer axle issues if they are beat on.

 

[jlcantor]

Valiant67 raises some good points about efficiency and performance and I believe the mechanical weaknesses are also accurate. That said, of all the cars I've had, my '87 5th Ave was by far the most reliable. Bought it with 95K and sold it five years later at 250K and the only two things I did beyond oil changes was replace the timing chain (mostly as a precaution) and the computer that runs the carb after it failed. They engine still ran well and didn't burn or leak a drop of oil at the end. The only reason I sold it was I had inadvertantly put the wrong coil in it which caused stalling issues after a few months. Unfortunately since I had just done a tune-up, I never thought to go back and look at the coil again. They buyer called me two weeks later with the news on the fix. :facepalm:

 

[Bearhawke]

According to Ed Sanow's books on Mopar police cars: the 1988-89 (possibly late 1987 as well) 5th Ave's/Diplomats/Volares actually had quite stout K members............the sagging flaws were finally corrected.

 

[mydodgedip]

I've never had a K frame issue and I've had a ton of Police and civie M bodies (And I beat the shucks out of most of my cars). I got cut off in the rain in one of my Diplomat AHBs and slid over an island at like 35. Jumped the curb up, jumped it down and half hopped the curb on the other side of the island. Didn't even need an alignment.

 

[valiant67]

Unfortunately I had a saggy late 1988 (it was late enough to be an airbag car) so it can still happen. And it was an Ohio State Patrol car, they took good care of their cars.

 

[mydodgedip]

yep, seems like there was no real rhyme or reason for the sag, just some people had problems some didn't.

 

[geraldg]

I have owned at least 6 of these and never had a problem with the front ends, right now have a 87 fifth ave with 123K and it drives beautiful. Moat of the problems I have hear of where with the police package and Curtis Regave has a article on allpar about that. And as far as the plastic timing gear chrysler used them on alot of cars I had a 69 sport fury with the 383 engine and it had the plastic timing gear which wiped out on me. And the rear end if you didn't hot rod it they lasted just fine never had a problem with one.

 

[valiant67]

Believe what you want, but the 7.25" axle is junk. Years ago, I bought a little old lady 1982 New Yorker Fifth Avenue with less than 80k miles from an estate. At the time she passed away, the car was sitting at a dealer because the 7.25" axle had failed. Since the dealer had not started work on the car, I bought the car from the estate and had it hauled to my shop where I put an 8.25" axle in it.

Some Fifth Avenues, like the 1989 I had, came with an 8.25" from the factory, but most did not.

Most of the weak points (plastic timing chain gear, 7.25" axle and sometimes the lockup torque converter) of the Fifth Avenue were eliminated in the police versions of the M body.

 

[mydodgedip]

seems lots of 88s and 89s came with 8 1/4s, must have figured that they had them, might as well use them. I never blew up a 7 1/4 personally but I've seen enough of them blown up (and sold a couple 7 1/4 rears) to know that they fail.

 

[geraldg]

like I said the plastic timing gear gear was used on alot of chrysler products. And the rear end I have owned at least 6 of them and never,never had a problem. So to me they are a reliable car. I have only good things to say about them.

 

[Tom Dawson]

I had an 81 Diplomat that had a very tired /6 and a 8.25 rear with 3.2 gears in it(it still had the factory tag on it)
Tom

 

[Fifth87]

I was fortunate to not lose an axle or have timing chain issues with any of the M-Bodies I had. Suspension problems, though- that's another story.
My most recent, an 87 Diplomat- I swear must have had the k-frame issue as it ate front tires rapidly even after replacing the ball joints, tie rods, etc. It also would not hold an alignment for more that 5K miles. It also had vibrations at highway speeds that none of the others did. I picked it up with 39K on it- so the old lady that had it before must have been really rough on it. Or it might have to do with the bombed out roads in MA where I lived at the time. Otherwise, I love the cars longevity and durability.

 

[mydodgedip]

do you have a good front end guy? Some people have no clue how to line them up correctly. I'm lucky to have a guy who used to work on most of the police cars in the area during the 80s and remembers what to do.

 

[Fifth87]

do you have a good front end guy? Some people have no clue how to line them up correctly. I'm lucky to have a guy who used to work on most of the police cars in the area during the 80s and remembers what to do.

I envy you!
No, unfortunately. I would shop around and ask specifically " Are you familiar with transverse torsion bar Chrysler products?" followed with, "Do you know how to adjust the ride height?" Always got blank stares, even when I'd specify the model. So I'd end up setting the ride height and took it to one who got it into the range of specs, but wouldn't try to get it the same from side to side. The car always would pull, but it would trade sides, never would know whether it would go right or left. I ruled out brake components after they were all replaced. I figured the specs needed to be as close as possible from side to side to prevent that- but knowing the car had a front end collision early in life, I always wondered if something was tweaked. Has your guy let you in on any tips/secrets to doing it correctly?
I've been Mopar free since April- I swear I'm having withdrawals!

 

[Kevman892]

I've got a similar car, 2 things I've had problems with.. The ignition, horrible from factory.. The Mopar kit ran me about $160 it was Pretty easy to install, too.

The other problem is the rear leaf springs.. The front eyelet is oval, instead of round, I had one broken one, and it's almost impossible to find a main leaf, It ran me about $200 for a new one, and a rebanding.

 

[geraldg]

do you have a good front end guy? Some people have no clue how to line them up correctly. I'm lucky to have a guy who used to work on most of the police cars in the area during the 80s and remembers what to do.

hey I am lucky bearhawke lives by me .

 

[mydodgedip]

I've had around 15 M bodies and never had one lean burn problem. Most people have carb problems that they can't figure out and swapping the lean burn and carb fix the problem with the carb and it gets blamed on the lean burn.

Only had one broken spring, but the car was incredibly rotted out. Local yard had multiple sets of springs cheap around here.

 

[Fifth87]

I've had around 15 M bodies and never had one lean burn problem. Most people have carb problems that they can't figure out and swapping the lean burn and carb fix the problem with the carb and it gets blamed on the lean burn.

Only had one broken spring, but the car was incredibly rotted out. Local yard had multiple sets of springs cheap around here.

A few sagging springs, but none broken. Lucky for me- these cars are gone from yards here.
One bad mixture control solenoid, one broken carb wiring harness at the connector and one bad lean burn sensor ( can't remember which one) The bad wiring harness took awhile to figure out, pretty straightforward otherwise.

 

[nickdalzell]

I still have my 1984 Fifth Avenue, although the paint has worn to beater status, and i have put that car through it all and it still runs great. i did replace the lean burn with a points system long ago and never have anymore trouble. i am NOT a big fan of the Carter BBD Feedback Carburetor. they also used the same lame junk on the AMC Spirit/AMX in the '80s and it's pretty much crap (although the Spirit/AMX has a 'Carb Check' lamp to alert you to a problem while the Fifth Avenue just runs like crap)

Aside that and what Valiant said, they seem to hold up rather well. unlike the Cadillac Fleetwoods and Buicks, there was far less 'gadgetry' to mess up. Chrysler put more into aesthetics in their Fifth Avenue 'luxury' sedan than GM and Ford ever did. if you think Lean Burn is awful, try the early CCC (Computer Command Control) on the Fleetwoods in the late 70s and early 80s.

The beauty of the M-bodies is that any part from any 318 V8 from the late 60's on has parts that fit. they are the last rear wheel drive Mopar to have the all-cast iron engine block and heads. the trucks got aluminum heads when they switched to Magnum engines. the points system in mine (just the distributor and carb, the rest was tossed) came from parts of both a late Dart and an old Champion motor home that had a 318 in it.