Big Clunk! when shifting 95 SC into reverse when cold

Hello and thank you in advance for any advice.   I have a 95 SC that otherwise runs perfectly.  I have 130K miles.  The car has recently started registering a loud clunk in the mornings when I shift into reverse to back out of the carport.  If I instead shift into drive, then reverse, it does not clunk.  It seems to shift and drive just fine.  I asked a mechanic, and he of course said i needed a new transmission.   My reading tells me that a broken motor mount would cause a clunk all the time, not just when the engine is cold.  Any thoughts?  Thanks.

Sounds a little odd but I wouldn't rule out the mount.
You say when cold, but is that also high idle?
High idle would cause more movement/clunk.
Does your transmission have any other symptoms?
Maybe check fluid condition/smell & level and then take a real good look at your mounts.

Exactly my thoughts, Jeff.

What is the temperature when it is happening? My car does it when it is really cold out after sitting for a long time and has done it for many years. It doesn't do it once the engine is warmed up. I always figured it was due to the high idle when it is cold, cold transmission and maybe due to worn engine mounts. If that is your only problem I wouldn't think your transmission is bad. Take a look at your engine mounts and if they look good I wouldn't worry about it. I'll shift it from park to drive and then to reverse to try to prevent it from clunking as it isn't a good feeling when it clunks.

Thanks. The fluid looks good, smells good, and I tossed in some Lucas ATF conditioner. It clunks, hot or cold, and this is pretty much the warmest time of year in Seattle. I will have the mounts inspected.

jbird wrote:

Sounds a little odd but I wouldn't rule out the mount.
You say when cold, but is that also high idle?
High idle would cause more movement/clunk.
Does your transmission have any other symptoms?
Maybe check fluid condition/smell & level and then take a real good look at your mounts.

I'm with jbird on this one so far -- +1 on the mounts especially the rear transmission mount and the drivers side mount that's hidden in the wheel well.

Also -- I dimly recall a TSB that said something about resetting the adaptations in the PCM to remedy this but have *no* details. Might want to investigate by buying a short subscription to AllData or some such where you can look them up for yourself. Dealer service techs are tired of customers that argue that TSBs are recall notices (they are *not*) and so want the TSB fix for free (it is not free, unless the TSB says so; it is frequently not that costly though, such as the extra magnet for the pan of the 4T65E to solve a TC stuck on condition - which is provided only in conjunction with a fluid flush or other transmission service)

What happens - in general as the transmission warms up the PCM changes the transmission clutch apply pressures to suit and the clunking goes away, depending on what adaptations the transmission has adopted - which depends a lot on how you drive.

For me I've found that every so many years it pays to have the techs at my local GM dealer simply reset the transmission adaptations to factory specs. It is convenient for them to do so when flushing/filling the transmission, which I have done every 45-60K miles (I have 370 K at the moment).

Bad news good news.  I took it to a recommended shop to check all the mounts.  They called immediately and said the rear trans mount was bad, and it would be $394 to replace it.   I hate crawling under cars these days, so I agreed.  Unfortunately, when I got to the shop that evening, they said they had good news and bad news.  The bad news was that the clunk was not fixed.  The good news was that they were only going to charge me $300.  They then diagnosed that the transmission would have to be replaced, and recommended a place that might charge only $2K.

The death of the transmission on an old car is often the death of common sense in choosing to repair it to keep it on the road.  Where I live, I often see Riv's sold for parts starting at $200.  

I am now at a crossroads, and my questions go to the core issues of owning one of these beauties.  Bridgitte (Blue 95 SC) needs an intake manifold, a job I planned to do myself (bought parts, including belts and a water-pump.)  Do I tear her apart and replace the transmission while I am fixing the intake? Should I sell her while she still runs?  Do I drive her until the transmission goes? (keeping a jug of distilled water with me at all times), and postpone any decisions until she is truly crippled?  She is otherwise in good condition, with about 135K miles, and I don't need her to be my daily driver.  I've had her for almost 3 years, and I certainly have got my money's worth of enjoyment out of her.

Hmm, the most expensive rear trans mount option on Rock Auto is $72.79. So, say it's $100 at O'Reilly's. How hard is it to change one of these? It looks like you could just support the engine, turn three or four bolts, and be done. Am I wrong? Is there really $200 of labor here?

We'll see what other board members say, but I'd get the number for the transmission shop but drive the car around for a while and see if there really is a problem with the transmission. If the car is otherwise in great shape, what else are you expecting to replace? Rivieras are well built and should last a long time. IIRC AlbertJ has 300,000 miles on his.

Jack the R wrote:

Hmm, the most expensive rear trans mount option on Rock Auto is $72.79.  So, say it's $100 at O'Reilly's.  How hard is it to change one of these?  It looks like you could just support the engine, turn three or four bolts, and be done.  Am I wrong?  Is there really $200 of labor here?  

We'll see what other board members say, but I'd get the number for the transmission shop but drive the car around for a while and see if there really is a problem with the transmission.  If the car is otherwise in great shape, what else are you expecting to replace?  Rivieras are well built and should last a long time.  IIRC AlbertJ has 300,000 miles on his.  

370,000 and counting.

There is a how-to for changing the mounts with hand tools, on this site. Not even the local GM dealer has charged me $300 for replacing that rear mount.

There is a service memo about that reverse clunk. If I remember it right, if you don't like the clunk someone with a Tech II can restore factory settings then make the PCM adjust the apply pressure. Your mechanics probably have forgotten more that I'll ever learn at this point about cars, BUT frankly I'd phone an older GM dealer within say 50 or 100 miles of you. The older dealers tend to keep more experienced mechanics, who've probably seen this before and corrected it way back when. Phone first.

One last thing - do you know how to easily check motor mounts? You need an accomplice but basically you stand on the brake so the car does not move then you put it into reverse, blip the throttle, then put it in say first, and blip throttle again. If the engine rocks too far (I forget, I think an inch or 2) your mounts are basically done.

albertj wrote:

 Not even the local GM dealer has charged me $300 for replacing that rear mount.

Well there you go. To the OP, take AlbertJ's advice. The mechanics you've been using may just be trying to shake money out of you.

Jack the R wrote:

albertj wrote:

 Not even the local GM dealer has charged me $300 for replacing that rear mount.  

Well there you go.  To the OP, take AlbertJ's advice.  The mechanics you've been using may just be trying to shake money out of you.

...water over the dam so to speak, his rear mount's replaced and the shop is talking 'new transmission.'

Really, for the reverse clunk I'd talk to a shop with some experience working on the GM 4TXX transmssions.

These may be informative (same/similar transmission)

https://batauto.com/threads/99-lumina-clunk-into-reverse.7152/
https://www.alldatadiy.com/TSB/07/950704fd.html

David Jennings wrote:

Hello and thank you in advance for any advice.   I have a 95 SC that otherwise runs perfectly.  I have 130K miles.  The car has recently started registering a loud clunk in the mornings when I shift into reverse to back out of the carport.  If I instead shift into drive, then reverse, it does not clunk.  It seems to shift and drive just fine.  I asked a mechanic, and he of course said i needed a new transmission.   My reading tells me that a broken motor mount would cause a clunk all the time, not just when the engine is cold.  Any thoughts?  Thanks.

Hey David: My Riv. does exactly the same thing at exactly the same time, 1st thing when cold. Rest of the time, no clunk. Maybe if you discover the problem, I can glean your experience to solve mine.

Current plan is to reset the codes to see what happens. Have to figure out my Radio Code first, or figure out how to reset it before unhooking the battery.

slugranch wrote:

David Jennings wrote:

Hello and thank you in advance for any advice.   I have a 95 SC that otherwise runs perfectly.  I have 130K miles.  The car has recently started registering a loud clunk in the mornings when I shift into reverse to back out of the carport.  If I instead shift into drive, then reverse, it does not clunk.  It seems to shift and drive just fine.  I asked a mechanic, and he of course said i needed a new transmission.   My reading tells me that a broken motor mount would cause a clunk all the time, not just when the engine is cold.  Any thoughts?  Thanks.

    Hey David:  My Riv. does exactly the same thing at exactly the same time, 1st thing when cold.  Rest of the time, no clunk. Maybe if you discover the problem, I can glean your experience to solve mine.

Update: Had rear transmission mount and one front trans. mount and crossmember bushings (because the had to remove crossmember to change mounts) replaced, and clunk has been fixed. I would question your mechanic if he really feels like you have to have a new tranny.

I believe the least expensive solution to this problem, that I have found, is to back the car into the driveway while it's still warm.
Then when you leave in the morning you don't hear or feel any "clunk".

But, I guess changing the mounts is a good idea also.