Transmission Bang?

[N0DIH]

My Cad (91 4.9 Dev) has an interesting, although scary problem.

When you are in neutral or park, doesn't matter, although more prevalent in Park, and you rev the engine, all of a sudden BANG! it sounds like you just revved into the parking pawl (that tone, like when you put it in park and let the car roll into the pawl). The engine torques up when that happens. It is taking a lot of power when it does it. The bang sounds like someone just hit the engine/trans with a 20 lb sledge hammer, HARD. It will scare the crap out of you.

It strikes me as coming from around the chain belt for the transaxle, but it is hard to tell. All it takes is rev it up to around 1000-1500 and it will do it randomly, only once, and I guarentee you will take your foot off the gas!!!

Is the chain slack and whipping or catching on itself? Is the parking pawl loose?

It never does it driving. Only while you parked or in N and revving it, when you are working on it.

No, I don't practice doing it, but obviously it isn't a good thing.

Thanks!
Tom

[illumina]

perhaps the TC is loose or something may have been caught up inside there?

[cad_90]

on a *somewhat* related note.... i have a 1990 deville that makes a loud, disturbing sound almost every time i start it.

sound like the same kind of sound you are hearing, but it comes from somewhere more near the rear of the car. like someone took a sledge an hit the underside of the car.

no, it;s not backfiring. i verified this. the system that pressurizes the air ride shocks is not hooked up or even working, so its not that. there is no other moving part back there, when the car is not driving. this is before i even shift into drive, and i am not revving it.

any idea whatsoever what this could possibly be?

exhaust blockage? fuel lines pressurizing and moving? brake lines doing a similar thing? trunk release solenoid? fuel door solenoid?

i can't think of anything else plausable.

plz help.

[BeelzeBob]

Originally Posted by N0DIH

My Cad (91 4.9 Dev) has an interesting, although scary problem.

When you are in neutral or park, doesn't matter, although more prevalent in Park, and you rev the engine, all of a sudden BANG! it sounds like you just revved into the parking pawl (that tone, like when you put it in park and let the car roll into the pawl). The engine torques up when that happens. It is taking a lot of power when it does it. The bang sounds like someone just hit the engine/trans with a 20 lb sledge hammer, HARD. It will scare the crap out of you.

It strikes me as coming from around the chain belt for the transaxle, but it is hard to tell. All it takes is rev it up to around 1000-1500 and it will do it randomly, only once, and I guarentee you will take your foot off the gas!!!

Is the chain slack and whipping or catching on itself? Is the parking pawl loose?

It never does it driving. Only while you parked or in N and revving it, when you are working on it.

No, I don't practice doing it, but obviously it isn't a good thing.

Thanks!
Tom

This is a sure sign of a worn sprag clutch. The clutch overruns normally when when the engine is revved in neutral the sprag has to overrun at a faster speed and as it wears it will sometimes momentarily engage and jerk the componenets it is attached to in the trans.

There is no solution except to pull the trans and replace it.

Stop revving it up in neutral. Now that you know that it does this do not do it again. The trans may live for tens of thousands of miles. It is not necessarily a sign of am impending trans failure...but...if the sprag breaks the trans will loose drive and it will have to be rebuilt at that point. The next time you rev it up and it grabs like that it may break the sprag clutch so.....


It isn' the chain or anything like that...it is the sprag clutch for sure.

[BeelzeBob]

Originally Posted by cad_90

on a *somewhat* related note.... i have a 1990 deville that makes a loud, disturbing sound almost every time i start it.

sound like the same kind of sound you are hearing, but it comes from somewhere more near the rear of the car. like someone took a sledge an hit the underside of the car.

no, it;s not backfiring. i verified this. the system that pressurizes the air ride shocks is not hooked up or even working, so its not that. there is no other moving part back there, when the car is not driving. this is before i even shift into drive, and i am not revving it.

any idea whatsoever what this could possibly be?

exhaust blockage? fuel lines pressurizing and moving? brake lines doing a similar thing? trunk release solenoid? fuel door solenoid?

i can't think of anything else plausable.

plz help.

More likely the exhaust system grounding and it moves when the engine rocks at startup....

[cad_90]

exhaust grounding? electrical grounding, or how it is attached to the car?

and it happens like 10-15 seconds after startup, not when the engine rocks.

[BeelzeBob]

Grounding as in banging gainst the underbody somewhere....

The exhaust system is suspended by rubber isolators to isolate any vibration. If the exhaust has been bent or something it may be touching the underbody and the noise you hear is the exhaust hitting somewhere when the engine starts.

Have someone else start the car the next time or reach thru the window and start it so you can run to the back and listen to get a better idea what is going on.

[bschelle]

My 91 Eldo w/105K has all of the sprag symptoms. I plan on driving it until I HAVE to fix it. Should I also avoid WOT or any other driving actions?

[BeelzeBob]

Originally Posted by bschelle

My 91 Eldo w/105K has all of the sprag symptoms. I plan on driving it until I HAVE to fix it. Should I also avoid WOT or any other driving actions?

I would tend to take it as easy on it as possible....

The main thing to avoid is revving it up in neutral where it wants to bang...just do not do that.

[cl1986]

Originally Posted by N0DIH

My Cad (91 4.9 Dev) has an interesting, although scary problem.

When you are in neutral or park, doesn't matter, although more prevalent in Park, and you rev the engine, all of a sudden BANG! it sounds like you just revved into the parking pawl (that tone, like when you put it in park and let the car roll into the pawl). The engine torques up when that happens. It is taking a lot of power when it does it. The bang sounds like someone just hit the engine/trans with a 20 lb sledge hammer, HARD. It will scare the crap out of you.

It strikes me as coming from around the chain belt for the transaxle, but it is hard to tell. All it takes is rev it up to around 1000-1500 and it will do it randomly, only once, and I guarentee you will take your foot off the gas!!!

Is the chain slack and whipping or catching on itself? Is the parking pawl loose?

It never does it driving. Only while you parked or in N and revving it, when you are working on it.

No, I don't practice doing it, but obviously it isn't a good thing.

Thanks!
Tom

Hmm, that is really funny, my 91 deville with 4.9L did same exact thing starting at around 170,000 miles. The thing is, mine was trying to shift into 1st gear while in park or neutral. I sold the car with 189,000, during the summer it wouldnt do it. Winter is the problem. I am 95% positive that it is a valve not closing and causing it to try to go into first. One time the car even moved ahead a little because of it.

To get the most out of the tranny, start the car and immediatly put in Drive. You could set the parking break first, but this is a problem because the car automatically releases the brake when started. Maybe you can change the parking break back to old style somehow.

Main thing is, your tranny is going to go. When?? Not sure. We drove ours for over a year like that.

[N0DIH]

Any advice on getting a core trans to rebuild?

One with good gearing already that I can rebuild and prepare to drop in?

The 91 up's in Cadillac and 92 up in most all other 4T60E cars were "E" trans, electronic controlled.

Can a 4T65E fit and work? If not, why?
If not, what will make a 4T60E survive harder life? I want it to last forever....

I am not abusive to my cars, but would prefer better gearing . I know I can change the link chain gears to 35/35 or 33/37 and not change the diff and get better gearing. The Deville Touring Sedan has the 35/35 ratio. So the final drive being 2.73, but the engine is not overdriving the trans BEFORE it gets to the final drive. (Tip on internal gearing was from a GM Dealer who had a trans guy on staff who rebuilt them in house, dealer was Buick dealer in Colorado Springs on Motor City Drive)

Ideally I would like around 3.33 or 3.73 gears. I spend 90% of my driving from 40 to 60 mph. So having those gears would make it a dream to drive.

Tom

[BeelzeBob]

Originally Posted by cl1986

Hmm, that is really funny, my 91 deville with 4.9L did same exact thing starting at around 170,000 miles. The thing is, mine was trying to shift into 1st gear while in park or neutral. I sold the car with 189,000, during the summer it wouldnt do it. Winter is the problem. I am 95% positive that it is a valve not closing and causing it to try to go into first. One time the car even moved ahead a little because of it.

To get the most out of the tranny, start the car and immediatly put in Drive. You could set the parking break first, but this is a problem because the car automatically releases the brake when started. Maybe you can change the parking break back to old style somehow.

Main thing is, your tranny is going to go. When?? Not sure. We drove ours for over a year like that.

I'll bet it was the sprag. When it grabs like that the inertia of the spinning elements inside the trans does tend to rock the car forward...but it is the sprag clutch causing that.

Good advice, though, to start the engine and immediately shift into gear so that the sprag will not have to overrun while the engine fast idles in neutral. The shift into drive or reverse will be far less traumatic to the trans than the sprag grabbing.

[cl1986]

That could very well be, im not sure what the sprag is but i will look into it.

Also, if i remeber right, starting and putting it into reverse didnt do anything to stop the sound, thats why i thought it was trying to go into drive. If you put it in drive, it wouldnt make the sound, even if you step on the gas. Only in weather colder than 40 F also, summer didnt do it at all. Good luck!!

[90devilleguy]

Originally Posted by bbob

I would tend to take it as easy on it as possible....

The main thing to avoid is revving it up in neutral where it wants to bang...just do not do that.

my car doesn't have a park or netrual problem but when i drive it for a long period of time and shift the car under heavy or moderate throttle the tranny will bang into second usually it only happens when i leave from a stop.

[cl1986]

Oh yeah, that reminds me, in the winter under heavier braking, it would shift really hard into 1st, felt like the tranny fell out of the car. If you slowed down slowly it wouldnt do it.