ok i just had my tranny fluid changed and a new filter and gasket were put on,we changed about 6-7 quarts so half got changed it feels alot smoother and drives alot lower in rpms then before,but my problem is that when i floor it like up to redline or about 4000 the car will shift like it should but when it switches gears it thunks into the next gear very harsh,more like a slam into the next gear,but the lower the rpm like 3500 it does it but not as harsh, below 3000 it's fine smooth shifting.what the hell is going on here i might try some lucas tranny fluid stuff ,it worked on my old taurus. but i don't like the way it does this at all.some clarification would be great.

ok i just had my tranny fluid changed and a new filter and gasket were put on,we changed about 6-7 quarts so half got changed it feels alot smoother and drives alot lower in rpms then before,but my problem is that when i floor it like up to redline or about 4000 the car will shift like it should but when it switches gears it thunks into the next gear very harsh,more like a slam into the next gear,but the lower the rpm like 3500 it does it but not as harsh, below 3000 it's fine smooth shifting.what the hell is going on here i might try some lucas tranny fluid stuff ,it worked on my old taurus. but i don't like the way it does this at all.some clarification would be great.


how long ago did you change the fluid and such? i know a fluid/filter change will help your tranny to shift firmer and better, but a "thunk"? i would just let it drive a few more miles to see if it gets worse, and go from there. check the vaccume modulator for restrictions in the hoses going to it. good luck, and if you use the lucas, let me know how it works out.

how long ago did you change the fluid and such? i know a fluid/filter change will help your tranny to shift firmer and better, but a "thunk"? i would just let it drive a few more miles to see if it gets worse, and go from there. check the vaccume modulator for restrictions in the hoses going to it. good luck, and if you use the lucas, let me know how it works out.
let's see about a week ago i did the tranny fluid change and i just drove it about 300 miles this weekend and it didn't get any better.where's the vaccum modulator?

let's see about a week ago i did the tranny fluid change and i just drove it about 300 miles this weekend and it didn't get any better.where's the vaccum modulator?

it is on the front of the tranny, it looks like a cannister about the size of a fist. follow a 3/16 metal line from the throttle body to the bottom/front end of the tranny. that should lead to it. you should make sure the vaccume hose is not restricted and in good shape. you stated that it shifts fine when not under WOT? does it do this at normal operation?

it is on the front of the tranny, it looks like a cannister about the size of a fist. follow a 3/16 metal line from the throttle body to the bottom/front end of the tranny. that should lead to it. you should make sure the vaccume hose is not restricted and in good shape. you stated that it shifts fine when not under WOT? does it do this at normal operation?

normal operation it's perfectly fine no shifting problems just basically WOT takeoffs it shifts harsh.

i should also add that it does it only when shifting from 1st to 2nd, any other gear is fine no problems.

the 1-2 shift is always the firmest on an auto tranny. when you changed out everything, it probably just removed some of the gummy residue and such, therefore letting your fluids to move more freely and alowing it to shift firmer at WOT. i would still look into the vaccume regulator to make sure it is clean and the vaccume lines are in good condition. as sometimes, when there is a lack of vaccume to that unit, shifting will be much firmer than you would like. in fact, i think it was an old hotrod trick to take it out completely so that it would shift wayyyyyyy up in the RPM range.BTW, did you do this yourself? or did you have it flushed?

had my friends dad do it for me at his mechanic shop took about 45 minutes to drain it put in new filter and gasket ,which was a crappy cork one so we ended up going to the dealer and getting a AC Delco gasket and it was fine.took about 6-7 quarts which i didn't think it would take that much but it did.i'll check the hose on the tranny, but is it different from the 4t60-e or are they the same for the vaccum hose.

had my friends dad do it for me at his mechanic shop took about 45 minutes to drain it put in new filter and gasket ,which was a crappy cork one so we ended up going to the dealer and getting a AC Delco gasket and it was fine.took about 6-7 quarts which i didn't think it would take that much but it did.i'll check the hose on the tranny, but is it different from the 4t60-e or are they the same for the vaccum hose.

all of them have the regulator, so yes, it should be the same. one question left...did he do a flush? or is it like you said, just a fluid swap?

no flush just fluid change of what ever was in the tranny by dropping the pan

i dont know if you should worry or if it is because of the free-flowing of the fluid that is causing this. is the tranny high mileage? if so, have you had the fluid changed before? and if so, how long ago was this? because any "thonk" would make me wonder. if it gets worse, then you may have a problem. if not, then i guess i would'nt worry about it. as long as it does not start to slip or lose drive or anything, you should be ok. you mentioned lucas before, but im not real sure the effects that would cause in this situation. i use the lucas for the oil, but have never done it for a tranny. i would be careful with that. good luck.

Hey 90devilleguy, I just changed the fluid, filter, and pan gasket on my 89 Sedan deVille which had not been done for about 50k (I know thats bad, but its a Cadillac). So the pan was nice and dirty from the lack of service etc, etc. I did notice similar simptoms to yours after the fluid and filter change with a qt. of lucas. Mine tranny ended up taking about 7 qts total (including the lucas) and after the service I noticed firmer shifts when giving the car about 1/2 throttle but without any thuds or such. When I am crusing along the car shifts smooth as silk. (I do have a code e39 for a tcc solinoid) Good luck with your car man.

Hey 90devilleguy, I just changed the fluid, filter, and pan gasket on my 89 Sedan deVille which had not been done for about 50k (I know thats bad, but its a Cadillac). So the pan was nice and dirty from the lack of service etc, etc. I did notice similar simptoms to yours after the fluid and filter change with a qt. of lucas. Mine tranny ended up taking about 7 qts total (including the lucas) and after the service I noticed firmer shifts when giving the car about 1/2 throttle but without any thuds or such. When I am crusing along the car shifts smooth as silk. (I do have a code e39 for a tcc solinoid) Good luck with your car man.
yeah i checked for codes,no codes were stored but i order tonite a new vaccum modulator and my friend's dad said that it could be the cause of it so will wait and see if it doesn't help it i'll bring it to a tranny shop and have them diagnose the tranny instead.which i have a felling that it will come to that.i also think that the guy that owned the car before probably never did the tranny flush or a fluid change and now that i am doing it all the gunk and stuff is gone and now the problem are going to preveil.

i dont know if you should worry or if it is because of the free-flowing of the fluid that is causing this. is the tranny high mileage? if so, have you had the fluid changed before? and if so, how long ago was this? because any "thonk" would make me wonder. if it gets worse, then you may have a problem. if not, then i guess i would'nt worry about it. as long as it does not start to slip or lose drive or anything, you should be ok. you mentioned lucas before, but im not real sure the effects that would cause in this situation. i use the lucas for the oil, but have never done it for a tranny. i would be careful with that. good luck.

car has just over 97,000 on it and i don't have service records from the original owner so,it wasn't discolored or anything when we dropped the pan so it might have been done in the last few years but there's no way to know.well anyway i ordered the tranny modulalor and it's arriving by tuesday so will see next week what happens.$75 for a ac-delco part where as autozone brand in stock was 16.99???i hope ac-delco makes the problem go away.i can tell that atleast the oil was changed regularly,i figured that the oil would have been black like my eldorado was when i had that,and i was wrong, the oil on this baby is golden even when the 3000 mark is close,and my eldo only had 94,000 on it!

car has just over 97,000 on it and i don't have service records from the original owner so,it wasn't discolored or anything when we dropped the pan so it might have been done in the last few years but there's no way to know.well anyway i ordered the tranny modulalor and it's arriving by tuesday so will see next week what happens.$75 for a ac-delco part where as autozone brand in stock was 16.99???i hope ac-delco makes the problem go away.i can tell that atleast the oil was changed regularly,i figured that the oil would have been black like my eldorado was when i had that,and i was wrong, the oil on this baby is golden even when the 3000 mark is close,and my eldo only had 94,000 on it!


make sure the hose to the modulator is in good shape too. and yes, for a caddy, i would definitly go for ac delco as opposed to off-brand parts. i just hope the modulator satisfys the problem on you ride. good luck, :cool: