so I just got my tranny rebuilt at 152k, and I drove about 400 miles with it and it started slipping, but when i got my tranny replaced, the said they didnt replace the tranny cooler, they said it was clogged up and they tried flushing it out as much as they could and told me i needed to get one asap but never did. I got about 55 mph down the road and my tranny just like slips(like a thump)

Any help would be appreciated, thanks.

 

BUMP. any idea what it might be?

 

The rebuild may have been a bad one. Who did it?

These transmissions pretty much need a good transmission cooler to run properly. The factory one is barely adequate (if that), and when that one gets gunked up, good bye transmission. Without it, they will overheat easily, especially in O/D, as that is when they work the hardest.

My two cents: Get a new, better-than-factory tranny cooler. If it still slips after that, take it to the transmission shop and tell them they mucked up the rebuild.

 

Sooo, did they bypass the clogged transmission cooler or re-use it? (anything is possible!)

How's the trans fluid level look? Check it on level ground, with the engine running with the transmission in Neutral (<-- important!) and with the parking brake engaged. Use ONLY ATF +4 fluid to top it off through the dipstick tube if needed.

Unfortunately, a transmission fluid cooler is almost a requirement for a reliable long life with these transmissions. jasonw covered this pretty well.

If the fluid level is normal, then the transmission might be toast... Could be a bad rebuild. Or, it could have overheated. The first few hundred miles for a rebuilt unit is considered to be the break-in period. It probably wouldn't be very hard to cook the clutch packs during break-in period without a cooler (especially in OD). In this case, install a new cooler, and hope your shop will warranty the repairs if it's toast.

Good luck!

-JT

 

I'm going to say that there's a good possibility that your filter is plugged full of crap from the cooler,and your starving the pump of fluid. That is if it actually has enough fluid in the first place.

It could be a bad rebuild, that's 50/50.

A little info though..... OD doesn't increase heat in the trans causing it to go bad.
The torque converter lock-up is actually used to cool the trans. That's why the computer will hold third gear if the trans gets to hot. Being in third or OD with it locked up,reduces heat.

The reason the trans fails in OD while towing or hauling is because OD in itself is not a gear by itself. OD is more like a half gear. All your gears pass through the direct drive clutch which is right behind the OD clutchesat the rear of the trans.These clutches are held in compression by a large spring.

The comes when OD engages.......The piston pushes on the OD Clutches,compressing them and then also disengageing the direct drive clutch pack to use a set of planetary's to speed up the out put shaft. While in OD,your running at the loss of the direct drive clutches and replacing that with less than half the amount of clutches. The heat builds from the clutches slipping.

If they burn up bad enough,sometimes they get stuck,holding the direct drive spring released,and then there is no forward gears or reverse because everything but OD transfers through direct drive clutches.

 

So the shop said you have a bad cooler but they didn't replace it? That doesn't sound right to me. Why would the shop not have replaced it with the rebuild?

 

Depends on which one it was. The primary cooler (and the one that 99% of trucks will have) is in the radiator. Replacing it requires replacing the radiator. If it's the aux cooler they were talking about... well, that one could be bypassed.....

When I worked at the dealer, is a standard procedure to thoroughly flush the tranny cooler lines, etc, with a trans rebuild. If you didn't, chances were real good you were going to see the car back within a hundred miles.

 

thanks alot for you help guys, I called the place that did my transmission and he said that I need to get that new transmission cooler asap, I drove my truck today and it didn't slip as much. I did put a qt of tranny fluid in though because when i checked it in neutral it was on "min". im going to buy a heavy duty cooler for it tomorrow, will that make a difference or do you think my tranny is toast cause I drove it with a bad cooler?

 

which one is bypassed? Do you have the aux cooler between the radiator, and a/c condenser? Driving it with NO cooler is VERY bad.

 

Mine has the cooler in front of the radiator, and I had it replaced when my tranny was installed. Is there also one in the radiator, or is that only if there is not one mounted in front of radiator????