Auto trans not engaging after braking

02vertable · Oct 7, 2019

I've got a automatic 2004 gt, the transmission shifts fine, not particularly smooth, but acceptable. After braking hard without stopping like entering a corner, the transmission let's go like it's in neutral and wont re-engage for a second or two, it will just rev up freely and then snap back into gear. It only does this when it's hot which leads me to believe it needs thicker fluid, I added about quart of Lucas stop slip and that seemed to help. Any ideas on what I should do? Do a full Lucas treatment? New fluid? Torque converter? Primary clutch? Solenoid? Any helps appreciated, thanks.

Sluggie24 · Oct 8, 2019

I think using stop slip was a bad idea. Addatives like that cause the seals and clutches to swell to temporarily help slipping but most of them ultimately cause those same clutches and seals to start falling apart.

Was the fluid level ok? Any leaks? If you shift manually does it act the same?

If it were me I would do a pan off trans service with new filter and filter seal to see if that helps. If that doesn't help then the trans would probably need a rebulid.

02vertable · Oct 8, 2019

Sluggie24 said:
I think using stop slip was a bad idea. Addatives like that cause the seals and clutches to swell to temporarily help slipping but most of them ultimately cause those same clutches and seals to start falling apart.

Was the fluid level ok? Any leaks? If you shift manually does it act the same?

If it were me I would do a pan off trans service with new filter and filter seal to see if that helps. If that doesn't help then the trans would probably need a rebulid.

I'll probably end up replacing the fluid and filter. How much does a rebuild on one of these trannys end up costing?

Sluggie24 · Oct 8, 2019

I rebuilt 2 with performance internals. One cost less than $1k in parts and the other beefier build was less than $1500 in parts.

A stock rebuild would probably save $ in parts (unless some expensive internal parts need to be replaced due to damage) but would still be prone to some of the common issues the 4R70W has. You would also have to pay labor for the job unless you could do it yourself. If you cant do it yourself you can still save money by pulling the trans yourself and bringing it to a person to rebuild. (If they are ok with that, not all of them are)

02vertable · Oct 8, 2019

Sluggie24 said:
I rebuilt 2 with performance internals. One cost less than $1k in parts and the other beefier build was less than $1500 in parts.

A stock rebuild would probably save $ in parts (unless some expensive internal parts need to be replaced due to damage) but would still be prone to some of the common issues the 4R70W has. You would also have to pay labor for the job unless you could do it yourself. If you cant do it yourself you can still save money by pulling the trans yourself and bringing it to a person to rebuild. (If they are ok with that, not all of them are)

I think I'm going to start by replacing the fluid and filter, anything I should be looking for in there other than metal shavings? Are there solenoids I should replace while I've got the pan off? I've never opened a 4r70w before.

Sluggie24 · Oct 8, 2019

The problem you described sounds like air getting sucked into the system somehow when the fluid moves when stopping. Just do the fluid and filter first. Set the level correctly. See if that fixes it. It's the cheapest attempt to fix it. Look at the filter for cracks and at the filter gasket for a split.

Some fine metal powder on the magnet in the pan is normal but big chunks of material in the pan isn't good.

The 4R70W is a fairly easy trans to build and there are great step by step videos on youtube for rebuilding it if you ever decide to try.

Auto trans not engaging after braking

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