Tranny Fluid Full, Put In 4 Low, Now Shifting Hard

[misweetrevenge]

ok so I topped off my tranny fluid a few days ago because it was low (I recently bought it and don't know why it is low. It hasn't lost fluid in the 2 months I've had it)

I put it in 4high every once in awhile on a straight neighborhood street to keep the parts moving and fluid flowing, well last night I put it in 4low as well. I know the gear ratios change in 4low but I feel like it revved up too high so I stopped and put it back into 2high. now all of a sudden it shifts hard and looks like the tranny fluid is way low again. It was dark out so I will be checking again tomorrow but is there any reason putting it in 4x4 would cause the tranny to lose fluid? specifically 4low?

It is a 91 GMC Burb with a 4L80E 4 speed auto (atleast thats I've read in the research I've done)

 

[375 H&H]

you do not need to put it in 4x4 to get the parts lubed. the '91 has a NP241 transfer case and it has an oil pump built into it that handles this job.

hard shifting in the 4L80e is often due to a faulty throttle position sensor. check to see if it shifts into overdrive. if no, replace TPS

but there may be a limp mode that needs cleared.

if your trans is low, check your transfer case. i'ts probably over full and the seal between transmission/transfer case is probably leaking.

 

[misweetrevenge]

you do not need to put it in 4x4 to get the parts lubed. the '91 has a NP241 transfer case and it has an oil pump built into it that handles this job.

hard shifting in the 4L80e is often due to a faulty throttle position sensor. check to see if it shifts into overdrive. if no, replace TPS

but there may be a limp mode that needs cleared.

if your trans is low, check your transfer case. i'ts probably over full and the seal between transmission/transfer case is probably leaking.

How full is my TC suppose to be? Is it the same as a manual transmission? At the fill hole?

 

[k5ryder]

How full is my TC suppose to be? Is it the same as a manual transmission? At the fill hole?

yes. if it starts rushing out on level ground then is overfilled

 

[misweetrevenge]

yes. if it starts rushing out on level ground then is overfilled

That's what I thought. Thanks. How hard or expensive is it to replace the seal between the tranny and tcase? I assume it's time consuming.

 

[owenst7]

That's what I thought. Thanks. How hard or expensive is it to replace the seal between the tranny and tcase? I assume it's time consuming.

You'll have to pull the tcase, which may or may not be a pain depending on your abilities, tools, etc. Otherwise, its fairly simple, just nuts and bolts (and heavy lifting). You will probably spend less than $20 in parts.

The slip yoke seal on the tcase might be a good thing to check out too. The bushing that the slip yoke rides on tends to wear out, and people just keep throwing seals at it. If the seal is worn out, I'd consider replacing the bushing too.

 

[misweetrevenge]

You'll have to pull the tcase, which may or may not be a pain depending on your abilities, tools, etc. Otherwise, its fairly simple, just nuts and bolts (and heavy lifting). You will probably spend less than $20 in parts.

The slip yoke seal on the tcase might be a good thing to check out too. The bushing that the slip yoke rides on tends to wear out, and people just keep throwing seals at it. If the seal is worn out, I'd consider replacing the bushing too.

Yeah if I open it up I'll be replacing any seals and bushings at the same time so I don't have to do it again. Are those the only two in there?