1988 Suburban Hard Shift After Using 4wd

Hello all.

I have an 88 Suburban v20, 3/4 ton, 4wd with 183,000 miles on what I believe to be the original motor and tranny. I havent owned it long, so I dont really dont the vehicle's history. It used to shift like a dream, however I was off-road yesterday and got stuck in the sand with my bald tires :banghead: , I shifted into 4 wheel high and low, and everything seemed to work great (thank god). I got myself out of the sand, got to secure ground, and when I shifted into 2wd, and got back on the road, it started shifting hard between 1st, 2nd, & 3rd gears. (It's also clunking now when shifting into Drive, and Reverse - never did that before either) I pulled over and checked for trannny leaks and any other visual problems, but found none. Any brain-storming ideas before I have it serviced, or should I just have the tranny flushed???? What would cause to start shifting hard after using 4wd? Thanks in advance........

No flush.
Just a pan drop and new filter.

What transmission does it have in it?
Gas engine?
Check TV cable and modjulator vacume if it has one.

No flush.
Just a pan drop and new filter.

What transmission does it have in it?
Gas engine?
Check TV cable and modjulator vacume if it has one.


Im not sure which transmission it has, Im almost embarrased to say that I dont know how to find that out. I know its not a 700R4 because it is only a 3spd. It does have gas engine.

350-400
350 has a square type oil pan with a modjulator valve on back and a TV cable from carb/TBI to transmission.
Check both and for vacuum to modj. valve.

400 has a long odd shaped oil pan and modjulator valve on right side.
Check vacuum hose and vacuum line to it and for good vacuum.
MT

It's a 350, 5.7liter, TBI..... Sorry should have posted that first. The modulator valve is on the back of the engine block, the tranny, or the oil pan? I will check the TV cable and modulator valve tonight. Thanks

Mod. is on the rear of the trans case just above the trans pan.

Hello all.

I have an 88 Suburban v20, 3/4 ton, 4wd with 183,000 miles on what I believe to be the original motor and tranny. I havent owned it long, so I dont really dont the vehicle's history. It used to shift like a dream, however I was off-road yesterday and got stuck in the sand with my bald tires :banghead: , I shifted into 4 wheel high and low, and everything seemed to work great (thank god). I got myself out of the sand, got to secure ground, and when I shifted into 2wd, and got back on the road, it started shifting hard between 1st, 2nd, & 3rd gears. (It's also clunking now when shifting into Drive, and Reverse - never did that before either) I pulled over and checked for trannny leaks and any other visual problems, but found none. Any brain-storming ideas before I have it serviced, or should I just have the tranny flushed???? What would cause to start shifting hard after using 4wd? Thanks in advance........


with the vehicle in neutral rotate drive shaft and check CV joints on drive shaft.....

block front wheels first !

UPDATE:
Tranny is Def. TH400, not 350.............

Knowing that,

U Joints, drive shafts, axels, etc all appear to check out. There are no obvious vacum leaks in the modulator, etc. I got up under the truck and realized that there are bolts missing in the strut rods that support the transmission and transfer case. (I hope I am explaining this right)

There are 2 rods that mount on the bottom/front of the transmission and then to the left and right motor mounts. The bolts are present on the transmission side, but are missing at the motor mount side, they are just kind of flopping around. THere is also a support rod that bolts to the transfer case and to the engine blobk just above the starter. Same deal with that one, its bolted to the transfer case, but the bolt is missing above the starter/engine block. Could these have vibrated out when getting stuck in the sand? I was getting some pretty bad wheel hop from not gaining traction in the sand. Anyone know what these bolts are called, what size, etc? I cant find any info on these on the internet, etc. Is it safe to be driving it with these unbolted? Could this cause the hard shift? Also, it has been leaking oil and tranny fluid whch is new. Thank again in advance...
:banghead:

UPDATE:
Tranny is Def. TH400, not 350.............

Knowing that,

U Joints, drive shafts, axels, etc all appear to check out. There are no obvious vacum leaks in the modulator, etc. I got up under the truck and realized that there are bolts missing in the strut rods that support the transmission and transfer case. (I hope I am explaining this right)

There are 2 rods that mount on the bottom/front of the transmission and then to the left and right motor mounts. The bolts are present on the transmission side, but are missing at the motor mount side, they are just kind of flopping around. THere is also a support rod that bolts to the transfer case and to the engine blobk just above the starter. Same deal with that one, its bolted to the transfer case, but the bolt is missing above the starter/engine block. Could these have vibrated out when getting stuck in the sand? I was getting some pretty bad wheel hop from not gaining traction in the sand. Anyone know what these bolts are called, what size, etc? I cant find any info on these on the internet, etc. Is it safe to be driving it with these unbolted? Could this cause the hard shift? Also, it has been leaking oil and tranny fluid whch is new. Thank again in advance...
:banghead:

on my sons 94 s10 4x4 when i did starter i found the bolt missing on support rod that goes to back of engine to side of transmission..the bolt on back of engine was a 3/8-16 thread i used a washer and medium lock tight to secure bolt ....the transmission bolt was loose but rusted in place so i had to use small torch to heat then i removed cleaed threads and installed with med. lock tight...


this could explain the sudden hard shift effect..also check that transmission mount very possible that is why those rod bolts are loose...

Well...Turns out I was 1qt low on transmission fluid. That fixed the hard shift, but not the clunking when engaging into park and reverse. Im almost positive I have a bad u-joint because of where the clunking sound is coming from (rear passanger underside). Is replacing a u-joint a 1 man job? I have never attempted it. Thanks

Well...Turns out I was 1qt low on transmission fluid. That fixed the hard shift, but not the clunking when engaging into park and reverse. Im almost positive I have a bad u-joint because of where the clunking sound is coming from (rear passanger underside). Is replacing a u-joint a 1 man job? I have never attempted it. Thanks


this is an easy job for a person that has been shown how to do this ... some tools will be needed to remove and install U joint without damage to drive shaft.... this is not an expensive repair so i would say for you to have this done by a repair shop...


when removing drive shaft make sure it is marked so that it goes back exactly the same not 180 out...make sure the transmission mount is good..



since the transmission was slipping due to the low fluid i would drop pan and replace the fluid as i'm sure its burn't......good luck.....