Problems moving in Reverse

[Spencer Wescott]

Hey guys

77 GMC Jimmy
non original th350 w/ new torque converter ( I think its out of an 86 that got scraped)
NP 203 part time

Have moved it around property a bunch over the past few months no problems but first drive into town in a few months about 30 miles each way. Seems to be driving and shifting as good as it usually does, but when I pull up to bar and try to parallel park Reverse starts acting really strange.

Put in reverse and let foot off brake- No problem just rolls back

but

Give it gas in reverse and motor starts getting really bogged like you let the clutch out in a high gear and it wants to stall

If I put transfer case in neutral and then transmission in reverse it spins and revs no problem which makes me think this is a rear end problem

coincidentally rear end is all leaky and wet

any thoughts?

 

[diesel4me]

Might be the rear brakes are dragging in reverse--if it has sat awhile,the shoes and drums can rust up and bind only in one direction..sure the e-brake is released ?..

If it is in the transmission,it may have an issue with it getting fluid pressure in two circuits at the same time in the valve body or a crack in the case where the maize of oil passages are,making it act like a trans brake..(locked in two gears at once )..

It could well be the rear axle too..I'd jack both rear wheels up and put it on stands or blocks and try running it in 2WD in reverse (be careful,a NP-203 may try sending power to the front axle and could make it want to move!)--see if it will spin the rear wheels in reverse as well as it does in drive...there might be some shrapnel floating around inside the diff like a roller from a failed bearing getting wedged in between the gears in reverse..

 

[Bent77]

If you have forward and not reverse, it’s probably in the tranny

 

[Spencer Wescott]

Might be the rear brakes are dragging in reverse--if it has sat awhile,the shoes and drums can rust up and bind only in one direction..sure the e-brake is released ?..

If it is in the transmission,it may have an issue with it getting fluid pressure in two circuits at the same time in the valve body or a crack in the case where the maize of oil passages are,making it act like a trans brake..(locked in two gears at once )..

It could well be the rear axle too..I'd jack both rear wheels up and put it on stands or blocks and try running it in 2WD in reverse (be careful,a NP-203 may try sending power to the front axle and could make it want to move!)--see if it will spin the rear wheels in reverse as well as it does in drive...there might be some shrapnel floating around inside the diff like a roller from a failed bearing getting wedged in between the gears in reverse..

Thanks so much for all your ideas, I was thinking maybe breaks catching too

I did a lot of testing in the walmart parking lot and reverse totally works will a little bit of gas or very very slowly adding more
but when you give it gas fast (or normal) it bogs motor. but it works

I also feel like if it was tranny then, putting t-case in neutral and testing reverse would also bog motor, but t-case neutral with reverse test was fine.

e-brakes cables are detached but maybe they got caught on something

thanks again for all you ideas

 

[rdn2blazer]

Dude just step backwards, come on now ... damn kids lol!

 

[Spencer Wescott]

So, the problem mysteriously disappeared the next day. Its but its back again.

I know the tranny could be failing, but heres whats weird

It is intermitant
It has no direct response to fluid level or adatives
I feel if if the tranny was failing it wouldn't come and go.
When I put t-case in neutral, I rev it in reverse like crazy no issues

I checked the brakes they seem fine and not wet or oily
I check rear pinion and that seems solid too

has anyone had problems with np203 acting up like this?

 

[K5wrench]

So, the problem mysteriously disappeared the next day. Its but its back again.

I know the tranny could be failing, but heres whats weird

It is intermitant
It has no direct response to fluid level or adatives
I feel if if the tranny was failing it wouldn't come and go.
When I put t-case in neutral, I rev it in reverse like crazy no issues

I checked the brakes they seem fine and not wet or oily
I check rear pinion and that seems solid too

has anyone had problems with np203 acting up like this?

I've got a 76 K5 with a 400 sbc turbo 350 np203 combo.
Mine has been converted to part time.
Is yours stock?
If you suspect a problem with the center diff in the t-case, you can remove the rear yoke, and center diff housing and inspect.
Maybe the center diff has come apart or is thrusting into the case in reverse only.

A couple of things;
The nut on the rear yoke of an np203 is an oddball size; mine is 1-5/16"
The np 203 takes MOTOR OIL, not gear lube or ATF.

Have you tried driving it in reverse in 4hi loc?
I've never had problems with mine.
But if anything besides the transmission could cause those symptoms, the only place in the np 203 that i can imagine is the center differential.
Like the thrust from reverse is shoving the spider gear housing into something.
It is a guess.
But it is really easy ti find out.
Maybe drain the t-case and inspect the oil.
If theres a ton of metal, go further into it.

But really, like others said, probably transmission related.
Really doubt the t-case could do that.

 

[Bent77]

30w motor oil to be specific

 

[K5wrench]

30w motor oil to be specific

Thanks!

Also wanted to mention, np203s usually get sloppy over time if they have been converted with the cheaper kits that replace the spiders with blocking gears.
If bangs really hard going from drive to reverse, and it isnt the driveshaft or rear end, may be a clue.

 

[Spencer Wescott]

I've got a 76 K5 with a 400 sbc turbo 350 np203 combo.
Mine has been converted to part time.
Is yours stock?
If you suspect a problem with the center diff in the t-case, you can remove the rear yoke, and center diff housing and inspect.
Maybe the center diff has come apart or is thrusting into the case in reverse only.

A couple of things;
The nut on the rear yoke of an np203 is an oddball size; mine is 1-5/16"
The np 203 takes MOTOR OIL, not gear lube or ATF.

Have you tried driving it in reverse in 4hi loc?
I've never had problems with mine.
But if anything besides the transmission could cause those symptoms, the only place in the np 203 that i can imagine is the center differential.
Like the thrust from reverse is shoving the spider gear housing into something.
It is a guess.
But it is really easy ti find out.
Maybe drain the t-case and inspect the oil.
If theres a ton of metal, go further into it.

But really, like others said, probably transmission related.
Really doubt the t-case could do that.

Hey! Thanks so much for the ideas,
It is part time, and it does have alot of slack in it, took alot of fidling with linkage to get it to even shift

I know everyone had s different opinion of what should be in 203, never used atf, ive had so many of then I cant remember whats I cant remember whats in this one, motor oil sounds right but it mighf have gear oil, I know i have used gear oil in the past but I’m pretty sure it has sea30 in it and a small bottle of seal saver, not the thick glue type but the thin clear type.

Yes it does do it in 4Lo but not nuetral

And it could be low because it leaks like crazy

 

[K5wrench]

Hey! Thanks so much for the ideas,
It is part time, and it does have alot of slack in it, took alot of fidling with linkage to get it to even shift

I know everyone had s different opinion of what should be in 203, never used atf, ive had so many of then I cant remember whats I cant remember whats in this one, motor oil sounds right but it mighf have gear oil, I know i have used gear oil in the past but I’m pretty sure it has sea30 in it and a small bottle of seal saver, not the thick glue type but the thin clear type.

Yes it does do it in 4Lo but not nuetral

And it could be low because it leaks like crazy

There is no difference of opinion on proper lube for an NP203
An NP205 takes diff lube because it is all gears and they spin all the time and has no lube pump other than splash from the gears.
An NP 208 takes ATF because the chain stops spinning when the hubs are unlocked and it is shifted into 2hi.
It has a pump to supply atf to the rear output bearing.
An NP 203 was designed to be lubed by oil slung from a chain that never stops spinning.
When the part time kit gets installed, it becomes important to lock the hubs or shift into high loc occasionaly to fling oil up into the output housing or it will run dry and burn up the output bearing.
NP 203 has no pump like a 208.

Diff lube will only make matters worse in an NP203.
Never was supposed to have diff oil and sure as heck will wreck it in a part time conversion.

 

[Fordum]

This could still be a transmission issue, which is the most logical. But I agree that the fact that it doesn't do it with the t-case in neutral sounds strange. Unless the transmission problem has to have a load to show up.
Second most likely is the brakes. Drum brakes are self actuating, in that the wheel cylinder pushes the shoes against the drum, then the shoe assembly rotates to use the force of the moving drum to jam the shoes against the drum harder.
If someone assembled the brakes in some weird way, that one shoe was always against the drum slightly, then it might self apply the brakes in only one direction.

However, let me throw an idea in that no one has mentioned yet, and its real easy to check.
Depending on how much clearance you have under the back side of the hood when its all the way open, you may or may not need someone else to help. If you can see the top of the engine plainly when sitting in the driver's seat with the hood open, then you are set.
As always, safety first. Make sure you have lots of clearance behind you in case of a brake failure.
Then, crank the truck with the hood open. Apply the brakes, put the transmission in reverse and give it some gas while watching the engine or having someone else watch it from the side.
Don't floor it, just give it enough that it would roll back smartly if the brakes were not holding it.
You should see a small amount of engine movement, along with a small amount of floor shifter movement. That is normal and means my idea was wrong.

But, if it looks like the engine is trying to climb out of the engine compartment, or the shifter moves hard over to one side or both, I bet you have found your problem.

Broken engine mounts, and/or transmission mounts can cause all kinds of problems. My cousin, Baitfish2 had an engine mount break on his old GM. He drove into a hard bottom stream crossing back in the swamp where we were hunting, and had to call me to come pull him out.
I drove up, looked at his truck sitting on a rocky stream bed with the water not even up to the wheel lugs. Asked him how he could possibly be stuck.
Turned out, it was a little steep going up the other side, and whenever he tried to drive up, the engine would rise up and pop the throttle linkage off. He just could not get it to deliver power long enough to get out.
I suggested he back out, and it worked fine. Engine torqued the opposite direction and linkage stayed on.

In your case, the engine/transmission might be moving in reverse under load and causing something to bind.