91 Jimmy Overdrive problem

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cdutton977

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I have a 1991 GMC S15 Jimmy 4x4, 4.3L, automatic with overdrive.

First question, is overdrive on my vehicle just a ockup, or is it an actual 4th gear?

Second question/problem: My Jimmy does not shift into overdrive/lockup(?). At 55mph, I'm running 2500+ rpm. I know this isn't right. I've only had the vehicle for a couple weeks.

Is there an overdrive button? Or is something crapped out? I've been wrenching awhile, but I know nothing about this. How do I test this and fix it?
 
cdutton977 said:
I have a 1991 GMC S15 Jimmy 4x4, 4.3L, automatic with overdrive.

First question, is overdrive on my vehicle just a ockup, or is it an actual 4th gear?

Second question/problem: My Jimmy does not shift into overdrive/lockup(?). At 55mph, I'm running 2500+ rpm. I know this isn't right. I've only had the vehicle for a couple weeks.

Is there an overdrive button? Or is something crapped out? I've been wrenching awhile, but I know nothing about this. How do I test this and fix it?
Click to expand...

First thing that comes to mind on the 3-4 problem is the governor. Pull off the side cover on the trans (very easy to do) and pull the gov out and check the gear. Its plastic and tends to break or strip off. If its ok, make sure the valve inside the gov moves freely too.

Overdrive lockup is a function of the convertor, and if you are not supplying power to the TCC (torque covertor clutch) it'll sure feel like you have no 4th gear, when, in reality, you've got all gears but cannot realize the full .70 ratio of 4th due to the convertor "slipping". The lockup clutch makes a full mechanical connection in the convertor , thus rendering full overdrive and some 700R4's were triggered from 2nd gear, some from 3rd, some from 4th only.

Here is also a link for you to check if your TV cable is adjusted right and how to check your transmission line pressure.

Good luck and keep us posted. ;)

http://www.tvmadeez.com/article/index.php
 
Molson02536 said:
First thing that comes to mind on the 3-4 problem is the governor. Pull off the side cover on the trans (very easy to do) and pull the gov out and check the gear. Its plastic and tends to break or strip off. If its ok, make sure the valve inside the gov moves freely too.

Overdrive lockup is a function of the convertor, and if you are not supplying power to the TCC (torque covertor clutch) it'll sure feel like you have no 4th gear, when, in reality, you've got all gears but cannot realize the full .70 ratio of 4th due to the convertor "slipping". The lockup clutch makes a full mechanical connection in the convertor , thus rendering full overdrive and some 700R4's were triggered from 2nd gear, some from 3rd, some from 4th only.

Here is also a link for you to check if your TV cable is adjusted right and how to check your transmission line pressure.

Good luck and keep us posted. ;)

http://www.tvmadeez.com/article/index.php
Click to expand...

700R4? I was under the impression this is only the full-size transmission. My Jimmy is the S15, the little version. Also, my little truck goes 1st, 2nd, and 3rd. That's it. These solutions will help?
 
I was under the impression that the 700R4 is a full-size Jimmy transmission only? I have the S15, the smaller version.

Also, I don't think my vehicle has 4th. The shifting sequence when the selector is in OD is 1st, 2nd, 3rd. That's it. There's no lockup at all.

Will your solutions still help me?
 
cdutton977 said:
I was under the impression that the 700R4 is a full-size Jimmy transmission only? I have the S15, the smaller version.

Also, I don't think my vehicle has 4th. The shifting sequence when the selector is in OD is 1st, 2nd, 3rd. That's it. There's no lockup at all.

Will your solutions still help me?
Click to expand...

You have a 700R4 in your Jimmy and just follow the previous suggestion to help narrow down what's causing your transmission not to have 4th gear. :D

Good luck and keep us all posted. :cool:
 
Now you've really confused me. Does my 700R4 have a 4th a gear AND a lockup (overdrive), or just 4th, or just a lockup?
 
Okay, I took it on a test drive to catalogue all the problems. Here's what I came up with:

-Doesn't shift into 4th gear while selector is in either OD or D
-Doesn't lockup because it doesn't shift into 4th
-Doesn't downshift. It simply drops down to 750-1000 rpm and coasts.
-1st to 2nd has a bit of a delay, like it disengages 1st, waits half a second, and shifts into 2nd. It is not this way with 2nd-3rd. (However, with the selector in "2", it shifts up and down normally between first and second)
-Clunks and jerks when shifted from park to reverse. If it's cold and I try shifting right away, it'll actually kick the wheels loose on gravel for a quick second cause it's idling so fast
-After I let it warm up about a minute and shift into reverse, it does the jerky-thing, bogs down and almost dies, like the dash dims and everything, then goes normal again and idles backwards no problem.

What the hell?! Are there fixes for all these, or would a $200 used tranny from Pick-n-Pull be better? Be advised, if I can fix all these problems, I'd rather do that then let it sit while I try to find $200. I'm a college student, and I have a machine shop at home, so if I can fix it, I will, rather than buy a new transmission and pay someone else to do the work.
 
cdutton977 said:
Also, I called a chevrolet dealer and found out that I have the 4L60 transmission, NOT the 4L60-E I don't know if this helps.
Click to expand...

Your right kinda on your transmission, yes it's a 4L60 which is a 700R4. There the same transmission and was renamed i believe in 1990, and also in 1993 there was a change in the 700R4 (4L60) was an added checkball to the valve body.

As mentioned above, For Improper Shift Point verify full TV pull at the trans. Or a guage on the pump pressure port will show line rise as the cable is pulled even at idle. Your trans expert will have the tools to test this.

If the line rise is good, then put softer springs in the govenor. This should raise the shift points. If the shift points are raised, but not enough, grind the weights off or install a vette govenor and try that. The govenor springs can be cut off a little too. If that does not work, you need a stiffer spring in the 3-4 shift valve. Start with a spring 1 pound stiffer.......it does not take much to change the shift point.

Also check the TV "up" and "down" valves in the valve body. if one or both is stuck that will cause it too. Regardless as mentioned to inspect your Governor for any damages gear, and replace. :D
 
Molson02536 said:
Your right kinda on your transmission, yes it's a 4L60 which is a 700R4. There the same transmission and was renamed i believe in 1990, and also in 1993 there was a change in the 700R4 (4L60) was an added checkball to the valve body.

As mentioned above, For Improper Shift Point verify full TV pull at the trans. Or a guage on the pump pressure port will show line rise as the cable is pulled even at idle. Your trans expert will have the tools to test this.

If the line rise is good, then put softer springs in the govenor. This should raise the shift points. If the shift points are raised, but not enough, grind the weights off or install a vette govenor and try that. The govenor springs can be cut off a little too. If that does not work, you need a stiffer spring in the 3-4 shift valve. Start with a spring 1 pound stiffer.......it does not take much to change the shift point.

Also check the TV "up" and "down" valves in the valve body. if one or both is stuck that will cause it too. Regardless as mentioned to inspect your Governor for any damages gear, and replace. :D
Click to expand...

Okay. So you think these are the main problems?

Sorry for all the questions, but I can't have a disabled vehicle for any longer than necessary, so I'd like to have all the answers before I start ripping things apart.
 
Also, I've called around a few local shops and basically been told that this model trans has a history of the 3/4 clutch packs crapping out.

I can't find the side panel on my trans. It's a 4x4, I don't know if this matters. Which side is it on, pass or driver, front or rear?
 
cdutton977 said:
Also, I've called around a few local shops and basically been told that this model trans has a history of the 3/4 clutch packs crapping out.

I can't find the side panel on my trans. It's a 4x4, I don't know if this matters. Which side is it on, pass or driver, front or rear?
Click to expand...

3-4 clutch packs go bad from a poorly adjusted TV cable as mentioned earlier, also a bad governor gear can cause what you have described. Here is a link to your 4L60 transmission internal parts. Governor gear will be on the driver's side close to the tail end.

http://www.compnine.com/index.php?u...delid=7018&capuid=1&majorgroup=04&grouptype=B

http://www.compnine.com/index.php?u...delid=7018&capuid=1&majorgroup=04&grouptype=B

http://www.compnine.com/index.php?u...delid=7018&capuid=1&majorgroup=04&grouptype=B
 
More details:

TV line has been appropriately adjusted, it works just fine.

Also, when I'm driving, my transmission makes no attempt to shift into 4th. I've heard that when a clutch pack goes, it's like shifting from 3rd to neutral. That happened to a friend of mine.

My truck just stays in third. What's this mean?
 
cdutton977 said:
More details:

TV line has been appropriately adjusted, it works just fine.

Also, when I'm driving, my transmission makes no attempt to shift into 4th. I've heard that when a clutch pack goes, it's like shifting from 3rd to neutral. That happened to a friend of mine.

My truck just stays in third. What's this mean?
Click to expand...

If you are sure your TV cable is adjusted right, then check your 3/4 pressure switch or the 3/4 friction plates going out. The 3-4 valve is removable and replaceable. If you do this you may want to purchase the GM part #8673948. This kit includes a new 3-4 upshift valve/sleeve/spring and a larger boost valve (along with a pan gasket).

It is called the B body fix kit or such. This 3-4 upshift valve will prevent a high speed (> ca. 75 mph) WOT downshift to 3rd. The boost valve will increase line pressure for better holding of the clutches. **Note that this kit ONLY works on '87 & up 700R4/4L60's. No 3-4 upshift can be caused by:
1. Governor,
2. Oil pump assembly,
3. Valve body assembly,
4. 2-4 servo,
5. Case ( missing or misplaced balls and /or plugs,
6. 2-4 band assembly.
 
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