Printable View
Hopefully someone can answer my question since I don't know sh!t about transmissions. I got my swap done into my 84 GMC 4x4 and have been driving it none-stop since Saturday. Runs like a champ! Only problem is, it shifts really hard and it won't go into overdrive. Could it be the fact that I'm not using the original transfer case and it thinks its a 2wd?
Do you have both speed sensors connected on the driver side of the transmission?
Yeah they're both there. The rear one is brand new since originally it was just a plug.
is there a pulse counter wheel thing in the transmission? Some transmissions didn't have two pickup points in the 80e, one was blocked off and the reluctor wheel thing isnt there.
Yeah the reluctor ring is definitely there. I know its all there because I felt really stupid when I swore up and down that it was a sensor and it turned out to be just a plug. Before I found that out, it wouldn't shift past second gear.
It may be your TP sensor? Mine did that and shifted really hard into 2nd and 3rd. The TP sensor was off, but I have a drive by cable.
Jamest
Yeah mine is drive-by-cable too. I checked the TP sensor and it checked out ok. A friend of mine who's a hardcore tranny guru is gonna look at it for me tomorrow after work. He's got a kool little scan tool specifically FOR transmissions so he can see exactly what its doing while its doing it. I'll wait and see how it checks out on the test drive.
Alright ladies and gents, my friend looked at my transmission for me on a little test drive found out the transmission is perfectly fine, I've just got a sensor problem somewhere. According to his scan tool, the PCM only registers my speed at 35 when I'm really actually doing about 50, and even shifting from drive to overdrive it won't go into 4th gear. So......install a new VSS in my tail house on my t-case or reprogram PCM?
is that a late model 80e? Sounds like something is way off in the tune if thats happening. Get your tuner to correct program your PCM for your gear, transmission, transfer case, tire combination.
I think it is a late model, but don't quote me on that. I didn't even think about the gears and tire sizes. I should do that again, only thing is I'm afraid to hook up my tuner to it again. I wiped out everything once I really don't want to do it again lol but I'll give it a shot. Thanks.
Well I sent my truck to the shop on Thursday morning and I found out from their diagnosis that I am missing a VSS sensor and that my transfer case is "incompatible" with the engine/tranny setup. Whatever. SO should I adapt a VSS sensor into my original transfer case or should I have that sensor deleted out altogether and make the PCM think its a 2wd? Or would that be bad?
you should have two speed sensors. Supposedly the front one can be disabled. The two are used to determine slippage. I've wondered if the PCM could be tricked by hooking both sets of wires to one functioning sensor.
I do now, both in the transmission, but I think the computer still thinks there should be a VSS back there in the transfer case. Well I did have one thought though, when I brought it home, the transfer case was locked in 4 wheel drive and I never changed it. Could that be the problem? Maybe it thinks its still in 4 wheel drive?
do you maybe have it tricked into thinking its in tow-haul mode?
Also, have you done a circuit check on the TCC solenoid to see if the windings are good?
Oh ya know, I didn't even think about the towing mode. How do I check that? And if it is in towing mode, how do I change it? No I haven't checked the TCC solenoid but I will definitely look into it.
I'm not sure on the tow mode since I've always run car PCMs. PM GasGuzzler and maybe he can tell you which wire on the PCM triggers tow mode in the PCM.
Tow/Haul switch is wires directly to the 2000 BCM. The BCM sends a Class2 message to the PCM to engage T/H mode. I don't think you have that issue but I'm not sure how some of these swaps work without the use of a BCM.
I also originally missed the fact you have no VSS in the transfer case. Yes, you need it...badly. It makes no real difference if the T/C is in 4WD or not AS LONG AS IT'S NOT IN 4LO. I doubt a 4L80 will shift into OD in 4LO. Also, I'm surprised it shifts at all with no VSS. It's my understanding that the two speed sensors on an 80 are for internal trans slip diagnosis and TCC application. The VSS does all the work for shift timing/pattern, etc.
Here's the GM internal component checks for no 4th gear.
Seals (527) (531) Nicked or cut
Cup Plug (530) Missing
Bolt (26) Loose, broken, or missing
Piston (528) Jammed
Spring Assembly (532) Jammed
Retainer Ring (523) Not seated
Friction Plates (525) Worn or burned
Reaction Plates (526) Worn splices
Housing (529) Damaged or cracked
Housing (504) Broken
Reaction Plates (508) Worn splines
Sun Gear (650) Worn
1-2 Solenoid (313)
• Stuck Off
• Pinched wire
• O-ring failure
• No voltage to the solenoid
No signal to the solenoid
3-4 Shift Valve (308) Stuck
PCM Quad Driver Module Failed
Check the PCM for current DTCs.
Since he has both speed sensors in the trans, shouldnt he be able to run a 2wd PCM and it should shift the transmission perfect regardless of transfer case gearing? Isn't the reluctor wheel on a transfer case shaft 40 pulse, too? Putting the sensor in the transmission should have alleviated the transfer case issue, unless there isnt the reluctor plate in the 80e transmissions that are built for 4wd trucks, correct?
I see...yes, I guess that makes sense with 2WD tune....unless the pulse count is different.
There is a reluctor ring in the back slot, we checked it out and it is a 40 tooth. I just don't understand why it has the 2 sensors and it still won't shift.
Is there a reluctor ring in the front slot?
As far as I know, that sensor was there when I bought the engine.
It's got to have something to do with the tune compared to switching from 2WD to 4WD I'd bet.
So do you think the guy I originally sent my PCM to did something wrong?