1994 Chevy C1500 - 4L60e Only Shifts/Stays in 4th Under Acceleration/Load - Hot Rod Forum : Hotrodders Bulletin Board
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Old 12-18-2017, 10:35 AM
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1994 Chevy C1500 - 4L60e Only Shifts/Stays in 4th Under Acceleration/Load

Hi All,


About a year ago I asked for some help regarding the 4L60e in my '94 Chevy 1500.


I have been having issues with getting it to shift into 4th. At times, it prefers to bog between 3rd and 4th. I replaced the TPS, along with the temperature sensors and they seemed to have helped the transmission become more smooth. But it still bogs between the two gears.


So I replaced the VSS as well as a new connector for it. Now, the transmission will only shift into 4th after 65 mph as its it is either acceleration or going up hill. It seems like a pressure issue to me.


Any ideas?


Thanks in advance!

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Old 12-21-2017, 07:38 PM
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The word "bogs" is not enough.
Bogging isn't a trans issue, unless you have a bind-up.
When 4l60s first came out they had a 6 cyl set-up in the drum that used a different stack up in the overun clutch. the overun clutch must be off in OD.
Well we found out what happended when the mix was wrong, as it bound up right now, going into 4th.
If you have a bind up in your trans big enough to bog the engine, it will not b long before the fluid smells and you notice something slipping.
The only thing that could bind and not be a clutch is if your input sprag flipped and still holds good enough to pull the truck.
If you feel the problem is definitely in the trans and not engine, The sprag did flip and the 2-4 band is getting the snot burnt out of it.
So... How does the fluid smell ??
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Old 12-22-2017, 08:28 AM
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Is your exhaust plugged up?
It would be nice if you could get some data readings on your TPS, Map, and Vss
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Old 12-24-2017, 07:58 AM
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Hey KutzlerTranz,

Quote:
Originally Posted by KutzlerTranz View Post
The word "bogs" is not enough.
Bogging isn't a trans issue, unless you have a bind-up.
When 4l60s first came out they had a 6 cyl set-up in the drum that used a different stack up in the overun clutch. the overun clutch must be off in OD.
Well we found out what happended when the mix was wrong, as it bound up right now, going into 4th.
If you have a bind up in your trans big enough to bog the engine, it will not b long before the fluid smells and you notice something slipping.
The only thing that could bind and not be a clutch is if your input sprag flipped and still holds good enough to pull the truck.
If you feel the problem is definitely in the trans and not engine, The sprag did flip and the 2-4 band is getting the snot burnt out of it.
So... How does the fluid smell ??
Perhaps "bog" is not the right description.

The trans just seems to be confused about whether to stay in third or go into fourth. If going up hill or when accelerating past 70 mph, it will shift and stay in fourth. But after the slightest release of the gas pedal or as soon as the road become more horizontal, back into third it goes. So I try to stay around 55 mph when on the freeway.

The fluid has that nasty Dexcool-ish smell.


Quote:
Originally Posted by KutzlerTranz View Post
Is your exhaust plugged up?
It would be nice if you could get some data readings on your TPS, Map, and Vss
From what I can tell, the exhaust is not plugged up.

I will try to get some data on the VSS and MAP. I did do a video when testing the TPS in my previous thread. Seemed to check out just fine in all ranges.

Quote:
Originally Posted by lt1silverhawk View Post
I did test the original and aftermarket AutoZone TPS today with a volt meter.


I used this video on Youtube as a guide. video on Youtube


The original TPS shows a reading of 4.8. The AutoZone aftermarket unit shows a reading of 6.9. based on the numbers provided in the video (between 4 and 6), the new unit is no good.


I took the truck for a spin before doing this test, with the AutoZone TPS still installed. The bogging and surging was much more obvious with this unit. After doing the test, I kept the original TPS installed and went for another spin. The truck stayed in third, but had much less bogging and surging.


Someone on another forum suggested it might be a clogged exhaust.








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Old 12-26-2017, 09:13 AM
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What is the voltage during normal traffic light take-off where the upshifts take place @
15mph (1st-2nd)
25-30mph (2nd-3rd)
35-40mph (lock-up)
45-48mph (overdrive)

These shift points should get you into overdrive without having to move your gas pedal.

hook a vacuum gauge to a good manifold vacuum port and tape it to the windshield.
If your vacuum is dropping off too far under a steady load, the computer will hold lock-up back but may still allow overdrive. Make sure you can distinguish between the two. Your scanner will give you that info. Without lock-up you can slightly raise engine rpms by "slightly" goosing it. Lock-up is direct engine coupling and will be more a sense hearing, as the engine gets louder and tach stays fixed. Its a feeling you learn and its common to have customers, even shops, mix up the two or think they are the same and call lock-up, overdrive. Learning this stuff takes time and i have fooled my self many times on testdrive's without a scanner.
the engine or exhaust has issues. Carbon on valves, ect.
There are some smart guys on here that can help you figure this out.

A good place to start with any computer controlled vehicle is with the grounds. Make sure every wire that bolts to a ground is pulled and cleaned.

Check for AC Voltage right at the battery, running with a (good) dvm. Close to zero ac volts is what you want.

Does the engine surge at higher rpm's? When is the last time you checked your Timing with a light?
Worn Distributor bushings will make you chase your tail. Using a timing tape on the damper and a light, while slowly revving it up, will tell you if anything is wrong there.

In order to check your computer TPS and Map sensors, do base idle readings and get your decimal in the right place. then slowly power brake it while watching the readings. they should start around .6vdc and go to 4.6vdc full throttle.
They should be smooth as they transition up. Make sure gas pedal fully opens the tbi first.

The best place to start is with the scanner. The only time you (may) actually have a transmission issue is when you see the computer shift into a gear and the trans does not respond. Give it a few seconds for the hydraulics to catch up to the command.

With your trans it is more common to have no 2nd and still have fourth, caused by an egg wear on band lug. The 4th piston ring is pretty reliable unless someone had the cover off and messed it up.
If the band was out, i believe it could come out of the cover far enough to blow it out, but you would have no second way before that, as the second piston is limited in its travel..

Real gauges don't lie, electronics will. Trust your vacuum gauge. DVMs will also lie to you. I used to fix stereos and one day i compared six of my dvm's and 3 of them got ****canned on the spot. Make sure the battery is good first though.
John
P.S. Sorry for the long rants, I work alone and this forum is good therapy.

Last edited by KutzlerTranz; 12-26-2017 at 09:35 AM.
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Old 12-26-2017, 09:38 PM
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Use Your Computer.




Plug in a respectable code scanner and that will point you in the correct direction. One covering both your engine, transmission, and abs should be able to found easily. In some cases even rented.

Right now everything from throttle body to egr issues to vss to transmission clutches to the coolant sensor to fuel pressure to many other things could be pointed at blindly as the cause.

Use Your Computer.
It will help you.
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Old 12-27-2017, 02:16 PM
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Maybe BOTH TPS are bad...

I scoured a junkyard looking for a good used TPS for a Fiero years ago... every one was bad... May have been the reason many of the Fieros were in there... They looked better than the one I was repairing...

BTW, the readings you are getting should vary smoothly from idle to WOT... no dropouts in between...
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