Yeah I think the newer ones are like motorized from what it looked like in that video I posted.
The older thermal ones are always criticized for slow or no action in colder temps or submersed.
99 Tahoe 4wd not engaging.....however.
- Thread starter res02p35
- Start date
Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
The older thermal ones are always criticized for slow or no action in colder temps or submersed.
east302
Full Access Member
The 1999 GM manual has the diagnostics for the transfer case, it may be worth checking out. The two volumes can be downloaded at this link (see post #77)…
www.gmt400.com
Here is a screenshot example of the tables from that manual…
Regarding your unconnected red plug from your initial post, it kind of looks like the EVO sensor plug on the back of the power steering pump. If the EVO system has been deleted (and they often are as they’re problematic), the plug is just tied up out of the way when the sensor’s solenoid valve is removed. If you don’t have a connector and valve on the back of your PS pump, that’s likely what it is. This is where it would go if it hasn’t already been converted…
Here’s the pump with the EVO deleted:
88-98 Service Manuals
Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...
www.gmt400.com
Here is a screenshot example of the tables from that manual…
Regarding your unconnected red plug from your initial post, it kind of looks like the EVO sensor plug on the back of the power steering pump. If the EVO system has been deleted (and they often are as they’re problematic), the plug is just tied up out of the way when the sensor’s solenoid valve is removed. If you don’t have a connector and valve on the back of your PS pump, that’s likely what it is. This is where it would go if it hasn’t already been converted…
Here’s the pump with the EVO deleted:
stevedonato
Member
- Joined
- Dec 15, 2017
- Posts
- 66
- Reaction score
- 26
Might try a new actuator they are Cheap and simple 10 min. install. I put new one in my 1996 GMC 5.7L 4WD pickup, and it worked perfect. Just a guess on my part. If it does not fix it, return to amazon for refund.
Thanks for the diagnostic manuals much appreciated! I'll check it out.
I will also check the power steering pump. Thanks.
I already tried a new actuator, did not resolve issue.
Should have a new tccm by Wednesday.
I'll update afterwards.
I will also check the power steering pump. Thanks.
I already tried a new actuator, did not resolve issue.
Should have a new tccm by Wednesday.
I'll update afterwards.
OK, I could not download those files referenced in the above post. they showed to be infected.
I put on a new TCCM and still nothing. Must be something inside the front diff that is causing me grief.
As stated before, the front driveshaft turns providing rotation into the front diff. I can hear the front actuator motor engage, however there is still no rotation to the front wheels.
If I remove the actuator I can manually push in on the arm/spring and it locks up both wheels so they turn at the same time.
Any other suggestions?
Guess I have a new winter project. Pulling the front diff and see what's going on.
I put on a new TCCM and still nothing. Must be something inside the front diff that is causing me grief.
As stated before, the front driveshaft turns providing rotation into the front diff. I can hear the front actuator motor engage, however there is still no rotation to the front wheels.
If I remove the actuator I can manually push in on the arm/spring and it locks up both wheels so they turn at the same time.
Any other suggestions?
Guess I have a new winter project. Pulling the front diff and see what's going on.
Was the TCCM you installed pre-programmed? (Mfr & model?) Not all require programming, but that varies by the replacement. The documentation should say whether it needs it or not.
The model was exactly as I removed. It came from a rebuilder.
The other day when I was working on this it did not seem like the actuator was engaging far enough.
I proved this out tonight. I pulled the actuator and inserted a 3/4 inch socket in and then the actuator. Wheels did not turn in 2wd as expected. When I put it in any 4wd the wheels then started turning.
This tells me the diff has an issue. Either the spring behind the plate pushing back against the actuator is weak or something else is going on. Nonetheless, I have it figured out for now. When I get around to it I will pull the diff and check it out.
The other day when I was working on this it did not seem like the actuator was engaging far enough.
I proved this out tonight. I pulled the actuator and inserted a 3/4 inch socket in and then the actuator. Wheels did not turn in 2wd as expected. When I put it in any 4wd the wheels then started turning.
This tells me the diff has an issue. Either the spring behind the plate pushing back against the actuator is weak or something else is going on. Nonetheless, I have it figured out for now. When I get around to it I will pull the diff and check it out.
One thing to keep in mind an electrical circuit on a vehicle needs a good ground. just because there is power and even if the actuator works off of the vehicle increased resistance in the circuit might be a problem. Be sure to check all connections in the circuit.
