'97 GMC overdrive intermitent

OssipeeSteve · 03-06-2008, 12:28 PM

Usually goes into OD @ 40 MPH. Now it may not until 60 MPH after 5 miles travel, then I set Cruise Control. It may then several miles later fall out of overdrive and cruise drops off. I changed Throttle Position Sensor. No Change. Tranny shifts smoothly in all gears, up and down, even when falling out of OD. Would appreciate any comments. Truck well cared for. 125K miles.

leolkfrm · 03-06-2008, 01:12 PM

check and see if your distributer has a small pickup switch(like a murphy switch) in the base. My 91 had it at about 130,000 mi, the lower bushing in the distributer went bad and would not keep the switch made up. put a rebuilt dist in and all has been good for 50,000 mi.
I thought it was major tranny work dropped it off, the wrench in the tranny side of the shop coudn't find anything with a filter change, The wrench on the mechanical side of the shop found it as hae had seen it once before.
good luck

OssipeeSteve · 03-06-2008, 01:20 PM

That's interesting. The distributor crossed my mind but it was not something like that. I'll look for something there. You say"Murphy Switch", and I have no idea what you mean. Can you clarify?
Thanks.

leolkfrm · 03-08-2008, 10:10 AM

Its a makeup switch, Look up your distibuter online (like parts america) if it has 2 connectors the small one is for the tranny

OssipeeSteve · 03-10-2008, 06:58 PM

Thank you. In the interim, I cleaned the connector at the Vehicle Speed Sensor before I read your response, which does in fact control the Cruise and Torque Converter Clutch, the issues I'm having with the truck. I did put a new cap and rotor on yesterday and ran today with no troubles for 30+ miles until, ya, you guessed it, Cruise dropped off and I lost Overdrive. Mind you I probably did touch that connector at the distributor you spoke of. I'll get into it in the AM. I took an Ohm reading on the VSS hot as it may be faulty hot/ not cold. I'll see what the ohms are in the AM.
Thanks again,
Steve

jimbo543 · 03-11-2008, 01:08 AM

how bout brake switch, does trans act up with cruise off?
sounds like cruise is cutting out causing throttle to drop off cutting tcc and od.
check brake switch cruise switch

OssipeeSteve · 03-11-2008, 06:46 PM

Cruise will not operate when overdrive will not engage. That's not to say the switch isn't always knocking it off, huh? But I think I've run that truck in Cruise below OD speeds. I did check ohms on vss this AM and they matched the part at the store so it's unlikely to be the vehicle speed sensor. There is one three wire connector on the distributor. Prior to spending the $$ for a rebuilt distributor, I have a call in to a tranny guy. I think I'll do the AC volt test for the vss, wheels off ground in gear.
Thanks for the comment.
Steve

keithr0005005 · 03-11-2008, 07:46 PM

i bet its the brake switch....any engine sensor....such as the ones in your dist....will throw a code

OssipeeSteve · 03-11-2008, 08:01 PM

I'll be sure to get to the brake switch in the AM. Of course I looked at it the other day and its a real dream job to work on. I'll put a spring load to hold it up with rubber cord and take 'er for a hwy spin.
Thanks, Keithr

O'Steve

OssipeeSteve · 03-27-2008, 08:09 PM

Well, I checked brake switch operation and connection and it seemed to be operating just fine. Several days later everything went back to normal. Cruise and overdrive work perfect. Was it a bad conn. at the brake switch, VSS, dumb driver? I haven't a clue but if ever it acts up again and I figure it out I'll be sure to give you all a shout. Now tomorrow's another day.
Thanks a million for the help.
Steve Foley, Plymouth, MA

03-06-2008, 12:28 PM	#1
OssipeeSteve Full Member Join Date: Mar 2008 Location: Plymouth, MA Posts: 27	'97 GMC overdrive intermitent Usually goes into OD @ 40 MPH. Now it may not until 60 MPH after 5 miles travel, then I set Cruise Control. It may then several miles later fall out of overdrive and cruise drops off. I changed Throttle Position Sensor. No Change. Tranny shifts smoothly in all gears, up and down, even when falling out of OD. Would appreciate any comments. Truck well cared for. 125K miles.

03-11-2008, 01:08 AM	#6
jimbo543 Senior Member Join Date: Sep 2007 Location: MN Posts: 205	how bout brake switch, does trans act up with cruise off? sounds like cruise is cutting out causing throttle to drop off cutting tcc and od. check brake switch cruise switch Last edited by jimbo543; 03-11-2008 at 01:13 AM. Reason: .

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03-06-2008, 01:12 PM	#2
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 4,300	check and see if your distributer has a small pickup switch(like a murphy switch) in the base. My 91 had it at about 130,000 mi, the lower bushing in the distributer went bad and would not keep the switch made up. put a rebuilt dist in and all has been good for 50,000 mi. I thought it was major tranny work dropped it off, the wrench in the tranny side of the shop coudn't find anything with a filter change, The wrench on the mechanical side of the shop found it as hae had seen it once before. good luck

03-06-2008, 01:20 PM	#3
OssipeeSteve Full Member Join Date: Mar 2008 Location: Plymouth, MA Posts: 27	That's interesting. The distributor crossed my mind but it was not something like that. I'll look for something there. You say"Murphy Switch", and I have no idea what you mean. Can you clarify? Thanks.

03-08-2008, 10:10 AM	#4
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 4,300	Its a makeup switch, Look up your distibuter online (like parts america) if it has 2 connectors the small one is for the tranny

03-10-2008, 06:58 PM	#5
OssipeeSteve Full Member Join Date: Mar 2008 Location: Plymouth, MA Posts: 27	Thank you. In the interim, I cleaned the connector at the Vehicle Speed Sensor before I read your response, which does in fact control the Cruise and Torque Converter Clutch, the issues I'm having with the truck. I did put a new cap and rotor on yesterday and ran today with no troubles for 30+ miles until, ya, you guessed it, Cruise dropped off and I lost Overdrive. Mind you I probably did touch that connector at the distributor you spoke of. I'll get into it in the AM. I took an Ohm reading on the VSS hot as it may be faulty hot/ not cold. I'll see what the ohms are in the AM. Thanks again, Steve

03-11-2008, 06:46 PM	#7
OssipeeSteve Full Member Join Date: Mar 2008 Location: Plymouth, MA Posts: 27	Cruise will not operate when overdrive will not engage. That's not to say the switch isn't always knocking it off, huh? But I think I've run that truck in Cruise below OD speeds. I did check ohms on vss this AM and they matched the part at the store so it's unlikely to be the vehicle speed sensor. There is one three wire connector on the distributor. Prior to spending the $$ for a rebuilt distributor, I have a call in to a tranny guy. I think I'll do the AC volt test for the vss, wheels off ground in gear. Thanks for the comment. Steve

03-11-2008, 07:46 PM	#8
keithr0005005 Senior Member Join Date: Jan 2008 Posts: 156	i bet its the brake switch....any engine sensor....such as the ones in your dist....will throw a code

03-11-2008, 08:01 PM	#9
OssipeeSteve Full Member Join Date: Mar 2008 Location: Plymouth, MA Posts: 27	I'll be sure to get to the brake switch in the AM. Of course I looked at it the other day and its a real dream job to work on. I'll put a spring load to hold it up with rubber cord and take 'er for a hwy spin. Thanks, Keithr O'Steve

03-27-2008, 08:09 PM	#10
OssipeeSteve Full Member Join Date: Mar 2008 Location: Plymouth, MA Posts: 27	Well, I checked brake switch operation and connection and it seemed to be operating just fine. Several days later everything went back to normal. Cruise and overdrive work perfect. Was it a bad conn. at the brake switch, VSS, dumb driver? I haven't a clue but if ever it acts up again and I figure it out I'll be sure to give you all a shout. Now tomorrow's another day. Thanks a million for the help. Steve Foley, Plymouth, MA