transmission help please

Hollywoodk3 · 01-16-2005, 01:41 PM

Hi I am new here. I just bought a '78 GMC truck and the transmission is acting funny. I have changed the fluid,filter and modulater valve. It still won't change automaticly but I can shift it manually. It dosen't slip when in third but if I come to a stop I have to do it all over again. Can someone help me please. Thanks.

Goofball1984 · 01-19-2005, 12:13 AM

Sounds like your torque converter might be the culprit. You might want to pick up a Chilton's and read up on it. Also,.. grab the make and model of the tranny and look it up on the net independent of the truck for research. I personally just bought an 87 sierra that has not run for two years. It is a manual like my 94 Z28. I do not have as much experience with auto's. However, it does not sound like linkages, seals, bearings, etc. are fubarred due to the ability to change manually; so check out the torque converter.

Hollywoodk3 · 01-19-2005, 06:42 PM

Thanks man I'll do it.

chevynut · 02-11-2005, 07:31 AM

Your problem can be one of two things first the easiest,check vac.at the mod. valve while engine running,if ok,it will be the govenor gear stripped orgov. valve sticking,...for sure

silvervortek200 · 09-05-2005, 11:58 PM

there is a cable going from the throttle body to the tranny this is called a TV cable.
It helps control shift points and tells the tranny when to shift. This cable may have broke i would check that first.
its usually right beside the throttle cable on the throttle body. When you pull the end of the cable it should come out about 2 inches ans spring back in when released/its real easy to pull cable there isint much tension on it.

932500 · 09-10-2005, 10:52 PM

Quote:

Originally Posted by silvervortek200

there is a cable going from the throttle body to the tranny this is called a TV cable.
It helps control shift points and tells the tranny when to shift. This cable may have broke i would check that first.
its usually right beside the throttle cable on the throttle body. When you pull the end of the cable it should come out about 2 inches ans spring back in when released/its real easy to pull cable there isint much tension on it.

First off this is a 1978 truck we are talking about so it doesnt have a throttle body, it has a carb, secondly,the cable you are talking about wont affect it. If this is improperly installed it wouldnt shift in either manual or automatic, or would just shift real early do to lack of position signal to the transmission. Check the modulator valve. check the hose/line for vacuum leaks. If nothing found it is internal. The torque converter could not cause these symptoms either. Good luck

silvervortek200 · 09-19-2005, 10:08 PM

ok 93 2500, i didnt realise it was a 78 truck, i was thinking of the pre 99 trucks with fuel injection.
he changed fluid and filter i wonder if filter could have dropped down giving the valve body no oil pressure.[i suppose if that was the case the torque convertor would be starved for oil also.
I havent been around any of the pre 85 trucks with auro trans/ any we had were manual.

01-16-2005, 01:41 PM	#1
Hollywoodk3 Junior Member Join Date: Jan 2005 Posts: 2	transmission help please Hi I am new here. I just bought a '78 GMC truck and the transmission is acting funny. I have changed the fluid,filter and modulater valve. It still won't change automaticly but I can shift it manually. It dosen't slip when in third but if I come to a stop I have to do it all over again. Can someone help me please. Thanks.

02-11-2005, 07:31 AM	#4
chevynut Full Member Join Date: Feb 2005 Posts: 33	A to Z Transmission Exchange Your problem can be one of two things first the easiest,check vac.at the mod. valve while engine running,if ok,it will be the govenor gear stripped orgov. valve sticking,...for sure

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
truck pics	03harley	Ford Truck Forum	15	11-01-2004 12:39 PM
1996 Auto transmission question	Blueoval	Ford Truck Forum	0	09-18-2004 01:24 PM

01-19-2005, 12:13 AM	#2
Goofball1984 Junior Member Join Date: Jan 2005 Posts: 5	Sounds like your torque converter might be the culprit. You might want to pick up a Chilton's and read up on it. Also,.. grab the make and model of the tranny and look it up on the net independent of the truck for research. I personally just bought an 87 sierra that has not run for two years. It is a manual like my 94 Z28. I do not have as much experience with auto's. However, it does not sound like linkages, seals, bearings, etc. are fubarred due to the ability to change manually; so check out the torque converter.

01-19-2005, 06:42 PM	#3
Hollywoodk3 Junior Member Join Date: Jan 2005 Posts: 2	Thanks man I'll do it.

09-05-2005, 11:58 PM	#5
silvervortek200 Full Member Join Date: Sep 2005 Location: georgia Posts: 11	there is a cable going from the throttle body to the tranny this is called a TV cable. It helps control shift points and tells the tranny when to shift. This cable may have broke i would check that first. its usually right beside the throttle cable on the throttle body. When you pull the end of the cable it should come out about 2 inches ans spring back in when released/its real easy to pull cable there isint much tension on it.

09-19-2005, 10:08 PM	#7
silvervortek200 Full Member Join Date: Sep 2005 Location: georgia Posts: 11	ok 93 2500, i didnt realise it was a 78 truck, i was thinking of the pre 99 trucks with fuel injection. he changed fluid and filter i wonder if filter could have dropped down giving the valve body no oil pressure.[i suppose if that was the case the torque convertor would be starved for oil also. I havent been around any of the pre 85 trucks with auro trans/ any we had were manual.