Transmission going out????? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Chevyguy111786 · 08-02-2003, 07:01 PM

I have a 70 chevy with a 350 and a th350. I pulled a frame for about 50 miles two days ago on a tandom axle trailer and when i got home i noticed my tranny wasn't shifting right. it lets the revs get up real high before it shifts and doesn't get into 3rd unless i get on the highway...is there an easy fix or is my tranny on it's way to the truck heaven.

tom hand · 08-02-2003, 07:27 PM

First check the fluid.Second check for vacuum leaks...anything on the motor with a vacuum leak will cause the trans to shift late because the modulator is not getting enough vacuum. Might even put a new modulator on it to see if it improves before you have it rebuilt.

Class of 69 · 08-02-2003, 09:35 PM

Could the down shift cable possibly be stuck out?? That may tell the trans to shift at higher RPM. You didn't mention slipping, which is usually the first sign of failure. If the shifts are solid, just late, I would look for external causes first...vacuum leaks, modulator, downshift cable extended. Good Luck!!

Chevyguy111786 · 08-02-2003, 11:56 PM

where is the downshift cable...i have checked the vaccum hose going from the engine to the modulater and it is secure and without leaks....i am low on fluid and i'm hoping that will solve my problem, but it seems to be a little more than just low on fluid, i do have solid shifts, just late. THANKS FOR ALL THE HELP!

jcueckert13 · 08-03-2003, 01:47 AM

i dought it would be the modulator usually if that goes you suck the trans fluid in to the engine and the results are a large cloud of blue smoke (particulary at stop lights) ive gone through five on my 79 blazer

fast71 · 08-03-2003, 10:04 AM

I would pull the line off the modulator valve and check for fluid . if fluid is present in the line replace the valve and see what happens . If you cant afford another tranny find someone who sells lucas oil products . Lucas make a trans additive that works .I dont believe in mechanic in a bottle but I have seen this stuff take a trans that I thought was gone and make it last another 6 months .

Class of 69 · 08-03-2003, 09:58 PM

The downshift cable can either go to the carb linkage, or on some models to a bracket at the throttle pedal under the dash. Will be a black hard plastic cable. While you are under the truck find the cable at the trans and follow it up to the end. It is spring loaded in the trans and should return after you pull it out manually. If you can'y pull it out, and it seems slack, it may be stuck out. If you don't usually engage the downshift feature during normal driving, and did to tow the trailer, that would be the cause of it stuck in the out position....Does this make sense ?? I don't feel like I'm explaining it very clearly, sorry.

Chevyguy111786 · 08-03-2003, 11:52 PM

that actually does make since. I will check that tomorrw, it links to the carb and is getting worn out, i need to replace it anyway. I am probably going to replace the modulator valve and if that doesnt work i have a neighbor who can get the whole trans rebuilt for 350 bucks...i thought it was a good deal. So far I'm gonna replace the modulater valve and what i was told was a tv cable which is what i believe class of 69 was talking about. i put some trans-x in it today but it didn't make a difference. If all that doesn't work maybe i'll just have it rebuilt. any other suggestions? thanks for all the info guys, i really appreciate it.

Chevyguy111786 · 08-04-2003, 01:27 PM

well guys, i replaced the modulator valve and all is well. priced the cable and it's like 60 bucks so that's next weeks project i guess, lol. thanks a lot for all the help, i'd prolly be stuck on the road somewhere if it weren't for this board. thanks again!
Cory

Longhorn Man · 08-04-2003, 03:41 PM

If all is well, why you replacing the kick down cable?
Also, the kickdown cable can be found a little cheaper through aftermarket places instead of regular parts stores. Might even be able to get one from the tranny guy you were going to use.
TV cables are for overdrives while a regular kick down cable is for non-overdrive trannys. They are kinda the same...but not the same.

Chevyguy111786 · 08-04-2003, 04:29 PM

My kickdown cable is worn at the carb linkage. some of the wire is split so it needs to be replaced before it breaks. Thanks for the tip on aftermarket and the overdrive difference. Chevyguy

08-02-2003, 07:01 PM	#1
Chevyguy111786 Registered User Join Date: Apr 2003 Location: Garland, Texas Posts: 1,127	Transmission going out????? I have a 70 chevy with a 350 and a th350. I pulled a frame for about 50 miles two days ago on a tandom axle trailer and when i got home i noticed my tranny wasn't shifting right. it lets the revs get up real high before it shifts and doesn't get into 3rd unless i get on the highway...is there an easy fix or is my tranny on it's way to the truck heaven.

08-02-2003, 07:27 PM	#2
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	First check the fluid.Second check for vacuum leaks...anything on the motor with a vacuum leak will cause the trans to shift late because the modulator is not getting enough vacuum. Might even put a new modulator on it to see if it improves before you have it rebuilt. __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

08-02-2003, 09:35 PM	#3
Class of 69 Registered User Join Date: Mar 2003 Location: Stillwater MN Posts: 1,166	Could the down shift cable possibly be stuck out?? That may tell the trans to shift at higher RPM. You didn't mention slipping, which is usually the first sign of failure. If the shifts are solid, just late, I would look for external causes first...vacuum leaks, modulator, downshift cable extended. Good Luck!! __________________ 69 GMC K10 ..some restoration required....still..

08-03-2003, 10:04 AM	#6
fast71 Drive it like U stole it Join Date: Mar 2000 Location: tunnel hill ,GA /Chatt,TN Posts: 956	I would pull the line off the modulator valve and check for fluid . if fluid is present in the line replace the valve and see what happens . If you cant afford another tranny find someone who sells lucas oil products . Lucas make a trans additive that works .I dont believe in mechanic in a bottle but I have seen this stuff take a trans that I thought was gone and make it last another 6 months . __________________ 71 custom 10 swb 72 nova ss 72 nova custom 87 s10 96 burb 94 camry 53 5 window 3100

08-03-2003, 09:58 PM	#7
Class of 69 Registered User Join Date: Mar 2003 Location: Stillwater MN Posts: 1,166	The downshift cable can either go to the carb linkage, or on some models to a bracket at the throttle pedal under the dash. Will be a black hard plastic cable. While you are under the truck find the cable at the trans and follow it up to the end. It is spring loaded in the trans and should return after you pull it out manually. If you can'y pull it out, and it seems slack, it may be stuck out. If you don't usually engage the downshift feature during normal driving, and did to tow the trailer, that would be the cause of it stuck in the out position....Does this make sense ?? I don't feel like I'm explaining it very clearly, sorry. __________________ 69 GMC K10 ..some restoration required....still..

08-02-2003, 11:56 PM	#4
Chevyguy111786 Registered User Join Date: Apr 2003 Location: Garland, Texas Posts: 1,127	where is the downshift cable...i have checked the vaccum hose going from the engine to the modulater and it is secure and without leaks....i am low on fluid and i'm hoping that will solve my problem, but it seems to be a little more than just low on fluid, i do have solid shifts, just late. THANKS FOR ALL THE HELP!

08-03-2003, 01:47 AM	#5
jcueckert13 Registered User Join Date: Apr 2003 Location: Edgewood New Mexico Posts: 2,088	i dought it would be the modulator usually if that goes you suck the trans fluid in to the engine and the results are a large cloud of blue smoke (particulary at stop lights) ive gone through five on my 79 blazer

08-03-2003, 11:52 PM	#8
Chevyguy111786 Registered User Join Date: Apr 2003 Location: Garland, Texas Posts: 1,127	that actually does make since. I will check that tomorrw, it links to the carb and is getting worn out, i need to replace it anyway. I am probably going to replace the modulator valve and if that doesnt work i have a neighbor who can get the whole trans rebuilt for 350 bucks...i thought it was a good deal. So far I'm gonna replace the modulater valve and what i was told was a tv cable which is what i believe class of 69 was talking about. i put some trans-x in it today but it didn't make a difference. If all that doesn't work maybe i'll just have it rebuilt. any other suggestions? thanks for all the info guys, i really appreciate it.

08-04-2003, 01:27 PM	#9
Chevyguy111786 Registered User Join Date: Apr 2003 Location: Garland, Texas Posts: 1,127	well guys, i replaced the modulator valve and all is well. priced the cable and it's like 60 bucks so that's next weeks project i guess, lol. thanks a lot for all the help, i'd prolly be stuck on the road somewhere if it weren't for this board. thanks again! Cory

08-04-2003, 03:41 PM	#10
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	If all is well, why you replacing the kick down cable? Also, the kickdown cable can be found a little cheaper through aftermarket places instead of regular parts stores. Might even be able to get one from the tranny guy you were going to use. TV cables are for overdrives while a regular kick down cable is for non-overdrive trannys. They are kinda the same...but not the same.

08-04-2003, 04:29 PM	#11
Chevyguy111786 Registered User Join Date: Apr 2003 Location: Garland, Texas Posts: 1,127	My kickdown cable is worn at the carb linkage. some of the wire is split so it needs to be replaced before it breaks. Thanks for the tip on aftermarket and the overdrive difference. Chevyguy

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