C6 Trans shift problems
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Senior User
Joined: Jun 2005
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From: Manitoba Canada
C6 Trans shift problems
Ok Guys... lets see how good you all are... I have been pulling my hair out by the roots on this one. I have an 81 150 explorer.. with a worked over 94 5.0. C6 transmission. My problem is, it shifts too soon when I have anything more than 300 lbs in the box. Various Transmission shops have said there is nothing wrong, some have said the valve body needs cleaning.. and one said the modulator is faulty.
So I removed the valve body, cleaned and re-installed it(new filter and fluids) and tried that with no change. I then replaced the modulator and tried that with no change again. I then thought it over and checked the kick down linkage adjustment with no change AGAIN!
Am I missing somthing here...it's not like this is rocket science! The engine isn't that wild... I have 20 inches of vacuume at idle, so that rules that out.
Well, as you can tell, this is getting fusterating and expensive. Any ideas will be greatly appreciated.
So I removed the valve body, cleaned and re-installed it(new filter and fluids) and tried that with no change. I then replaced the modulator and tried that with no change again. I then thought it over and checked the kick down linkage adjustment with no change AGAIN!
Am I missing somthing here...it's not like this is rocket science! The engine isn't that wild... I have 20 inches of vacuume at idle, so that rules that out.
Well, as you can tell, this is getting fusterating and expensive. Any ideas will be greatly appreciated.
Elder User
Joined: Oct 2004
Posts: 984
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From: Winnipeg, Manitoba
Check your bands. They have adjustments according to the particular trans, and need to be tightened with a tourque wrenche properly. A good trans shop should be able to do this if you are in question of it. Also, if towing, get a trans cooler installed, as it will save your trans in the long run. If you have a shift kit installed, it may be causing the early shifts, or your converter might not be working with the power of the engine, as you've stated....it's reworked, and newer than the truck.
Any performance mods done to the engine we could use as information?
Any performance mods done to the engine we could use as information?
Elder User
Joined: Oct 2004
Posts: 541
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From: Fleming Ga
The c-6 trans uses two signals to shift by.
Normally if there is a problem with the govenor it's because the valve in the govenor is stuck causing high rpm shifts only.
That leaves only the the modulator circuit or valve body fluid pressure to cause early shifts. You changed the modulator but did you change to the correct one with the proper color band to identify it. You might want to use one of the adjustable types and adjust for the correct shift points.
One other cause could be a sticking valve in the valve body or a weak pressure regulator spring. If working with the modulator doesn't fix the problem then try a good shift kit. Most come with an assortment of pressure regulator springs that allow you to adjust shift firmness and shift points.
- Engine load signal supplied by vacumn to the modulator.
- Drive shaft speed supplied by the govenor on the output shaft.
Normally if there is a problem with the govenor it's because the valve in the govenor is stuck causing high rpm shifts only.
That leaves only the the modulator circuit or valve body fluid pressure to cause early shifts. You changed the modulator but did you change to the correct one with the proper color band to identify it. You might want to use one of the adjustable types and adjust for the correct shift points.
One other cause could be a sticking valve in the valve body or a weak pressure regulator spring. If working with the modulator doesn't fix the problem then try a good shift kit. Most come with an assortment of pressure regulator springs that allow you to adjust shift firmness and shift points.
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Senior User
Joined: Jun 2005
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From: Manitoba Canada
Well guys, in order of responces... RR4E, The bands were adjusted as per spec.. and there is a heavy cooler installed... as far as the torque converter, it's still factory... so that gives me some food for thought.
Ron Clark: you made mention of a govenor... that is one thing that I haven't really looked at. as far as the modulator being adjustable, I relpaced it with what came out..and made no further adjustments to it. Maybe your idea of an adjustable one would be the ticket and a shif improver kit may also be somthing to look into...seeing as I do alot of towing with it (nothing too heavy...just a popup camper).
Your help is greatly appreciated..if and or when I ever get this sorted out, I'll be shure to post what it was...maybe someone else can benifit from my headaches.
Thanks again gents!!!!!!
Ron Clark: you made mention of a govenor... that is one thing that I haven't really looked at. as far as the modulator being adjustable, I relpaced it with what came out..and made no further adjustments to it. Maybe your idea of an adjustable one would be the ticket and a shif improver kit may also be somthing to look into...seeing as I do alot of towing with it (nothing too heavy...just a popup camper).
Your help is greatly appreciated..if and or when I ever get this sorted out, I'll be shure to post what it was...maybe someone else can benifit from my headaches.
Thanks again gents!!!!!!
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Senior User
Joined: Jun 2005
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From: Manitoba Canada
also.. RR4E.. you asked about engine mods...well I'll see if I can get this correct... it's a 94 5.0 ho out of a stang...and I used keith black flat pistons (020 over), crane compucam grind 444211 (intake @ valve .530 exhaust @ valve .530, intake duration 262 exhaust 270), crane ehergiser rockers (44746-16 1.7 ratio), crane 99838-16 valve spring/retainer kit (dual springs), edelbrock performer 289 manifold, holley 4160 vacuume secondaries carburetor (list 0-80475S), accel distributor, msd blaster coil. I hope that gives people some ideas! thanks again guys!!!
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