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First Gear Shifts Hard & Late
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xJohnDoe001x
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Sep 22, 2013, 4:40 PM
Post #1 of 10
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First Gear Shifts Hard & Late
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My Friends,
My tranny shifts to second gear late, around 15 MPH and kind hard, it would seem that it should shift earlier with the rear end that it have.
I have a '90 GMC C1500 Sierra 2WD that originally had a V6 which was swapped out with a '91 5.7L TBI, I think the tranny came with the engine. The old rear geared for the V6 is still in the truck also.
How do I troubleshoot this problem?
Fgghjggffgh
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 22, 2013, 5:36 PM
Post #2 of 10
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Re: First Gear Shifts Hard & Late
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OK - Let's go. IMO it's not so surprising for first upshift at 15 mph but since you said HARD that could be a problem.
Basics on when automatics shift:
* Load on engine which is either direct actual intake manifold vacuum to a modulator (probably not for 1991 but not certain, RPM of the engine and throttle position quite possibly a cable along with the throttle cable - most cable types can be adjusted.
** It should be forced to upshift by rpms @ about 45 or so MPH if you floored it, full load of course doing that.
?? Not so sure the rear end is different for a six or 8 in a 1500 truck? You could order new lower or higher ratio and probably limited slip or regular.
OK - the actual intake manifold vacuum is a measure of load on engine. If zero (you could see this with a gauge with a long hose to vacuum gauge to where you could see it) would think you have floored it or heavy load. The higher vacuum would tell it less load so OK to upshift. That message is either converted to an electrical impulse or direct vacuum to a diaphragm modulator on trans. If so those if hose disconnected or leaking would be late and could be hard -- by that I mean it's abrupt.
I'm a bit unsure of why "hard" at such a low speed really.
The others may have some better ideas for sure on what you could check or do if things are as a 91 was set up and what you could or couldn't do. My guess is not much even that old. All 700R transmissions I've really known have been pretty dang good at least lasted well with basic care and no abuse.
See what else the others have to say as to what to check or do. Avoid additives - just proper approved ATF should be all that it needs and I don't believe in about 99% of what junk is sold out there for assorted things,
T
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xJohnDoe001x
User
Sep 22, 2013, 9:19 PM
Post #3 of 10
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Re: First Gear Shifts Hard & Late
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?? ?? ?? ?? I didn't quite under...... well I did understand, mostly but I couldn't couldn't exactly. .... never mind. .
I have a throttle cable and it is adjusted it to where when the cable is pulled out completely the throttle is completely opened, both reach maximum at the same time. In my limited research engines of different strengths get different ratios but I am not interested in taking on the expense of a rear end, larger tires may be able to compensate. It's not that bad actually. I once put a 350 in a '70 Nova that came with a straight four cylinder engine. Now that was bad, it started in second gear and sounded like first gear when in last gear.
Fgghjggffgh
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 23, 2013, 2:12 AM
Post #4 of 10
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Re: First Gear Shifts Hard & Late
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Can I/we call you John?
Sorry if I confused you on how an automatic shifts and when. That was the basic idea of what prompts it to do what and when. How each vehicle does it is going to vary but it is monitoring all those factors whether all mechanical or computer controlled which is still getting info from all those things and converting it.
I wouldn't worry about the rear end right now or take on expense of tires to try to change ratio. In fact just use the tire sizes suggested for the truck or handling, alignment will also be affected unless there's a specific reason and I reserve that for trucks not ordinary cars which IMO should always use only the tires suggested.
Back to the trans shifting. I take it that the cable is not even attached - is that correct? That is what I call a kick down cable. It's mechanically sensing where the throttle pedal is and pulls the cable making it along with all other factors shift. That meaning if you locked it pulled like your throttle was to the floor it would shift a lot later. If not attached it would think throttle was at home position all the time and not downshift well when needed as the loads change like going up a hill and you ask for more power or any reason. This stuff should be attached and set to proper settings or you'll just fight to get this to shift as it was intended to.
Please explain what you mean by "hard" shift again. If it just isn't smooth for that one shift I'm not sure what to say or suggest. Some kits are or were available for automatics to make them shift without that smooth feel on purpose as the faster it changes the better for plain performance as in for racing or sport.
Again - I'm not sure there's much wrong with this yet but not there to feel the shifting.
Note that the trans is really a 3 speed and the torque converter locks giving it the feel of the 4th gear. Many vehicles do that trick which is good for general efficiency. When those don't "lock" at the right time or have a problem it's annoying to drive so many you would have a choice to enable or disable that action. Your shift indicator on dash may say "D" then the next choice a "D" with a circle or some designation that you are still in drive mode but the second choice was to disable the locking action. Once GM just put on dash "PRND321" and owner's manual said to use the "3" if you didn't want it to lock up! No arguments boyz, family owned one new!
<><><><><><><><<><><>
Off the topic. Your '70 Nova. I owned that exact year Nova with a 250 straight six (I think it was a 250) and was such a light car it was plenty. Didn't own it long for some reason and don't recall having to do much to it at all. Another '74 and didn't own that one long either. No problems just not my type cars and owned zillions - frequently 3-5 at the same time!
Tom
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 23, 2013, 11:28 AM
Post #5 of 10
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Re: First Gear Shifts Hard & Late
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Of interest John. I own a '97 Chev 2500 and because of this thread took note when it shifted exactly. 15 MPH from first to second light acceleration not hard or too easy. That one you wouldn't notice much anyway in quite some years I've owned it. Never gave it too much thought as it runs new and feels new except it rides like a coal cart!
5.7, HD everything 4X4 but just 55K on the thing which helps of course. It's not the 700R but what replaced it. It's also synthetic ATF that I didn't notice a change doing that just wanted that in it.
No matter, its just that I thought that was about right for these critters and now would only worry about the "hard" shift you noted,
Tom
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xJohnDoe001x
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Sep 24, 2013, 11:24 PM
Post #6 of 10
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Re: First Gear Shifts Hard & Late
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The throttle cable is on and adjusted correctly,I did a lot of research to find out how. As for the hard shifting it could be the low geared rear end.
Fgghjggffgh
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Discretesignals
Ultimate Carjunky
/ Moderator
Sep 25, 2013, 4:46 AM
Post #7 of 10
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Re: First Gear Shifts Hard & Late
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Does it only shift hard going from 1st to 2nd? Lower gear ratio isn't going to cause harsh shifting.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 25, 2013, 9:43 AM
Post #9 of 10
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Re: First Gear Shifts Hard & Late
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Some questions and thoughts:
*When was last time ATF was changed? If unknown or a while I'd do at least a change w filter, use synthetic. I mean drop the pan and clean it out of any muck which there would be some and be normal. Just pan drop and filter job doesn't change it all but I say better than nothing. If a trans has some real wear problem it could make it worse but IMO it was coming anyway.
*Was driveshaft altered when engine was changed? Some absorb vibrations and a little shock w inner outer case with rubber really the driving connection. Never cut one wide open to see what the heck those were all like but notice some like that
* Are mounts all good?
Just groping for some things that may not indicate a real trans problem itself,
T
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Discretesignals
Ultimate Carjunky
/ Moderator
Sep 25, 2013, 9:58 AM
Post #10 of 10
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Re: First Gear Shifts Hard & Late
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You could check the 1-2 accumulator. Broken accumulator spring can cause that.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Sep 25, 2013, 10:03 AM)
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