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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: FlatBlack77 on February 02, 2016, 10:44:51 pm
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not too long ago i posted about an issue with my 79 k10. th350/203. it wasnt downshifting into first gear when i would come to a stop. i had replaced the pan gasket and added new fluid. the fluid was nice and pink and there was very minimal "sludge" in the pan. very minimal. turned out to be a sticky govenor. got that cleaned up and had no trouble after that till tonight. never slips or misses a shift
im saying this to answer some of the obvious questions people ask. fluid level, modulator vacuum line, ect.
so im driving home going about 45mph just cruisin along and i hear a very quick high pitched wine it lasted not even 2 seconds and bam the truck downshifts into 2nd gear and wouldnt upshift into 3rd. it wasnt a hard downshift it just felt like i got on the gas enough to make it drop a gear only i did not get on the gas at all. i was about 2 miles from home so i just kept driving and hoping it wouldnt quit.
reverse works. first and 2nd work. shifts from first to second fine.
could this be the govenor again? ive done a bunch of reading around on forums but i cant seem to find my exact problem of just loosing third like that.
to make matters worse im on alot of overtime and have no time to tinker untill the weekend
thanks in advance guys ill take any help/advice i can get!
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it sounds like your back to a governor issue but dont rule out a vac leak in or to the modulator
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Yes, physically check to see if the vacuum line is still on the modulator.
This happened to me and it wouldn't go into 3rd.
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when i was younger my th350 lost 3rd much like you described. i dove her for a good bit with only 2 gears, i was young didnt have any bills so the mpgs didnt matter lol. but after a while the whole thing just went up lost everything.
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it sounds like your back to a governor issue but dont rule out a vac leak in or to the modulator
im hoping it is the governor but im trying not to get my hopes up too high
Yes, physically check to see if the vacuum line is still on the modulator.
This happened to me and it wouldn't go into 3rd.
first thing i am going to check!
when i was younger my th350 lost 3rd much like you described. i dove her for a good bit with only 2 gears, i was young didnt have any bills so the mpgs didnt matter lol. but after a while the whole thing just went up lost everything.
driving in 2nd makes it feel like a powerhouse lol but this is just no good im so spoiled having a 4x4 and not having to worry about snow. plus i just love this truck to death
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ok i had some time this afternoon to investigate.
i warmed it up and checked the fluid. it was down to the add 1 pint line. topped it off and took it for a spin and it shifted without a problem. could 1 pint really cause it to loose third gear?
i keep a regular check on these things 2 weeks ago it was just a tad below the full line. maybe 200 miles ago.
im gunna pull the governor out as soon as it cools off just to check it out
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govenor is fine and the vac mod is still hooked up
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One pint low shouldn't cause shifting/engagement symptoms. Any chance the dipstick and/or tube was traded out at some point, so the dipstick is no longer accurate? Losing one pint in 200 miles, if there are no visible external leaks, could indicate a perforated modulator diaphragm or fluid passing into the transfer case.
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there is a good chance that the dipstick and tube are not original. it is a Jasper transmission from who knows when. the trans is wet here and there i mean there are small leaks and topping it off occasionally is routine. and the transfer case leaks a bit too but nothing major.
the modulator looks like it could be original to the trans so i am guessing what you are getting at is it could be sucking fluid out?
its just so odd it shifts fine now but now i cant trust it
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and the transfer case leaks a bit too but nothing major.
this is a misstatement. since there is only one way to check the trans fluid, unless you climb under the truck and sticking your finger into the hole you wont know youre out of fluid till you wreck the T case
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i keep a check on it. topping it off every few months ive never put more than half a pint in it. and depending how much i drive it sometimes it needs none at all
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nice
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I replaced the vacuum modulator with this one. mine had a red stripe so i bought a red striped one to replace it
http://shop.advanceautoparts.com/p/pro-king-automatic-transmission-vacuum-modulator-md-48/5152976-P?navigationPath=L1*14925|L2*15047
my old one is cruddy inside the vacuum line side. not wet but oily crud. i cant see how it would get anything like that in there my only guess is BD could be right about it allowing fluid to pass.
still driving and shifting fine
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1 pint low can definately cause you to lose 3rd gear and the problem is magnified if your using the felt style filter instead of the mesh screen type like fram FT1021A you can use this filter from 69 up to early 90's
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but you might be low still yet - a good way i learned from back in the day is to run down the highway at 60 mph for about 5 miles , pull over on level ground and at that point you should be at the full mark -if not top it up to the top of the full hot line
when you've driven for awhile its normal for the fluid to rise past the full mark as the it expands under heat
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it is a mesh style filter in there now.
I havent had a single issue since. ive put about 500 miles on the truck and no fluid loss
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sorry i forgot you cant get 3rd all the time - so when you drain the pan - it takes exactly 3.75 litres to fill it to proper level or 4quarts u.s. thats how ive done every trans fluid change on a th350 ( double checking when hot of course ) and its never failed me you could try a drain and refill but it sounds like the 3rd gear clutches are gone which is normally how they end up going in for rebuild .