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trouble shifting into 3rd gear after tranny is warm

stevolwevol

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After my transmission is warm I sometimes have trouble with not shifting into 3rd gear (350 thm). If I go to neutral then back into drive it will shift. It also kicks down into 2nd well after it should as in if I am going 70, it kicks down almost hitting redline. I thought I'd post this before I take it to my transmission shop. Maybe there's something I can do.
 

Hib Halverson

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Sounds like a trip to the trans shop is the right thing to do.
 

Tom Bryant

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Sounds like it is only shifting on the governor and not the vacuum modulator. Check your vacuum hose to the modulator. Could also be the diaphragm in the modulator. I like to check the easy stuff on the outside before going inside.

Tom
 

stevolwevol

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Well, I can certainly check the vacuum hose, and replace if necessary, I of course would like to avoid removing the transmi$$ion. It only does this when the tranny is thoroughly warmed up. I'll see what I can do.
 

stevolwevol

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I watched a youtube on removing and replacing the vacuum modulator. One bolt to loosen, and it comes out. Anywhere between $15 - $25. Maybe a local auto parts store will have one. I'm gonna "throw parts at it" and replace it along with the vacuum line. If the line is grossly cracked, I just may try replacing it only, but the parts and labor is too easy to not just replace.
 

Tom Bryant

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I don't have one in front of me but there is probably a rod or plunger on the back that you can push in. Then hold your finger over the hose connector and release the rod. If it holds until you take your finger off the connector it's ok. If it comes out immediately it has a bad diaphragm.

Tom
 

stevolwevol

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I am going to buy a new vacuum modulator tomorrow morning. I replaced the hose, but it's still acting up. I put the car on ramps, and had trouble getting a wrench on the bolt that holds the retaining bracket which holds the modulator in. My exhaust pipe is very close, I tried a fine click ratchet, but had no luck so far. I believe it's a 7/16, or maybe a 1/2. I wish I had a hoist. Any suggestions would be appreciated.
 

Tom Bryant

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Wrenching in tight areas sucks. Maybe this will help.

Tom
 

stevolwevol

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My transmission guy recommends a rebuild. He told me the modulator would not act that way when warmed up, vs cool. Anyway I added a bottle of Lucus Transfix, and it acts somewhat better, but it still kicks down when it shouldn't. If an unknowing driver were going 70 it would kick down and red line. It isn't as capricious though. $2000 for a rebuild. I would get better clutches, seals, torque converter, etc. He told me the seals get hard and brittle with age.

Does anybody know what the stock stall is on an L48? I would like to bump that up a tad. With the cam it tugs just a bit at idle.

It's a beautiful original red with black interior car, and I really love it, so I'm probably going to get the tranny overhauled.
 

Tom Bryant

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Might be a good idea. It's 43 years old. There could be a bad seal or something stuck in the valve body.
 

stevolwevol

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Might be a good idea. It's 43 years old. There could be a bad seal or something stuck in the valve body.

Rebuild is happening next week. He's gonna ad a mild shift kit, and put a 2200 stall torque converter. There is a difference between L48, and L82 stall speed. He has a guy that puts torque converters together. I thought they just came in a box, Mine is about 1700 rpm. I brought the car to my transmission guy, and he recommended the higher stall due to my cam. This car I believe has 3.55's I rev at 3400 @ 70. My 77 revs at 3000 at the same speed, and it's a 3.08 gear. I'll post when I get it back.
 

stevolwevol

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I picked up my Vette Friday afternoon after a rebuild. He set it up so it shifts firmer than stock, but not a shift kit. This is what I wanted, since it's a street driven car. It shifts nice and firm, in 2nd, and third. I have a 2200 stall converter, and I can tell the difference. With the after market cam he recommended I go to a higher stall. Doesn't tug when at a stop. So I consider this not just a rebuild, but a nice upgrade as well. Thanks for the input.
 

Tom Bryant

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Bet it’s fun to drive now. Sounds like you have a good transmission guy. It’s ok to give his shop a plug if you want.
 

stevolwevol

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Bet it’s fun to drive now. Sounds like you have a good transmission guy. It’s ok to give his shop a plug if you want.
Yes, this guy is great! His business name is Pine and 17th transmission Holland, MI His name is Jerry Mullengraff. BTW I get a nice chirp in 2nd if I get on it now. The hard part is driving it "nice". Thanks again Tom..
 

Tom Bryant

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I used to get up to Holland a lot before I retired. Still did occasionally afterwards when I was working part time in the summer for the same company. I haven't worked this year since April though.
 

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