Transmission not shifting correctly - Second Generation Pontiac Firebird (1970 - 1981) - Firebird Nation

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Transmission not shifting correctly


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#1 1980_Red_TA

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Posted A week ago

Hi. I am a new member and this is my first post.

 

I love the site. I am a newbie so please be gentle. :-)

 

I have a 1980 Firebird Transam, 4,9 engine, automatic. the car is original. I got it with 3 km on it. I have had it since new. It has worked really good but after 40 years and the last 30 years sitting in my garage, it was starting to have a few issues.

leaking transmission pan, leaking oil pan, power steering pump, existing exhaust falling apart, leaking carb, old hoses and belts etc.

 

A friend of mine who works on old cars has had it for the past 3 to 4 months going through all the problems.

The kick down cable was found to be damaged. I got a new one at Rock Auto. it came with a universal fit. I also ordered the seal for it. it was found out that the original seal was larger than the new seal. it was installed however the shifting is not correct.

 

The revs go from 3500 to 4000 from 2nd gear to third gear. I can shift manually but it just does not shift like  before the update. 

 

Does anyone out there know what we did wrong. I have looked around the internet and it says to look for a vacuum hose that may be missed. Just wondering what vacuum hose?

 

Thanks in advance

 

Mike



#2 sea dog

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Posted A week ago

Since you installed a new generic kick down cable, are you sure it was adjusted correctly? While I'm not real familiar with the TH350 trans, on 700R4 trans is a throttle valve cable that if adjusted incorrectly, will cause all sorts of shifting problems.

 

I'm thinking a maladjusted kick down cable will have pretty much the same affect. Just my 2 cents worth.



#3 Aus78Formula

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Posted A week ago

There's the vacuum hose to the Trans modulator. I'd also check the new kickdown cable was setup correctly and not fouling the carb linkage.

#4 1980_Red_TA

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Posted 6 days ago

Thank You all for the comments. I will look into this.

I love this site :-) you guys are great with the quick response



#5 1980_Red_TA

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Posted 6 days ago

Would anyone out there know where would I be able to obtain an original GM kickdown cable. the one i got was from Rock Auto. I will try and find/Post the original end of the cable with the one from Rock auto. maybe someone out there can tell me if correct or if they have recently changed theirs?



#6 1980_Red_TA

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Posted 4 days ago

Hi Aus78Formula
where would the vacuum hose to the Trans modulator be located? is there any way you could show me a picture of it?
Thanks in advance


#7 Mickey_London

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Posted 4 days ago

Hi 1980_Red_TA
The modulator is arrowed in this picture, the vacuum hose comes off this
Hope it helps
Mick

Attached Files



#8 JoePeek

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Posted 3 days ago

The kick down cable can be disconnected, then go for a drive. It won't downshift to "passing gear" by itself if you nail it, but it should upshift just fine.....that is, if the modulator is working and it is getting full manifold vacuum (not ported) from a good vacuum line that is hooked up. I drove a '71 Esprit for years TH350 with the kick down cable disconnected, because I put a Holley on it and never bothered to sort out the kick down cable linkage. I had to pull it down to second by hand if I wanted to pass someone, and it dropped down into second fine, but if the cable is adjusted so short that it's tricking the transmission into thinking you have the accelerator pedal 3/4 of the way to the floor, it could very well make the trans not want to upshift correctly.



#9 1980_Red_TA

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Posted A day ago

Thanks Mick & Joe for all the information.

 

how do I confirm what type of transmission do I have on my car, 350 or 200? under the car it is stamped METRIC Hydra-Matic DIV OF GMC

 

Mike



#10 Aus78Formula

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Posted A day ago

Likely a TH-200 based on both later years and pan stamping. It's a narrower version of the TH-350 pan, may be hard to tell by some angles. An easier way may be that a 200 has 11 pan bolts, a 350 has 13.

 

http://tech.oldsgmai.../pan_thm200.gif

 

http://tech.oldsgmai.../pan_thm350.gif


Edited by Aus78Formula, A day ago.


#11 1980_Red_TA

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  • Transmission: TM 350

Posted A day ago

Thanks Ben. I will look into this

 

Mike



#12 Skien

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Posted A day ago

If has the words metric on the pan it is a 200. On the modulator you can take it off and shake it with the vacuum end down any fluid comes odd of vacuum end it's no good. Or keep it in the trans and take ear swab insert the end in the vacuum side pull it out and see if fluid on swab the mod no good.

#13 1980_Red_TA

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  • Transmission: TM 350

Posted 10 hours ago

Thank you Mark for your comments






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