1978 Pontiac Bonneville Tranny

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  #1  
Old 01-21-04, 06:03 AM
meagle
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1978 Pontiac Bonneville Tranny

Referenced vehicle - 301 CID - Auto Trans - 82,000 mi (Yes. that is correct)

Does not want to upshift. Down shifts OK. Reverse, Neutral, Drive (low gear) engages just fine. Fluid is a little low but within the "operating Level" - A bit dirty - not the bright pink color, but I've seen worse.

Ideas, please!
Thanks
 
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  #2  
Old 01-21-04, 09:02 AM
toivo
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78 pont. tranny

change the tranny oil and filter and check your vacuum line from the back of the carburator or intake manifold behind the carb to the vacuum module on the tranny. since your fluid is a touch low try some transmission seal conditioner before you change the fluid and drive it and see if it helps.
 
  #3  
Old 01-21-04, 10:09 AM
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you need to ID the...

...type of trans as it could be a THM-350 or a THM-200...the 350 has a modulator (not a module)...but the 200 does not. The modulator could cause this but is not the most likely. The governor valve may well be stuck. the only wau to know is to remove the governor and move the weights and watch the valve move up and down.

for clarity sake...does it upshift or not?? you said it doesn't want to...and that could mean that it does shift but waits too long to do it...in which case, a whole different thing might be going on.

bottom line...find out what tranny it has in it by looking at the bottom pan and comparing it to a chart...don't call someone and ask them what tranny came in it. once identified, we may be able to guide you.

PS...don't waste your time with sealers and additives in automatics...they DO NOT work!!
 
  #4  
Old 01-21-04, 11:00 AM
meagle
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Thanks - Seems to downshift ok - either by slowing or giving or pucnhing the accellerator. I'll chech to see what type 200 or 350. There is indeed a vaccum line that runs from the manafold top the tranny.
Mark
 
  #5  
Old 01-21-04, 11:21 AM
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if you're sure...

...about the vacuum line, then it's a 350. make sure the vacuum hose is good at both ends. there is a metal cover on the right side at the tail end of the tranny. with a punch and a hammer, drive it off...a little at a time alternating sides...then pull the governor out. it has a plastic gear on the inner end...the teeth should be spiral but flat...not apple-cored. if the teeth are worn you can still buy a gear kit.

if that's ok...hold it up by the gear end...the weights will be at the bottom and at rest...you should be able to push them toward the center (as if you are trying to pinch them together) and if you watch the valve (it's inside but you can see it through the slots) it should move freely up and down...weights at rest--valve up...weights pinched in toward the center--valve down.

it doesn't move much...an eighth of an inch or so...if it moves at all, it's probably ok and your problem is elsewhere.

PS...if oil drips from the vacuum line when you pull it off at the trans end...replace it (the modulator) and then roadtest before doing the governor thing.

good luck
 
  #6  
Old 01-22-04, 06:58 AM
toivo
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78 pont. tran.

good job carguy, i meant modulator but it came out module, must be a short circuit somewhere. my cousin had one of these so i quite sure it was a t-350. i don't think the 200's came out until in the 80's. you seem to know way more than i do, so i'm outa here. like i said, good job.
 
  #7  
Old 01-22-04, 08:09 AM
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merely pointing something out...

...by correcting terminology. i wouldn't want the poster to go into a parts store and ask for something that didn't exist on that model...no offense intended, dude.

BTW...the THM-200 came out in 1976...at least it's in the 76 service manual.
 
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Old 01-23-04, 03:45 PM
meagle
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Thanks to all for the suggestions and inputs. Carguy, before I received your initial response, I bought and dumped a bottle of transmission conditioner down the tube and replaced a section of vaccuum line that did not go to the tranny, but was on the same "T" as the modulator. It was cracked and leaking. The tranny is now behaving, but, I let time get in the way of good problem solving techniques - I performed two tasks at the same time without validating one at a time. So, I don't know which fixed the problem - My bet is the vaccuum line....

On another subject...
I have tried and tried to find a repair manual with the vaccum diagrams and component identification. I was able to find a new decal found on the fan shroud, however, that just confirmed that some parts and routings have been detoured and components missing. A have make magnified copies but can't find a shop manual. The 3 major dealers here in the Nashville area have not been able to help. A search of e-bay over the past several months and posts to this forum haven't yielded what I need. Any advise or help is GREATLY appreciated!

MORE.....
Can someone please outline the process of adjusting the choke and high idle setting (DualJet)? I cannot find a "happy medium". If the choke engages on cold mornings, I can't get it to kick down to slow idle when warm. Conversly, If I set it to where it will go to warm (slow) idle, the choke will not engage when the engine is cold.
Both the primary and secondary vaccuum pull-offs are operating properly. I have to push the high idle weight hard to get it off of high idle. To get it to the low idle, I have to turn the choke adjustment approximately 1.5 to 2.0 turns - In other words, I have to put some rather extensive tension on the choke sping (coil) to get it to slow idle which prevents the choke from closing on cold mornings. Grrrrrrr. Had the carb re-built 6 months ago by a highly reputable garage.
Help!
 
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