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Old October 3rd, 2011, 04:04 AM   #1
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TH 400 Turbo problem!!

hello guys
I have a problem with the transmission, I have a TH 400 of 1967 and at some point no longer enters the secod and third gears, first gear and the back work fine.
Oil is ok and the new
all internal components are new
everything worked fine.
Can you help me?
thanks!!!!
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Old October 3rd, 2011, 04:49 AM   #2
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Check the vacuum supply to the modulator. Unplug the kickdown wire from the side of the trans, see if that makes a difference.
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Old October 3rd, 2011, 04:52 AM   #3
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Quote:
Originally Posted by olds67 View Post
hello guys
I have a problem with the transmission, I have a TH 400 of 1967 and at some point no longer enters the secod and third gears, first gear and the back work fine.
Oil is ok and the new
all internal components are new
everything worked fine.
Can you help me?
thanks!!!!
I see youre in Italy and dont know how your availibility of parts is --- so if this problem just started after the trans had been working OK - then 1st thing to check is to see if you dont have a vacuum leak in the line from the engine to the modulator valve. If you are losing that vacuum the trans wont upshift to next gear when selector is either in D or S. If vacuum line is OK - then the modulator valve utself may have gone bad and need replaced. One test you can perform to determine if the modulator is creating the problem is to put the thing in drive and and accelerate it up to maybe 30-40 mph (or 50kph) and see if it then upshifts to the next gear. If the shift DOES occur at that higher kph then you DO have a modulator problem and need to replace it(provided you are sure you are getting sufficient vacuum to the valve!! Make this test and "report back" your findings.
T.
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Old October 3rd, 2011, 06:59 AM   #4
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thanks guys
to get the parts I bought everything I have no problems in the U.S.A.
I'll try to do the tests that I recommend.
I was afraid it was the oil pump but the pressure is also powerful else and when I press the accelerator.
thanks and greetings from Italy.
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Old October 3rd, 2011, 01:01 PM   #5
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I tried to pull air from the tube that connects modulator valve and then to blow but it seems blocked.
Today it was raining and I could not bring the Olds out of the garage, I did not want it dirty
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Old October 5th, 2011, 12:45 PM   #6
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I tried to disconnect the wire but still no changes kickdown gear.
may be the governor to give the problem?
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Old October 7th, 2011, 07:51 AM   #7
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hello guys
What do you think, the problem may depend on the governor.
tomorrow I try to open the governor house
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Old October 7th, 2011, 09:00 AM   #8
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If none of the above remedies the problem then you need to check your line pressures using a hydraulic high pressure gauge avaliable through a quality vendor. One of the first steps when troubleshooting a trans is checking its pressures. Think of a auto trans as nothing more than a hydraulic pump. If the pressures are not within spec somethings leaking/bypassing. This can be seals, the pump, the clutches, seprerator plates et al...Google surf and find that info or get a book or CD on TH400s. There is a ton of info on troubleshooting and modifying this venerable GM trans.
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Old October 7th, 2011, 11:54 AM   #9
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Make sure the modulator valve and the manifold vacuum to it is functioning!
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Old October 7th, 2011, 12:28 PM   #10
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If the vacuum modulator is not working the tranny will not get out of first. Had this happen when I changed a intake manifold and the guy who done the work did not reconnect the hose to the valve. good luck with it.
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Old October 8th, 2011, 09:15 AM   #11
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I did everything the manual said, checked everything but the problem was still present.

I finally opened the governor and check it out!!

Luckily I had another change, and I recovered the piece
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Old October 9th, 2011, 05:26 AM   #12
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Quote:
Originally Posted by olds67 View Post
I did everything the manual said, checked everything but the problem was still present.

I finally opened the governor and check it out!!

Luckily I had another change, and I recovered the piece
Wow! I never saw one eaten up like that before? Anyone have any idea of what caused this? maybe just fatigue from age? Anyway I hope this solves your problem. You need to change fluid and filter again too!
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Old October 9th, 2011, 09:45 AM   #13
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Wow! I never saw one eaten up like that before? Anyone have any idea of what caused this? maybe just fatigue from age? Anyway I hope this solves your problem. You need to change fluid and filter again too!

in fact it is the only part that I left old.
fluid, which do you recommend?
I use Castrol TQ 3 is the best in Italy
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Old October 9th, 2011, 05:29 PM   #14
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Hopefully the governor bore isn't chewed up. If so, it time for a rebuild and a governor repair sleeve installed.
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Old October 9th, 2011, 05:29 PM
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