Late Shifting Problems

Matt15 · December 16th, 2008, 10:45 PM

Hi

I have a few problems with my 1970 oldsmobile tronado. I had found that recently When the car is accelerating normally or lightly it will rev really high before shifting.

Also when say the car is shifting from 2to3 it revs very high in 2 then shifts into 3 but the car only will only rev for about 5 more seconds, in 3, then it would stall as if its not getting fuel. I will add that when the car is in park I can rev it very high with no problems.

I Have driven the car no more than 40km within the last year as I have been working at it in the garage. But I have recently noticed this issue now and are sure I did not have this issue when I bought the car.

If anyone has information regrading this give me a yell.

Thanks

dan2286 · December 16th, 2008, 11:44 PM

How does the fluid look? Is it full? Do you know the last time the filter was changed?

Matt15 · December 17th, 2008, 12:51 AM

Havent changed the fluid or filter since I've had the car. Give that a try first but from the looks of the fluid it seems ok.

joe_padavano · December 17th, 2008, 09:02 AM

Late shifting on the TH350/400/425 transmissions is nearly always due to problems with the vacuum modulator. The vac modulator senses manifold vacuum to determine engine load: high vacuum = light throttle opening = low engine load and early shifting; low vacuum = heavy throttle opening = high engine load and thus late shifting. The vac modulator has a diaphragm connected to manifold vacuum by a pipe that moves a valve and thus regulates line pressure and shift points. If the diaphragm is bad or the pipe has come loose, the trans thinks there is low vacuum (ie, at atmospheric pressure) and thus the trans shifts late.

Start by checking the vacuum line to the vac modulator. Be sure it's connected then put a vacuum gauge on it and check that there is vacuum at the connection to the modulator. If so, change the modulator.

85olds442 · December 20th, 2008, 06:15 PM

Matt, under load ( when you are driving the car it will use more fuel ) as opposed to when you are just sitting there reving the engine without a load on it. You might want to check the fuel pump, the the fuel filter..If they check out then replace the fuel line with a larger size. Factory was probably 5/16th I would replace it with 3/8".
Hope this helps.

December 16th, 2008, 10:45 PM	#1 (permalink)
Matt15 Registered User Join Date: Jun 2008 Posts: 23	Late Shifting Problems Hi I have a few problems with my 1970 oldsmobile tronado. I had found that recently When the car is accelerating normally or lightly it will rev really high before shifting. Also when say the car is shifting from 2to3 it revs very high in 2 then shifts into 3 but the car only will only rev for about 5 more seconds, in 3, then it would stall as if its not getting fuel. I will add that when the car is in park I can rev it very high with no problems. I Have driven the car no more than 40km within the last year as I have been working at it in the garage. But I have recently noticed this issue now and are sure I did not have this issue when I bought the car. If anyone has information regrading this give me a yell. Thanks

December 17th, 2008, 09:02 AM	#4 (permalink)
joe_padavano Super Moderator Join Date: Mar 2007 Location: Northern VA Posts: 4,396	Late shifting on the TH350/400/425 transmissions is nearly always due to problems with the vacuum modulator. The vac modulator senses manifold vacuum to determine engine load: high vacuum = light throttle opening = low engine load and early shifting; low vacuum = heavy throttle opening = high engine load and thus late shifting. The vac modulator has a diaphragm connected to manifold vacuum by a pipe that moves a valve and thus regulates line pressure and shift points. If the diaphragm is bad or the pipe has come loose, the trans thinks there is low vacuum (ie, at atmospheric pressure) and thus the trans shifts late. Start by checking the vacuum line to the vac modulator. Be sure it's connected then put a vacuum gauge on it and check that there is vacuum at the connection to the modulator. If so, change the modulator. __________________ Joe Padavano 64 Jetstar 88 Conv 66 442 L-69 Conv 68 W-30 69 H/O 69 442 70 W-30 72 442 84 Custom Cruiser 86 Caprice wagon (w/307 Olds)

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December 16th, 2008, 11:44 PM	#2 (permalink)
dan2286 Registered User Join Date: Mar 2008 Location: North Ridgeville, Ohio Posts: 338	How does the fluid look? Is it full? Do you know the last time the filter was changed?

December 17th, 2008, 12:51 AM	#3 (permalink)
Matt15 Registered User Join Date: Jun 2008 Posts: 23	Havent changed the fluid or filter since I've had the car. Give that a try first but from the looks of the fluid it seems ok.

December 20th, 2008, 06:15 PM	#5 (permalink)
85olds442 Registered User Join Date: Nov 2008 Location: Colorado Posts: 15	Matt, under load ( when you are driving the car it will use more fuel ) as opposed to when you are just sitting there reving the engine without a load on it. You might want to check the fuel pump, the the fuel filter..If they check out then replace the fuel line with a larger size. Factory was probably 5/16th I would replace it with 3/8". Hope this helps.