won't shift to higher gear

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Feb 3, 2010 | 06:32 PM

jwolfe60

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won't shift to higher gear

I have a 88 f250 7.3 xlt lariat 4x4 that refuses to shift into higher gear so my top speed is about 35mph with her going almost full bore.
Any ideas of where to start, i've already used lucas transmission product.

Feb 3, 2010 | 08:38 PM

Mark Kovalsky

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From: SE Florida

It is probably a problem with the vacuum modulator. It's located on the right side of the trans. There is a vacuum line to it. Take the vacuum line off and see if there is oil inside. If so the modulator has failed. If it is dry start the engine and see if there is vacuum on the rubber line. There should be quite a bit of vacuum with the engine at idle speed.

Feb 3, 2010 | 08:57 PM

jwolfe60

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thank you for the information, I will check out the modulator first.

Feb 3, 2010 | 10:10 PM

stuart1

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From: Somewhere Saskatchewan

You can also look at the kd linkage.
It should have a small return spring.

If it breaks the kd rod will be in a kickdown position which will affect upshifts.

Feb 4, 2010 | 04:20 AM

Lazy K

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What they said. However as well as those things you have a vacuum valve mounted on the side of the injector pump (between V at front of engine) that varies the vacuum to the trans depending on throttle position. Check the vacuum pipes to it for leaks. One pipe should go to it from the engine vacuum pump and the other down to the trans,
Also make sure your vacuum pump is giving around 18-20in of vacuum. If the brakes are good then the vacuum pump is good.

Feb 7, 2010 | 01:06 PM

jwolfe60

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i just replaced the modulator since the vacuum line behind it was slightly wet. I bought the one with the purple stripe (not the green striped one) and i had to take the metal pin that stuck in the front hole of the old modulator and put it in the new one since it didnt come with one.
It's about 10 degrees outside so as soon the heater warms it up ill give her a test drive.

Feb 8, 2010 | 05:52 AM

mistakenID

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From: West Valley Utah

Quote:

Originally Posted by Lazy K

As long as it's a diesel, what Lazy K says is correct. If not diesel, good luck finding the vacuum pump, injection pump and VRV LOL!

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Feb 8, 2010 | 08:34 AM

stuart1

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From: Somewhere Saskatchewan

Quote:

Originally Posted by mistakenID

As long as it's a diesel, what Lazy K says is correct. If not diesel, good luck finding the vacuum pump, injection pump and VRV LOL!

7.3 should be a diesel.

Feb 26, 2010 | 07:10 AM

#10

jwolfe60

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still not working

I replaced the vacuum modulator and checked the KB spring and still isn't working. When it was idleling i took the tube off the vacuum modulator and really couldn't feel with my finger a vacuum at all, but the brakes are working fine.... any more suggestions?

Feb 26, 2010 | 09:18 AM

#11

stuart1

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From: Somewhere Saskatchewan

You must have vacuum to have a correct shift speed.
Look for a leaking or disconnected hose.

Feb 26, 2010 | 09:53 AM

#12

Lazy K

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Quote:

Originally Posted by Lazy K

Check this out. At idle you should have strong vacuum at the pipe in and out of the valve at the injector pump. If weak vacuum out the valve may be bad or need adjusted.

Feb 27, 2010 | 08:36 AM

#13

jwolfe60

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all the lines looked tight, i pulled off the valve and i have a strong vacuum in, so I'll look to replace this valve. Any ideas on where to find it, the local Napa said they can't get it in.

Feb 27, 2010 | 10:28 AM

#14

Lazy K

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It is a Ford only part so if you can`t get one on ebay.com then try partsguyed.com for a good price from Ford.

Mar 4, 2010 | 06:26 PM

#15

jwolfe60

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replaced the vrv and now i get a good vacuum to the tranny, but it wants to shift early at low speed and no reverse. could this be from the purple stripe vacuum modulator i put earlier or something else. i didn't know if this had to be a green striped one since it is a diesel?