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PLEASE HELP My '99 7.3L F250 transmission won't engage

3K views 15 replies 4 participants last post by  Mark Kovalsky 
#1 ·
I was driving my family and I up to the mountains for a camping trip and about an hour into the trip my trans shifted hard like three times in less than ten seckonds then made a loud squealing noise. I shifted into neutral and then back into drive but it wouldn't engage had to role to a stop on the side of the highway. My trans temp was within a normal range the whole time. There was no certain smells or anything out of the ordinary just wouldn't go into drive or reverse. Any help would be greatly appreciated!
 
#2 ·
PLEASE HELP My 99 7.3 F250 transmission won't engage

Mark can tell you for sure, but I suspect something let loose inside- like a snap ring. Will it move if you manually put it in low or second?


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#3 ·
That's a good question - will it move with the shift lever in 1 or 2?

Almost certainly something mechanical broke inside the transmission.
 
#6 ·
You can do some diagnostics and get a better idea of what broke, but no matter what it is the transmission has to come out of the truck.

If you try to start the engine and only get noises, most likely the flex plate broke. This is the least expensive possibility.

If you want do diagnose it further, get a 0-350 PSI gauge and install it in the test port. Get the pressure readings at idle in each position, and at stall in R, D, 2, and 1. If you get zero pressure at anytime you can stop. That will be the problem.

This is one of those rare cases where reading the codes won't help at all. This is not an electronic problem, it's mechanical.
 
#8 ·
Or the input shaft. Or the pump. Or the filter fell out. If the starter spins but the engine does not it's probably the flex plate.
 
#10 ·
Then the flex plate isn't broken. Something inside the trans broke. The only way to know for certain what broke is to take the trans out and tear it down.
 
#11 ·
Pull the pan- maybe you'll get lucky and find the wrong filter was in there and it fell out...


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#14 ·
Could have been a casting defect that finally gave way. Somehow, the force through the converter was greater than the shaft could handle. They sell billet input shafts just for this reason.
 
#15 ·
That's a first. Usually it takes 400+ Hp to have input issues.

They usually strip or ruin the splines before they break.

A new stock shaft should be fine.

Consider new raybestos gpz clutches and a sonnax sure cure kit when it's apart.
 
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