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1988 F250 7.3 ZF5 won't shift into 4th gear


superds

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2" body. 1.5" coil spring spacers/rear block
I have an 88 F250 with manual transmission and it won't shift into 4th gear. Ever. It shifts into all other gears just fine but fourth won't go. I just bought this truck and it was like this from the first time I drove it. You have to skip 4th gear and shift from 3rd to 5th. I'm trying to get this truck back on the road so I can use it for towing, so 4th gear will be really nice to have!

I tried searching the internet and this site and can't find very many people with such an issue, as most have clutch hydraulic issues which prevent proper shifting. I even saw the ZF troubleshooting manual and it basically says the transmission is garbage.

Anyone have an idea what specifically would cause this in the transmission? I'm trying to weigh my options:
A. Replace transmission with another of questionable longevity
B. Try to repair it myself (don't really know how yet)
C. Take the transmision out and to a transmission repair shop (almost sounds like the scariest option since who knows what they'll charge for something that could be simple!)
 


RonD

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Well the transmission will have to come out regardless of what option you choose.

5-speed transmissions have 3 shift rods and 3 shift forks, and 3 Dog Gears
1 each for:
1st/2nd
3rd/4th
5th/reverse

This is why the shift pattern is the way it is.
When you move the shifter over to the left then push it forward you are selecting the 1st/2nd shift rod an its fork which holds the Dog Gear, and then pushing that Dog gear to mesh/lock into 1st gear.
When you shift into 2nd you are pulling the same Dog Gear out of its connection with 1st and moving it to connect to 2nd.
Same for 3rd/4th and 5th/Reverse
Neutral is when all 3 Dog Gears are between, not touching, their respective "gears"

1st, 2nd, 3rd, 5th, and reverse Gears are always engaged and always spinning when transmission is.
The Dog Gear is what connects these "gears" to the output shaft/rear wheels.
So the 3 Dog Gears are what actually engages the engine to the rear wheels.

4th "gear" is not really a gear, on a 5-speed 4th gear is a 1 to 1 ratio between input shaft(engine RPM) and output shaft(drive line RPM), so no "gear" is needed, when you shift into 4th the Dog Gear connects input and output shaft together directly.

If you can not psychically move shifter in the 4th gear position it could be a mechanical problem with that shift fork or shift rod which is usually not hard to fix, usually being the key word.
If shifter goes into 4th position but there is no engagement could be another issue, usually full rebuild issue, but again usually is the key word.

But in any case transmission would need to come out so you can have a look, no way around that.
And a look inside would also tell you if a rebuild or exchange would be best.
 
Last edited:

superds

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1984
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Ford Bronco II
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Engine Size
5.0
Transmission
Manual
2WD / 4WD
4WD
Total Lift
2" body. 1.5" coil spring spacers/rear block
Thank you for the reply and useful information. I did forget to mention that the shifter does not even go into the 4th gear position.



I realize it's probably going to have to come out regardless of which of the three options I end up doing. I'm just trying to understand if I need to search for another transmission or if there might be hope for what I have. If it has a chance of being repaired I can rip it out right now but if I need a new one I would leave it in until I can find one at a good price since it's still somewhat drivable as is.
 

RonD

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Outside of a broken case I am sure it can be repaired.

I would first check out worse case scenarios.
Full rebuild, turn around time and cost, warranty??
Used replacement, warranty??
New/rebuilt replacement/exchange, no waiting, warranty??

Once it is out you may find the trans is in good condition, if it isn't "whiny", or otherwise noisy, that could be the case and repairing 4th might not require a rebuild.
Then when looking at the cost of fixing 4th you have the comparison prices from above.

I would budget for new slave at the least, whole clutch setup if funds permit.
 

superds

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Ford Bronco II
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Engine Size
5.0
Transmission
Manual
2WD / 4WD
4WD
Total Lift
2" body. 1.5" coil spring spacers/rear block
I was hoping to avoid removing it until I had a good idea what I'll be doing to fix the issue but it sounds like I'm going to have to take it out to diagnose further.

It has an external slave so I won't probably replace that when it's out (takes about 10 minutes to replace with the transmission in place) but for sure I'm going to replace the clutch and rear main seal (even though it isn't leaking, one of the few vehicles I've ever acquired that didn't drip oil onto the floor).
 

RonD

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You lucky dog..............about the external slave.

Maybe some one has fixed similar issue with that trans, and you will find it with a search, but I didn't see much about losing 4th gear only
 

superds

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1984
Make / Model
Ford Bronco II
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V8
Engine Size
5.0
Transmission
Manual
2WD / 4WD
4WD
Total Lift
2" body. 1.5" coil spring spacers/rear block
Yeah, I've been on the other side of the slave cylinder issue before. Generally I've replaced clutches before because, hey, I've got the transmission out to replace the slave cylinder so I might as well replace the clutch too.
 

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