AQ 250 transmission replacement

mitsu_matt said:

I have developed a shifting problem with my VP 250 drive. When shifting into forward I don't get engagement until I bring the RPM up to about 1200. Once engaged the drive operates fine until RPM drops under 900 or so. Reverse engages normal at any RPM. It has a brand new shift cable, I have tried maxing adjustment with no improvement. The retaining plate for the cable is there and tight. The problem is becoming progressively worse. I am thinking I have a worn cone clutch issue.
You most likely have some metallic debris stuck in the oiling groves on the FWD side of the brass sliding sleeves.
If so, you will want to remove the sliding sleeve.

You will start by removing the aluminum clamping collar and the steel bearing box.
DO NOT attempt to remove the 4 cap screws without first applying heat to the main gear case at the area of the 4 thread inserts.

After the bearing box is removed, you will remove the top cover and will remove the LH thread nut.
Once the nut is removed, the upper driven gear/bearing assembly can be lifted out.

The vertical shaft along with the lower driven gear will be lowered out of the main gear case.
Once out, you will have access to the sliding sleeve.
Pay close attention to the caged needle bearings and spacers.

All of this can be done without the need for any re-shimming when going back together.

By chance did you install gear oil, or synthetic oil, instead of 30W engine oil?

I have a spare drive and would like to just swap the transmission portion out.
The 250 transmission is a small bearing unit. It must be replaced with another 250 transmission, or an early 270.


What do I need to look out for as far as shimming is concerned? If it is too much of a pain I can just swap the entire drive but I would rather just use the transmission.
If you do this, I can explain the shimming process.

Thanks in advance for any help.

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mitsu_matt said:

Plot twist! Pulled the transmission off last night, pulled the shift fork assembly out and felt the cone clutch slide freely to both cups and engage easily.
Even with debris in the oiling groves, the sliding sleeve will appear to shift easily and correctly.

I don't think it's a wear or debris issue since the drive doesn't slip once it is actually in gear.
The sliding sleeve rides on the steep spiral cut splines of the vertical shaft.
As the sleeve contacts the rotating gear cup, friction is created.
The steep cut spiral splines want to further pull the two components together.
This friction between the sliding sleeve and the rotating gear cup is what creates engagement.
As the load is increased, friction increases to the point of eventual full engagement.
In other words, the more friction the greater the engagement.


So I started investigating the tee lever closely and found it not fully engaging to the end of it's throw in forward.
Please explain "tee lever".

I could see some galling on the brass. I looked up an online service manual and figured out how it all comes apart. Drove out the roll pin and removed the brass eccentric. I cleaned it up with some scotchbrite and smoothed out the bore with some 800 grit and now the lever rotates smooth and free. I reassembled the shift housing and now it positively locks pin at the end of it's travel in forward.
Hopefully you replace the eccentric piston seal.
By the way, this seal is directional.
Also, when polishing the eccentric piston you must polish in a radial fashion and with very fine paper. We want an absolutely smooth surface for the seal lips.

I am going to reinstall the transmission after work tonight and make sure I have the cable adjustment correct now that I know where fully engaged is and make sure it is getting there when I shift it.
Make sure that the cable can move the gear yoke further than need be for full eccentric piston rotation.
Also make sure that the gear yoke does not contact the Intermediate housing in either direction with full cable movement.

Divide this gear yoke travel equally (for neutral) and only then adjust the vertical rod as to fit into the eccentric piston arm.

FWD engagement will be a result of a fully retracted cable at the gear yoke.
REV engagement will be a result of a fully extended cable at the gear yoke.

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mitsu_matt said:

I used straight 30 weight mineral oil, non synthetic. I polished the brass eccentric shaft (what I first referred to as the tee lever) in a radial fashion, and did not need to polish at the seal end to get smooth movement again.
You would be polishing this surface as to give the seal lip a good sealing surface.
Swirl marks can cause a seal to breach oil.

You raise a good point about cleaning out the cone clutch, I might as well while I have it off. I will bring home a torch this evening and open up the bearing box to clean the cone clutch and cups.
Use a small hand held propane or map gas torch only. Oxy/Acet is too hot.

What is your opinion on lapping in the cone to the clutch with valve lapping compound while it is apart?
I've done this many times. There is a trick as to how you would rotate the cup in one direction as you rotate the sliding sleeve in the other direction, creating an equal pressure pattern.
DO NOT mix orientation of cup/gear and top/bottom of sleeve.

Also, do you know the torque spec for the left handed thread nut for reassembly?
I am reluctant to offer torque specs...... (too much risk of misinterpretation, etc).
See your OEM service or work shop manual.
Be sure to prime the threads (clean of any oil) and use a thread-locker.

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