ZF shift linkage adjustment

[Doug Dyar]

My RBT transaxle shifter linkage needs adjusting. It wants to kick out of third gear on hard acceleration. My car is RHD with the sill-mounted shifter.

Looking for info on how to adjust the linkage. I'm thinking just a minor change will solve my issue. I tightened the top two studs holding the transaxle to the frame and now it wants to misbehave in third gear.

Is there a procedure to go through like the one used for a Hurst shifter where the linkage is pinned in place and then the rods are adjusted to fit the centered levers?

Thx!

Doug

 

[Randy V]

Doug - do you have “Shift Stops” on your shifter? When I encounter these, I typically set them so there’s a mm or so between the shifter and the stop when the gear is fully selected.

 

[Ian Clark]

Hi Doug,

Can you post some pictures of your shifter, the operating rods or cables and the input connection to the transaxle? It's best to get ahead of this before transaxle damage occurs.

In this situation, with neutral selected (2-3 gate) in the transaxle, see how far out the gear selector is from the middle of all throws. That's a good place to start.

However, it's not possible to properly diagnose and clearly recommend adjustments without pictures.

Cheers
Ian

 

[Doug Dyar]

Hi Doug,

Can you post some pictures of your shifter, the operating rods or cables and the input connection to the transaxle? It's best to get ahead of this before transaxle damage occurs.

In this situation, with neutral selected (2-3 gate) in the transaxle, see how far out the gear selector is from the middle of all throws. That's a good place to start.

However, it's not possible to properly diagnose and clearly recommend adjustments without pictures.

Cheers
Ian

Ian
I'll get some pics tomorrow when I am at the shop.
Thanks for the replies!
Doug

 

[Doug Dyar]

Here's a shot of the shifter mechanism.

 

[Ian Clark]

Hi Doug, from the picture we can see a u-joint tightened on the splines. That's one point of adjustment. There will be at least one more u-joint and support bearing between the transaxle and the shifter assembly.

It's important to know if any of the u-joints or bearings have moved or shift rods bent since the last time the car shifted properly. When the transmission kicks out a gear it's probably not fully engaged.

Put the car up on stands while adjustments are made and be kind to the transmission while rowing through the gears. If any gear doesn't want to just engage adding force will not tell you anything about shifter alignment.

Since the car is up in the air, you can turn the wheels a bit to help the syncros do their job. This would be the time to have a helper (or two) on hand to push the clutch in while changing gears and turning the wheels. If you have an open diff, both rear wheels will have to turn simultaneously in the same direction.

Turning the wheels and depressing the clutch is required to prevent the shift forks, detent springs and syncros from allowing you to find the optimum shifter alignment.

Additional note: the ZF 5DS-25 and RBT are machined to optimum tolerances at racing temperature. So, on driving or adjusting from cold the shifter will feel stiff and gears harder to engage.

The first step is to release the u-joint shown (does not have to come off the splines - just loose), put the transmission in neutral and confirm the shifter no longer moves the input shift rod in and out on the 2-3 gate.

Take a look at how central the shift stick appears in the housing for center and across the gate. The middle of the throw should be equal between neutral and 2 and 3. Position the stick so it looks right then tighten the splined u-joint at the transaxle.

Another note: Middle of the throw and central on the stick is based on available travel in the shifter assembly, therefore in the middle your shift stick may not be "strait up".

Now you can select 2nd, confirm it's fully engaged and the pull the stick back to neutral. If it comes back to the same position, you're good, if it does not, Do Not attempt to select 3rd gear. Something is wrong.

"Something" includes a) the initial resetting not centered on the gate b) shifter was out one spline but worked on loose driveline mounts c) bent intermediate rod c) hanger bearing loose or its support has bent or moved d) something bent worn or misadjusted in the shifter assembly in the cockpit.

Hopefully it works ok, then gently go through the gears in sequence starting with reverse since it's on a dogleg. If there are further adjustments to be made reverse will be difficult or impossible to engage, remembering to turn the wheels as you go from neutral into any gear.

Let us know how it goes...

Cheers
Ian

 

[Julian]

It is common to incorporate a turnbuckle sleeve separating the rod somewhere so one can finesse adjustment fore aft and side to side to center the shifter in the gate.

 

[Doug Dyar]

So if I interpreted the above posts correctly, the clocking is likely ok, but the length of the shift rod needs adjusting.

If I loosen the splined connector and place the shifter in neutral, how do I confirm that the shift rod is in neutral?

 

[Ian Clark]

Hi Doug,

The first step after loosening the splined connector is to put the transmission input shaft in neutral.

Don't worry about where the shifter is positioned. The base line for all gear selection has to start at the transmissions' neutral position.

The transmissions detent springs will go to the 2-3 gate automatically, check to make sure the input shaft is sitting equal to 2nd or 3rd.

Once you absolutely know the transmission is in neutral you can make an initial setting of centralizing the shifter in the 2-3 gate and tighten the splined connector. Then carefully attempt to engage each gear. If all gears engage positively and completely - great. If not start over again.

Check all moving parts for binding or bending, you don't want to take chances with the transaxle.

It's tempting to think if you simply put the transmission in first and the shifter in the 1st gear position the tighten the splined connector you'd be done. Unfortunately, it's not that easy. All tolerances and any irregularity in angles, bearings and rods will be optimum for 1st but will accumulate to work against you as move through the gears.

About the clocking, that's hard to know for sure if the initial settings were made on loose mounts. On power upshifts there can be large torque reversals (as you noticed were reduced by tightening the transmission mounts). The entire drivetrain wants to wind up and rotate on hard acceleration so you could be slightly off on clocking too, probably not but still possible.

Take your time, don't force anything and you'll get it.

Cheers
Ian

 

[Tom]

confirm the trans is in neutral by lifting back end of car and attempting to turn rear wheels by hand when clutch is locked. Assuming it has a limited slip diff. If they turn, it's def not in gear.

 

[Doug Dyar]

The solution to my problem was to adjust the turnbuckle in the linkage.

The movement of the engine/transaxle assembly resulted in the shifter going out of adjustment. The shifter itself was interfering with the shifter gate, preventing the transaxle from going fully into gear. Re-centering the shift handle in the gate proved to be the fix.

On my SPF MkII car's rh shift, rh drive configuration, one needs to remove the seven sheet metal screws, shifter knob, and 3 forward shift gate screws in order to remove the sheet metal shifter linkage cover alongside the driver's seat.

This exposes the shifter shaft and the adjustment turnbuckle. Loosen the jam nuts and you can shorten or lengthen the shift rod assembly. It might be helpful for a second set of hands to hold the shifter while tightening.

It's a bit of a trial-and-error process. I started with the shifter in the middle of its throw and standing vertically in the gate. A small adjustment in the turnbuckle goes a long way...