Adjusting Bypass Vavle for smooth shifts

ovrszd

Well-known member
I'll try to explain and clarify the adjustment of the Bypass Valve to allow for easier shifts. We've all experienced and dealt with our RTVs being stubborn to get out of gear. I believe the '08 and newer models have a double Bypass Valve that is operated by the pull knob on the dash and/or the application of the brakes using the pedal. Older models only have the dash knob, not sure of the years. Older still models don't have either. Someone can clarify the years of those changes??

So the mechanical purpose of the Bypass Valve is to relieve hydraulic pressure from the drive system to allow the shifter to change range selection and/or reverse.

On my '08 model the valve is located just above and rearward from the driver's side (left) rear axle ujoint protruding from the side of the transaxle housing. It has two levers vertically stacked.

The top lever is connected to the dash knob and activated by pulling the knob. This is a simple mechanism and is adjusted by changing the cable adjustment.

The bottom lever is connected to the left rear wheel brake cam lever and activated by applying the brakes using the foot pedal or by activating the park brake lever. This one is much more complicated.

The first picture is taken from just above the left rear tire. It clearly shows the two bypass valve levers. It also shows the top lever being connected to the dash knob cable. And it shows the bottom lever being connected to a spring which goes forward and connects to the brake cam lever with an adjuster.
 

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ovrszd

Well-known member
Now, if the first picture and description is clear, we can move on.

The Brake Cam Lever is used to activate the "wet disc" brake for the left rear wheel which is enclosed in the transaxle housing. The cam lever when pulled forward or toward the front of the machine activates the internal brake. This action is performed in two ways. Applying the pedal brake, which pulls the lever using a hydraulic brake cylinder. Or pulling the hand/park brake.

The lever has three linkages connected to it. The top linkage is the hand brake cable and is adjusted by changing the cable adjuster. The lower forward linkage is the pedal brake and is adjusted using the threaded bolt in the picture. It is the linkage marked by the blue paint. The rearward linkage is attached to the spring we discussed earlier which is connected to the lower lever on the bypass valve.

This picture is taken from in front of the left rear tire. Again, the linkage marked with blue paint is the brake pedal linkage. The brake hydraulic cylinder which is activated by the pedal is just out of the picture to the left. Apply the foot brake pedal and you pull this linkage which moves the brake cam lever and applies the brake.

Above the painted linkage you can see the hand/park brake cable fastened to the top of the brake cam lever and going forward. Apply the hand brake and you pull the brake cam lever applying the brake. Just behind this linkage is a large spring attached to the cam lever running rearward. This ensures the brakes are released when not being activated.

Behind the painted linkage and going rearward is the adjuster and spring that fastens to the bypass lever lower lever. This transfers any action that activates the brake cam lever to the lower bypass lever which, if properly adjusted, should relieve the HST pressure and allow shifts. This can be adjusted by removing the cotter pin and pin assembly, releasing the clevis so it can be turned, or by unhooking the spring from the threaded shaft of the adjuster and turning it. To apply quicker bypass valve relief tighten the spring. To apply later bypass valve relief loosen the spring.
 

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ovrszd

Well-known member
I started adjusting, tightening the linkage attached to the lower bypass valve lever one turn at a time. Each time I would test drive. It immediately started improving the shifts. I continued to tighten, one turn at a time until the fourth turn. At that time, on a steep grade, in gear, let off the gas pedal and machine stopped. Slowly start applying brake pedal and just before the brakes would hold the machine the HST would release and allow the machine to coast. I didn't want that action. So I went back to three turns of tightening. At this adjustment the machine brakes apply and hold the machine before the bypass valve is activated releasing the HST pressure. The best scenario I could get.

If I rush my shifts by trying to shift gears just as the machine stops movement it still tries to bind for a split second. If I relax the shifts at a more normal pace it doesn't bind. I haven't had to use the dash knob at all since adjusting.

Here's one last picture for any clarity that I might have missed. This one is taken from behind the left rear wheel facing forward. Note exhaust pipe in upper right corner.

Anyone that sees anything I missed please chime in for clarification. Don't want to mislead anyone.
 

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bczoom

Senior Member
Staff member
Gold Site Supporter
Great info, thanks!

I've added this thread to our "Sticky" Index to some popular / useful RTV threads
 

RealtreeRTV

Member
Thanks Richard for taking the time to make this excellent tutorial. I am going to give it a go. I will definitely keep track how much I move it, like you did. I'm glad this all came up because I didn't even know my pressure release was tied to the braking. I think brake pliers to release the rear part of the spring would work great to ease adjusting.

There is a grease fitting on top of the pivot for the bypass that some people may not know about. It can be seen in Richards first and third picture.
 

ovrszd

Well-known member
Yeah, I did the adjustment by repeatedly unpinning the clevis. Probly could have save some effort by unhooking spring.

I'll also add my amount of adjustment might not match yours. So I'd suggest some trial and error to get it right. Post your results.
 

RealtreeRTV

Member
I'll do it this weekend. I know mine will probably vary from yours but I'll adjust in 1 turn increments like you did.
Looking forward to hopefully not using the dash knob as much.
 

ovrszd

Well-known member
After spending a few minutes reading my $10 WSM I'd like to add something.

By the Manual, the brake cam levers on both sides should first be adjusted. This creates a properly adjusted brake system. Assuming you have that situation, then the adjustments discussed above can be accomplished.

An assumption on my part was that a machine with less than 200 hrs on the meter probably already has properly adjusted brakes.

I'll play with this over the next couple days when I get time and confirm my assumption.

If you have a machine with high hours I would suggest adjusting the brake system first, then adjusting the bypass valve linkage.

If the bypass linkage is adjusted first, then the brakes are adjusted, it changes the dynamics in the bypass linkage and could lead to an improper adjustment.

Clear as mud right??

I can go thru the process of adjusting the brakes if anyone needs it??
 

ovrszd

Well-known member
Gladly.

The manual says to move the brake cam levers forward until resistance is felt. Then adjust the hydraulic brake cylinder linkage until the slack is removed. I don't like that concept. Your interpretation of when slack is removed and mine might differ. The problem is you could possibly adjust your brakes so tight that they would be dragging all the time and cause heat/wear issues.

So,, I lifted the rear tires off the ground. Then while rotating the tire I by hand moved the brake cam lever forward until I felt brake resistance. I then looked at my linkage to see if there was slack. On the driver's side (left) I had none, it was properly adjusted. On the passenger side (right) there was considerable slack. So I tightened the adjuster.

The adjuster is the linkage with the blue paint that I referred to earlier. It's a threaded bolt with left hand threads on one end, right hand threads on the other. So, if you turn it one direction it gets shorter, turn it the other and it gets longer. You'll figure that out once you mess with it.

On the right side things are pretty simple since the only other thing attached to the brake cam lever is the hand brake cable. On the left side you are also dealing with the bypass valve linkage. So you might feel resistance when trying to pull the brake cam lever forward on that side. That's why I suggest elevating the tire, turn the tire while prying the brake cam lever forward with a screwdriver or whatever tool you prefer until you feel the brake applying.

Understand that if your brakes are out of adjustment the hydraulic brake cylinder is going to be hanging onto the brake cam lever because there isn't significant force to cause the cylinder to fully extend. So I start by manually extending the cylinder all the way by pulling rearward on the linkage. I can't think of any other way to clarify that.

I'll take some additional photos if needed.

I used a large screwdriver to pry my brake cam levers forward until I felt brake resistance while turning the tire. All the other linkages just have to come along.

My result was the I gained brake pedal. What I mean is my brakes activate when the pedal is higher than they used to. My right rear being out of adjustment was using up pedal travel before the brakes activated. How I understood this was if I pushed the brake pedal hard, and then released it and pushed it hard again, it was higher the second stroke. That indicated to me that I had brakes out of adjustment. A rising pedal with subsequent applications indicates brakes out of adjustment. A soft pedal indicates air in the system.

If I didn't describe this clearly feel free to ask more questions. Kinda hard to pass on this type of information without being physically together. :)

Also, it's my opinion that a new machine might be purchased and delivered out of adjustment. I doubt the brakes or the bypass valve are adjustments that the selling dealer is required to check.

Clear as mud, right..... ;)
 

RealtreeRTV

Member
I assume that you have to unpin the linkage between the hydraulic brake cyl. linkage and the cam levers, so that when you manually apply the brakes with a bar you can tell if you need to adjust to make everything line up again??
 

ovrszd

Well-known member
I assume that you have to unpin the linkage between the hydraulic brake cyl. linkage and the cam levers, so that when you manually apply the brakes with a bar you can tell if you need to adjust to make everything line up again??

I didn't. Actually the hydraulic brake cyl linkage is slotted where it fastens to the brake cam lever. This lets you figure it all out without unpinning it.

Hopefully. :)
 

ovrszd

Well-known member
If you look at my second pic you can see the slot on the blue painted clevis.

Remember to pull the hydraulic cylinder plunger rearward as far as it will go. This will have the front end of the plunger about a 1/16th of an inch from flush with the cylinder housing.
 

RealtreeRTV

Member
I adjusted brakes but struck out on the brake operated pressure release.
To make a long story short, there are 2 reliefs. The top one is operated by the dash knob and the bottom is tied into the brake linkage.
After adjusting the brakes I started on the brake operated relief linkage.
The bottom relief is going all the way in but it is not relieving any pressure.
I'm guessing there is a problem with that spool.:pat: Not sure if I want to get into pulling it.


I ended up getting the workshop manual download, thanks for the link.
 

ovrszd

Well-known member
I adjusted brakes but struck out on the brake operated pressure release.
To make a long story short, there are 2 reliefs. The top one is operated by the dash knob and the bottom is tied into the brake linkage.
After adjusting the brakes I started on the brake operated relief linkage.
The bottom relief is going all the way in but it is not relieving any pressure.
I'm guessing there is a problem with that spool.:pat: Not sure if I want to get into pulling it.


I ended up getting the workshop manual download, thanks for the link.

Hmmmmmm... I can't answer this question.

Does the hand brake relief work??

Hard to imagine one half of the valve works and the other doesn't.

What the heck?? I'll play with mine some more and offer tests to apply to yours.
 
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