Backlash in the Transaxle?

[DoctorDex]

I came up with an idea on how to fix the backlash in the transaxle problem, but I'm having a hard time putting it into action. I bought a new VCU and the seller included a new planetary gear assembly. Unfortunately, there is still a small amount of play between the new VCU and the planetary gear assembly.

Here is what I want to do:

1. In the planetary gear assembly there are a total of 6 pins, three long dowel pins and three shorter pins. I'd start by tapping out the long dowel pins on the "old" planetary gear assembly and I'd save them for later.

2. Tap out the small pins on the "new" planetary gear assembly and drill 3 new holes in the VCU in a pattern that line up with the holes where the short pins once were.

3. Take the long dowel pins from the "old" planetary gear assembly and put them into the "new" planetary gear assembly. The new pins would occupy the holes once occupied by the short pins

This would create a planetary gear assembly that would have a total of 6 dowel pins and there would be 6 dowel pin holes on the VCU.

This plan sounds nice and dandy (to me at least), the only problem is I'm having a very difficult time trying to find a shop that can either drill or machine out the 3 new holes in the VCU. Surely there has to be a way to make new holes in hardened steel? Does anyone know how I can get three new holes made in the VCU?

Thanks.

Declan

[blindmist]

there should be a little to allow oil in there. same way rods on a crank work.

um, if you drill the vcu, you have ruined it.

[DoctorDex]

The holes in the VCU wouldn't be all the way through and they woudn't penetrate into the inside of the case. They'd only be ~ 4-5 mm deep, just like the 3 holes that are already in their when it comes from the factory.

As far as the dowel pins holes are concerned, why would they need room for oil? It's not like as if they are moving parts. They remain fixed in the same position at all times.

Declan

Edit: From what I gather the 25 spline 5 speed and 6 speed dowel pins holes are round and they have very little, if any, room for oil.

[DoctorDex]

The only alternative I can think of would be to use flared dowel pins, where the ends that stick into the VCU would be larger in diameter to take up the extra slack. Does anybody know where you'd find something like that, perhaps you could get them custom made?

Declan

[maddog]

be careful

there might be more metal around the original bores to accomidate for them

where u want to make a bore might not be thick enough. maybe its 6mm thick and if u bore 5mm that could be an issue. just saying u dont know if it was a solid piece or cast and then machined

[DoctorDex]

I have a bad VCU I'm willing to experiment on and I'm going to try and bore through it to see how much metal there is to work with.

From the looks of things, the metal around the original bores is hardened to a greater degree than the rest of the case. I think this could create issues down the road, as the new holes wouldn't be as strong as the OEM holes. Hence, my latest idea, the flared dowel pins.

Flared dowel pins (made with 300m or harder steel) could be used to take up the OEM slack. The planetary gear assembly could then be "tapped" into the VCU. It would be a press fit and thus zero back lash to begin with. This would prevent the hammering effect from occuring and it would reduce the strain on driveline components. I suppose the only thing I'd have to worry about with this idea would be heat related metal expansion.

Here's a thought, perhaps the excessive backlash in 18 spline center differentials contributes to the "weakness" of 18 spline output shafts?

I've included some pics to help everybody know what I'm talking about.

Declan

[DoctorDex]

Nix both of those ideas. After a great deal of thought, I think the best/easiest/simplest solution is just to tap the long dowel pins out of the planetary gear assembly, weld them in place on the VCU and then tap the planetary gear assembly onto the VCU.

Can anybody see any downsides to doing it this way?

Declan

[red_3000]

Originally Posted by DoctorDex

Nix both of those ideas. After a great deal of thought, I think the best/easiest/simplest solution is just to tap the long dowel pins out of the planetary gear assembly, weld them in place on the VCU and then tap the planetary gear assembly onto the VCU.

Can anybody see any downsides to doing it this way?

Declan

You'd have to weld the pins perfectly. I think there is prtty tight tolerance between the three dowell holes in the planetary gear assy.

I take it the pins coming out of the planetary gear assembly are slopping around in those 3 holes on the VCU?
I do think the idea to have some new dowell pins machined is the best bet. The inner part would and length would stay the same, but would expand out how ever much it would need to press fit the planetary assembly onto the VCU. Or if not press fit, at least tighter tolerance.
I don't see what could be bad about that. And I also don't know why it'd need oil t get in there.

[DoctorDex]

I was planning on tapping the pins 9/10th's of the way out of the planetary gear assembly and then I'd put the planetary gear assembly on top of the vcu and insert the dowel pins into the VCU holes. This would allow ~ 2 - 3 inches to get in there with a welding equipment and it would ensure that the holes were aligned correctly because the planetary gear assembly would be holding them in place. Once all the welding is done, all I'd have to do is tap the planetary gear assembly back into place.

Does this seem like it would work? I'm hoping to try it later on today, first on the bad vcu I have laying around and then if it works, on the good one.

Declan

[DoctorDex]

Just figured I'd post an update and conclude this thread.

As of tonight, I have officially thrown in the towel with regards to this project. The welding fixes are impractical to do, have questionable longetivity and I'm fearful I'll end up ruining the new VCU.

With that being said, I was examining my old bad VCU and I noticed that it makes a clunk when I hit it with my hand (the new one doesn't do this). I'm hoping this is the cause of the clunk I've been hearing when going from decel to accel. If my car continues to clunk with the new VCU, I think I'll have the custom flared pins made. I made some measurements tonight and I found the planetary gear assembly dowel pins to be 2mm too small in diameter for their respective holes in the vcu. Can anybody think of a reason why the pins are so much smaller? Perhaps, ease of installation?

Declan