RBT stuck in reverse!

[Jeff Boulais]

I've got a RBT 5-speed in a Superformance GT-40 and the transmission is stuck in reverse. The shifter will move to all positions except reverse, when the shifter is in the neutral position the car will move in reverse. When the shifter in in any forward gear and the clutch is slowly released the car does not move and the rpm will drop, like its in 1st and reverse at the same time.

I hope that makes some sense....

Any ideas?

 

[Gary Kadrmas]

Only sense it does for me is spelled in dollars.

But that's not what you wanted to hear, right?

You might select reverse.....let out on the clutch, while backing up...and tap the brakes with your right foot...and at the same time, try to shift it out of reverse....or a combination of that and at the same time, touching the clutch with your left foot....too.

Other than that, sounds like you may have to pull the unit out of the car, and take it to the shop.

 

[Jeff Boulais]

The transmission is in reverse, the shifter however is free to select any gear, except reverse.

For example with the shift lever (inside the car) is in the neutral position the transmission is in reverse and upon release of the clutch the car will move backwards.

With the shift lever in 1st (or any forward gear) upon release of the clutch the car will not move and the engine rpm will drop. Like I'm in reverse and 1st at the same time.

If it doesn't make dollars it doesn't make sense, and this makes neither!!

 

[Jac Mac]

I have never been inside a RBT/ZF, but it sounds like the selector finger has slipped thru between the gate on the reverse fork and gate for the fork for whatever gears are next door to it. The fact that you can select one of the forward gears ( essentially get it in two gears at once ) while it is still in reverse would suggest that there is a problem with the interlock/detent system although this may have been overcome by brute force.Even if you manage to get it out of reverse by partial dissassembly the interlock system needs to be investigated to ensure it does not happen again. If it does somehow manage to select two gears at highway/race speed the initial problem will be insignificant compared to the end result.

Im starting to think these ZF things and all there copys are a bit like a Rolls Royce- If you can afford to buy em -you should be able to afford to fix em-often!!!

Jac Mac

 

[Fran Hall RCR]

I have heard about this phenomena before.....from what I am led to believe its not something that can be quick fixed without taking the box apart...sorry.

Denis at Pantera Performance or Jerry Jansing may be able to help....

 

[Johan]

This has happened to me. It happens when you select reverse when the car is rolling. Never put a ZF in gear unless the car is stationary.
I believe I put the car in 3rd and revved it up and let the clutch all the way out slowish and it popped out of reverse.
Call Rob Ginn at McMichael Motorsports(770 965 9330) as it was his car I was driving and it was not the first time it had happened. It does not happen in forward gears, only when you select reverse with the ncar rolling, was my experience.

 

[Johan]

I hope it does not explode..........

 

[Jeff Boulais]

Thanks for the help. I will call the suggested shops on Monday.

I'll be sure to post back and let you guys know what happened!

 

[Ross Nicol]

I had it happen when I was reassembling my ZF once.The reverse idler gear is on a short shaft in the rear of the gearbox.It has a sprung loaded detent that holds it out of mesh until the cross shaft is moved to select reverse. I found as I was reassembling the gearbox to the diff/gear housing I somehow bumped the reverse Idler off it's detent.The result was locked box when selecting forward gears as you have described. I have never had any problem while driving the car though and I'm careful when reassembling the box now.Sounds like you will have to take the ZF out split the box off the back and reset the reverse Idler into it's detent.Not a huge amount of work but PIA all the same.
Ross

 

[Bob Childress]

Hi Jeff,

You are very lucky to be in Phoenix. You could have the box fixed locally. Talk to Les, former employee of RBT, (or Mike) at Vehicle Performance Center 602-437-3517. They do a lot of the local Panteras.

I had the same ZF problem. It was traced to an out of spec spur gear & shaft which had frozen on the shaft. Exact same symptoms but it could obviously be another cause. It was repaired by Les with free parts from RBT. I paid the labor. Les and Mike also takes care of the ZFs for 1061. I am out of town traveling this week but good luck with the trans.

Bob

 

[Russ Noble]

Not an isolated incident then!

Maybe there is scope for some switched on entrepreneur to produce plates that can be riveted onto the sill next to the gearlever, warning not to use use reverse gear on these megabuck, wait for a year trannies!

Cheers,

 

[Ross Nicol]

Ah Russ I hope that 930 is reliable. Actually I remember now in my case while putting the box back together and lining up the selector rails, I moved the gear shift cross shaft, which is not a good Idea.In the photo Bob posted you can't see it but there is a pin that locates into the reverse gear selector lever. I had shifted the gear off its detent and so was totally my fault.I can understand how this problem would occurr if the gear seized on the shaft but don't see how that would happen unless there wasn't enough or no oil in the thing. Critisize all you like But I like the box and I can shift it real quick, check my video again if you don't believe me.It was my fault for the missed gear first time on the straight by the way.
Ross

 

[Dutton]

When Jeff described how the trans 'locked-up' in his initial post, the first thing that came to mind was racing the FF years ago and how I used to torque the box during reassembly after changing gears.

Being as I'm not real familiar with the inside of a ZF however, I opted to read the comments from those who've personally dealt with this issue. I'm especially interested in the solution as I'll be using that same 'wait-for-a-year' transaxle in my 40... thanks guys - learned a lot here!

Russ, I believe you're closer to a down-the-road solution than you may have thought when you commented on Jeffs post. I'm willing to bet (1) there is a way to replicate the trim as found around the gearshift of an original 40 and (2) come up with a finished installation that will keep one from selecting reverse without going to some trouble to do so.

Give me a few days and I'll let you all know what I find.

Best,

T.

 

[Steve C]

Take a look at posts in the SPF section showing Rt hand shift and note that the shift plate has a "flip lever" that requires the spring loaded lever to be raised before the lever can be engaged in reverse. Of course if the lever is left up all bets are off but, if a proceedure is followed ( always flip it down after a reverse engagement it will work for this issue too. I believe this is also a feature the originals had....My P2125 will have this; thought it was only to prevent accidential 1'st to reverse but, good to know it will help with this issue too....Steve

 

[Ross Nicol]

It's not possible to accidentally select reverse gear in the ZF after shifting from 1st. The reverse gate is further to the left and is not directly above first. In other words when you move off in first gear, you move the stick forward to neutral and the springs set the shifter into the 2nd/3rd gear gate allowing you to just push the stick forward to select 2nd. To select reverse you have to pull the stick well across to the left beyond the first gear gate and against a fair bit of spring tension, before pushing forward for reverse. Compare this with the Datsun 240Z where it has an H pattern shift and reverse is under 5th. I was forever accidentally hitting reverse when changing down from 5th gear.I ended up fitting a reverse lockout on the Datsun shift, but the ZF doesn't need it.I feel I should say IMO but I don't feel I need to, in fact I'll go further and say you would have to be an idiot to accidentally select reverse with the -2 ZF selector layout.Sorry if I offend anyone, not intentional.
Ross

 

[Bob Childress]

ZFs do seem to require good preparation plus careful precise shifting to avoid problems. Several methods to eliminate vagueness in the shifters have already been presented by Ross, Gary, Ian, Jim, and myself in a prior thread. I would add to the comment Ross made that fast shifts require a solid shift mechanism. And, a reverse lock-out also seems like a good idea.

As for a careful shifting warning label, here is a picture of a metal and silkscreen warning label from a GT40. Maybe someone knows the story behind this tag.

 

[Ross Nicol]

Bob I'm pretty sure that sequential business related to the earlier ZFs. From what I've read they were set up so you were forced to go through all gears up and down and you weren't able to change from 4th to 2nd for example, which I do all the time with mine.I agree with you that the shift must not have any play in the linkages and this is important for fast changes. Personally I hate sloppy gear shift systems as they cause doubt about which gear you've just selected and even worse mis shifts and baulking. My advice to anyone trying to improve a rod shift is -

1/ use 2 high quality race type universal joints
2/ keep the angle of the diagonal rod shallow
3/ Fit a rose joint to the side of the gear box just behind the universal and diagonal.
4/Fit a rose joint to the rear of the sill panel just in front of the forward universal and diagonal.
5/ use a solidly built shifter box with bearings/bushes front and rear.There is a pic of mine on this forum somewhere.
Ross

 

[Jeff Boulais]

Quick update...

I contacted Les at Vehicle Performance Center, he's coming to my home tomorrow to remove a portion of the transmission. It's awfully nice of him to make a house call! I'll post an update when we find the offending part.

Thank you Bob and everyone else for the help and suggestions!

 

Jeff
Spoke to the ZF guys in Austin.
2 questions: Were you driving the car when it happened?
or Was it like that on install and it will not come out of reverse?

What can happen is the reverse gear can be bumped to the next detent if dropped in shipping. We have heard of 2 trannies with this problem in the last year.
Can be fixed through the drain plug hole. Drain the oil. Shine a light in and with a screwdriver the reverse selector fork can be pushed back. This should fix the problem.

The transmission should not be able to go into reverse when moving forward. If so, something broke inside to allow it
Hope this helps
Dennis Olthoff.

 

[JimmyMac]

Those warning plates were in original cars. There is definitely one in chassis 1008.
I believe the instruction referred to operating early ZF dash 0 transaxles.