Moto One

It's an interesting problem. Right now I'm also dealing with the frozen pilot bearing problem. Three pullers have failed, I be at it again today with an expensive puller. Lets hope it works.

Mark

Moto One

The new puller arrives tomorrow, wish me luck... If this doesn't work maybe I'll just buy a new motor with my tax refund (Not, even though I'm all retired and w-2d 0, I still owe.)
enough winning.

Mark

Moto One

It's all back together now, and no reverse kick out. Reverse now engages 100%...

Mark.

cyberGS10

My reverse just crapped out in my '10 Grandsport. I wonder if this fix will work on the TR6060 trans as well? I'm going to be pulling my trans in the next few weeks and see what I can see.

DC 155

Any idea how much it should cost in a shop to have the reverse shift fork replaced? I'm not gonna tackle the tranny removal myself.

MetalMan2

Little bit older thread, but I think it is this forum's most concise thread on the T56 reverse fix.

Quick background: My '01 Z06 was incurring gradually-worsening reverse shifting. By the time I stopped driving it, getting into reverse resulted in popping out half the time, grinding most of the time, if I could get reverse at all. It was horrendous! Made it seem like I didn't know how to drive stick, despite daily driving on manual transmissions exclusively for 10 years prior.

Anyways, I have a whole saga if you're at all interested: https://www.corvetteforum.com/forums...verse-1st.html

So what's relevant here: I decided to replace pretty much all of the reverse components that can have an impact on shifting into reverse:

• Full synchro assembly (synchro hub, slider, keys, springs) [the old synchro slider had already been flipped - indicating the trans was previously "fixed" for this same reverse issue]
• Brass blocker ring
• Reverse gear (the points on the old one were quite worn)
• Reverse gear caged needle roller bearing (why not)
• Reverse steel thrust washer (old thrust washer was fine)
• Reverse shift fork with plastic pads (old fork was fine, not bent)
• Mainshaft snap rings above and below reverse gear (old ones were fine)

I put it all back together with the new parts (for mock-up) and with the trans shifted into reverse there was a 0.137" gap between reverse gear and the reverse synchro slider:


Back on the bench, with the synchro slider completely bottomed out into reverse gear, that same gap measured 0.047":


Simple math: 0.137" - 0.047" = 0.090". That means for my "reverse fix" I would space the shift fork upwards with a 0.090" washer/shim and remove that same amount from the top of the shift fork.

With a 0.090" washer in-hand and placed under the shift fork, this is how it looked mocked up:


That engagement looked and felt great to me. The shift fork pads weren't binding on the synchro slider and generally things could still wiggle around. This is important to me because I daily drive this Z06 and don't want the trans to incur excess wear.

Now I'm removing 0.090" from the shift fork, and afterwards will do final assembly. I'll be sure to update this thread once the car is back together and I've had a chance to put some miles on the transmission to see how reverse feels.

TastyBacon

Great post! That's how it's done. Thanks for the excellent pictures and measurements.

Bill Curlee

Please show us how and where you removed metal from the fork.

What kind of washers did you shim the fork up with?

Thanks for the detailed post.

Bill

MetalMan2

Unfortunately, I'm often not one for taking pictures and the transmission is all buttoned up anyways. I hope this will suffice:

As calculated in my prior post, I needed to adjust the shift fork by about 0.090". So I removed 0.090" from the top of the shift fork as shown in the image below, which is one of my pictures from above.
I happened to have laying around a washer for a 9/16" bolt, which luckily had an inner diameter of just a hair over 15mm, and was 0.090" thick. The reverse shift rail diameter is 14.98mm, for reference.


I removed that material from the shift fork by clamping it onto the table of a vertical mill, and cut it with a square endmill (probably the ideal method). But it could be done with a grinder if you can have good accuracy with one.

Bill Curlee

WOW! That all you needed to do to explain what was done.. I bet you solved the reverse shift issues 100%.. You do excellent work! Thanks for posting the outstanding directions..

Bill

MetalMan2

Glad to help.
I certainly was one to benefit from your diff rebuild posts... the bellevilles and clutch packs in mine were toast! https://www.corvetteforum.com/forums...post1601593264

Hoping to find out pretty soon if this was worth the effort

bobick

I'm currently doing the same hack and I want you guys to be careful with this.
The problem I see is that reverse synchro blocker ring starts touching the reverse gear cone being in neutral.

More details:
First, without any mods. I only removed the wave washer between blocker ring and reverse gear, so I am confident that reverse gear and blocker ring have no contact at all.
And in neutral when I rotate the reverse gear back and forth I see no movement of blocker ring. The gap between ring and gear is ~1.6 mm (without wave washer, once again).

The shift fork shim thickness in my case should be ~1.2 mm.
So, now with this shim under the fork and in neutral again: I see that blocker ring is moved together with the reverse gear - it means they have a slight contact. The gap between ring and gear is now ~1.4 mm.

What does that mean? In my understanding, it would:
1. cause all other synchronizers to overcome this additional friction
2. introduce premature wear to blocker ring and gear cone (probably, not a big problem, since you shift to the reverse only when car is not moving, so fast synchronization is not necessary)

The ways to fix that which I see:
1. slightly grind top of the synchro keys so they would engage blocker ring a bit later (and so it would not touch the gear in neutral)
2. slightly grind key slots in blocker ring (the same)
3. reduce fork shim thickness a bit - so we still have increased synchro engagement (but not full), but not having the neutral contact

Generally, in my opinion, the initial problem is not with the fork position, which we try to fix with the shim.
It looks like we have not enough shift fork travel. And I have no idea how to address that.

@MetalMan2 have you checked the blocker ring and the gear contact during your mod? Do you have some thoughts about that? Thank you in advance!

MetalMan2

It's good you're putting in plenty of analytical work to try to figure this out for yourself.
In general the issue IMO is insufficient synchro engagement, which can be a result of a fork problem and/or insufficient fork travel.

Shifter fork travel is determined by the shift guide plate. As you can see, both the ball detent and hard stop show the same travel for reverse as the forward gears. So, IMO it's not a travel issue if all the other gears have adequate travel.



In my other thread, I did briefly address your question on blocker ring contact to the synchro slider with this modification (picture below).
From the photo, I show 0.090" thickness and where that would end up on the blocker ring.
The space on the synchro slider where the blocker ring teeth engage, it's a little bit recessed. The image below is my attempt to demonstrate this.

I confirmed there was no contact between blocker ring and synchro slider when trans is in neutral.

bobick

@MetalMan2 sorry, but I did not get your point regarding blocker ring to slider gap.
What I was talking about is blocker ring and reverse gear cone contact. I've done short videos to show that, please take a look.

First, without any mods, trans is in neutral, wave washer between blocker ring and gear removed (just for check).
As you can see, there is no contact between blocker ring and gear cone - this is how things should be in neutral.

Now, with 1.2mm (0.047 inches) shim under reverse fork, also in neutral:
The blocker ring starts briefly touching the reverse gear cone. Slight contact is most likely not a problem, but I'm still going to shave the shim a little bit to eliminate that.
I'm not trying to say that this fix is bad, no, this fix is a must, but I just want to warn people: blindly adding shims could cause problems. Especially 1/8 inch shims (almost twice thicker than mine) - this definitely will cause blocker ring to bite the gear.

Yes, synchro engagement is the root cause, 100% agree with you here.

Yeah, this sounds reasonable.
But why I still think the fork travel is insufficient - because the stock fork position seems to be correct for neutral.

I tried to figure out where could we get some more travel, so I measured the reverse shift shaft endplay. It is ~0.35mm in neutral and ~0.45mm in gear.
Well, it's not that bad and there probably should be some play for thermal expansion and so on.

And now I wonder how is it possible that there are so many T56s without reverse problems, how does their synchro engagement and fork travel look like?

MetalMan2

Okay I understand better now. I had assumed that you 'accidentally' typed reverse gear instead of synchro slider. My mistake.

What you are showing certainly does seem to be a problem. Looks like the blocker ring is being preloaded and making contact with reverse gear, which means that the wave spring between blocker ring & reverse gear is being compressed. Perhaps this is showing as a worse problem because there isn't any oil in there? (less lubrication)
I can't recall checking for free rotation of reverse gear while in neutral after this modification.

Looking at a picture of the reverse gear synchro arrangement: https://i.ebayimg.com/images/g/bZ8AA...gK/s-l1600.jpg
I can see how it would be possible that the blocker ring could be preloaded. But maybe with additional lubrication the components will better return to a looser position when shifted back to neutral from being in gear.

I still have my old reverse gear/synchro components and I can play around with that. Obviously I can't mimic the 0.090" for adjustment, though.

But like I mentioned before - travel is the same for reverse as other gears, so then why does reverse seem to need more travel? I believe the brass blocker ring can be replaced with 5/6 multi-piece carbon/paper blocker ring arrangement, so maybe that would help fix the problem as well.
And agreed, it surprises me also that more people don't have T56 reverse issues.

bobick

Correct, I did not oiled it, there are just traces of ATF left after disassembly. Surely it must get better with proper lubrication, but still - contact is not desirable.

Don't know, my initial thought was that due to excessive play somewhere in shift rails we are losing the required fork travel, but... I only located 0.35-0.45 mm play in the fork shaft - that's a noticeable play, but not enough to get things right.
I also measured the reverse gear play (gap between the reverse gear and its snap ring): it was 0.7mm for the old gear and 0.85mm for the new gear.
I already got a set of 0.1-0.15mm shims to address this gap to, let's say, 0.5-0.6mm. Unfortunately, T56 repair manual does not contain any specifications for this gap, so I'll try it as a small part of reducing gear pop out.

Sounds interesting, unfortunately I don't have any other blocker rings, but I'll think about it or maybe there is something similar in our local shops.