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Discussion Starter #1
There was a little bit of interest on here when I posted last month about rebuilding my T56 so I thought I'd share some thoughts about it now that I've just about got it all back together.
First off, here are a couple of resources that I found really helped in the rebuilding:

After that I'd say that having gone through the process, there are probably a good few more people who've taken apart T56s than those who've put them back together. There are a couple little trickeries like getting the 5-6 shift rail in position right that isn't really covered in most written tutorials I went through. Making sure that you heavily document/mark the synchro removal is very helpful in making sure it all goes back together as well being that the inner synchro hubs are directional and won't sit right if it's upside down when pressed back onto the mainshaft. Also If you're looking to do the job in a home garage, a shop press if not an absolute necessity is still super helpful in making the job easier. I picked up a 12 ton press from HF for around $150 that has been very useful for the rebuild.

You will 100% need to make the gear puller like shown in one of the above links. I used a HF gear puller and some steel straps from Home Depot that I cut into 12" bars to extend it enough for 5-6 driven gear. With this in mind there is a distinct possibility that if your T56 has some miles on it that the mainshaft splines that hold the 5-6 driven gear in place will be worn, causing a slightly loose fit and allowing the gear to come off by hand. If this happens you have a couple of options. Many shops just send it and leave it as is if the splines aren't too damaged. In doing so though you essentially allow a ticking time bomb to stay in your freshly rebuilt trans as once they wear enough they WILL shear, more than likely taking out the driven gear and the accompanying 5&6 mainshaft gears. The other 2 options are replacing the mainshaft with a new unit or having your existing mainshaft worked on to fix the issue. The fit on mine was loose but the splines were still in good shape so I ended up sending my mainshaft to Jason at TDP to weld and remachine it. Total cost was around $125 with shipping both ways from FL which was a good bit cheaper than buying a new mainshaft.

Next be aware to compare the replacement synchro springs against the ones that came out of it when replacing the synchro keys. The replacement springs for the 3-4 synchro had alignment tangs on both ends whereas the ones that came out only had a tang on one end. Using the springs as is was causing an issue with the synchro keys not being supported correctly, which was keeping it from actuating as intended. After confirming with TDP who sold me the rebuild kit on this, I needed to slightly grind down one of the tangs for the synchro to engage as it was intended to. Apparently that's how Tremec is selling them now but I suppose depending on the supplier of the rebuild kit your mileage may vary.

When taking everything apart, make sure to inspect not just the main teeth of the gears but also the synchro engagement teeth on both the gears and the synchro sleeve. Chances are if you're rebuilding a T56 you had an issue with either synchro engagement or the slightly bigger problem of having more than one neutral. In either case, it doesn't do any good to reassemble the trans with damaged or more notably heavily worn engagement teeth. This is actually a problem that delayed my build as I found that my 5-6 synchro teeth were very worn on reassembly being that I didn't thoroughly inspect it enough on disassembly.

My last point might not apply to everyone but is worth noting anyways when getting replacement parts. Borg Warner / Tremec used the T56 in a ton of applications and almost all of them came with slightly different gearing configurations. The T56 I've been rebuilding is actually a '93 "M29" T56 that's going back into my '82 El Camino which has been my Guinea pig for deciding if it's worth rebuilding the T56 in my GTO. The reason I bring this up is being that they all had different gear ratios, that can limit your options as far as cross compatibility goes. My specific problem is that being a '93 model, it has gear ratios in it that aren't shared with any other T56. This caused a problem for me being that my 5th and 6th gear synchro engagement teeth were damaged from a failed synchro key and the gears can't be purchased anymore. The solution for this is to use 5th, 6th, and the 5-6 driven gears from a later model which have taller gear ratios.

If wanted I can go through my file dump for pictures on the whole process. Hopefully this can help someone. If I had to do it again I probably would though it certainly is a pain to go through everything right.
 

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Good info and about what I determined when considering to do the rebuild myself on a GTO I had. Had about 130K on it with a slight whine. Turned out to be the reverse gear and bearing. Synchros were about ready to go soon also. Had it rebuilt by a shop because for $500 more I got a warranty and didn’t add to my already long list of projects.

What I also learned is that a GTO M12 T56 is what most would consider a stage 2 or 3 trans having billet synchro keys and steel 3-4 shift forks. Plastic or bronze shift pads is a common debate and my builder suggested plastic.

Having the time and patience, I would rebuild it myself. Many who are savvy would tear a good working trans down just as a part of regular maintenance. I didn’t trust my ability to ID bad gear wear and a couple other excuses I used to psych myself out of it.
 

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Discussion Starter #3
Good info and about what I determined when considering to do the rebuild myself on a GTO I had. Had about 130K on it with a slight whine. Turned out to be the reverse gear and bearing. Synchros were about ready to go soon also. Had it rebuilt by a shop because for $500 more I got a warranty and didn’t add to my already long list of projects.

What I also learned is that a GTO M12 T56 is what most would consider a stage 2 or 3 trans having billet synchro keys and steel 3-4 shift forks. Plastic or bronze shift pads is a common debate and my builder suggested plastic.

Having the time and patience, I would rebuild it myself. Many who are savvy would tear a good working trans down just as a part of regular maintenance. I didn’t trust my ability to ID bad gear wear and a couple other excuses I used to psych myself out of it.
Yeah that's actually how this whole process started for me. I bought a low mileage GTO trans that I was going to put in my El Camino instead of rebuilding the T56 I had, but I found out the hard way that the input shafts aren't cross compatible between the LT1 and GTO trannys so I ended up rebuilding the one I had instead and kept the trans I just bought for a rainy day. LT1 T56s will bolt up to a gen 1 SBC so I needed the LT1 input shaft for that reason. Paying a shop to do the work is definitely a financially viable option with the tools you end up needing to buy but sometimes it's a good challenge to try and do it yourself. I can't recommend Texas Drivetrain enough though when it comes to rebuilding these. Jason is more than happy to help with any questions if you rebuild it yourself and their rebuild costs really aren't that bad either if you just have them rebuild it.
 

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Thank you for sharing all of this!
 

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Out of curiousity whats a rebuild diy cost? Probably not the route id go just cause of time though
 

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Not the OP but I was right around $1,200 for a complete kit which is all wearable items: shift pads, synchro blocker rings, bearings, seals, synchro keys and shim kit.

No hardware so assumes all gears are reusable and 5-6 shaft doesn’t need machining as noted above. Which reminds me, if you’re going to pass do it in 4th to avoid messing up this shaft.

Also account for a press, puller and 1”x1/4” plates from HF & HD oh and a dial indicator thing to measure end play, 5-8 thou, IIRC.
 

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Discussion Starter #9
Not the OP but I was right around $1,200 for a complete kit which is all wearable items: shift pads, synchro blocker rings, bearings, seals, synchro keys and shim kit.

No hardware so assumes all gears are reusable and 5-6 shaft doesn’t need machining as noted above. Which reminds me, if you’re going to pass do it in 4th to avoid messing up this shaft.

Also account for a press, puller and 1”x1/4” plates from HF & HD oh and a dial indicator thing to measure end play, 5-8 thou, IIRC.
I didn't end up replacing the bearings, just followed the service manual for inspection and when I saw they were fine I didn't bother. If you don't touch the bearings then you don't have to re-shim it at least according to TDP so I didn't do that either. My out the door cost with shipping was $785 which was Texas Drivetrain's stage 2 kit along with a steel 3-4 shift fork (not needed for the GTO trans), new 5-6 fork, new reverse fork, machined mainshaft, and replacement 5-6 synchro sleeve. With the tools, rtv, etc. we can round up to an even $1000 for everything I needed to do it. I think the rebuild kit for the GTO T56 is a bit more cost wise though than the F-body one.
 

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Squag27 thanks for posting this
 
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