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 T56 HELP - hard to shift into 3rd after rebuild 
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Post T56 HELP - hard to shift into 3rd after rebuild
Just rebuild my transmission as part of the conversion from LT1 to LS1. It shifted perfectly before the rebuild and everything was in great shape inside.

The T56 was an LT1 unit, so converted the front plate & input shaft.
Used the gearbox.org Stage 2 rebuild parts, so new carbon fiber/kevlar blocker synchronizer rings, Bronze fork pads, billet keys, 3-4 steel shift fork.

I DIDN'T put in new synchro assemblies.
Used GM Dex 3 fluid.
Brand new SPEC Stage 2+ & billet flywheel.
Tilton master (same as Tick), bled the crap out of it.

The issue is that all gears shift well except 3rd. If I ease it in it will go without grinding, but if I try a quick shift it grinds.

Should I proceed with a 500 mile breakin and hope it works in, or is this more serious..like tear it back down?

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86 IROC
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Build thread: http://ls1tech.com/forums/conversions-hybrids/1819001-1986-iroc-turbo-lq4-t56-build-ac.html
Formerly 95 LT1 [LE2.2]/T56/4.11 9 Bolt..12.6@114MPH


Sat Jun 13, 2015 8:32 pm
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
No thoughts??

I think it may be that I didn't rough up the synchro mating surfaces on the gears when I rebuilt it. The guy at "TheGearBox" said to rough them up with 80grit emery cloth so the new synchros have something to bite on to.

Do you guys do this?

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86 IROC
LQ4/T56/3.50 8.8 (next step..TC76)
Build thread: http://ls1tech.com/forums/conversions-hybrids/1819001-1986-iroc-turbo-lq4-t56-build-ac.html
Formerly 95 LT1 [LE2.2]/T56/4.11 9 Bolt..12.6@114MPH


Sun Jun 21, 2015 12:31 pm
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
I never had to do that. How where the teeth on the synchro 3-4 assembly? They could have been rounded too much.

6speedIROC wrote:
No thoughts??

I think it may be that I didn't rough up the synchro mating surfaces on the gears when I rebuilt it. The guy at "TheGearBox" said to rough them up with 80grit emery cloth so the new synchros have something to bite on to.

Do you guys do this?

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Mon Jun 22, 2015 1:34 pm
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
Teeth were in great shape, no rounding..

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LQ4/T56/3.50 8.8 (next step..TC76)
Build thread: http://ls1tech.com/forums/conversions-hybrids/1819001-1986-iroc-turbo-lq4-t56-build-ac.html
Formerly 95 LT1 [LE2.2]/T56/4.11 9 Bolt..12.6@114MPH


Mon Jun 22, 2015 5:23 pm
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
When you down shift from 4th to 3rd. Same grinding problem?

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Mon Jun 22, 2015 5:34 pm
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
Yes, if I hold pressure on the shifter it will go in no issues after a second or two upshift or downshift.
If I try and shift fast it grinds as its not synchronized.

I think its like replacing a clutch, you always resurface.. gives something for the new frislction surface to bit onto. This box was super clean inside..nothing actually needed replacing, just did it as it was apart for the conversion. Had maybe 100,000k.s on it.

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86 IROC
LQ4/T56/3.50 8.8 (next step..TC76)
Build thread: http://ls1tech.com/forums/conversions-hybrids/1819001-1986-iroc-turbo-lq4-t56-build-ac.html
Formerly 95 LT1 [LE2.2]/T56/4.11 9 Bolt..12.6@114MPH


Mon Jun 22, 2015 5:50 pm
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
With the engine not running is the 3-4 as smooth as the others? I had a 3-4 synchro that wouldn't let me shift into 3 or 4 no matter how hard I tried.

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Mon Jun 22, 2015 6:48 pm
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
3rd does seem a little stiffer than the others when its not running but no issues with the motor running and the car not moving.

Did you replace the whole syncho?

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86 IROC
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Build thread: http://ls1tech.com/forums/conversions-hybrids/1819001-1986-iroc-turbo-lq4-t56-build-ac.html
Formerly 95 LT1 [LE2.2]/T56/4.11 9 Bolt..12.6@114MPH


Mon Jun 22, 2015 10:24 pm
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
Yes the whole synchro was replaced

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Tue Jun 23, 2015 7:01 am
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
You installed the CF blocker rings yes? If so they take a while to bed in. Mine wasnt "bad" , no grinding, but it sure was notchy for a while. Its still a bit tight when cold but after a hot pass or two? BUTTA!!! I think id run it for a while, so long as your not grinding teeth and theres no noise it wont hurt anything.

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1987 IROC ww 99 LS1,TR224/112, STG2 heads ported by American Speed, P Gold springs, LS6 intake, SVO 30's, Ported TB, Comp Cromo Push rods, Katech Rod bolts, LS6 oil pump, T56, SW LT's, 8.8 hybrid rear 3.73, 275/40/17 MT ET streets, lots more
12.1 @ 112 mph 1.69 60'

89 R7U 1LE Players Challenge car all stock.


Tue Jun 23, 2015 11:35 pm
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
Pulled the trans last night.
Welded a steel plate to my floor jack and used 2pc 3/8" rods to secure it to the front ears of the trans to stabilize it. Rolled the jack backwards, no manual lifting this beast from the garage floor.. I should have done this 10yrs ago!

Wanted to check the gap from the slave as well. It's right at the high end of the window of .175 to .250" with the .115" shim installed.
I called SPEC as I have a 2+ in there and they said the optimum gap is .200 so I may shim it to be 100% sure I have all the travel possible.
I'm also running a Tilton (Tick) type master.

On a good note, I was able to pull the trans without disconnecting the slave lines.

I think I'll still pull it apart to re-inspect 3rd and likely roughen up the gear synchro taper faces.

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86 IROC
LQ4/T56/3.50 8.8 (next step..TC76)
Build thread: http://ls1tech.com/forums/conversions-hybrids/1819001-1986-iroc-turbo-lq4-t56-build-ac.html
Formerly 95 LT1 [LE2.2]/T56/4.11 9 Bolt..12.6@114MPH


Wed Jun 24, 2015 9:06 am
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
Check end play as well and imo a 3-4 billet shift fork is essential

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1987 IROC ww 99 LS1,TR224/112, STG2 heads ported by American Speed, P Gold springs, LS6 intake, SVO 30's, Ported TB, Comp Cromo Push rods, Katech Rod bolts, LS6 oil pump, T56, SW LT's, 8.8 hybrid rear 3.73, 275/40/17 MT ET streets, lots more
12.1 @ 112 mph 1.69 60'

89 R7U 1LE Players Challenge car all stock.


Wed Jun 24, 2015 11:34 am
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
Tore it apart..third gear blocker ring is cracked!
3/4 synchro also doesn't slide so easy anymore. Likely a result of the blocker and a few bad shifts.

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86 IROC
LQ4/T56/3.50 8.8 (next step..TC76)
Build thread: http://ls1tech.com/forums/conversions-hybrids/1819001-1986-iroc-turbo-lq4-t56-build-ac.html
Formerly 95 LT1 [LE2.2]/T56/4.11 9 Bolt..12.6@114MPH


Fri Jul 03, 2015 10:32 am
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
Oddly enough mine let go the other day too. Not sure what all is involved yet, but it aint happy, AT ALL, just a pile of crunchy no movement total failiure :shock: My very first 8.8 is surviving through many other part failures though :D

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1987 IROC ww 99 LS1,TR224/112, STG2 heads ported by American Speed, P Gold springs, LS6 intake, SVO 30's, Ported TB, Comp Cromo Push rods, Katech Rod bolts, LS6 oil pump, T56, SW LT's, 8.8 hybrid rear 3.73, 275/40/17 MT ET streets, lots more
12.1 @ 112 mph 1.69 60'

89 R7U 1LE Players Challenge car all stock.


Fri Jul 03, 2015 1:26 pm
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Post Re: T56 HELP - hard to shift into 3rd after rebuild
Call Liberty Gears for parts..they seem to be the cheapest.

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86 IROC
LQ4/T56/3.50 8.8 (next step..TC76)
Build thread: http://ls1tech.com/forums/conversions-hybrids/1819001-1986-iroc-turbo-lq4-t56-build-ac.html
Formerly 95 LT1 [LE2.2]/T56/4.11 9 Bolt..12.6@114MPH


Fri Jul 03, 2015 3:17 pm
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