Thread: HD differential swap to non-hd transmission

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  1. #1 HD differential swap to non-hd transmission 
    SE Level Member snutmeez's Avatar
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    Hey, there is some info I need to know on doing this HD diff to non-hd transmission. I just swapped the engine in my car to L67 and I want to know if the the Non-HD@(3.29) will be changed to (2.93) when I swap to HD. And, is that all I need to do, or do I have to go in beyond the valve body and swap other internal trans parts? BTW, i already have the axle and Torrington bearing.
    03 Grand Prix GT L67/4T65-E(HD) swapped, Speed Daddy headers w/ 2.5'' cat(less)back exhaust, ZZPerformance PCM tune. 3.4'' pulley, 4'' fenderwell
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  3. #2 Re: HD differential swap to non-hd transmission 
    Turbo is the way to go. BillBoost37's Avatar
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    The drive and driven gears in your non HD are 1:1 ratio with a 3.29 diff. The HD diff is 3.29 as well but the drive and driven gears are 1:2.121. You'll retain the 3.29 ratio you currently have.

    You only need the diff, diff cover, bearings, selective washers and the axle for the swap.
    I drink..so consider that when reading my posts.

    2010 Audi A6 Dual IC's
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  4. #3 Re: HD differential swap to non-hd transmission 
    SE Level Member snutmeez's Avatar
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    So I basically have to get an HD 4t65e from 2003 with 2.93 final drive for this to work properly. My PCM is tuned for GTP.
    03 Grand Prix GT L67/4T65-E(HD) swapped, Speed Daddy headers w/ 2.5'' cat(less)back exhaust, ZZPerformance PCM tune. 3.4'' pulley, 4'' fenderwell
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  5. #4 Re: HD differential swap to non-hd transmission 
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    The transmission I have from the donor car is year 2000, so that will not work because they changed the electronics in 2003 and installed pawl sprag for strength.
    03 Grand Prix GT L67/4T65-E(HD) swapped, Speed Daddy headers w/ 2.5'' cat(less)back exhaust, ZZPerformance PCM tune. 3.4'' pulley, 4'' fenderwell
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  6. #5 Re: HD differential swap to non-hd transmission 
    Turbo is the way to go. BillBoost37's Avatar
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    Negative, negative and nope

    An HD diff is an HD diff from 1998 to 2008 period.
    Gear ratio.. you can't make an ending gear ratio of 2.93 unless you open that transmission up and put in 1:1.121 gears. Aka 33/37, because right now it has 1:1 35/35 gears in it. Do the math with me and maybe it'll help explain it. 3.29 diff NA transmission divided by 1:1 diff equals 3.29. HD trans has 3.29 diff and divide it by the 1:1.121 and you get 2.93.
    If your pcm is tuned for 2.93 gears it likely won't be happy about seeing 3.29
    I drink..so consider that when reading my posts.

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  7. #6 Re: HD differential swap to non-hd transmission 
    SE Level Member snutmeez's Avatar
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    By open the transmission, you mean just the side cover and valve body cover, take the gearing/chains from the donor transmission(33/37) and swap all of it along with the HD diff to the other transmission, take out the 35/35 and chain, making it 2.93
    03 Grand Prix GT L67/4T65-E(HD) swapped, Speed Daddy headers w/ 2.5'' cat(less)back exhaust, ZZPerformance PCM tune. 3.4'' pulley, 4'' fenderwell
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  8. #7 Re: HD differential swap to non-hd transmission 
    Turbo is the way to go. BillBoost37's Avatar
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    Search on a how to by me for fixing the 4th gear clutch hub. That'll give you an idea what you need to do to get to the chains.
    I drink..so consider that when reading my posts.

    2010 Audi A6 Dual IC's
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  10. #8 Re: HD differential swap to non-hd transmission 
    Turbo is the way to go. BillBoost37's Avatar
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    and gears
    I drink..so consider that when reading my posts.

    2010 Audi A6 Dual IC's
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  11. #9 Re: HD differential swap to non-hd transmission 
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    ​Ok, thnx.
    03 Grand Prix GT L67/4T65-E(HD) swapped, Speed Daddy headers w/ 2.5'' cat(less)back exhaust, ZZPerformance PCM tune. 3.4'' pulley, 4'' fenderwell
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  12. #10 Re: HD differential swap to non-hd transmission 
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    So after diggin' in, I to get the 3.29 drive/driven gears out, I pull out the 4th clutch shaft and wowwwwwww, all of the teeth are gone gone. I turn it around to find a date(08/21/02) stamped on it... My car is a mid 2003. Not hardened at all so that will be replaced too.
    03 Grand Prix GT L67/4T65-E(HD) swapped, Speed Daddy headers w/ 2.5'' cat(less)back exhaust, ZZPerformance PCM tune. 3.4'' pulley, 4'' fenderwell
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  13. #11 Re: HD differential swap to non-hd transmission 
    Turbo is the way to go. BillBoost37's Avatar
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    Not surprised .. I have seen a lot of 03 cars that had that same issue. It depends on when the trans was built and we need to keep in mind that GM is going to use up their stock before putting the new parts in.
    I drink..so consider that when reading my posts.

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  15. #12 Re: HD differential swap to non-hd transmission 
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    Well I bought the parts to replace all of the weak stuff. I really want a single chain for the gears but cannot find one. Will the chain from the 4.6 Bonneville be the same length? What would you suggest?
    03 Grand Prix GT L67/4T65-E(HD) swapped, Speed Daddy headers w/ 2.5'' cat(less)back exhaust, ZZPerformance PCM tune. 3.4'' pulley, 4'' fenderwell
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