TH350 - Lost 3rd gear - Team Camaro Tech
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post #1 of 6 (permalink) Old Aug 9th, 01, 09:21 PM Thread Starter
Join Date: Sep 1998
Posts: 15

Recently replaced stock 327 with a built 350 backed with a TH350 and TCI 2400rpm converter. Now when I put the car in drive, it acts like it's in neutral---rev the engine and no go. All the other gears work fine (park is still park, 1st still 1st etc) and the REAL neutral is still there (ie - pull the shifter back from neutral and it acts like a second neutral). To drive around town, I put it in 2nd and it goes thru 1st and 2nd gear fine, but obviously doesn't get up to 3rd gear.
Any thoughts? Could the fact that the engine is making only 10 in vacuum make a difference? The tranny worked ok before the swap and I haven't messed with the linkage. (I'm shifting with a Hurst V-matic2 shifter). Thanks in advance.

[This message has been edited by JohnC (edited 08-10-2001).]
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post #2 of 6 (permalink) Old Aug 10th, 01, 04:01 AM
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Location: Austin, TX
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This does sound like a vacuum problem...either you are not generating enough vacuum or there is a leak somewhere in the vacuum lines.

Do you have power brakes? If so are they working correctly? If you do and they are you should be getting enough vacuum.

What kind of cam do you have in the 350?

I would double check all the vacuum lines, connectors etc. for pinholes/ cracks first and see if you find anything.

If that checks out ok you may need to invest in a vacuum cannister.
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post #3 of 6 (permalink) Old Aug 10th, 01, 04:18 AM
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I had the exact same problem last week when I installed my new motor and tranny in my 68 RS. The vacumm line for vacumm modulator on the tranny was never plugged in. I could shift from first, second and into third and it would work, but if I put it just in drive it would go but when it would shift into second it would free-wheel. I would have to do it maually all the time and downshift too. I only run 10 inches of vacumm off the manifold and mines works fine now. Good Luck.
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post #4 of 6 (permalink) Old Aug 10th, 01, 09:06 AM Thread Starter
Join Date: Sep 1998
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Thanks for the replies. It seems like it started exactly right after the new engine went in, so I suspect that the low vacuum has something to do with it.
I do run power brakes and they don't work very well at all, even with the vacuum canister installed. The engine is basically the Performer RPM setup (cam included: lift .488/.510 duration 234/244). It still needed a lot of tuning, but I am getting 10 in vacuum. The vacuum lines all look ok.
How do I solve this? Can I just adjust the tranny's vacuum modulator? I have got to get a vacuum pump so I get my brakes back; do I just plumb the vacuum modulator in with the brake booster, or does the vacuum modulator rely on varying engine vacuum to make shifts?
Choptop - are you a UT alum?

[This message has been edited by JohnC (edited 08-10-2001).]
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post #5 of 6 (permalink) Old Aug 11th, 01, 02:31 AM
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I had this problem in a truck i had,the vacuum line at the modulator kept comming off ( replaced)and was fine.yes the vacuum to the tranny controlls the shifts;so a vacuum pump will not work.also you can get an adjustable modulator,but that only adjusts shift points ( mph ).i have about 8-10" (19hg?) of vacuum and my tranny shifts fine but i also have a trans-go pack ( shift kit ) and a small stall (2200).As it was said previously check for leaks,pinched lines,and that its hooked up to the manifold,not the carb. good luck.

My '68 Camaro
Doug G.
68 Camaro
406 ci.
[email protected] W/ 2.73POSI.

[This message has been edited by DOUG G (edited 08-11-2001).]
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post #6 of 6 (permalink) Old Aug 11th, 01, 03:15 AM
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Your power brakes should work with 10in of vacuum are you sure there isn't a leak in the line or check valve. If I understand correctly you have the trans line hooked up there too that would explain the problem. If you have an adjustable modulator play with it
if you don't they are easy to change. I have tried running too much cam with a stock setup in the trans but it always went into gear it just shifted like the gov. was stuck and everything inside was slipping. I have not run the RPM cam but from what I hear it really isn't streetable.
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