Turbo 400 modulator problem? - Chevelle Tech
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Transmission & Driveline Transmissions and Differentials

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  #1  
Old Jun 24th, 10, 12:16 PM
zombie1969 zombie1969 is offline
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Default Turbo 400 modulator problem?

I have a turbo 400 that I got from a friend of a friend that said it was rebuilt.I do beleive him that it was but think some things were overlooked seeing that the shift shaft seal was pissing fluid and should have been replaced during the rebuild.The problem im having is 50-75% of the time when the trans is cold and I shift to rev or dr there is nothing there.When the trans is warm no problems at all and first geer seems fine as it is not slipping in any way when driving it.Seems if I put in p and rev the engin and try again will work most of the time.I was reading a trouble shooting chart and a few possable causes were listed and the easiest to try was the vacume modulator.Although I cant see how a faulty modulator would cause this problem?I do have a good turbo 350 and wondering if the modulator from that would be the same?Any input on this problem would be helpfull thanks.

{EDIT} One other thing is the trans has not been used much for the last 3 years and now finaly registered and on the road.Wondering if the seals went bad from sitting and has anybody had any luck with aditives?
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Last edited by zombie1969; Jun 24th, 10 at 12:58 PM.
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  #2  
Old Jun 24th, 10, 1:09 PM
hpsherlin hpsherlin is offline
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Default Re: Turbo 400 modulator problem?

Sounds like a filter and fluid change would help.
My transmission sat for 5 years after being rebuilt. I got it on the road and drove it a little and changed the filter and fluid. No problems.
The shifter shaft seal on mine leaked also. Replaced with labor for 20.00 bucks. No leak now.
I was told that sitting for years that there would be some oxidation happening on the internal gears and such and that as soon as I drove it that it was all cleaned off and in the fluid.
Made sense to me. Regardless, the fluid and filter was the fix.
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Old Jun 24th, 10, 1:27 PM
zombie1969 zombie1969 is offline
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Default Re: Turbo 400 modulator problem?

I replace the pan gasket at first because I didnt relize the seal was leaking and new fluid at same time.Guy that rebuilt the trans painted it black so I didnt see it comming from the seal.It would suck if this thing has to come apart again because it sat around.
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Old Jun 24th, 10, 3:56 PM
zombie1969 zombie1969 is offline
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Default Re: Turbo 400 modulator problem?

Nobody here has used an aditive to revive hardened lip seals?Would like to know what works best without buying 20 different kinds.
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Old Jun 26th, 10, 1:52 PM
driveshaft-texas driveshaft-texas is offline
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Default Re: Turbo 400 modulator problem?

DO NOT use any additive to expand seals ...they never stop expanding until the seals pop out of the groove then an overhaul is necessary.Try putting brake fluid on any non-brake system rubber and see what happens.(I once put power steering fluid in the master cylinder with the same effect,even tho I sucked it out almost immediately...had to completely rebuild brakes in a months time)Lubegard is the only thing I would try ($15 from a transmission shop or I can send it to you).It is a friction modifier and might loosen up the modulator/valve body at cold start.Put in a new shift seal , they shrink up over time or non-use anyway.If all else fails ,pull the modulator first to see if it is sticky,then the valve body and clean it up and free the valves
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Old Jun 26th, 10, 2:18 PM
zombie1969 zombie1969 is offline
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Default Re: Turbo 400 modulator problem?

Quote:
Originally Posted by driveshaft-texas View Post
DO NOT use any additive to expand seals ...they never stop expanding until the seals pop out of the groove then an overhaul is necessary.Try putting brake fluid on any non-brake system rubber and see what happens.(I once put power steering fluid in the master cylinder with the same effect,even tho I sucked it out almost immediately...had to completely rebuild brakes in a months time)Lubegard is the only thing I would try ($15 from a transmission shop or I can send it to you).It is a friction modifier and might loosen up the modulator/valve body at cold start.Put in a new shift seal , they shrink up over time or non-use anyway.If all else fails ,pull the modulator first to see if it is sticky,then the valve body and clean it up and free the valves
Too late.I ended up calling a local trans shop and the guy recamended lucas trans treatment.Im waiting to see if it makes any differance.I had the same thing happen with my brakes years ago.Went to one of those drive through oil change places and a retard topped off my master with something other than brake fluid.About a week later my brakes locked up and had to replace everything.I wanted to kill that guy.
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Old Jun 26th, 11, 9:42 PM
zombie1969 zombie1969 is offline
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Default Re: Turbo 400 modulator problem?

I'm digging this up again with an update that I haven't followed up on yet but 90+ % sure its my problem.During the winter the pump would make a whine when my problem was happening like a ps pump starving for fluid.When the whine went away revving it in park for a few secs or more the trans worked fine as before.I googled the symptom and came to the conclusion it needs a pump.I did drop the pan again and check the pickup tube and replace the filter.Luckily the pump new from TCI is relatively inexpensive so Ill have to save for a bit till I can get it.Hope this might help anybody having the same problem.
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