T400 help please - The 1947 - Present Chevrolet & GMC Truck Message Board Network

lux · 06-14-2021, 01:34 AM

I have a 383 with a T400 transmission and BTE 310800 11” converter Stall Speed 2600-2800 rpm.
On my last drive the trans would not shift until it reached 4000rpm.
What could be going wrong?
What should I look for?

Thank You

cadillac_al · 06-14-2021, 06:08 AM

Check the vacuum line for full vacuum.

**kwmech** · 06-14-2021, 11:25 AM

Vacuum line most likely---OR the governor (under the 4 bolts on the side) has stripped a gear from the bushing walking in the case

lux · 06-15-2021, 12:42 AM

Thanks guys, I know the vacuum line is hooked up but, what's the best way to test it?

**kwmech** · 06-15-2021, 01:22 AM

Hook a vacuum gauge to the line at the trans

SunSoaked · 06-16-2021, 10:39 AM

I had same issue bit I had my vacuum advance cannister off the HEI T-d into it. The diaphragm in the cannister went bad and raised my shift points like you.

lux · 06-16-2021, 11:25 AM

Quote:

Originally Posted by SunSoaked

I had same issue bit I had my vacuum advance cannister off the HEI T-d into it. The diaphragm in the cannister went bad and raised my shift points like you.

i have my vacuum line straight to the intake on a Edelbrock pro flow 4. I made sure and use hard line for most of the route with rubber fittings on the ends.
I'll get a chance to look at it this weekend. Hopefully its just a line that came unattached.

lux · 06-20-2021, 08:51 PM

Well, I tested vacuum at the transmission it was 20-22 at 3000rpm. Does that sound about right?
Then I checked the kick down switch and it was stuck on. I took the Lokar switch apart and sprayed it with silicone lube. That seems to have done the trick. All is well now, thanks for the help.

06-14-2021, 01:34 AM	#1
lux Registered User Join Date: Oct 2016 Location: Austin, Texas Posts: 306	T400 help please I have a 383 with a T400 transmission and BTE 310800 11” converter Stall Speed 2600-2800 rpm. On my last drive the trans would not shift until it reached 4000rpm. What could be going wrong? What should I look for? Thank You

06-14-2021, 06:08 AM	#2
cadillac_al Registered User Join Date: Oct 2013 Location: Maine Posts: 2,332	Re: T400 help please Check the vacuum line for full vacuum. __________________ 76 Chevy K20 76 GMC K15 77 Chevy C10 77 Chevy K10

06-14-2021, 11:25 AM	#3
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,387	Re: T400 help please Vacuum line most likely---OR the governor (under the 4 bolts on the side) has stripped a gear from the bushing walking in the case

06-15-2021, 12:42 AM	#4
lux Registered User Join Date: Oct 2016 Location: Austin, Texas Posts: 306	Re: T400 help please Thanks guys, I know the vacuum line is hooked up but, what's the best way to test it?

06-15-2021, 01:22 AM	#5
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,387	Re: T400 help please Hook a vacuum gauge to the line at the trans

06-16-2021, 10:39 AM	#6
SunSoaked Registered User Join Date: Dec 2011 Location: Yuma Arizona Posts: 1,524	Re: T400 help please I had same issue bit I had my vacuum advance cannister off the HEI T-d into it. The diaphragm in the cannister went bad and raised my shift points like you.

06-20-2021, 08:51 PM	#8
lux Registered User Join Date: Oct 2016 Location: Austin, Texas Posts: 306	Re: T400 help please Well, I tested vacuum at the transmission it was 20-22 at 3000rpm. Does that sound about right? Then I checked the kick down switch and it was stuck on. I took the Lokar switch apart and sprayed it with silicone lube. That seems to have done the trick. All is well now, thanks for the help.



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