Transmission Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Eyegore · 11-14-2005, 01:34 AM

My son was driving his 78, 3/4 camper today and his transmission would not shift from first to any other gear, works ok in reverse and first but not second or third, also will not manually shift into those gears either. This is a 78 with I believe at th400. Was working great no trouble, trans fluid does not smell burnt, any ideas?

Thanks ahead of time.

Tom

Russell · 11-14-2005, 02:34 AM

Check the vaccum modulator, the line may have fallen off, or the modulator may have failed all together.

The TH400 will not shift out of 1st gear until the govenor tells it to at a very high rpm if the modulator isn't working properly, and it will be a very hard shift when it does.

Eyegore · 11-14-2005, 09:49 AM

Thanks Russel, will check it this evening when I get home

11-14-2005, 01:34 AM	#1
Eyegore What Hump? Join Date: Apr 2003 Location: New River AZ Posts: 2,009	Transmission Help My son was driving his 78, 3/4 camper today and his transmission would not shift from first to any other gear, works ok in reverse and first but not second or third, also will not manually shift into those gears either. This is a 78 with I believe at th400. Was working great no trouble, trans fluid does not smell burnt, any ideas? Thanks ahead of time. Tom __________________ Lil red 86 c-10 99 Sub 78 Camper Special w/ 454

11-14-2005, 02:34 AM	#2
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	Re: Transmission Help Check the vaccum modulator, the line may have fallen off, or the modulator may have failed all together. The TH400 will not shift out of 1st gear until the govenor tells it to at a very high rpm if the modulator isn't working properly, and it will be a very hard shift when it does. __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

11-14-2005, 09:49 AM	#3
Eyegore What Hump? Join Date: Apr 2003 Location: New River AZ Posts: 2,009	Re: Transmission Help Thanks Russel, will check it this evening when I get home __________________ Lil red 86 c-10 99 Sub 78 Camper Special w/ 454



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.