What makes the trany shift at 2800? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

67chevemall · 02-24-2005, 12:41 PM

Hello
I just got my 78 running great but the tranny likes to shift
at 2800 rpm in all the gears?
What would cause this and is it fixable???
Thanks again!

corn · 02-24-2005, 07:49 PM

My guess is the shift modulator. Its either bad or the hose came off. Its mounted on the RR corner of the trans. Easy to change out & some can even be adjusted. Pop the hose off & turn the screw inside of the fitting...corn

magnethead · 02-24-2005, 09:29 PM

or the TV cable is mis-aligned.

86k10 · 02-25-2005, 12:53 AM

Which model are we talking about, 350, 400, 700?

MylilBowTie · 02-25-2005, 05:34 AM

I would say th350 maybe th400 being a 3/4 ton.

67chevemall · 02-25-2005, 09:56 AM

Sorry its a 400. I'll look at the mod. How can you tell if the shift modulator is NFG??
It shifts real strong but at 2800rpm??

MylilBowTie · 02-25-2005, 10:17 AM

That to me sounds a little more like the governor is sticky or worn out. Does it always shift there or does it change? Modulator valve might play with it a little bit. Usually that's we it wont shift out of 1st until the rpm is really really high like a WOT shift.

67chevemall · 02-26-2005, 10:32 AM

Alwas shifts at 2800! Very hard bam shift like it was a preformance tranny?

MylilBowTie · 02-26-2005, 11:13 AM

Have you checked the fluid level? There might be a small flat head screw in the modulator valve you have to take off the vacuum hose off it. It will be in the center of the hole, need a pretty small flat head screw driver to turn it. Some have them some don't. If there is turn it in to raise the shift points a little more and out to lower them. You can turn it all the way in but that will always make it shift very high and will not shift unless you reach that high rpm and it will stay like that.

Do you know what your rear gear ratio is and what size tires you run?

67chevemall · 03-03-2005, 02:08 PM

The tires are 30" and the rear end is 78 stock.
Fluid is topped up. I have to locate this Mod valve.How do you know if the
valve is good?

MylilBowTie · 03-03-2005, 02:16 PM

There will be transmission fluid coming out of it, they arent that much to replace (20.00) if it does need replaced. Take the vacuum line off and see if it shifts different. If the transmission is a th400 the modulator valve should be on the passenger side where the transmission cooler lines are, right above the pan.

If you need a picture I can post one.

alf4444 · 03-03-2005, 03:56 PM

mine was doing the same thing it would rev up around 3000 then SLAM into gear, Looked underneath and the modulator wasn't hooked up! Mod valve on a th350 is on the pass side with the hose coming off it to your intake

67chevemall · 03-03-2005, 09:53 PM

Thanks guys I'll let ya know as soon as I dig it out of the
20' of snow!
where the he!! did I put that 4X4!LOL

02-24-2005, 12:41 PM	#1
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	What makes the trany shift at 2800? Hello I just got my 78 running great but the tranny likes to shift at 2800 rpm in all the gears? What would cause this and is it fixable??? Thanks again! __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

02-25-2005, 12:53 AM	#4
86k10 Registered User Join Date: Feb 2003 Location: Bertrand, Nebraska Posts: 355	Which model are we talking about, 350, 400, 700? __________________ 98 Neon 97 Grand Prix GT 02 Grand Prix 40th Anniv. 86 GMC 5.0 77 Olds 98 6.6 REAL AMERICANS, DRIVE AMERICAN

02-25-2005, 05:34 AM	#5
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	I would say th350 maybe th400 being a 3/4 ton. __________________ 1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI

02-25-2005, 09:56 AM	#6
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	Sorry its a 400. I'll look at the mod. How can you tell if the shift modulator is NFG?? It shifts real strong but at 2800rpm?? __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

02-25-2005, 10:17 AM	#7
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	That to me sounds a little more like the governor is sticky or worn out. Does it always shift there or does it change? Modulator valve might play with it a little bit. Usually that's we it wont shift out of 1st until the rpm is really really high like a WOT shift. __________________ 1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI

02-24-2005, 07:49 PM	#2
corn Registered User Join Date: Dec 2003 Location: here Posts: 5,789	My guess is the shift modulator. Its either bad or the hose came off. Its mounted on the RR corner of the trans. Easy to change out & some can even be adjusted. Pop the hose off & turn the screw inside of the fitting...corn

02-24-2005, 09:29 PM	#3
magnethead 7000 #'s of american IRON Join Date: Dec 2004 Location: north tx Posts: 883	or the TV cable is mis-aligned.

02-26-2005, 10:32 AM	#8
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	Alwas shifts at 2800! Very hard bam shift like it was a preformance tranny? __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

02-26-2005, 11:13 AM	#9
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	Have you checked the fluid level? There might be a small flat head screw in the modulator valve you have to take off the vacuum hose off it. It will be in the center of the hole, need a pretty small flat head screw driver to turn it. Some have them some don't. If there is turn it in to raise the shift points a little more and out to lower them. You can turn it all the way in but that will always make it shift very high and will not shift unless you reach that high rpm and it will stay like that. Do you know what your rear gear ratio is and what size tires you run? __________________ 1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI

03-03-2005, 02:08 PM	#10
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	The tires are 30" and the rear end is 78 stock. Fluid is topped up. I have to locate this Mod valve.How do you know if the valve is good? __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

03-03-2005, 02:16 PM	#11
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	There will be transmission fluid coming out of it, they arent that much to replace (20.00) if it does need replaced. Take the vacuum line off and see if it shifts different. If the transmission is a th400 the modulator valve should be on the passenger side where the transmission cooler lines are, right above the pan. If you need a picture I can post one. __________________ 1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI

03-03-2005, 03:56 PM	#12
alf4444 Registered User Join Date: Dec 2002 Location: taylorsville, UT Posts: 778	mine was doing the same thing it would rev up around 3000 then SLAM into gear, Looked underneath and the modulator wasn't hooked up! Mod valve on a th350 is on the pass side with the hose coming off it to your intake __________________ 2011 CCSB GMC 2500HD DMAX 73 GMC 3/4 ton 4x4 96 Chevy 1500 STD Cab Shortbed Z71 Owner of WickedWolfRC.com

03-03-2005, 09:53 PM	#13
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	Thanks guys I'll let ya know as soon as I dig it out of the 20' of snow! where the he!! did I put that 4X4!LOL __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD



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