35's and shifting?

[motormayhem]

My m1009 has 35's and does 1st to 2nd at 25-30 and 2nd to 3rd at 45-50. Is this high? The engine is really roaring when it shifts, but this is my first diesel. Do the 35's affect this? I heard the vacuum lines from the IP the the tranny might be dry rotted and I checked them. They look pretty old. What size lines are they so I can get more?

Thanks,
Miles

 

[gt1009]

1st to 2nd sounds normal but 2nd to 3rd should be about 35mph. In case your wondering 35s only made my spedometer off by 3 mph, as clocked by one of those police radar things with the big numbers saying how fast you are going.

 

[motormayhem]

1st to 2nd sounds normal but 2nd to 3rd should be about 35mph. In case your wondering 35s only made my spedometer off by 3 mph, as clocked by one of those police radar things with the big numbers saying how fast you are going.

Wait, if it shifts into 2nd at 30 and then 3rd at 35 2nd seems useless.

 

[gt1009]

Ya, mine usually are 10 mph apart depending on throttle input. If it shifts to 2nd at 25 it shifts to 3rd at 35 and such.

 

[hobie237]

Wait, if it shifts into 2nd at 30 and then 3rd at 35 2nd seems useless.

It pretty much is. Welcome to the dog**** ratios of the TH400. I mean, 2.48, 1.48, 1 may be good for some things, but a diesel truck with a fair amount of low end grunt isn't one of those things.

 

[AJMBLAZER]

I've got 38's and it still shifts pretty early. I'm in 3rd by 40-45mph at the most.

 

[IRWFO]

In case your wondering 35s only made my spedometer off by 3 mph, as clocked by one of those police radar things with the big numbers saying how fast you are going.

According to my Garmin. My speedo is off by about 3mph up to 30mph. Then it starts getting worse. Buy the time I am at 55 on the speedo my GPS says I'm going 64mph. When showing 65 the GPS says 75. I'm running 36's.

As for the shifting. I always felt my second to third was taking to long also. As soon as I changed my fuel filter and found a lot of new power my truck feels like it is shifting when it should. As in I don't even notice.

 

[motormayhem]

Would the trouble going into 3rd be from the decayed vacuum lines? When I hit 45-50 I have to let off the throttle to get it to shift otherwise it will stay in 2nd.

 

[hobie237]

Sounds like a vacuum and/or valve issue. Just pick up a new modulator valve and a couple feet of vacuum line.

 

[IRWFO]

I have found that a bad vac line to the modulator would cause the trans to shift hard. How does it feel when it shifts?

 

[motormayhem]

I have found that a bad vac line to the modulator would cause the trans to shift hard. How does it feel when it shifts?

It slams into gear, but I though that was just because it was revving high.

 

[IRWFO]

Then I would replace the vac line first.

 

[Somemedic]

They sell the right size vac hose at the Zone. Cut a piece off and go in and get urself some. Also that plastic device that the hoses plug into can be adjusted to how soon you want the tranny to shift. Its toward the front of the motor and you have to loosen 2 bolts (believe its the vaccuum modulator). Its adjustable for when your driving around town or towing.

 

[corelokt]

Mine, as stock will stay in 2nd, with the pedal down, up to 55mph, as per my gps. It's a M1009, Blazer, with the highway gears.

 

[motormayhem]

Mine, as stock will stay in 2nd, with the pedal down, up to 55mph, as per my gps. It's a M1009, Blazer, with the highway gears.

Highway gears?

 

[hobie237]

The Blazers have 3.08 gears. They're good for the highway. Not much else. The pickups have 4.56 gears. They suck on the highway.

 

[scottc]

Mine has always done what it wants. Depends on the day. Shifts smooth most of the time, every now and then not so smooth. I think it is the nature of the beast.

 

[scottc]

Mine has always done what it wants. Depends on the day. Shifts smooth most of the time, sometimes it seems like I forgot to push in the clutch pedal.

 

[Bobert]

Do the adjustable vaccum modulators work? I heard they let you adjust 2-3 mph.

Since I got a rebuilt transmission, Mine shifts later which is nice for on ramps but annoying if you want to maintain 35-40mph.