Newbie Question 98 12 valve Jasper Auto Trans

[Adam81]

Apologies in advance if this question has been asked and answered. I looked and didn't see this specific issue. I recently had a jasper automatic transmission put in my '98 3500. This weekend was the first chance I've had to really drive it and test it. Hooked to an enclosed trailer with OD OFF, I couldn't get over 50 mph. With the trailer and OD ON, I couldn't get over 60. No trailer and OD ON, I couldn't get over 70. Both RPM and MPH wouldn't go any further no matter how far I pressed the pedal. I've been told a few things from the possibility that the transmission happens to be bad or that the truck is governed some how. The people I bought it from pulled campers years ago, and it sat for 5 years. I've done a lot of work to it already. Now this. Where do I start checking?

 

[petersonj]

You haven't provided enough information to know whether or not you have a transmission problem, or possibly a fueling problem.

Each time you are experiencing a speed restriction, what is the tachometer reading and what is the throttle position? Give examples.

Is the torque converter locked or unlocked when the incidents occur?

Also, what is your axle ratio?

- John

 

[Adam81]

You haven't provided enough information to know whether or not you have a transmission problem, or possibly a fueling problem.

Each time you are experiencing a speed restriction, what is the tachometer reading and what is the throttle position? Give examples.

Is the torque converter locked or unlocke when the incidents occur?

Also, what is your axle ratio?

- John

So, at 50mph, with trailer and no OD, the RPMs are at 2500; at 60 with trailer and OD, the RPMs were around 2000; at 70 with no trailer and OD, the RPMs were at around 2500. Both tachometer and speedometer needles were almost in identical places when running if that makes sense. No idea about the torque converter. How do I know if it is locked or not? I'll have to check the axle ratio.

 

[petersonj]

So, what was your throttle position in each of these scenarios?

The torque converter will lock up in 3rd gear and 4th gear. When the torque converter is locked in a specific gear (3rd or 4th), the transmission will behave like a manual transmission in that there will be no slippage in the transmission - engine rpms will not increase unless road speed increases, regardless of throttle position.

Do you have a boost gauge? A boost reading will help determine the engine load when your unwanted events occur.

at 60 with trailer and OD, the RPMs were around 2000

Were you at full throttle?

Drive your truck around and experiment at different speeds and engine loads to observe torque converter locking and unlocking. Pay attention to throttle position and engine load and then report back.

In general if a transmission is slipping, the engine will rev suddenly, but road speed won't increase.
If the engine is not producing power, then road speed will be limited to the power available, but there should be no rpm spikes or abnormal transmission slippage.

- John

 

[Adam81]

Yes, I was at full throttle. The transmission wasn't slipping, I do know that. I plan on driving it again tonight, and I'll report back what I learn based on what you've suggested to look/listen for.

thanks in advance!

 

[petersonj]

It's beginning to sound like you have a fueling problem.

Do you have a boost gauge installed?

- John

 

[Adam81]

I don't believe so, but I'll double check. I've had the truck in the shop more than the road because it had sat for 5 years and needed a lot of work to get it back to par. Good thing is I got it cheap enough, it's still a cheap truck with what all i've had to do to it.

 

[Cummins12V98]

Fuel filter???

 

[Adam81]

It's beginning to sound like you have a fueling problem.

Do you have a boost gauge installed?

- John

So, I don't have a boost gauge. I drove it last night, and everything sounded fine, the transmission shifted fine. It did seem the RPMs were a little high for an automatic shifting at times. But just regular driving down a straight, flat portion of the road, everything was fine. It was when I tried to take off fast or punch it on down before hitting 4th gear that the RPMs seemed a little high, but that may be normal.

 

[Adam81]

Fuel filter???

I thought a new filter was put on when I had engine work done. However, that's been a year or so ago, and it has sat more than it's been driven because of the work that's been done to it, and mechanics taking too much time to do a simple fix. I'll probably change it out this weekend just out of precaution.

 

[petersonj]

I drove it last night, and everything sounded fine, the transmission shifted fine.

But, you are still having a problem with not being able to go faster than 60 or 70 mph (from your first post)?

I will be able to tell you what axle ratio your truck has if you post your tire size and your engine rpms at 70 mph in 4th gear with the converter locked up.

- John

 

[BigPapa]

It was when I tried to take off fast or punch it on down before hitting 4th gear that the RPMs seemed a little high, but that may be normal.

Sounds like your TV Cable is out of adjustment.

 

[Adam81]

Sounds like your TV Cable is out of adjustment.

Got ya. I'll have that checked. Thanks!

 

[Adam81]

But, you are still having a problem with not being able to go faster than 60 or 70 mph (from your first post)?

I will be able to tell you what axle ratio your truck has if you post your tire size and your engine rpms at 70 mph in 4th gear with the converter locked up.

- John

At 70mph it is at 2250 rpm

 

[petersonj]

Tire size?

- John

 

[Adam81]

Tire size?

- John

235/85 16

 

[Adam81]

At 70mph it is at 2250 rpm

70 mph at 2250 RPM is as fast as it will go with the "pedal to the metal."

 

[petersonj]

I would say that you have a 4.10:1 axle ratio.

If the exhaust is clear at "pedal to the metal", then you are not getting the fuel requested.

Possible causes:

* restricted fuel supply
* faulty throttle linkage
* broken boost hose clamp / leaking intake manifold (likely to see black smoke, though)
* exhaust manifold leak (again, likely to see black smoke)
* faulty injection pump

- John

 

[Adam81]

I would say that you have a 4.10:1 axle ratio.

If the exhaust is clear at "pedal to the metal", then you are not getting the fuel requested.

Possible causes:

* restricted fuel supply
* faulty throttle linkage
* broken boost hose clamp / leaking intake manifold (likely to see black smoke, though)
* exhaust manifold leak (again, likely to see black smoke)
* faulty injection pump

- John

Ok, thanks for all the help. I'll have these checked out and go from there. Thanks again!