Hey guys. It came time to replace my 302 powered F150 regular cab with something a little bigger. I purchased a 1996 F250 Dually with a 7.3 PSD and I noticed that on the highway it shudders when its low on the tach...say 12-1500 and shifting into fourth. The shift is smooth but the motor feels like it shudders until the turbo spools high enough, about 1900 and then she takes off.

Any ideas?

Also when the speedo breaks 100km/hr it starts bouncing around....100-90-105-100-etc. My speed doesn't change but it seems a little weird.

 

That speedo is weird because it is electric.

I don't know about the shudder. Have you changed the oil since you purchased the truck?

 

There is a sensor on the rear axle. I think it is the vss sensor. Anyway take it out and clean it up. It may have shavings stuck to it. That should fix the speedo.
The shudders could be as simple as the clutch.
What have you done to the truck since you bought it.

 

F-250 DRW????????? Ford never produced a 250DRW.
Shutter can be an issue with the tc.
Some DRW trucks have speed limit programming.

Bill

 

Well I have only had the truck a couple days now. Yes the oil has been replaced. It is very likely it is not a stock dually. It just feels like the motor is under powered or not shifting down fast enough right then and there. The rest of the gears feel great.

 

I've always had this issue with mine but when I'm decelerating not accelerating. Say I come into a town and get down to 30 mph. My truck doesn't always downshift and it shudders at low rpm. Hit the overdrive buttom, it downshifts, and all is good. I wonder if we have the same issue even though it's when I'm slowing down.

 

Sounds more like a late unlock than a shutter.
My wag is it only happens due to you have not stepped on the brake.
It can/will hold the gear with light throttle.
As a test after a roll down in speed just tap the brake.
I will bet your issue is gone.

What is your TPS idle voltage?
Bill

 

A shudder at low RPM under acceleration strikes me as a slipping torque convertor lock up. I came across it on another truck of mine(nissan), as soon as it hit overdrive and the convertor locked up it would begin to shudder under light acceleration, it will hold a cruising speed on flat highways but as soon as their is any incline what so ever it would start to shudder again. Fortanitly on this truck I was able to unplug the torque convertor lock up and the shuddering went away.

It may not shudder in 2nd or 3rd but 4th with the low rpm's your requiring more torque to hold the speed and thats when your convertor is slipping. I've seen torque convertor slippage and not trigger a transmisson fault because it was not slipping enough but yet it was still slipping.

Thats my thaught on it anyways.

Besides that, way to go on the dually f250, I dont feel so lonely now.

 

Thanks everyone. That's a good base to start my search from. Does a torque converter slipping mean I will be tearing that drivetrain apart really soon or do you think I have some time before it comes to that? David, was your F250 an after thought or did it come from the factory? As well I see you have a 3" DP, most people are pushing for 4". Would you say the 3" is sufficient?

 

Go with the 3" DP. It's much less work to get it in there. The 3" is far better than the flat stock one.

 

IF it is the torque convertor you will have to pull the transmmision out, I'm not there to physically asses your truck so like I said, I speculate its that. Best advise I can give you is to have a reputable transmission shop diagnose your problem. Locally where I am you can get a rebuilt torque convertor if your planning to stay at near stock power numbers and if you have the tools and know how a torque convertor replacement is in your grasp. Keep in mind, these e4od transmissions are heavy units, so if you dont have a suitable jack you cannot do it by yourself.

As for how long it will last, I would not drive the truck a whole lot with it until your issue is fixed, thats my opinion.

As for the down pipe, I have the 3 inch going into the factory exhaust with the muffler and CAT cut out and a straight pipe put in place. A 3inch down pipe can handle some nice power numbers (providing your EGT's stay in check) as well with a 3inch down pipe as mentioned is alot easier to install. All you have to do is hammer the bottom firewall flange smooth with the firewall for clearance. Anything bigger, your cutting from what I understand. If you have to pull your transmission out, that would be a good time to install a down pipe. Thats what I did when my transmission came out and the downpipe install was a breeze.

 

OK Well all that sounds fine. I have a transmission jack and though not as knowledgeable as some of you I believe I have the skills. Are these transmissions famous for issues? Is there another kind of tranny I should keep my eye out for?

 

There is nothing else for the tranny unless you build up the one you have to make it stronger or you convert to a stick.

While you have the tranny out I would suggest getting an updated convertor seal(seal on the pump that seals the convertor shaft) and the brass bushing as well. They are bad for leaking when the trannies get hot. Thats why my tranny came out, tranny gets hot and oil started pouring out of the inspection cover. Check your rear main seal, if it leaks replace it, check your exhaust pipes from manifolds to turbo for broken bolts and leaking gaskets and replace. Those pipes that leak will affect your boost leevls and power.

Its really not a bad job, its just heavy as heck.