Automatic 90 series question

[Sarge001]

Hello guys, I have a 90 series D4D 4 speed automatic. When I travel above 40mph and I release the acceleration, the rpm drops to idle speed, when I reapply the throttle, the rpm jumps back. At that moment, when I apply throttle and the rpm jumps back, I get a big hit, like something is loose down under...
Some bushings were replaced in the back, the situation is better, but still present...
At 60mph when I enable the cruise control, I get a so big hit, when the engine starts pulling that a sleeping person would rouse from sleep.
Do you have any tip what to look for, what could be wrong?

 

[diggerdave]

Hello guys, I have a 90 series D4D 4 speed automatic. When I travel above 40mph and I release the acceleration, the rpm drops to idle speed, when I reapply the throttle, the rpm jumps back. At that moment, when I apply throttle and the rpm jumps back, I get a big hit, like something is loose down under...
Some bushings were replaced in the back, the situation is better, but still present...
At 60mph when I enable the cruise control, I get a so big hit, when the engine starts pulling that a sleeping person would rouse from sleep.
Do you have any tip what to look for, what could be wrong?

It's really hard to diagnose thumping and clunking in the drivetrain over the internet. And it's not helped by the number of potential causes (just do a search on here for something like 'shunt' or 'clunk' to see what I mean). In no particular order and not exhaustive:

1. It could be an autobox fault - I don't know autoboxes but there's plenty of info on here.

2. It could be failure of the suspension turrets on the back axle (cracked/rusted through allowing axle to move when accelerating). Easy to check

3. UJs worn in the propshafts (usually the rearmost one next to the rear diff, but could be any of them). Also an easy thing to check.

4. 'Slack' somewhere in the driveline. Could be the front diff/rear diff/or transfer box. Lots of people have this to some extent - it's the curse of permanent four-wheel drive. Power is applied to the front or rear axle at slightly different times. Very hard to do anything about, and hard to track down. I've had some moderate shunt for the last 4 years, but its never got any worse since I got the vehicle.

5. Splines worn in driveshafts (usually front?). Not something that seems to affect LCs much, but you hear about it in other 4x4s. Results similar to 4, but likely to deteriorate. Most likely if the vehicle's been thrashed off-road?

6. Worn bushes in various control arms, allowing the axle to move under load. Shunt will be quite small.

 

[Sarge001]

Woow, thank you for the tips.The car was never on hard offroad. I will check everything in a week and I will report back with the solution. Thank you!

 

[AndycruiserguyLomas]

Woow, thank you for the tips.The car was never on hard offroad. I will check everything in a week and I will report back with the solution. Thank you!

It will be interesting to see the diagnosis. Where in the world are you to have CC on a D4D or did you retro fit it?

 

[Sarge001]

It will be interesting to see the diagnosis. Where in the world are you to have CC on a D4D or did you retro fit it?

Retrofit, I love CC, it was to easy fit to miss

 

[AndyCook]

Also check the engine mounts , there is one under transfer box for example