I put a 4bt Cummins diesel in my 93 F150. I had the flywheel refaced and new everything to the transmission. I also swapped in a 2.73 rear end because the best mileage is at 1800 to 2000 RPM at 70 MPH and this thing only makes 2500 RPM. It has a 5 speed Mazda transmission and I think first gear ratio is 3.90, pretty high especially with 2.73 gears. When I take off in first and reverse it has a bad shudder. Do any of you have any idea what is causing the shudder? I read thru several pages of threads looking for shudder when letting the clutch out but didn't find anything like my problem. I did see one post that said a u-joint could cause it. I put a ZF-5 in first and it has 5.72 first gear and it was nice and I didn't notice any shudder but it made an awful noise and I assume it needs new bearings. I only drove it 2 or 3 miles and put the Mazda transmission back in. Thanks in advance for any help.

 

My guess is the clutch is chattering while slipping because of the high first gear and highway rear gear.

 

That is usually caused by glazed flywheel but you had it resurfaced. Is the clutch new or used?

 

Did you have to change clutch disc for the Mazda transmission? What kind of disc? Either it is oiled up or is more a metallic disc and it will be chattery, just nature of the beast.

 

Check the motor and transmission mounts. Sometimes the rubber pulls away from the metal. My old 1976 F350 dump truck had a horrible shudder in granny first and reverse. The entire truck would vibrate/jump. Turned out one of the motor mounts was deteriorated then broke. I would inspect the transmission mount as the first suspect since it started when you put the Mazda trans. back in.

 

jas88, every thing is new refaced flywheel, pilot bearing, clutch disk, pressure plate and clutch master and slave cylinders. I got the clutch set from Rock Auto and that's all I know about it. This truck also shuddered before I replaced every thing and that was using Mazda transmission. I've had this thing on the road since 2014 and I think it shudders worse now.

Freightrain, every thing that I replaced new was also used on the ZF 5 transmission. The only difference in the two is the ZF 5 is twice as big, shorter and the gear ratios are different.

rla2005, the transmission mount looked good when I had it out and I checked the motor mounts by watching the engine when I tried to move it and it didn't appear to be an excessive amount. I had a 73 Chevy that shudders in reverse and I cured it but putting a turnbuckle between the frame and the head. 3 or 4 days ago I set the emergency brake and tried to move the truck and there was no shudder. In one of the threads I read u-joints was mentioned as a possible cause. Before I came in today I checked the u-joints and the first two seemed OK but the one at the rear end had a small amount of movement in it. It also had no grease zerk and may be an original. The other 2 had zerks. The rubber in the carriers bearing is still good too. Do any of you think some wear in a u-joint would make it shudder? The Cummins engine is a 4 cylinder and I've read the the power pulses are a lot harder than in a gas engine. The only thing I haven't replaced is the drive line so the u-joints may be causing it.


Thanks for the reply mudsport96. One thing I forgot to mention, a couple days ago I was thinking of ways to test it. I set the emergency brake and started letting the clutch out and it didn't do anything, It was nice and smooth.

 

Any play at all in the U Joints can cause a shudder or vibration, but usually will show up as a vibration. Either way, U Joints with any play in them gotta go.

​​​​​​Diesels in general don't run as smooth as gas engines (higher compression, longer stroke, bigger bang). 4 cylinders in general don't run as smooth as 6 or 8 cylinder motors, so put them together, and you should expect an engine that doesn't run quite as smooth as a gas I-6 or V-8.

But if this shudder was happening before, you may want to check the input and output shaft bearings in your M5OD. That's where I would be looking.

​​​​​​Also I'd love to see some pictures of your swap!

 

This is exactly what I thought when I first read your rear end ratio with the m5od. 2.73 is absurd, to be honest.

Also, your tach or math is totally wrong. 2500 rpm in od with 31" tires is 100+ mph with 2.73 in the drive axle.

 

Actually 2.73 rear end is no more absurd than 31 inch tires with a 3.21 axle with a .80 overdrive. My tires are 235-75R-15 and the rolling radius on them is 13.5 inches or 27 inch diameter. I did crash reconstruction and was taught to use rolling radius to calculate speed. Both of these examples result in around 1900 RPM. I stopped in at a transmission repair shop and I asked the head man what would cause the shudder and he said the pressure plate. I asked if any thing else would cause it and he said not likely.

 

Turning the flywheel can cause this. Some flywheels are conical so that the clutch grabs progressively. When you machine them flat it causes the judder.

Any looseness in the mounts as mentioned can cause it. Any bell housing bolt that is missing, not properly tight or out of spec can do it. I've heard air in the hydraulics can do it but …

Google with the word judder.

I've also been told if you burn the clutch down good it might make it stop. Don't blame me if it stops forever. Put it in high gear and do like you are taking off, let it slip real good. Burn it. Read about it first. And again, don't blame me.

I have the tractor version of that engine. It pushes dirt around real good.

You know with a conversion like that you are going to break stuff. It's already broke, you just don't know it yet.

https://www.advancedclutch.com/revie...bearing-pb1009

https://www.onallcylinders.com/2012/...m-the-experts/

 

The 4bt is a rattle trap. My 6 bt shakes if the rpm gets too low so I can imagine the 3.9 gets bad, but did you say you checked u ujiont angles? If they are off then you can get a low speed wobble

 

Is your avatar a picture of it? If you have a divorced case then it is likely an angle issue

 

Nothing taller than 3.50 gearing belongs in a truck imo.I would start there.
(Save for modern stuff,where they're now providing extensive gearing options in transmissions so you no longer need steep rear gears for performance,to which I say; What took so long!)

Two wrongs don't make a right.

 

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Hey Mate, did you ever sort out the Shudder issue? My 89 F150 has a similar problem. Mazda M50D box but the diff is 4.09 8.8inch. I have replaced the flywheel, clutch and slave cylinder and the problem is the same. I am thinking the issue might be in the transfer case BW 1356. If i disconnect the rear tail shaft and drive off the front diff it is the same. If i put the transfer case into low range there is no shudder on take off.