Need help-bucking bronco!

[blazinchuck]

ok here is the back ground, 1970 bronco(302,3sp,d20,3.50 gears-32x1050 tires)

this truck came to me after 1st gear died and the owner drove from NC to SC with only 2nd and 3rd. Clutch was burned up. I installed new clutch, pressure plate, resurfaced fly wheel. I didnt want to use the fly wheel, but the owner tried to save money. well the truck would buck so bad, felt like it would break the truck in half!he thought axle wrap maybe, so we install some duff upper anti-wrap bars-no luck.

i told him the fly wheel could be warped, so he bought a new one. I installed it and all the problems went away!

drove smooth as can be. one years later and less than 1000 miles(truck basically sat for the last 8 months) and its back! I have checked to see if disc calipers are sticking-they are not. I swapped the rear drive shaft-lots of play in the original-no help.

only if i engage low range, not locking the front hubs in-then it will drive smooth and nice. If its on jack stands, rear wheels up...its smooth and no problems. I can not figure this out!! The owner is coming in a couple days-was hoping to get this fixed-but its not looking good.

motor mounts, trans mount all look good. rear springs all look good, and everything is tight. please give me some other ideas what would cause this. I really down want to pull the clutch out again. I know the tires and axle ratio are not perfect, but close enough it should drive ok. Thanks

 

[blazinchuck]

quick update, with the rear drive shaft removed-front axle engaged and in 4 hi- problem seems to be gone. drives ok-havent driven around the block, but definitely better. the rear yoke has more play than it should, guess I need to remove the pumpkin

 

[Timmy390]

Check the clutch linkage. The bushings in my equalizer bar were GONE metal on metal and I had to replace due to the damage. It all looked good but when I removed it, it was clear I found my problem.

The bushings are plastic and thus get old and crack and then fall out....All the vendors carry the parts.

I think installing a diaphragm style pressure plate also helps. The stock "3 finger" pressure plates are just not that smooth operating as they age.

Tim

 

[Crush]

Also i you have broken rear springs or a bad slip joint on your driveshaft it will cause bucking and shudder

 

[B RON CO]

Hi, do you hear grinding noise in the rear like bad spiders or ? Good luck

 

[charlie6976]

Check your transmission/transfercase mounting bolts to the bracket. And the brackets to the frame. Could have worn bushings or loose/broken bolts. Take a pry bar and pry on stuff.

 

[Rustytruck]

Can you swap the driveshaft with yours or another Bronco for a test drive. Shaft might be binding under load. Bad spring bushings, bad centering ball in the CV, re-torque the u-bolts. Bad tranny mount bushings and or bad motor mount can reak havoc. To me your running on the front is telling you the clutch is not the major factor. While the drive shaft is out check the output of the transfer case and make sure its not wiggly. You might have to hang a gopro under there.

 

[Scott_T]

Definitely check for anything in the linkage that might have a slight discontinuity in the clutch travel. With the engine off, actuate the clutch and feel for anything that is not a smooth linear spring force. If you feel a glitch, track down the source and fix it. One thing to check is the clutch actuating fork pivot. This is riveted to the bell housing and hence is never replaced even though it wears into the fork pivot point. I have the same 3 sp, gearing and 32'sp and had with a similar bucking problem. I had to replace the clutch fork and rework the pivot to smooth out the actuation.