Bronco Bump?

Hello all this is my first post! I am a proud new owner of a 1996 Bronco XLT 5.8 with only 96,000 miles. I had been looking for the last six months before I found a good solid Florida truck. Well I found it in Coco Beach finally!.. I have been busy with the truck for the last 45 days. I put new tires, new shocks, re-tinted it, new HD radio, new speakers and there is more to come. Now the problem at hand as I have two of them. Fist one is an oil leak I have one missing oil bolt from the pan and it looks like it is leaking. Now if I changed the oil gasket should I also change the rear main seal? If I go that far should I also changed the freeze plugs since I am there? Not sure how far I should go on this one.

Next issue is when I drive the truck and come to a stop I feel a very little bump. Then when I take off again and feel the bump again (both from a complete stop). It is very small and the truck shifts great. If I slow down really really slow I don

Hi Esmoglo, welcome to the 'Zone! You'll get tons of great advice on here - I've learned lots.

As far as the gasket - if it doesn't leak, I wouldn't mess with it. No need to risk stripping a bolt or something. I don't think that's a general maintenance issue.

The bump is very annoying. My '96 did it when I got the truck. My bet is that it's probably the slip joint (for lack of a better term) in the rear driveshaft. Easy to fix if that's the case.

For a couple days leading up to your job, hit the bolts holding the rear of the driveshaft to the differential with PB Blaster or something similar. Mine were a PITA to get off.

On job day, first, mark the orientation of the rear of the driveshaft where it meets the differential with some paint or something so you can reassemble the exact same way you took it apart. Also mark in front of and behind the rubber boot in the middle of the shaft.

Next, cut off the collars that hold the boot in place. They're one time users. Don't damage the boot.

Next, remove the bolts holding the rear of the driveshaft to the differential. I seem to remember that i had to use the round end of an end wrench because those bolts are kind of goofy shaped. A piece of pipe over the wrenchwill get you some leverage if necessary.

Next, slide the shaft in half. Clean up the splines and reapply fresh grease. Hit it good and don't use cheapie grease. This thing gets a lot of use and you don't want it binding up on you.

Reassemble everything and use zip ties to hold the boot in place on either side. Good and tight. Put the connectors for the zip ties on opposite sides of the shaft to prevent high speed driveline vibration due to driveshaft imbalance (not a huge issue with the weight of zip ties, but what the ****).

This may be a good time to inspect the U joints also. The front of the rear driveshaft has a CV joint. I think mine's going bad and giving me a shimmy at high speeds. That should be fun to replace.

Have fun running over stuff!

esmoglo said:

Hello all this is my first post! I am a proud new owner of a 1996 Bronco XLT 5.8 with only 96,000 miles. I had been looking for the last six months before I found a good solid Florida truck. Well I found it in Coco Beach finally!.. I have been busy with the truck for the last 45 days. I put new tires, new shocks, re-tinted it, new HD radio, new speakers and there is more to come. Now the problem at hand as I have two of them. Fist one is an oil leak I have one missing oil bolt from the pan and it looks like it is leaking. Now if I changed the oil gasket should I also change the rear main seal? If I go that far should I also changed the freeze plugs since I am there? Not sure how far I should go on this one.
Next issue is when I drive the truck and come to a stop I feel a very little bump. Then when I take off again and feel the bump again (both from a complete stop). It is very small and the truck shifts great. If I slow down really really slow I don

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It may also be the front radius arm bushings . Go to the front axle there is an arm on each side that runs back to a bracket on the frame . When the bushing at the end of the arm at the bracket wears out you will hear a bumping and probably be able to feel it in the floor on which ever side is doing it . If it is them you should change them in pairs , Welcome to the zone /emoticons/[email protected] 2x" width="20" height="20" />

there is a specific torque for the 12point bolts that hold the Ujoints on the drive shaft to their respective yolks. If you tighten them down too much you will distort the bearing causing the rollers to bind up. I dont recall exactly what the torque is on them but its pretty low for a driveline.

the bump could be so many things its not funny. You have to really pay attention to the truck and see if you can feel it. Could be the rear leaf bushings. could be ball joints etc. start at one end of the truck and look it over. start with suspension bushings in the rear, then look into the backlash of the rear diff(by seeing how much your drive shaft will turn without moving the wheel). If this is excessive it could be adding to the problem. Drive shaft, radius arms up front, ball joints, even your steering linkages.

I have bump creeks and clunks ive been tracking down for a long time so be patient with it.

to the Zone!

Oil Leak: I would get a new bolt for the oil pan and clean everything up real good. Keep an eye on it to see if you are still leaking oil, if you are then you now have an easier time seeing where it is coming from.

The Bump:

I'm thinking along the same lines as Blade on this one, or maybe the rear axle mounting bolts. Where are you feeling the bump coming from?

Have a buddy for this one and DO NOT get under the truck during this test, You need to look under the truck when it is under load. To do this have your buddy "power brake" the truck. This is done by keeping one foot on the brake and one on the throttle. You don't need to go nuts here just enough to make things move with out the truck moving then let off the throttle, do this a few times. You are looking and listening for the bumping or banging. Watch the radius arms where they mount to the frame under the doors. then look at the rear axle, this time you are looking to see if it is rotating forward under load then resting back in place when off the throttle.

You should see some movement as it is normal to have a little movement but if there is excessive movement then you have found your problem.

Good luck

Thanks for the responses! Now the radius arm bushings are new so I can rule that one out. I am thinking it is related some how to the drive shaft

Yes in 2 wheel only the rear shaft will move , The front will move in 2 wheel if one of the hubs is locked in but then the front wheels are driving the shaft . Does the truck have a lift ? I do remember a buddy had one and the lift block was cracked creating a gap and when the axle would rock youd hear a thump noise but like shift1313 said there is so many things it could be Shadow_D,s advice of having a buddy move the truck while you look under is good probably the only way youll find what,s doing it . /emoticons/[email protected] 2x" width="20" height="20" />

in reverse you are loading the suspension in a different way. For instance if your rear shackles were having problems on the leafs when you accelerate your are squatting the rear end. when you brake you are lifting it up unloading everything. In reverse you have already hit the brakes so you have "unloaded" the rear and when you go to reverse your slop is already at its extent until the rear squats when you go forward. If it was something to do with the rear suspension it would also show its face when making tight circles. You could go to an empty parking lot, go in reverse and hit the brakes. Then cut your wheels all the way to one side and go forward and see what happens. You can jack the rear of the truck up and set the frame on jack stands, then take a large pry bar to the rear shackle and see if you can induce any slop. because its a bushing it will flex but your looking for extra play between the bolt and the bushing. same thing up front on the rear leafs.

Ive had ball joints start to go bad and only "click" when i was pulling into a parking spot down hill and braking hard.

do you notice any weird handling problems at speed say when you are turning? If anything in your front end was loose it would probably also show its face at speed.

because of friction your front axles will still spin a bit when rolling even if your hubs arent locked in but your front drive shaft shouldnt be "driven" by anything if you are in 2H on your tcase. If you lock your tcase in 4H and your front spindles(manual locking hubs) are in the free position then you will be driving your front diff and axles but the wheels will not be driven. Conversely if you lock your hubs in and you are in 2H your front diff and drive shaft will turn because of your wheels but inside the tcase your front drive shaft will not be connected to anything.

also something else for you to try, next time you are pulling up to a stop pop the truck into N from drive and brake and see if you still get your noise. This will remove the engine braking from the drive shaft and take the load off of the Ujoints. The telescoping part of the drive shaft will still telescope under braking load but it wont have a torque on it. If you still get your bump you can take the tranny out of the problem list(for this problem) and more then likely rule out the drive shaft(but not completely).

just a few more notes for you. here is a spring perch on an 86 i purchsed. this truck had been towing a boat and more than likely pulling all the way into the water to unload.



this same truck(f150) had both gas tanks leaking from rust, both rear shocks blown apart and some horrible frame rot and the gas tank straps were about to let go.

this is what the outside of it looked like, you would never know



also on my 89 i had a thump in the rear. Both axles could move in and out because the limited slip clutches were so worn that around turns you would hear a thump. Replaced the clutches and got rid of the play, still had a thump. Found that the rear shackle bolts had rusted and worn about 1/2 the diameter away allowing the bushing to move around on the bolt on both sides.

good luck finding the problem