[SuperYeti]

Hey guys hoping someone can shed some light on the issue i'm facing. I"m getting a pretty significant vibration in my seats/rear end direction of hte truck when accelerating through and decelerating through 30-60km/h. I've now replaced the transmission, replaced all u-joints, had the driveshaft straightened (was out by 0.020") and balanced, replaced the rear end, had an alignment done, and now had the tires balanced as well, but its still there. I'm thinking the only culprit left could be the transfer case. Does this make sense? What could be wrong in a transfer case to cause this? I'm going to do a fluid change on it today, see if that resolves it, wondering if there are any other adjustments i can make that might resolve it. This is for my 1986 Fullsize Bronco, 351w, AOD, D44TTB up front, Ford 8.8 in the rear 33x12.5x15 on a 4" Lift. To confirm it was doing this before and after the lift and suspension upgrades. Oh its also doing it in and out of gear, but much more pronounced when in gear under load either decel or accel.

Cheers
Warren

 

[cyznit]

This is definatly a puzzling problem are you sure the work was done properly to your truck? I would suggest also looking at the simple things as well like motor mounts, tranny mounts n body mounts, ect... N also try it in 4 high and see if it's worse than 2 wheel

 

[SuperYeti]

Motor mounts are new, tranny mounts are new, body mounts aren't great, but not cracked or anything, I'll try it in 4-high tomorrow, see how it is. I'm thinking its either pinion angle or the transfer case is low on fluid or old nasty fluid. gonna change the transfer case fluid tomorrow and will take for a test drive, see if it gets any better. Yes I'm sure i've done the work correctly, good point tho

 

[Ulysse]

have you measured the pinion angle... and if so what is it? to confirm the pinion angle, try temporarily running in 4-Hi front wheel drive only (ie with the rear d/s removed)...

 

[SuperYeti]

No haven't measured the pinion angle yet. Any way to do that without a pinion angle finder, with just a digital level?

 

[Ulysse]

You're basically trying to find the angular difference between the d/s and the pinion. Yes you can use a digital level.

I'm shitty at explaining stuff on the net... so have a look at this link, scroll down to "Double-Cardan Measurements"

http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml

 

[LOUDFOOT]

I had a similar problem with with my Toyota and it turned out to be the bolt on the output shaft of the transmission connecting the yoke was loose. Tightened it up and it went away.

 

[SuperYeti]

You're basically trying to find the angular difference between the d/s and the pinion. Yes you can use a digital level.

I'm shitty at explaining stuff on the net... so have a look at this link, scroll down to "Double-Cardan Measurements"

http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml

Awesome guide, thanks. I didn't realize your pinion angle has to be 0deg on a double cardan. Do you know if that's' 0 at rest, or 0 under load, IE wouldn't i then want it to be 1-2deg under to compensate for load and torque during driving? Guess i'm going to measure my pinion angle

 

[SuperYeti]

So if it does turn out to be my pinion angle, how can i adjust that with a 1986 bronco on leafs with 4" blocks. Shave the blocks to get the adjustment i need i guess?

 

[Ulysse]

Awesome guide, thanks. I didn't realize your pinion angle has to be 0deg on a double cardan. Do you know if that's' 0 at rest, or 0 under load, IE wouldn't i then want it to be 1-2deg under to compensate for load and torque during driving? Guess i'm going to measure my pinion angle

You don't want 0Deg otherwise the needle bearings won't spin. You want 1-2 deg operating angle with the weight of the vehicle on the leafs.

Keep in mind that if your leafs are new that they will sag overtime and decrease your operating angle. If they are used leafs then you should try to go as close to 1-2 degree's otherwise you might be ok with 2-4 degree's. Last time I went through this I had issues because my angle was close to 6 deg, but things calmed down once I got it to about 4 deg.

 

[SuperYeti]

You don't want 0Deg otherwise the needle bearings won't spin. You want 1-2 deg operating angle with the weight of the vehicle on it.

Keep in mind that if your leafs are new that they will sag overtime and decrease your operating angle. If they are used springs then you should try to go as close to 1-2 degree's otherwise you might be ok with 2-4 degree's. Last time I went through this I had issues because my angle was close to 6 deg, but things calmed down once I got it to about 4 deg.

Yes I have brand new springs all around, and it looks like the arch on them and the mounting point of the new ones is a slightly different angle, turned a bit more down than the old ones. I'll go double check the angle, and then figure out what i need to do. BRB

 

[Ulysse]

So if it does turn out to be my pinion angle, how can i adjust that with a 1986 bronco on leafs with 4" blocks. Shave the blocks to get the adjustment i need i guess?

They sell tapered shims BUT I would machine the taper into the blocks. The shims would be prone to being spit out when stacked on to lift blocks. They also sell tapered blocks to deal with this. A 351W is very tourquey so I would expect some axle wrap from this set up.

 

[SuperYeti]

They sell tapered shims BUT I would machine the taper into the blocks. The shims would be prone to being spit out when stacked on to lift blocks. They also sell tapered blocks to deal with this. A 351W is very tourquey so I would expect some axle wrap from this set up.

Ok i just checked. I *think* its about 10 deg pinion angle currently. I got -19 deg on the drive shaft, and -9.2 or so on the pinion flange from the article that was provided i think that reads just under 10deg, am i reading this right?

I don't think its axle wrap, cause it happens with very little throttle on, and also during braking going through the same speed range. After seeing these numbers, looks like im putting another 6 or so deg into my blocks?

 

[Ulysse]

Yeah I'm not saying that its axle wrap... just saying that you might end up with some from the set-up you've described... I think you've read it right, and 10 deg is too much... with new leafs I would try to end up with 3-4 degs... also if you plan on running a big bumper or external tire carrier you might want to take that into account now, as that will also influence your final operating angle. It might take some experimentation because tapering your block to rotate the pinion upwards, will effect both the pinion angle and drive shaft angle...

 

[SuperYeti]

Yeah I'm not saying that its axle wrap... just saying that you might end up with some from the set-up you've described... I think you've read it right, and 10 deg is too much... with new leafs I would try to end up with 3-4 degs... also if you plan on running a big bumper or external tire carrier you might want to take that into account now, as that will also influence your final operating angle. It might take some experimentation because tapering your block to rotate the pinion upwards, will effect both the pinion angle and drive shaft angle...

Cool thanks for the advice. Already have the tire carrier, just no tire mounted on it currently, thats getting fixed on friday . How much does the average rear bush bumper weigh so i can throw that much weight at the very back of the truck to simulate it? So now the question becomes, what is the "best" way to shave a cast iron block LOL. I was thinking i'd take off 4 deg to start which should put me in around 5.8 before adding any other weight. so with extra weight i could probably count on .5 to 1 putting me in around 5 with brand new leafs, under 600km on them.

 

[Ulysse]

so... How did you make out with this?

 

[SuperYeti]

so... How did you make out with this?

Found a set of 4 deg shims, they're on order. Will be installing them next week when they arrive. I think if the angle is good, or at least once i have a more definitive answer to how much i need to move things I'll shave the blocks. How would you suggest cutting down the cast iron blocks, with a grinder, or take them to a machinist?

 

[Ulysse]

Well... I guess that depends on how surgical you are with a grinder or if you've got access to cheap machining... as was suggested in that other thread, if you are going to use shims then use steel shims that are secured to the leaf pack using the center pin, avoid aluminum shims or horseshoe shaped shims.

:beer_cheers:

 

[SuperYeti]

Well... I guess that depends on how surgical you are with a grinder or if you've got access to cheap machining... as was suggested in that other thread, if you are going to use shims then use steel shims that are secured to the leaf pack using the center pin, avoid aluminum shims or horseshoe shaped shims.

:beer_cheers:

I'll have to see, was kinda hard to see from the catalog but they sure looked aluminium with a hole in the middle. so i "think" they'd be bolt on. is there anywhere locally to get steel ones? I'll do fine with a grinder, did many years as a stone and tile mason so.... but still rather not have to suck cast iron if i dont have to heh.

 

[Bronco Boy]

Just buy some tapered blocks. Anything 2" or more comes tapered or non-tapered.