greetings all.

recently picked up a very original, and fairly clean 81 long bed single cab 4x4. really fun time capsule of a truck, the plan is to keep it as original as possible, but get everything working 100% so my youngest can drive it.

i've been chasing down a low speed vibration that's pissing me off, and i have narrowed it down to at least a bad pinion bearing in the rear carrier. being an 81, i understand that this is the 190mm diff, which isn't a big deal, but finding parts to get it right is turning into a challenge.

does anyone have a 4x4 with the 4.3 rear axle that they are parting out? or, i'd even go so far as updating it to a 200mm rear end, as long as A) it has the correct 4.3:1 ratio, and B) all of my brakes and such will swap over. willing to pay shipping for good stuff if anything's out there.

let me know what other details anyone needs to possibly assist here.

thanks for checking out the post.

--r

took these before i gave it a bath. nice and clean now, and all the bloody lights work. 8^)

just to show it off. i know y'all will appreciate it.

Super cool! I'll share this with our resident 720 expert, he may have some input and assistance.

thank you. most appreciated.

--r

I would advise removing the 3rd member of the axle and have a differential shop rebuild it. Bearings, seals, etc are still very much available. Serring up the diff proper can require special press tools to precondition and replace the bearings.

Another area to check with regard to the vibration is the slip yoke of the drive shaft. There is a grease zerk on it.

always good advice, that.

i'd prefer to get a spare and rebuild it at my leisure. that gives me the opportunity to show my son how it works, and we can walk thru the parts replacements and setting up the gears. he doesn't need to master the skill by any means, but understand the process and precision it takes to do the job correctly.

i have found some of the necessaries, i prefer to x-ref with factory part numbers to ensure that i get the correct parts the first time. having a spare to compare to parts i cannot cross ref is also helpful. any sources that you can refer me to for parts is greatly appreciated. also, reference material. alldata and mitchell have very sparse info on drive line specs for this particular vehicle.

first thing i've checked is slip yokes and universals. i have a full set of u-joints on the way, easy work and just good maintenance. slip yokes will be indexed, separated, cleaned, and then lubricated. easy saturday project for him to help me with, and we can cross those off the list of baseline work.

--r

The H190 4.375:1 rear diff can be found in 1974-79 620s and will bolt into a 720 just as easily. I have 2 4.375:1 ratio H190s on the shelf, but both need rebuilt with one missing part of a tooth on the gear.

You can change to a 1986 "ST" 4x4 C200 axle, as that year and trim had a 4.375:1 ratio. The complication is the need to either change the companion flange and shorten your driveshaft or swap to the later transfer case companion flange and use the later '86 driveshaft. In both cases you need to swap the brake wheel cylinders to the '82 ONLY ones for proper brake proportion.

Most folks elect to keep the H190 for simplicity. I've done the C200 swap myself and I prefer it, but I swapped the entire truck to the 4.11:1 final drive. Would have been better off keeping the 4.375 ratio.

But, back to vibrations: big issue on the early 4x4 720s is wear on the slip yoke which can make vibration at road speed quite bad. If you have any visible rotational play at the yoke, its time to consider a rebuild.

Also, there was a TSB back in '82 addressing low speed vibrations. At the time it referred to checking the primary driveshaft alignment. The straighter this shaft is to going into the transfer case, the better. It was suggested spacing up the transfer case to achieve proper alignment. I've had to do this on one of my trucks and it did help a lot. Also make sure the transmission mount is not collapsed. This can lead to an odd input angle to the transfer case which can lead to issues as well.

DA82KC: great input, very helpful. thank you.

since the truck is very original, preference would be to stay with stock. H190 is fine, not looking for adding strength to the driveline, was thinking there might be more availability for parts. probably keep this info in my back pocket for future inevitability.

i have not pulled the 3rd member yet, so i cannot attest to the actual condition of my ring and pinion. going to drain it completely this weekend and get a scope in there to see.

i've been eyeballing the slip yoke on the front driveshaft. there is a good amount of play in that one which concerns me. one thing i have been planning to do is drop that shaft out and drive the truck without to help isolate which end the vib is coming from.

it also makes a lot of sense to make sure that the stub shaft is as coplanar as possible. did you make shims to get the t-case lined up, or did you just use washers to get the alignment you were looking for?
this shaft is going to get the first set of universals as well. these have the most play of the three shafts on the truck. i also want to see how worn the support busing is in the output housing the gearbox. this is a little looser than i would like it to be.

i'll look into the transmission mounts tonight. i still have it up on the hoist. easy to get to. 8^)

--r

In my truck I spaced the transfer case using a set of thick shims I had for another project. We are talking about 7/16" in my case.

If the front shaft has a sloppy slip yoke, the rear has got to be worn too. But keep in mind, the front shaft does not rotate in 2H with the hubs set to free, so removal to isolate is not necessary.

the rear slip joint doesn't feel as if it has more than minimal play that i would attribute to normal clearance. i have not pulled the joint apart to inspect it. on the list for tomorrow.

looked at the front shaft a little closer last night, there is a pronounced offset. down and to the right of the truck. looks like the driver's side t-case mount has compressed down a bit. that one is longitudinal with the chassis, might take some slotting of the mounting to get it to line up, or just make a delrin or UHMW bushing to replace that.

net result is that it isn't really close to being inline. lots of gravel and dirt caked on everything for now. need to clean it up a bunch then get down to fixing things.

happen to know the size o-ring the speedo cable takes at the x-fer case?

--r