axle shafts need a shim...

[RMS]

a wile back I rebuilt two 4.89 chunks set the back lash and preload installed in truck and I could sure feel the preload. did a couple laps around the yard and it just felt too tight. rolled the 37 back into the shop, jacked one wheel and boy she was tight... jack both sides to see if maybe it was the the carrier gears or the preload on the pinion.... everything was tight and as I spun the drive shaft it felt like the bearings were square... so I commit to pulling the chunk out of the rear axle housing. I started by pulling the shafts then moved onto the the drive shaft ... it spun with ease..... jacked up the wheels and they spun with ease..... bolted the short side axle shaft back up and everything was jammed up tight. after fiddling around I found that the axle shafts were deadheading in the side gears leaving me with a .035 gap between the axle flange and the hub. the same was true with the other side. I went around and measured the depth of the side gears in a few loose diffs and found many differences between them.

to sort the issue I made up some 0.050 copper shims to space out the axles.

has anyone noticed their axles bottoming out in the diff ? and is 0.015 clearance good or should I make thicker shims ?

[Frank Irons]

Are you installing the outer axle seal plate and 2 gaskets?

Frank

[RMS]

yes. I even run the thicker early seal flange with the removable seal.

[Kaegi]

thats a weird one. did you replace the spider gears and side gears?

[RMS]

no, I just swapped out one chunk for another. the chuck did come out of a 2wd pilot house..... ?

[Kaegi]

I think that is an 8 3/4 diff. different animal than the stock 9 5/8 diff

[RMS]

well I had two 4.89s chunks from 2 different 2wd pilot house dodges, one chunk had a carrier with bad side gears so I swapped out the carrier with a carrier from a m37 that had a 5.83 ring gear. they both went together the same and fit in the m37 housing ?

[Kaegi]

they should fit in theory but they are 8 3/4" and the center line of the axle shafts/side gears will be slightly off and could be causing the binding.. the only non WC/M37/PW dodge truck I have every seen with 9 5/8 diff is the one ton Dodge Route Van and they only made them a few years and are rare

a place here in WA back in the day sold tons of surplus WW2 and M37 dodges and they would stuff 8 3/4 4.89s in some M37s and tho it might work I think it would break axles more frequently being out of alignment. plus it is a donwgrade in general due to smaller ring and pinion

[RMS]

will a 8 3/4 ring and pinion fit in a 9 5/8th chunk ?

[Kaegi]

will a 8 3/4 ring and pinion fit in a 9 5/8th chunk ?

dont think so. that is why people buy 9 5/8" ring and pinion in 4.89 from bob stahl or VPW. no factory stuff works. correction: factory power wagons were available with 9 5/8" 4.89s but very rare

[Elwood]

RMS, do you have a copy of TM 9-1808C Power Trains and Interchanges: Military / Civilian Trucks 1941 to 1971 (Dodge)? Section 5.3b discusses the installation of 8-3/4 third members into 9-5/8 housings.

It's not an official US publication, but was written by John Zentmyer (I think), and is in the style of a US Army technical manual. Available from Portrayal Press: https://www.portrayalpress.com/ProductD ... D9%2D1808C

[RMS]

I got that book and from everything I can see, I installed 9 5/8 chunk and gears. I did go around and measured other loose 9 5/8th chunk side gears and not one measured the same, they were all over the map. I am also running non stock shafts witch likely contributed to running out of depth.

[Elwood]

I got that book and from everything I can see, I installed 9 5/8 chunk and gears. I did go around and measured other loose 9 5/8th chunk side gears and not one measured the same, they were all over the map. I am also running non stock shafts witch likely contributed to running out of depth.

The variance in gears is disturbing.

Curious as to which aftermarket shafts you're using?

[MSeriesRebuild]

Fellows, this is why a precision installation and gearing set up are absolutely NECESSARY with any differential. There is any number of little issues that can cause what has been described here. One that is very often over looked is the pinion depth setting. The spec is different on every ring and pinion gear set. At the time gear sets are manufactured, they are run and a precise depth is established. If that setting is not adhered to when the set is installed in a differential, you will get binding, overheating, abnormal wear, noisy set up, and shortened gear life. This is one of the bigger issues I've seen in working with these. Another huge mistake is mixing and matching various parts that are not set up correctly to run together. This sounds like what may have happened in the description on this thread. Any differential must be a precision set up throughout from start to finish if it is to be THE BEST IT CAN BE. It takes builder expertise and ALL the needed special tooling in order to get to the best end. Approaching a differential build half way will not produce a good outcome. When we install 4.89 gearing, we completely rebuild the whole diff from the core outward. The pinion depth at which any given ring and pinion set is set up to run will be scribed on the gear end of the pinion shaft. Install it at that depth precisely, (special tooling is required) or you can expect issues. Most just do not understand the degree of precision that must be applied to a proper differential build in order to get a good, lasting, life long result. Understandably so, proper building of any gear box is critical for the best outcome, this is ESPECIALLY true of a differential.

[rickf]

Charles, What you say is true but, the depth setting is not a set in stone, cannot be moved point. It is the starting point for the entire process. Once the final endplay is set and you die check the gears if the pattern is too low or high you will have to move the pinion in or out a hair. And then reset the endplay all over again. All part of the fun game of setting up a diff. BUT, all that said, as Charles said, if you do not have the special equipment and expertise to do differential setup then it is best left to those that do. You will be money ahead in the long run. And using used parts is another whole ball game. I would not even take a job if it was not a matching set of gears since there is very little chance you will ever be able to get them to run quiet. You can get them to run for a long time but it will be a noisy ride.