Outdrives shot?

[jbmeyer13]

What are the tell tale symptoms that the outdrives are shot? I started hearing a high pitched squeal and pulled the car off the track. I immediately thought it was the diff but the Track/shop owner thought it was idler. After pulling apart my stealth tranny I confirmed the diff gear was shot and there’s wear on the outdrive but not sure if there’s any life left in them. I’m rebuilding the tranny and here’s some photos:

[XLR8]

FWIW, diff gear looks bad but I've ran worse.
Outdrives look fine, diff rings are obviously shot. Have the outdrive bearings seized?
Looks like classic case of a slipping diff causing the balls to groove the rings and melt the gear.
Just my 2 cents.

[jbmeyer13]

FWIW, diff gear looks bad but I've ran worse.
Outdrives look fine, diff rings are obviously shot. Have the outdrive bearings seized?
Looks like classic case of a slipping diff causing the balls to groove the rings and melt the gear.
Just my 2 cents.

I ordered new diff and rings. The outdrive bearings are fine so I’m lucky there. I’ve never had something like this happen but I’m also running a lot more power through the drive train nowadays. Odd part is that I tightened up the diff recently so if anything I was worried about it being too tight. Will have to pay more attention to this going forward.

[XLR8]

So bearings are okay. I was thinking that squeal + polished bearing surface on outdrive + smoked diff = seized bearing.

outdrive with polished bearing surface.jpg (29.14 KiB) Viewed 2080 times

outdrive with polished bearing surface.jpg (29.14 KiB) Viewed 2080 times

Somehow I don't think we've gotten to the root cause of the failure.

[jwscab]

no, the diff can make a squeal or bark kind of noise, it's the diff gear, balls and rings on the way out. I had a diff just stop working, no real noise. ended up grenading the diff rings.

just set up your slipper to slip a couple feet and it will extend the life of the diff, use new thrust assembly, and sneak up on the diff setting, rather than tighten then back off in one shot. tighten, rotate diff, tighten, rotate, until you get to full locked, then back off 1/8th turn.

[jbmeyer13]

no, the diff can make a squeal or bark kind of noise, it's the diff gear, balls and rings on the way out. I had a diff just stop working, no real noise. ended up grenading the diff rings.

just set up your slipper to slip a couple feet and it will extend the life of the diff, use new thrust assembly, and sneak up on the diff setting, rather than tighten then back off in one shot. tighten, rotate diff, tighten, rotate, until you get to full locked, then back off 1/8th turn.

Should I also be replacing the carbide diff balls as well? How would you know when they are shot? My understanding is that they very rarely need to be replaced and this car has less than a full season of racing on it and that was pre-brushless era with a stock trinity slot machine motor back in the early 90's. I'm guessing that moving to an 8.5 brushless motor with the diff too tight nuked it.

With regards to setting it up- I understood the slipper to be set up last and have always done it that way previously. If I read you right you would suggest to build it as the manual states but set the slipper looser than normal. Then adjust the diff based on the loose slipper. From a relative perspective where do you find that the slipper lock nut is on the shaft to allow the car to slip a couple of feet? I thought I had set things up to be loose but perhaps it was still too tight.

[jwscab]

you can, especially if the rings have been badly damaged and you have 'barked' the diff. They are supposed to be tough though.

no, i meant sneak up on the diff adjustment when you build it. the manual says to tighten the diff till the spring binds, then loosen 1/8th turn. I like to bring the bolt up a bit at a time and rotate the diff through as you tighten to let everything 'seat' this way the balls and rings aren't subject to the full spring tension/solid bottoming out before the balls and rings are rotated. it should be really loose and gradually tighten up as you start tightening against the spring until its bottomed out, then loosen 1/8th turn.

then you assemble the trans and slipper and tighten the slipper. As a start, I grab the wheels to prevent rotation and spin the spur by hand and it should slip with a reasonalbe amount of force. i can't tell ya how much as it's just a 'feel' thing. sort of used to it tightening bolts for 30 + years. Its much better to start loose and adjust a 1/8th of a turn at a time until you get a good 2-3ft slip.

once you run the car a bit, just ever so slightly adjust the diff tighter and you shouldn't need to touch it again.

[jbmeyer13]

you can, especially if the rings have been badly damaged and you have 'barked' the diff. They are supposed to be tough though.

no, i meant sneak up on the diff adjustment when you build it. the manual says to tighten the diff till the spring binds, then loosen 1/8th turn. I like to bring the bolt up a bit at a time and rotate the diff through as you tighten to let everything 'seat' this way the balls and rings aren't subject to the full spring tension/solid bottoming out before the balls and rings are rotated. it should be really loose and gradually tighten up as you start tightening against the spring until its bottomed out, then loosen 1/8th turn.

then you assemble the trans and slipper and tighten the slipper. As a start, I grab the wheels to prevent rotation and spin the spur by hand and it should slip with a reasonalbe amount of force. i can't tell ya how much as it's just a 'feel' thing. sort of used to it tightening bolts for 30 + years. Its much better to start loose and adjust a 1/8th of a turn at a time until you get a good 2-3ft slip.

once you run the car a bit, just ever so slightly adjust the diff tighter and you shouldn't need to touch it again.

I rebuilt the diff with new gear and rings only to have it keep barking. This fried the rings (luckily i bought 4 sets) so now I'm replacing the diff balls and the thrust bolt spring. I was talking with one of the shop techs who runs vintage cars and he says that he's found those springs to not last very long when they've been sitting compressed in a diff for 30-years. When you can't tighten the diff enough it's an instant kill shot to the rings. Aside from that, I can't see anything else which would be causing the barking.

[jwscab]

I can see that happening. it sounds like you are close, get a new diff spring and be sure to pre-compress it a few times with a set of pliers like the manual suggests. Otherwise, loosen the slipper a little and sneak up on it. it shouldn't bark if the slipper is loose enough.

[jbmeyer13]

I can see that happening. it sounds like you are close, get a new diff spring and be sure to pre-compress it a few times with a set of pliers like the manual suggests. Otherwise, loosen the slipper a little and sneak up on it. it shouldn't bark if the slipper is loose enough.

I definitely followed your approach to sneaking up on it and the slipper was definitely set loose. I also have a new set of the 5/64 diff balls for the thrust bolt so perhaps I should swap those out as well. This tranny was only run for one season back in 1991 and it was paired with a slot machine stock motor so the wear and tear was minimal. The carbide balls are supposed to last a long time and I doubt they have erroded but to be honest wouldn't know how to check them. I've never heard of the carbide diff balls failing and certainly not after such a short period of actual use.

I'm also switching to a 17.5S Reedy Sonic just to play it safe. I can't use the 8.5 in vintage competition anyway so might as well put that in my B5 or another modern car. I do like that motor though; very nice.

[jwscab]

8.5 is probably close to the limit to reliably run that trans anyway with good traction.

you should always change the thrust parts, balls and washers. they are the weak point of the design, as they handle all the loading the diff balls do but in a much higher concentration since they are smaller, the rings are hard and so you can re-sand them, but they can also pick up dust and dirt inside the grease due to being outside the case. most of the time a notchy feeling diff is the thrust assembly. the diff balls are damn strong but not indestructible so it's possible they could be blemished.

[jbmeyer13]

8.5 is probably close to the limit to reliably run that trans anyway with good traction.

you should always change the thrust parts, balls and washers. they are the weak point of the design, as they handle all the loading the diff balls do but in a much higher concentration since they are smaller, the rings are hard and so you can re-sand them, but they can also pick up dust and dirt inside the grease due to being outside the case. most of the time a notchy feeling diff is the thrust assembly. the diff balls are damn strong but not indestructible so it's possible they could be blemished.

Do you know if this kit is compatable? https://www.amazon.com/gp/product/B0006O72TM/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Parts looks the same but not sure if there is a difference to length of thrust screw. Scratch that- just checked B4 manual and the parts numbers are identical for thrust bolt/washer assembly. Too bad same can't be said for the gear and diff rings...

[jwscab]

yup agreed. stock up while you can.