New Member - Trying to rebuild an XX-T

[sunshineFC3s]

Hi guys,
I got my hands on a really clean XX-T with some graphite bits on it. Only part was a broken diff gear. Since these gears are no longer available to buy...only option was to find NOS. So, naturally, I bought a few parts lots - the stuff in the pix, plus some additional motors, a few okay bodies, two transmitters, and a bunch of wheels. I'd like to rebuild this thing, and beat on it a bit (not too badly...parts are hard to find!!!) Last, but not least, I want to send a big thanks to Mytimac at OldRC.com for pointing me to this forum.

So, I hope to document the rebuild of this driver here, and also ask some questions. I'm new to this hobby, but mechanically capable.

Question 1)

The diff. I'd like to set the diff up properly. I think I have all the parts I need, except the ball bearings and the lube. I'm also missing a hydra drive. Here is the question, besides the balls and lube, any other parts that need to be replaced as new? How necessary is the hydra drive? Can I just use the slipper? Will that affect longevity? The manual seems to strongly recommend that I should use it

Question 2)

Shock rebuilds. What was the stock oil weight? What is a recommended setup (oil weight / springs). Seems like my parts bin has a few extra springs I can try.
Same question as above, can I rebuild the shocks reusing the original parts if they seem in good shape? Or new valves highly encouraged?

Thanks guys! Good to be here.

Now, on to some pix...

[nagreend]

I'm not as knowledgeable as others here, but I had a XXT as a kid and recently fixed one up as a runner. Here's what my experience says...

The shocks probably just need new o-rings and oil. I believe 30 weight is a good place to start. Pink springs came stock, but a common setup at the time was to put yellow springs in the back for slippery tracks. I'd leave the pink on for now.

You might want to get new diff balls (3/32 carbide) and diff rings while you're replacing the gear. Some Associated black lube has worked well for me. Make sure it is set tight enough not to slip! I couldn't get mine tight enough, so I had to replace the conical washers that are used in the diff. I was actually missing one.

As for the Hydradrive, it is not necessary to run it, especially if keeping the motor to a stock equivalent. However, there are a few different variations of the XXT. The original that came with a Hydradrive would greatly benefit from the dual disc setup that came on the CR versions. If it's the sport model, then it didn't even come with Hydradrive. So depending on which model it is and what type of slipper setup is on there now, you may not need to change a thing.

Most of the parts are fairly easy to get a hold of, other than certain transmission parts, so you might not want to run to high of a kv if using brushless. Team Blue Groove makes replica bodies, so check them out on eBay, and MCIracing makes replica decals, so maybe pick up a couple of those! This truck has always been one of my favorites. Enjoy!

[RCveteran]

Use associated black grease on thrust bearing and clear diff lube on main balls. I like overkill so I use ceramic 3/32balls in diff as well.

[ManMan]

If your seals aren't leaking, you can just drain/clean/refill the shocks. I just did that to mine with 35wt oil. I was going to replace the o-rings, but had ordered the wrong ones.

I've seen carbine recommended for the diff balls over ceramic because they don't slip as easily. But ceramic is best for the thrust bearings.
You can use the XXXT-CR diff rings/shims for a little extra slip protection. Slip at the diff gear is what kills them (balls spin, get hot and melt their pockets).
Lapping the diff rings can provide a little smoother action. bfastrc.com has diff rebuild kits.

I do recommend titanium turnbuckles as an upgrade. I remember bending the stock ones easily as a kid. Also, Lipo batteries are phenominal compared to the old NiCad / NiMhi cells!

I'm in the process of getting my childhood XXT up and running again (again!) A couple of late nights drinking while on eBay may have spurred me to buy a couple of upgrades that weren't strictly needed, but it's almost done. Just have to finish fixing the upper brace my wife broke!

[isles1]

Welcome. I have rebuilt a few xxts so if you have more questions just send me a PM

[knixdad]

Question 1)

The diff. I'd like to set the diff up properly. I think I have all the parts I need, except the ball bearings and the lube. I'm also missing a hydra drive. Here is the question, besides the balls and lube, any other parts that need to be replaced as new? How necessary is the hydra drive? Can I just use the slipper? Will that affect longevity? The manual seems to strongly recommend that I should use it

Hydra-Drive is an option, not a requirement. The stock slipper works decently enough. The Hydra-Drive is neat but for general goofing around it is not necessary.

Question 2)

Shock rebuilds. What was the stock oil weight? What is a recommended setup (oil weight / springs). Seems like my parts bin has a few extra springs I can try.
Same question as above, can I rebuild the shocks reusing the original parts if they seem in good shape? Or new valves highly encouraged?

The kit stock shock oil is 30wt. Pink springs are a good starting point. The shock bodies are pretty durable and can last pretty much forever, as long as you don't let them get corroded or smash them in to things.

The shock cartridge can be rebuilt pretty easily. You can pop off the retainer, part with the slots, and remove the o-rings and spacer. Clean them up, check the rings for damage, replace as needed. Then use your choice of o-ring lube, like Associated Green Slime. Cram them back in and pop the retainer back on. It's pretty painless.

Like you mentioned, the diff needs to be setup correctly. Especially if you toss in a brushless motor and use LiPos. If it slips, your diff gear will melt, the balls will develop flat spots and the rings will get scored. If that happens, you need to replace the gear and you also need to replace the balls and lap the rings. If you don't, the diff will never tighten correctly and will slip no matter how tight you try to make it.

Like everyone else has said, if you have a question, just ask.

[RCveteran]

The old green slime trick on the o-rings. One of those things that is sort of common knowledge but not always known. If I recall there was an old Losi Tech Talk bulletin back in the day team drivers using some sort of lube on the o-rings when building shocks. It's probably somewhere over at vintagelosi.com.

[shoman24v]

My advice, rebuild to what the manual calls out. Note the part numbers in each step and verify in the back pages you are using the correct parts.

A 13.5 motor should give you plenty of speed, but I would install the slipper clutch (dual disk is better) and dump the hydra-drive. Your slipper will need to slip before the diff, you can hear the difference between the two.

As a 'basher', keep in mind that certain parts for this car are easy to find and are cheap, and certain parts can be easy to find, but not cheap. Use care when running. A broken front bulkhead, chassis, transmission case, pivot plate, etc. will be the expensive items on the car.

[snowfox]

Looks like you have the dual disc slipper in 1st picture in top left. thsi was used on the XXT+CR and XX Kinwald. It's a great design and can handle brushless no problem.

http://vintagelosi.com/SingleToDual.html

[RCveteran]

Also I would add we tend to automatically jump to you must have a slipper here. For general banging and recreational racing I have found it not necessary assuming you don't have your diff to loose. I have run a lot of batteries and fun through the LRM transmission no slipper without issue. If I recall someone here races his no slipper regularly including two VONATS with no issues.

You have the hardware to run slipper so go ahead but don't panic about it.

[sunshineFC3s]

Wow, thanks for the awesome replies, guys! Really appreciate it.

I don't plan on going brushless with this RC for a while. So everything for now will remain as close to stock as possible.

My main problem at the moment, as I see it, is that I have a bunch of parts without knowing what came from what car originally. So, lets tackle the diff first. I'm attaching a pic of the parts that I think I need to assemble a complete diff.

As far as I can tell, I'm missing a few shims (#80 1/4 x 5/16 shim, #82 thrust bearing seal, all bearings, and diff tube (#73)). I will also replace the ball bearings (#79), diff washer (#76). Do the six beveled washers (#72) need to be replaced as new?

As far as the slipper, I definitely want to use one. Looks like I have several sets of single slippers. The first green spur is an 88t, the Orange is a 90t. The middle two greens are not marked. So, to make a double slipper (based on the instructions at vintagelosi) I just need the special dual disk spur, but I got the rest of the parts. Correct me if I'm wrong.

Thanks again, all!

[RCveteran]

Yes, looks lie all you are missing is the dual slipper spur.

[sunshineFC3s]

Anyone clue me in to what this is, how it's used? I think it's some sort of adapter from Kimbrough Racing.

[sunshineFC3s]

Got some goodies from OldRC.com. Just waiting on my clear and black goo to arrive, and then I can rebuild the diff. While we wait, Ill work on the shocks.

Looks like the silver and black aluminum shock bodies are the same dimensionally, any difference in which RCs they were offered on? I have both, don't know which to use.

Thanks!

[RCveteran]

The silver are earlier JRX2/T, the black ones would have come with your XX. Yes you can rebuild both with same cartridges, Losi 5015 part #.