8.6 axle prep

[Dan_Austin]

I was looking to to update to rear disc brakes and add a limited slip. Through a bit of digging, I also thought I found one of those elusive 8.6 units in a yard 600 miles away. The freight company lost it for about a week, but it finally arrived today. It is an 8.6. The yard did me a favor did not cut the parking brake cables. I did not expect it, but they also include the calipers and rotors. I have new ones already, but that helped protect the backing plates (which I also have new).

The RPO codes indicated it has a gov-lock and a 3.42, so once that is verified I just need to install the new brakes and source a new 1.5" shorter driveshaft.
If the backing plates needed replacing, I was planning to order a tru-track, thinking if I got that far into it I might as well.

I've searched and looked through some older posts, and did not see very many details, so I'll add what I find during the process. If anyone knows the correct driveshaft length (30.5 u-jount center to center?), that would be helpful.

 

[gmemony2]

Interesting build. Looking forward to pics and write-up.

 

[DaveP's Ghost]

Syclone or Typhoon? If its a Sy, If you don't increase the front rotor diameter, you're going to have too much bias to the rear with the addition of the rear discs. It'll be dicey in a hard un-expected brake application.

I did a complete 2nd Gen transplant into my 93 Typhoon. Fronts, Disc brake rear axle complete (7-5/8, not an 8.5), master cyl, and modded the combo valve. I eliminated the 4WAL at the same time. I am VERY pleased with the braking and reduced pedal effort with the upgrade. And it didn't cost more than $750 all-in. Stock, easy to find, common parts.

Here's the thread. There's a lot of fluff in the thread, but I begin posting about the rear brakes at Post #15. There aren't any pictures, but I detail many of the little things I did to make it all work correctly. Especially the combo valve modifications. I feel changing the master cyl to the non-take-up 2nd gen style made a big difference too. Not easy to do because you need to make all new lines, but I feel it was worth the effort. Other Ty owners that have driven it notice the "better brakes" right away.

 

[Dan_Austin]

Typhoon. If UPS doesn't bugger it up a 14" CTS-V 4 piston setup will arrive on Tuesday, with an ABS delete. I started looking for the rear as I had the front planned/purchased, and knew the stock drum brakes were needing a refresh. Finding an 8.6 was just the cherry on top.

Today I replaced the parking brake shoes and rotors. Not this weekend, but next I hope to have all the bits to start the swap. Rear first, and if it goes well, then on to the front. Which reminds me I need to order what I think is the right length driveshaft if I want it to be here in time...

I'll go over the thread, thanks for the link.

 

[RealFastV6]

Nice find. Those are getting very difficult to come-by.

If I remember correctly the driveshaft needs to be shortened by 1".

 

[Dan_Austin]

If my measurement was correct, the stock shaft appears to be 32" u-joint center to center. Off the shelf length options that are close are 31.5 (not short enough) and 30.5. So I went with the second. Half an inch shorter than ideal should be fine and I can order a custom unit if I have to.

Finding it was interesting, I bought and returned one that was marked as an 8.6, and of course wasn't. This one was listed as a 7.625 but the vehicle had all the right RPO codes: L35, M50, GU6, G80. It was also the first part to be taken off the truck, the yard actually had to ask corporate if they could start pulling parts of it. The yard sent photos, but no angles covered the visual clues, except that it had the harmonic balancer weight on the pinion, and that is rumored to only be on the 8.5/8.6 manal transmissions.

 

[Poconojoe]

If my measurement was correct, the stock shaft appears to be 32" u-joint center to center. Off the shelf length options that are close are 31.5 (not short enough) and 30.5. So I went with the second. Half an inch shorter than ideal should be fine and I can order a custom unit if I have to.

Finding it was interesting, I bought and returned one that was marked as an 8.6, and of course wasn't. This one was listed as a 7.625 but the vehicle had all the right RPO codes: L35, M50, GU6, G80. It was also the first part to be taken off the truck, the yard actually had to ask corporate if they could start pulling parts of it. The yard sent photos, but no angles covered the visual clues, except that it had the harmonic balancer weight on the pinion, and that is rumored to only be on the 8.5/8.6 manal transmissions.

The balancer weights are also on 4 cylinder stick shift driveshafts

 

[Dan_Austin]

Did not stop to take photos, but will grab a few before putting the wheels back on. Took about 3.5 hours to finish installing the new rear calipers and lines, dropping the old axle and lifting the new one into place. I had no excessively corroded hardware, which may have helped. It came out faster the the new one went in, but no precision is required for pulling. Installing just requires fiddling until each side drops square on the saddle, then go fiddle with other side.

The parking brake cables are going to be interesting. I think I can visualize how DaveP's Ghost handled it, and that is priority #2 tomorrow. Priority 1 is going to town and seeing if I can use my brothers press to swap the yoke from my old drive shaft to my new.

Tall jack stands helped quite a bit. I only have one floor jack and kind of wish I had another, but I doubt it would have saved much time. The lift helped with loosening and tightening hardware but did not make much difference with the actual swap steps.

 

[DaveP's Ghost]

The parking brake cables are going to be interesting. I think I can visualize how DaveP's Ghost handled it, and that is priority #2 tomorrow.

The main take-away from how I did it is: I used the outer jackets from the Typhoon. I used the inner cables from the 2nd Gen which are way-longer than necessary. The McGyver part was how to terminate the forward ends to the balance-bar of the 1st Gen.;

I can put the Ty on the lift and post a couple of pics, if you think it will help. It looks jankey and rube goldberg, which is not how I normally do things, but it was quick, could be done with stuff I had on-hand, cost nothing, and the install was finished the next day. The park brake works. At the time (2017) the go-to alternative was to use special cables from Renz. These were difficult to obtain, cost a couple hun, and took weeks to arrive, if they ever arrived at all. I've been ok with my solution to the PB ever since. I never use the PB anyway, but I like things to work.

Not "pretty", but functional. No one can see it with the truck on the ground.

 

[Dan_Austin]

I went down a bit different path. For the passenger side I drilled out the balance bar slot to allow the threaded through it. This gives me a small it of extra adjustment. For the drivers side, I cut the end off the cable than super carefully cut the outer sheath about 9" back from the capture clip, slid the cut end off, then cut about 7" off it and slide it back on the cable. I made sure to confirm no burrs or sharp edges. This resulted in an outer that was just the right length. The inner is a couple feet too long, and will be cut once I pick a cable clamp. The drive shaft re-jigger was a bust. The 'original' had a hybrid large cap 1310 u-joint. I say original as it had junk yard yellow writing on it, so I don't know if it was a Sy/Ty drives shaft or one that happened to fit. One of the local parts stores claims they have on in stock, so maybe that will be completed today.

I 'finished' installing the 14 C6/CTSV kit yesterday, except as it happens, I am one fitting short and it is not something anyone in town carries. I installed what I had and left the missing one for the easiest of the bunch to get to. So even if I get the driveshaft in, the truck is parked for awhile.
The front brake install took about 8 hours and was largely drama free. Just a bunch of grind/install brackets/test fit/repeat, over 50% of the total time was in that loop.

Almost every part came off intact. Not that I will ever re-install them, but I had cutting usable parts. I did have to cut one brake line on the ABS module, it was good and stuck and just rounded off even with the right flair nut wrench. It was the last line so I did not feel too bad cutting it.

 

[Dan_Austin]

I received the last of the missing small bits to finish the brake install. The hybrid 1310/1350 u-joint also arrived and I assembled the new driveshaft only to find it to likely be too short. So I re-assembled the old driveshaft and I can get it installed but it takes a bit of fiddling, inserting one cap in the pinion and wiggling until the other side just clears. This is with the axle at full drop, but I am sure this one is too long. The only other ready made option is just 1/2" shorter than the old one, so that will likely be ordered.

I did not take as many photos as I planned, but in the end the only interesting ones are of the parking brake cable. The rest of the install looks like it is factory (cuz it is basically). No photos of the front brake install, other on here have the same setup. I will say that the 14" rotor does a nice job filling out the 18" wheel...

I still need to add a clamp to the cable after the balance back and adjust the parking brake, and I will be taping up the cut sleeve.

 

[RealFastV6]

This thread inspired me to do another round of yard hunting for an 8.6. Thought I found one 45m away, of course when I got there it was a 7.6.

I can pick them out because of the shape of the rear cover (7.6 is more square) but what’s something more concrete that I can have them check over the phone so I don’t waste an hour and a half round trip to say “nope”?

Very frustrating that they’re mismarked all the time.

 

[Dan_Austin]

If it already pulled the most reliable visual queue will be that the axle tubes change diameter about two inches before the pumpkin. It is not a huge change, but unmistakable. A lot of internet chatter points to the lugs on the bottom of the pumpkin being square and not pointed, but I've found that not everyone can see the difference, as silly as that sounds.

If it is still in the vehicle, the RPO code plate or the VIN so you can run it through a decoder. As mentioned above there is no code for the 8.6, but if it has an L35 and M50 (and is the original axle) you have a good chance of having found one. I used car-part, and searched nationwide. I focused on listings with an RPO plate photo. You can search for the 8.6 using their filters, but odds are super high you'll just get 4 pages on 7.5 units. Searching the 7.5 non-ZR2 units and look for code plates is your best chance. The yard that I found mine in sent photos, but they were not conclusive. One thing that did lean in my favor was that they had to adjust the shipping quote as they found it 50lbs heavier than they expected, but I doubt you'll get many yards to weigh it for you...

 

[RealFastV6]

Good info thanks. Need to get back on this - my rear end has developed an axle seal leak so "I might as well" (TM) swap it over now.

 

[Dan_Austin]

This project should have taken a long day, or at most two days. And for the most part it was. I lost a week waiting for a brake line fitting that no one locally stocked. Another week wasted trying to get a driveshaft made locally, either way over priced to 2+ month wait time, so I shortened the original my self. I had all the right tools, but did not trust my welding, well, it turns out I likely was being too cautious. In case anyone is interested I marked the tube and end cap with two line about 90 degrees apart using a fine point welding marker. I then used a bandsaw to cut the driveshaft one inch from one of the welds, making sure the blade and tube were square to each other. Next up was to chuck the short section with the cap in a lathe and turn the original weld off. Then I aligned the marks on the cap to the marks on the driveshaft. It was a super tight fit, but once I had it fully seated all the way around the tube I started tack welding. Initially opposite sides of the tube, then 90 degrees, then stitch it all together by moving to unwelded sections as far from the last weld as possible.

The final hiccup was mistaking the switch on the adjustable proportioning valve as having the same function as the factory valve. It is not a circuit imbalance sensor. It is a brake light switch. After multiple bleed attempts over a week and the dash light still coming on when pressing the pedal, I stepped back and thought about it, slapped my forehead and checked the specs online. One the positive side I am very sure the system is fully flushed and well bled.

I took it out today for test drives and errands. The big brakes do stop better, there are no vibrations in the driveline up to 60 mph, and as expected I cannot tell any difference between the original axle and the new. I will keep an eye on the driveshaft in case I was right and I am a terrible welder, but I think it may well be fine, at least until I can arrange to have a custom one built.