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Hello friends,
I'm looking for some guidance on repairing the factory LSD transaxle from my '86 951. I'm hoping to solve a rattling noise and occasional violent grinding while cruising in gear. The gear lube drained had lots of fine metallic particles. It was suggested to me that the ring/pinion gears might be toast but they looked perfect, so I've got the case split now and can inspect at least some of the gears. Does anyone more experienced see any obvious issues before I dig deeper?
I was hoping to spot an obvious issue when I cracked it open but frankly don't know what I'm looking at. This is a major learning experience for me. The notch in this gear is the only thing that seems odd so far:
If anyone has any suggestions I'd greatly appreciate hearing from you. I've had a build thread going but it isn't getting much attention so I've started this new thread to focus on the transaxle repair. I know it would be a lot easier to just replace this but I have yet to find a 951 transaxle at a reasonable price. Buying from the US and importing to Canada adds about 50% to my cost so I'm looking at $1500-2000 CAD from Lart or others for an open diff. Local guys are even worse, so unless I can find a deal I want to thoroughly investigate repair / rebuild.
For background here's a video of the noise it was making:
Keep disassembling and inspecting parts until you find what's worn, using the workshop manual as your guide. If you're grinding gears on shifting, more than likely your synchros are shot. If your transmission has never been serviced in its thirty-plus years of life, chances are excellent that the synchros and bearings are all shot, and it needs a complete rebuild. As you've split the gear carrier from the diff carrier, take a look at the front pinion bearing outer race: it's an excellent bellwether for the condition of the rest of the bearings: look especially at 5 o'clock where the heaviest load centers. I can arrange freight from Georgina to me if you'd like my help. Good luck!
What do the diff side bearings and races in the side cover and case look like...?
There is nothing evident in your pictures.
Do you have the rear cover off yet (rear alu housing)...?
T
Some pictures of the diff and races. They all look okay to me, some wear (did I mention the car has 180K miles on it?) but nothing that jumps out to me. I haven't taken the rear cover off yet.
Originally Posted by MooreBoost
Are you sure it's not the torque tube?
Edit. Just watched your video. sounds like a CV joint
Not sure about the torque tube. There is a slight rattle coming from it if I run the car with the transmission removed, so I'm planning to rebuild it "while I'm in there." However the transmission fluid I drained looked like this so something is wrong with the transaxle either way (this lube had 50 miles on it).
Originally Posted by KevinGross
Keep disassembling and inspecting parts until you find what's worn, using the workshop manual as your guide. If you're grinding gears on shifting, more than likely your synchros are shot. If your transmission has never been serviced in its thirty-plus years of life, chances are excellent that the synchros and bearings are all shot, and it needs a complete rebuild. As you've split the gear carrier from the diff carrier, take a look at the front pinion bearing outer race: it's an excellent bellwether for the condition of the rest of the bearings: look especially at 5 o'clock where the heaviest load centers. I can arrange freight from Georgina to me if you'd like my help. Good luck!
It doesn't grind when shifting, only when in gear and cruising. Shifts are all smooth. I have no service history on the car, however there is evidence of engine-out service in the past so I wouldn't be shocked if it has been rebuilt before. I'll try to take a picture of the front pinion race when I have a chance next but it looked similar to the differential races (no bad from what I can see).
I will send you a PM later today when I have a couple more minutes, I think I'm approaching the point of sending it in. Thanks in advance.
You'll need to get the rear cover off and proceed to remove the gears relating to 5th speed next.
There's nothing to fear, you can repair this transmission yourself.
Have you run the engine with clutch released with the transmission out...?
Have you recently done rear brakes before you discovered this noise...?
I appreciate your optimism. To give some more detailed backstory, the car sat for 10 years before I bought it and did the standard 944 maintenance (belts, seals, etc). I replaced the gear lube with Amsoil Long Life Synthetic Gear Lube (API GL-5 & MT-1). I didn't touch the brakes, bearings or CV joints. I got the car licensed and drove it gently around town, just to get a feel for it. No hard launches, high rpms, burnouts etc. I put about 40 miles on it when the noise began out of nowhere. It sounded pretty violent, almost like grinding gears or tire rub, except only happened while I was cruising at a steady speed in gear and was intermittent (less than a second of noise every minute or two). By the time I got home (10 miles later) it was happening every few seconds and making the car buck around. The last couple miles were crawling on the shoulder of the road with hazard lights on - probably an appropriate introduction to driving a 35 year old German sports car. In retrospect I probably should have called for a tow truck.
I put the car on jack stands and couldn't find anything loose or broken so ran it in gear when I recorded the original video posted above. I then tried removing the axles to see if I could isolate it to a CV joint or bearing/brake. I did notice some binding in the hub on the passenger side, but recorded the following video with the axles removed and the car making virtually the same noise. So servicing the brakes and probably replacing the rear bearings is on my to-do list but I don't think I can blame them for the noise.
This is when I checked the gear lube level (it was full) then drained it and you already saw how glittery it was with very fine metal particles. That was when I dropped the transaxle and brings us up to date where I've half disassembled it without seeing anything out of place. I have started the engine and listened with the transaxle removed and clutch engaged. There is still some very quiet rattling from the torque tube but it is nothing like this past video. Add a torque-tube rebuild to my to-do list. Probably a clutch while I'm in there because why the hell not. Car also needs a turbo rebuild. So yeah... Porsche ownership.
I love the idea of fixing the transmission myself but I'm stressed about special tools I'll need to properly reassemble it, and while I'm a decent hobby-level mechanic this is way past my comfort zone. I will keep going with the basic disassembly and hopefully see something obvious to fix. Failing that I'll need to put it back together and send it to someone or buy a replacement. If it weren't for this forum I wouldn't even try (probably wouldn't have bought the car at all) so thanks again.
Magnets doing their jobs. Is this a normal amount of filings to see or a really bad sign?
And the front pinion bearing outer race as requested:
Still nothing jumping out at me. I can keep going but I'm at the point where I need to start using gear pullers and reassembly becomes more daunting. I know if parts need replacement this is unavoidable but if I don't find anything wrong I'm making my life harder. I may take a closer look at the LSD and the lube pump first if they're any easier. Updates to follow.
Oh Man.. would be just crazy if the noise had nothing to do with the transmission! Honestly, I'd swear in the second video--where the noise seems different than the first--it's loose exhaust
There is one pic above that shows a thick ring in a groove but the ring doesn't go all the way around. I assume this is normal and not a broken ring?
EDIT: I used to laugh when I saw old mechanics using stethoscopes to listen for noises; now I'm thinking this is a very good tool to get
Oh Man.. would be just crazy if the noise had nothing to do with the transmission! Honestly, I'd swear in the second video--where the noise seems different than the first--it's loose exhaust
Believe me I've been wondering the same thing. The fact that the gear lube I drained was so full of particles is what keeps me focused on the transaxle. Whether it is responsible for the noise or not, something is wrong here...
...And I may have had a breakthrough! At least I've found a broken part. I looked at the oil pump and it seemed fine, so moved to the LSD. I first noticed these score marks but wasn't sure if that is how it is supposed to look.
Upon complete disassembly of the LSD I found one of the friction washers is broken into pieces. There is supposed to be a little nub on it that fits into the differential housing and there is no sign of it at all. This was on the lower side (driver's side), the other one is fully intact.
It also looks like the lower diaphragm spring was installed backwards and caused those score marks seen above because it was rubbing on the differential housing. I don't think these are supposed to be friction surfaces.
Correct me if I'm wrong, but I believe the tapered diaphragm spring should be installed so that the pointy side of the cone contacts the housing, while the wide side presses on the outer plate of the diff. (Point away from the middle.) That's how it was installed on the passenger side where everything looks normal. The service manual just says "Insert in the correct position."
Just an overall shot of all the bits. Everyone will appreciate the surgical cleanliness of my work space.
So question for the more experienced, would I be naive to declare the problem found? I guess I'm curious if others think this makes sense to cause grinding and metal bits in the oil or if it's likely unrelated. My terminology is probably wrong half the time too so if anything I've said is unclear please let me know. Thanks in advance.
Probably not the root issue. The broken thrust washer is a common occurrence: its pressed-in tab is a stress riser and design mistake. (Guard did something a little different in their LSD to avoid this.) This part is NLA from Porsche. Check the other thrust washer carefully for a crack propagating from the pressed-in tab.
The cup washer is installed "backwards" in some LSDs, from the factory intentionally. They mark these LSDs with a yellow paint dot on the LSD case, and with age the dot may look more brown than yellow.
You do have the second-generation LSD in your car, which is good. The case is a single-piece casting of a better quality steel, the "GGG" you see in one of your photos. The first generation had the mounting flange for the ring gear welded to the case, and plenty of those welds failed with time and use.
As best I can judge from your photos, the outer race for your front pinion bearing (installed in the diff carrier) and inner race rear input shaft bearing (split race) are heavily worn. Time for a rebuild, I am afraid.
02-16-2019, 12:56 AM
Help me repair my 951 transaxle
