First off, I inherited this car from a friend's dad. It broke down on him during a road trip so he had it towed Firestone. Where I picked it up and loaded it on a Auto Transport U-Haul trailer and brought it home to work on. The engine sounds great and it drove fine going forward onto the trailer. It had the 3 Amigos lights, which I fixed by replacing the shuttle valve and doing the electrical wiring mod, then cleared all the codes. The car still drove forward fine, but it was making a grinding or cracking sound as I was accelerating, it smelled like burned rubber & upon inspection the serpentine belt was very cracked, so I replaced that. Also, the intake snorkel hose to the airbox was shredded to bits, so I replaced that with an air intake kit from AutoZone and the noise got better & car seemed safe to drive at this point so I turned the keys over to my wife who will be the one driving this if I can get it running.

Relevant to the Title & reason for posting:
A couple of days later she calls me to say the car isn't accelerating from a standstill at a stoplight. Even when parked the car was rolling as if if the park gear was not actually engaging and she had to use the brake to stop. She couldn't even go in reverse. Nothing. So I start by dropping the transmission pan and replacing the filter & fluid. It's very dark red almost kind of black even. Magnet looked fine and know big metal chunks or shavings. Replaced the gasket as well and then refilled the fluid according the proper procedure (Atlantic British's transmission service YT video) of pre-filling the pan (with the engine off) until it starts coming back out then, start the car and add fluid with the car running until steady drip, cap, go through each gear for 3 seconds, then top off fluid. Still no forward gear works. In drive I try to rev it and the RPMs go up but the car goes nowhere and then starts making a grinding noise at about 1500-2000 RPMs so I stop.

It also makes a bad grinding noise when going from reverse to park. Interestingly, reverse now works after the transmission service. I also don't have any fault codes which is weird to me, but based on this post I was leaning towards it being the forward clutch. But I saw on the Torque converter being the cause of a no drive issue, but I was wondering if maybe he had no reverse either, because how could reverse work but the torque converter be the issue, that doesn't seem likely but I am definitely not an expert which is I why I am seeking your guys' help.

only other thing I can think of is low differential/transfer case fluid which is possible because I haven’t checked that yet but how could reverse work and drive not in that case? Still feel like it’s the forward clutch in my gut but I really would like some reassurance or second opinions before I order the part and start dropping the transmission.

Here is a video of me shifting through the gears and you can hear the grinding from reverse to park and also the grinding but going nowhere in drive.

Would this ZF4HP22 BMW rebuild be helpful? He mentions the same symptoms and ended up being clutch A which seems like the forward clutch unless I am mistaken.

Links to parts, diagrams, or any references would be helpful. Thank you!!

 

TLDR: Reverse works but no forward gears. Also grinding from reverse to park and car doesn’t actually park.

Forward clutch? Low diff/transfer case fluid? Bad torque converter? New transmission?!

 

Welcome to the forum!

Unfortunately I've seen posts about this in the past and it usually turns out to be the forward clutch. If your Disco has the 4HP22 transmission, it's the likely problem. There are a couple other things to check though.

After you changed the fluid did you shift through the gears several times and recheck the level? How much fluid came out when you changed it?

It could be the shifter cable. There's a cable mount on the transmission that might have come loose and only reverse gets selected properly. Not too likely though I'm afraid.

It's probably not the torque converter or you wouldn't have reverse.

Low diff oil (front, rear, center) won't have anything to do with it. The diff oil is to lubricate the gears. If you don't have oil in there it would have made whining noises before failing. You probably wouldn't have any drive at all, and if you did, it'd probably make bad noises.

 

Forward clutch. You can replace it if you are good with mechanical bits, but if concerned I would recommend getting a complete trans from Doc Heydary or Will TIllerey or one of the other breakers. They very rarely go out, so very low probability you would have a second failure.

 

But wait, It was making wining noises and I have reverse but no drive. When you say no drive at all, does that include reverse? I thought the noise was the serpentine belt and also a large vacuum leak (air intake snorkel) and it seemed like car was driving well after words, but I do faintly recall a noise around 1500 rpms but not sure if that matters or is helpful now.

So should I look at my diff & transfer case levels before replacing the forward clutch?

I ordered A forward clutch drum with clutches from eBay. I feel like I can handle it as I’ve done tons of engine, electrical, and other car repairs but never transmission because I’ve never had a transmission issue before. No one has mentioned the grinding from reverse to park though? Is that related the forward clutch, diff/transfer case, etc?

 

I’m confident with the transmission pan service that I did, but I haven’t checked the diff levels, transfer case levels, nor the shifter cable. Couldn’t hurt to try those before replacing the forward clutch right?

 

Also it does make an awful grinding noise around 1500 rpm when you rev it in drive and goes no where

 

The sound of a failing front or rear differential will be a loud low-tone whine / grumble as you drive before it fails. When it's broken to the point of not transmitting drive to the wheels it'll either make horrible metal cracking sounds or possibly no noise at all. To check, you can chock the wheels, put the car in drive and look underneath to see if your driveshafts are spinning. If either your front or rear driveshafts are spinning but the vehicle isn't going anywhere, it's probably a broken front or rear diff. If the one of the driveshafts is spinning and you have a CDL, lock it and put it in drive and see if you move forward (if one diff is broken, all the power goes there, if you lock it, the power is distributed evenly front-to-rear). It'll probably make terrible noises. When the center diff is failing, it will whine for quite a while before it fails. It would probably also make terrible sounds. You can check the fluid and look for metal parts, but what you describe sounds a lot more like the forward clutch pack. If a diff is broken / failed, it'll be broken for both directions of drive so you won't have reverse or forward. To check the fluid level, take off the fill plug and see if fluid seeps out. If it seeps out, it indicates that the fluid is full. If you want to check for metal, first remove the fill plug (Always remove the fill plug first in case you can't get it off at all. If you can't get it off and the diff is drained, you're in trouble) and then remove the drain plug. Inspect the plug for metal shavings (it's magnetic and some extremely fine shavings are normal) and look for glitter in the fluid that comes out. In catastrophic failure you'll see large chunks of metal. Don't forget to refill if everything is fine.

The picture below is an example of what's inside a differential. The front and rear diffs are pretty much the same. There are no clutches or anything like that in them, just meshed gears. If it's broken so badly that it won't go forward, it's extremely unlikely it'll go backwards. The most likely cause of your failure is the forward clutch in the transmission.

 

Wow this was a perfect explanation thank you so much! I will come back and update this thread this weekend or next weekend depending on when I get the forward clutch replaced and transmission back in place with results! Fingers crossed….

 

What solved the problem?