Leaking 700r4 from hell

[Obwonkonobe]

When I had my th350, no matter how many times I replaced the seals they would not seal, and when I bought my rebuilt 700r4 it sealed perfect. That’s until I swapped the electric speedo with a cable and had to remove the tail housing to do the job. I bought a new speedo housing with all new seals in it, and installed it. I did not replace the yoke seal because it was brand new and didn’t leak prior to the job. Now the speedo housing and yoke seal leak, and their both new! Anyone know why this happened or how to fix it?

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[1987 GMC Jimmy]

My 700s aren’t like that so I don’t think yours should be either. Is the little plastic housing for the speedo gear/shaft seated evenly and not cracked? Besides seal failure at the slip yoke, all I’m wondering is if the extension housing bushing is good. It should be if it’s new.

 

[73c20jim]

Look for a nick in the tailshaft where the seal presses in. Had this on my Corvette and when nuts until I figured it out.

 

[Obwonkonobe]

Look for a nick in the tailshaft where the seal presses in. Had this on my Corvette and when nuts until I figured it out.

That was the issue on my 350 but I’ve never touched that seal and it didn’t leak before, so I’m hesitant to mess with it yet. If it starts leaking anymore though I will

 

[HotRodPC]

Is it an aftermarket part or OEM? I'd say since it was on both transmission and it was sealed just fine before the swap, I'd be thinking Chinese made part fitamet issues.

 

[73c20jim]

If you removed and installed the driveshaft, maybe a nick on the inner lip of the seak

 

[Obwonkonobe]

Is it an aftermarket part or OEM? I'd say since it was on both transmission and it was sealed just fine before the swap, I'd be thinking Chinese made part fitamet issues.

That’s my thought, do you have any recommendations for good seals?

 

[rpcraft]

I'd recomend that once you replace the seal finger tighten the bolts on the tailhousing so that you can insert the yoke to center the tailhousing assmebly to the yoke, and then tighten it down to spec. It's not necessary but it will help center the seal and tailhousing to the yoke itself and maybe prevent any kind of oblong or side to side wear of the seal against the yoke. As others have said check your yoke for any burrs or knicks. Felpro is kind of the name to go with in regards to gaskets and seals, but I'm not 100 % sure when it comes to transmission seals.

 

[Zoomalot]

I always use a bit of silicone COPPER or P.S.T. on seal to casing.
The P.S.T. works wonders on Hydraulic Fittings also.

 

[JoeR Jr]

Saw a similar problem an awfully long time ago. Engine ground strap was bad. Engine was grounding through the driveshaft. It ate the rear bushing out of the trans and scarred the driveshaft yoke. How's the side play of the yoke?

 

[Obwonkonobe]

Saw a similar problem an awfully long time ago. Engine ground strap was bad. Engine was grounding through the driveshaft. It ate the rear bushing out of the trans and scarred the driveshaft yoke. How's the side play of the yoke?

No play, none that I can tell anyways. And no vibration. How’d you tell it was grounding through the yoke?

 

[WHEELMAN]

Go to the store or rockauto on line.buy an amerAmer made trans seal.did anything change to keep the yoke from going forward.did anything like that change.if it's a real old yoke you could buy a new yoke.change the ujoint.

 

[JoeR Jr]

No play, none that I can tell anyways. And no vibration. How’d you tell it was grounding through the yoke?

The bushing and yoke had arc marks on them. It took us a while to figure out what was happening, and even what the marks were from.