hydraulic to mechanical clutch conversion

Discussion in 'Transmissions' started by dwragon, Jul 30, 2020 at 5:35 PM.

  1. dwragon

    dwragon Newbie

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    Hello everyone, I read a few snipits of a GMT 400 hydraulic to mechanical clutch conversion, but never found any posts about it. I have a 1994 economized quadrajet GMC 454 one ton dually 4X4 that I bought and made one 600 mile trip between the time the Throw out bearing went from silent to exploded, driving the last 200 miles without any clutch. I am going to try doing this conversion on this truck because I hate the hydraulic setups. This is not my first truck with the hydraulic setup, and none of them have been worth a crap, and I can validly say this as a former GM service technician who cut his teeth on these trucks. bell housings.jpg

    The hydraulic setups were tried by GM in the early 60's and abandoned then because they could not get them out of warranty. GM went back to them later simply for assembly line ease of installation, not because they were the best setup. The aftermarket parts leave alot to be desired, and I have had horrible experiences with them, having had to replace throwout bearings at an average of every 9 months in many other trucks. I believe this is caused by a flat bearing riding on a coned pressure plate surface, with no freeplay due to hydraulic backpressure.

    t o bearings short, cc1705c, medium G1625C tall 1697C.jpg

    Of course to replace the T/O bearing, you have to pull the transmission, and on a 4X4 thats a royal pain. I searched until found a scattershield with the removable inspection section, which will keep me from having to pull the bellhousing to replace the clutch disk and possibly the pressureplate. That bellhousing off ebay cost me about 375$, and the machine work to make it fit the NV4500 cost another 200$. While in the process of this I discovered that the torsion bars were rust welded into the lower a frames and were impossible to remove. To get the transmission out, I had to cut the bracket into pieces, and by that found out that the bracket was stress fractured anyway, so I will also have to build a custom (read heavier duty) replacement bracket. This will not be a fast task, and time gaps may occur between posting, but I will complete this, so follow it if you are interested.
     
  2. smdk2500

    smdk2500 I'm Awesome

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    Im just trying to picture the bellhousing that you bought. You will still have to pull the trans to get the clutch and other parts out. So in my mind after that much work what's 6 more bolts. I understand somewhat to the change to mechanical linkage but the amount of extra work that it would be to remove and reinstall the clutch parts with the bellhousing in place doesnt make sense to me.
     
  3. Pinger

    Pinger I'm Awesome

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    There are two trains of thought on this.
    One, is no doubt a throwback to when release bearings were made from carbon and obviously freeplay was required.
    The second is that a touch of pre-load on a roller element (anti-friction?) bearing is good as it keeps the rollers/balls rolling preventing them having to be accelerated up to speed when the bearing is brought into use which can cause the rollers to 'skid' and wear prematurely.

    I have no idea which is correct for a roller element (anti-friction?) bearing - or what you mean by a ''flat bearing ''?
     
  4. MIHELA

    MIHELA King of the Scrapyard

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    I would prefer a concentric slave setup, but this is an interesting idea.
     

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