hydraulic to mechanical clutch conversion

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dwragon

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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.
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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.

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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.
 

smdk2500

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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.
 

Pinger

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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.

.

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 ''?
 

dwragon

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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.


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This is the same bellhousing I bought, by using it, I dont think you have to drop the bellhousing to change the pressure plate, clutch disk, and throw out bearing. You have to realize that this truck is a 4X4, and dropping it with the transfer case in the driveway is a total PITA requiring the Hulk to do the lifting. By scooting the transmission mount crossmember back and resting the transmission input shaft on the edge of the bellhousing/held by the jack, it makes it worlds easier.
 

dwragon

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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 ''?


What you mean by carbon, i have no idea, the quality of ball bearings (They are still made of ball bearings, not barrel, or tapered timkins.) has not changed that much, unless they have gotten worse.

As to bringing the bearings up to speed, change of speed is a constant in vehicles, and something not moving takes no energy compared to something that must be pushed.

The reference to flat bearings is to the TOB's in general. on some, the surface which pushes on the tines is completely flat, other TOB's have a rounded surface. The flat TOB's make full contact with the tines when the tines are flat. The rounded throwout bearings never make full contact with the tines, they "roll" on the tines.

THE WHOLE THING THAT I AM FIGHTING,

IS THAT THE HYDRAULIC SYSTEM IS DESIGNED TO WEAR OUT THE THROW OUT BEARINGS.

I even had a major supplier of these parts tongue in cheek admit that. I had another of these trucks, not a 4X4, and after changing the throwout bearing 4 times in three years, I got pretty good at it, but it takes a little more than that with this truck being a 4X4. I drove a 1964 C10 for 8 years and never replaced the throwout bearing, other than the first pressure plate replacement (Not sure it even needed it then.), because it had no pressure pushing it against the tines of the pressure plate. Unless it was engaged, it did not spin, thus it did not wear out. If my modification is succesful, others will see what it takes, and be prepared, because I readily admit that this modification is not going to be a cakewalk.
 
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dwragon

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Things have been going slow on this mod, as I expected they would. When I purchased the bellhousing, it did not have the backing plate, which was a one eighth of an inch loss in distance. Due to my engine being a two piece rear main seal block, the combination is tighter than with the one piece rear main seal. I will be required to have the same machine shop that did the bellhousing mods cut me a one fourth of an inch steel block to bell housing spacer.

I think that one of the possible reasons the TOB came apart is that it was wedge between the pressure plate and the bearing retainer tube hump. This would have obviously caused premature wear and grenading. My goal is to make sure that I have freeplay in this clutch assembly so the bearing will not wear out sooner than it should.

One of the things I have done was use the straight 1968 Chevy TOB fork, which gave me more travel, as the curved 73 up fork hit the scattershield. I also had to grind the forks inner claws to make them fit the wider bearing, as well as the fork opening of the scattershield. I also swapped the ball clutch fork ball from the 68 bellhousing to the scattershield without any problems, as the 68 fork does not work on the mushroom 73 up pivot. During the swap In cleaning the 68 fork pivot point, I broke the retainer clip spring and had to order a new one.
 
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Pinger

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What you mean by carbon, i have no idea, the quality of ball bearings (They are still made of ball bearings, not barrel, or tapered timkins.) has not changed that much, unless they have gotten worse.

Before rolling element bearings were used, plain unlubricated carbon thrust bushes were. Any pre-load or 'riding the clutch' killed them prematurely. From yesteryear though, they've not been used for decades.
 

dwragon

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Before rolling element bearings were used, plain unlubricated carbon thrust bushes were. Any pre-load or 'riding the clutch' killed them prematurely. From yesteryear though, they've not been used for decades.

Ah, my first contact was in 1987, when I helped my Dad replace the 327 engine in his 68 C10. due to the ease, he replaced the tob at that time, and I used it later on a truck I built, so I never had contact with a carbon one, though I may have them in a 55 1st series I own.
 

dwragon

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OK, I made some headway today. Attached is a photo of the scattershield installed into the driveline. The beauty is hidden though. The parts that are inside of the scattershield are a 1996 to 2000 454/7.4 pressure plate and clutch disc (O'really's power torque K70150-01) and Masterpro 614018 TOB. The reason for this is the additional clearance as shown below.

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I was also forced to abandon the 1697C TOB, as there was not enough clearance, which is also the reason that the 1965 through 1995 pressure plate and clutch disc were not used. As I stress, the entire purpose of this mod it to eliminate the constant pressure on the TOB. One of the contributing factors to the hydraulic throwout bearing wearing out, is that as the clutch disc wears out, the splines exert more pressure on the TOB, not less. While this natually keeps a nice dependable clutch pedal, it wears out the TOB.

One things that I will point out about this mod is that the 1/8 inch backing plate was not included in my purchase. I could have had one made but that is just something else being twisted in the driveline, so I took the chance of the transmission input shaft not clashing with the pilot bearing. After I had the transmission installed, I used a comealong to put pressure on the clutchfork/pressure plate to release the clutch disk. I then spun the tailshaft. If there was clash with the pilot bearing, then the tailshaft would not have turned.

Perhaps if I had used the spacer plate, and a factory style TOB*, I would not have had to use the 1996 to 2000 454/7.4 pressure plate and clutch disc (O'really's power torque K70150-01) and Masterpro 614018 TOB.

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*Another thing is do not try to use the powertorque TOB that comes in the K1909-2 powertorque set. To get around OPP, they put a lip on their TOB, as shown below

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This lip takes up clearance, and was one of the reasons I could not use the 94 pressure plate. I can see no mechanically advantageous reason for the stamped steel lip, unless it is to give strength to a flimsy pressed backplate. as shown below, it ends up pressed against the input bearing retainer.


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another thing of note is that the 96 -2000 pressureplate tines are flat when installed, so I dont really mind the TOB contact point being flat.


I will ad more as it happens, but this conversion will happen.
 
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