88 MACK/RENAULT Mid Liner Cabover MS300 Clutch Problems

[Mike Strait]

We have this older Mack truck its a 1988 MidLiner Cab over MS 300 T. What happened was the clutch made a snapping noise and quit working , after inspection i found that the rubber line going to the Air over hydraulic clutch slave unit had ruptured i had a new line made for it and replaced it. I have been trying to bleed the hydraulic system using the bleeder on top of the unit it is just brake fluid coming out now, no air. The clutch is still not working tho there is no resistance to pushing the pedal down like there is no fluid in it. when the clutch pedal is pushed a little spurt of air comes out of a little hole on the bottom of the clutch control unit and thats it the clutch rod dosent move at all. I am unfamiliar with type of clutch control slave unit. it is made by wabco i haven't got any numbers off of it yet.

What i am after is information as to how the unit is ssupposedto work and if i am bleeding it wrong or what or if there is something possibly broken inside of it.

Any information i could get would help me greatly.

[Mike Strait]

One update i have to the post is that Ive been told you need a special toll to bleed it ? and that they are a pain to bleed. can anyone confirm either of these? i think the guy just wanted me to bring him the truck so they could pull me over the coals.

[lynn]

i think the other guy is on the right track. done one in last few months- not a mack- i think it was a isuzu-- same problem. had to go into dealers to get fixed . started on key in 1st then just drove it into town without using the clutch.

[skip]

Gday mate. Sorry to hear you are working on a mid liner. They were called a G260 out here in Australia, they had a Volvo F7 cab. Am I on the right track? I had to replace a pressure plate and the slave cylinder and it was very difficult to bleed. The only way I could get any air out of it was to reverse bleed it, and to do that I had a little bit of fluid in the reservoir and i could see the bubbles coming out of it. I had a pressure bleeder clamped to the nipple on the slave, and pumped a small amount of fluid backwards through the system. It didnt work instantly, but after a couple of attempts it worked well. See how you go. Skip

[bbigrig]

After replacing a defective clutch master cylinder, I once made a "pressure bleeder" out of a spare clutch fluid resevoir cap. I drilled a small hole in the cap so I could put a (pressure regulated) air blow gun tip in the hole. It became a 2 man job but I would pressurize the resevoir ( very little pressure needed) as the other guy pumped the clutch pedal. After pumping the pedal several times, The guy pumping would hold the pedal down and i would bleed the cylinder at the trans. Yes, it sounds like a lot of work but it worked and I hope i never have to do it again. This was on a 97 mack CS300 but all of those clutch setups are pretty much the same.

[MorrisMe]

I know this is an older post but can anyone help point me in the direction of where the bleeder valve is located?

I cannot find it anywhere protruding from the unit in the truck.  do I need to disassemble the unit to get to the bleeder?

[67RModel]

https://www.ebay.com/itm/303437541988?hash=item46a6497264:g:jY8AAOSw-uheFgVS&amdata=enc%3AAQAIAAAA0D%2FwpcRCtlZSAi6k%2Fu%2Fxs0Iszv5wHurBV94JmZ7qEvgE%2BUZrOZ2dzbNdSgziLnNxwiXO3ofiPDOWK%2FHzDpYAZ04ZKHJIHLrkuYUZVMUfRhKnMyDrQUJgnRi4cFybsqGI78wmn8dFmB3xrR%2FRXC%2BJhtVdEL3wEUZVPSJNDVwWX%2BTCMFlkjwzTbesb6kQ%2FF0oH9ioQ7SHMX0gtSlfvEnwgW9bxCTpBB2cXORbRfKS2%2Bq8jOOKyrgFtjYMucT8TnP4X%2BNYPeLewQQPtLEPTzIhvM8Y%3D|tkp%3ABk9SR86frOyEYw

Do yourself a favor and buy that service manual. Looks like the information you need is on page 4-37. Not too many people know anything about Midliners.....they are beyond obsolete. Hopefully you don't need parts for it. Good luck.