Tommy Dat Posted January 17 Report Share Posted January 17 If it's not one thing- it's another.... right? trying to get my 1980 720 back on the road. I have gone through the brakes and had them working fairly well. I replaced the wheel cylinders and shoes on the rear. After sitting for a few days the reservoirs in the Master Cylinder are dry but no apparent leaks/wet spots. Is it the booster/Master cylinder? Also, are the Master Cylinder and Booster from a '79 620 interchangeable on the '80 720? thanks Quote Link to comment
Crashtd420 Posted January 17 Report Share Posted January 17 4 hours ago, Tommy Dat said: If it's not one thing- it's another.... right? trying to get my 1980 720 back on the road. I have gone through the brakes and had them working fairly well. I replaced the wheel cylinders and shoes on the rear. After sitting for a few days the reservoirs in the Master Cylinder are dry but no apparent leaks/wet spots. Is it the booster/Master cylinder? Also, are the Master Cylinder and Booster from a '79 620 interchangeable on the '80 720? thanks In the booster is definitely a possibility..... Check the firewall in the truck for wetness too.... Maybe you can pull the vacuum line off and look or smell or possibly reach in carefully... I'd Imagine it will be obvious if the brake fluid is in fact in there..... 1 Quote Link to comment
datzenmike Posted January 17 Report Share Posted January 17 Carpet may be wet. If the brake fluid is in the booster that isn't the fault of the booster but a leaky master. Loosen the master from the booster and see if wet. 620 boosters are not the same as the '80. It may fit if everything changed as the '80 720 had basically the same braking system as the 620. Masters are the same size. Th 620 booster is smaller so may not give the same performance. Quote Link to comment
Tommy Dat Posted January 23 Author Report Share Posted January 23 thanks very much, the area under the master cylinder in the engine bay has a lot of paint peeling. I wonder if the MC has been leaking for a long time. I may take the MC from my '79 620 and use it. Quote Link to comment
datzenmike Posted January 23 Report Share Posted January 23 The '80 is 7/8" master I think, so check. The late 620 will fit but is a 13/16" so just slightly smaller. At most the pedal should travel farther and may feel mushy. Quote Link to comment
Tommy Dat Posted January 28 Author Report Share Posted January 28 update: thanks to All who offered suggestions, they all were very helpful. I did find dampness on the interior fire wall and followed it up to find a crack in the booster. I guess I will replace the booster and Master Cylinder just to start with good components. thanks again 1 Quote Link to comment
Son_of_a_Nun Posted January 29 Report Share Posted January 29 Please let us know if you find a source for the booster. I did a quick check and could not find one a few month back. Thanks Quote Link to comment
Thomas Perkins Posted January 29 Report Share Posted January 29 (edited) Auto Zone has them for 106.99 with lifetime warranty.Oriellys has them for 106.99 with 3 year warranty.Napa has them for 98.97 with 5.87 core deposit.Seems they are found everywhere. Edited January 29 by Thomas Perkins Quote Link to comment
Tommy Dat Posted February 3 Author Report Share Posted February 3 I have tried AutoZone, Napa, O'Reillys, Advance, Rock Auto, and Amazon. No one has been able to find one. Would it be better to use a 620 model booster or will another model 720 fit? I have read about deleting the booster but not sure how I feel about that. thanks Quote Link to comment
datzenmike Posted February 3 Report Share Posted February 3 The 720 brakes till '83 were the same as the '78-'79 620 except the 720 master is larger at 7/8 to the 620's 13/16. The boosters are different part numbers and the booster sits on a pedestal which may not match the 720 pedestal. If the masters are different size almost certainly the boosters are also different. Quote Link to comment
Tommy Dat Posted February 3 Author Report Share Posted February 3 2 hours ago, datzenmike said: The 720 brakes till '83 were the same as the '78-'79 620 except the 720 master is larger at 7/8 to the 620's 13/16. The boosters are different part numbers and the booster sits on a pedestal which may not match the 720 pedestal. If the masters are different size almost certainly the boosters are also different. thanks very much Quote Link to comment
Thomas Perkins Posted February 4 Report Share Posted February 4 (edited) 10 hours ago, Tommy Dat said: I have tried AutoZone, Napa, O'Reillys, Advance, Rock Auto, and Amazon. No one has been able to find one. Would it be better to use a 620 model booster or will another model 720 fit? I have read about deleting the booster but not sure how I feel about that. thanks I found one here at Advance Auto parts for 97.99.The booster. life time waranty. Edited February 4 by Thomas Perkins Quote Link to comment
Tommy Dat Posted February 4 Author Report Share Posted February 4 7 hours ago, Thomas Perkins said: I found one here at Advance Auto parts for 97.99.The booster. life time waranty. My Advance says that they are not able to order one. What store did you find it at? I can drive to GA and pick it up. Thanks very much Quote Link to comment
Stoffregen Motorsports Posted February 4 Report Share Posted February 4 You could always have the booster rebuilt. I use a shop in Sacramento called Power Brake Sales. Quote Link to comment
Tommy Dat Posted February 4 Author Report Share Posted February 4 21 minutes ago, Stoffregen Motorsports said: You could always have the booster rebuilt. I use a shop in Sacramento called Power Brake Sales. thanks very much, I will give them a call Quote Link to comment
Thomas Perkins Posted February 4 Report Share Posted February 4 I dug a little deeper at Advance Auto parts and they can't get it either.I looked at the Napa site and they said to call them.So give them a call.I will post it on Facebook and see if anyone has a good used one for sale. Quote Link to comment
Thomas Perkins Posted February 4 Report Share Posted February 4 (edited) . Edited February 4 by Thomas Perkins Quote Link to comment
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