Vanagon EuroVan
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (September 2005, week 1)Back to main VANAGON pageJoin or leave VANAGON (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Wed, 7 Sep 2005 00:19:06 -0400
Reply-To:     Dennis Haynes <dhaynes@OPTONLINE.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis Haynes <dhaynes@OPTONLINE.NET>
Subject:      Re: doing more brake jobs
Comments: To: rrecardo@WEBTV.NET
In-Reply-To:  <3479-431E6317-9734@storefull-3175.bay.webtv.net>
Content-type: text/plain; charset=us-ascii

As the owner of a Diesel powered motor home that weighs almost 25,000 pounds empty, I can answer these questions.

Diesels do not have throttles, there is very little braking action going down hill. Compression does not matter. At speed, while a cylinder is compressing, another is decompressing. Turning an engine by hand, you feel what you think is only compression, but at that low speed, the air does not stay compressed as it escapes past the rings. So when you turn an engine by hand, you are actually feeling the resistance of one cylinder compressing and then pulling vacuum. At speed, the effect is more like a bounce. First there is resistance from the compression and ten the rebound of expansion. The engine braking effect on a gasoline engine is really created by the manifold vacuum of a closed throttle.

On large trucks, brake use is mostly avoided. Even though I have 16.5 X 7 " drums in the rear and 16.5 X 4" in front, it does not take a whole lot of braking effort to make smelly brakes. Especially if I'm towing. The exhaust brake works by restricting the exhaust, (another butterfly like a throttle) actually turning the engine into an air compressor. This is very effective. Some larger engines close the exhaust valves and some now even use hydraulic retarders in the transmission.

As for using the brakes on downgrades, I already talked about the heating of the brakes. Most trucks still use drums; discs simply do not offer enough surface area and do work well with the limited air pressure. As drum brakes heat up, the drums expand; the shoes then have to travel further to contact the drum. Add this and some glazing and you will get some serious brake fade.

Dennis

-----Original Message----- From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Robert Cardo Sent: Tuesday, September 06, 2005 11:49 PM To: vanagon@GERRY.VANAGON.COM Subject: Re: doing more brake jobs

<< In a diesel, there's no such thing anyway,>>

Really?

Add 20 to one compression on top of 6 coffee can sized pistons and see how much drag an oil burner has.

I wonder why they also use an accessory compression brakes too. Must like the noise.

I wonder why trucks don't use their brakes coming down long grades. Must be saving them for a rainy day.

Yep.

Must have a country full of idiots on the road. Them professional driver's don't know doodly.


Back to: Top of message | Previous page | Main VANAGON page

Please note - During the past 17 years of operation, several gigabytes of Vanagon mail messages have been archived. Searching the entire collection will take up to five minutes to complete. Please be patient!


Return to the archives @ gerry.vanagon.com


The vanagon mailing list archives are copyright (c) 1994-2011, and may not be reproduced without the express written permission of the list administrators. Posting messages to this mailing list grants a license to the mailing list administrators to reproduce the message in a compilation, either printed or electronic. All compilations will be not-for-profit, with any excess proceeds going to the Vanagon mailing list.

Any profits from list compilations go exclusively towards the management and operation of the Vanagon mailing list and vanagon mailing list web site.