I am currently converting my '70 Chevelle to front disc from Drum and I need a brake booster. I have seen some nice 7'' Dual diaphram models and was wondering if anyone is using thes and how they like them compared to the standard 11'' models. I also don't know if the proportioning valves are different or not. Any help would be greatly appreciated as I do not want to have to tow this car home ever again!!

Do a search for username "BC". He's had some experience running both and has given his opinion on the two.

Good luck!

Joe

I use one out of a 79 T/A in my 72. Been in there for about 5 years. The mount holes need to be elongated and the rod needs to be modified to accept the pedal bracket.

I got my '68 El Camino with an old looking 11" single booster and what look like original style disc/drum. This setup did not really have a "proportioning" valve. It does have a distribution block with brake failure switch in it. It also has a barrell valve to delay application of the front brakes.

I recently converted over to a dual booster from a 79 El Camino, probably a 7" or 8" size, for clearance with the BB and tall valve covers. I did an engine change at the same time, so there may be vacuum differences before and after. But bottom line is that I now have about 10" of vacuum at idle and the dual booster works just fine for me. Some claim that the dual boosters actually need more vacuum than singles, but that has not been my experience. Actually, if anything, I might complain that the brakes are too sensitive. But as I have said before, over boosted brakes kinda go along with the over boosted power steering on the El Camino.

I think there is probably more braking performance to be had in my system with an add-on proportioning valve. It definitely locks up the rear first, perhaps too soon before the front. But maybe this is an El Camino trait to compensate for possible loads?

Thank you for the reply. There is so much information out there, it is nice to hear from someone who has used one of these smaller diaphram boosters. Not to mention, they are WAY easier to install and look great. I bought a chrome unit with a powdercoated master for 150 bucks new.
thanks again,
Gotta Love 1970!!
Rider